Description, economic and environmental issues of renewable energy ...

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Table 2: Types of CSP plants, operational efficiencies and costs. .... Solar energy is a promising renewable energy resource because it can be used in various.
 

 

 

                                                                 

GENERGIS  -­‐  Green  Energy  for  Islands              2012-­‐IEF-­‐332028  

  Deliverable  V     Description,  Economics  and  Environmental  Issues  of   Renewable  Energy  Technologies  

   

Dr.-­‐Ing.  Fontina  Petrakopoulou   Scientist  in  charge:  Prof.  Maria  Loizidou  

  Unit  of  Environmental  Science  and  Technology     National  Technical  University  of  Athens       June  2015    

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

 

 

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 2 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

In   the   following   text,   a   brief   description   of   the   characteristics,   advantages   and   disadvantages   of   renewable   energy   technologies   are   presented.   The   text   is   largely   based   on   scientific   reviews,   selected  reports  and  statistical  databases.     More  information  on  current  and  targeted  costs  of  renewable  energy  technologies  are  provided  in   the  IEA  report  “Tracking  Clean  Energy  Progress  2014”  [1].     The  text  has  the  following  structure:      

List  of  Tables  .....................................................................................................................................  4   ABBREVIATIONS  ........................................................................................................................................  5  

ELECTRICITY  GENERATION  AND  HEATING  AND  COOLING  APPLICATIONS  USING   RENEWABLE  ENERGY  SOURCES  .................................................................................................  7   Solar  energy  ................................................................................................................................................  7   Wind  energy  ..............................................................................................................................................  11   Hydropower  ..............................................................................................................................................  14   Geothermal  ................................................................................................................................................  16   Biomass  for  bioenergy  ...........................................................................................................................  18   Municipal  organic  waste  ......................................................................................................................................  21   Cooling  and  heating  applications  .......................................................................................................  22   Water  heating  ...........................................................................................................................................................  25   Storage  technologies  ..............................................................................................................................  26   REFERENCES  ..............................................................................................................................................  31  

 

 

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 3 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

List  of  Tables   Table   1:   Confirmed   cell   and   submodule   efficiencies   under   the   global   AM1.5   spectrum   (1000   W/m2)  at  25  °C.  ...........................................................................................................................................................  8   Table  2:  Types  of  CSP  plants,  operational  efficiencies  and  costs.  ................................................................  10   Table  3:  Comparison  of  fixed  and  variable  speed  wind  turbines.  ...............................................................  12   Table  4:  Advantages  and  disadvantages  of  hydropower  ................................................................................  16   Table   5:   Global   energy   savings,   carbon   and   greenhouse   gases   of   geothermal   energy   (incl.   geothermal  heat  pump  cooling).  ......................................................................................................................  16   Table  6:  Positive  and  negative  impacts  of  geothermal  energy.  ....................................................................  17   Table  7:  Advantages  and  disadvantages  of  the  different  types  of  biofuels.  ............................................  21   Table  8:  Advantages  and  disadvantages  of  thermal  processes.  ...................................................................  23   Table  9:  Characteristics  of  solar  thermal  collectors  available  in  the  market.  ........................................  24   Table  10:  Comparison  of  different  TES  technologies.  ......................................................................................  28   Table  11:  Comparison  of  energy  storage  systems.  ............................................................................................  29      

 

 

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 4 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

ABBREVIATIONS   ASHP   Air-­‐source  heat  pump   BIPV   Building-­‐integrated  photovoltaic   BIPVT   Building-­‐integrated  photovoltaic  thermal   CAES   Compressed  air  energy  storage   COP  

Coefficient  of  performance  

CPV    

Concentrating  photovoltaic  

CSP  

Concentrating  solar  power  

DNI  

Direct  normal  irradiance  

EEMs   Energy  efficiency  measures   FAME   Fatty  ethyl  methyl  esters   GSHP   Ground-­‐source  heat  pump   HPVT   Hybrid  photovoltaic  thermal   HPWH   Heat  pump  water  heater   HTF  

Heat  transfer  fluid  

IEA  

International  energy  agency  

O&M   Operation  and  maintenance   PCM  

Phase-­‐changing  material  

PHS  

Pumped  hydro  storage  

PV  

Photovoltaic  

PV/T   Hybrid  photovoltaic  thermal   RES  

Renewable  energy  sources  

RETs   Renewable  energy  and  other  technologies   SMES   Superconducting  magnetic  energy  storage   SWH   Solar  water  heater   SWHS   Solar  water  heating  systems   TES  

Thermal  energy  storage  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

 

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

 

 

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 6 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

ELECTRICITY  

GENERATION  

AND  

HEATING  

AND  

COOLING  

APPLICATIONS  USING  RENEWABLE  ENERGY  SOURCES   Renewable   energy   sources   (RES)   are   an   inexhaustible,   sustainable,   indigenous   and   clean   energy   source   that   can   be   used   in   place   of   conventional   fuels   in   many   energy   conversion   applications   for   electricity   generation,   heating/cooling   production   or   biofuel   generation.   RES   are   classified   into  solar  energy,  wind  energy,  hydropower,  geothermal  energy  and  biomass.      

Solar  energy   Solar   energy   is   a   promising   renewable   energy   resource   because   it   can   be   used   in   various   locations,   while   the   operating   efficiencies   of   implemented   technologies   are   continuously   increasing  [2].  Solar  energy  can  be  converted  into  electricity  or  it  can  be  used   in  cooling/heating   applications.   This   Section   deals   with   the   conversion   of   solar   energy   into   electricity,   while   information   on   thermal   energy   generation   can   be   found   in   the   Section   “Cooling   and   heating   applications”.     Solar  energy  can  be  converted  into  electricity  with  photovoltaic  panels  (PV),  concentrating  solar   thermal   power   (CSP)   and   concentrating   photovoltaics   (CPV).   Challenges   to   the   use   of   solar   energy   include   the   cost,   the   manufacturing   procedure,   waste   products   and   the   requirement   of   direct  current  (DC)/alternating  current  (AC)  conversion  before  utilizing  it  for  home  appliances   or  in  the  utility  grid.       Photovoltaic  technologies  are  semiconductor  devices  that  generate  DC  electricity  from  sunlight.   PV  systems  consist  of  solar  panels,  DC-­‐DC  voltage  converters,  controllers  and  batteries  [3].  DC-­‐ DC  voltage  converters  are  used  to  match  the  characteristics  of  the  load  with  those  of  the  solar   panels.   A   number   of   solar   cells   connected   electrically   form   a   photovoltaic   module   and   the   combination  of  multiple  modules  form  an  array.  Between  1976  and  2012  installed  PV  have  been   increasing  by  a  factor  of  two  every  two  years  [2],  [4].  In  2014,  the  market  of  PV  panels  grew  by   30  %,  compared  to  the  previous  year  [5].     A   typical   PV   panel   can   operate   for   up   to   10   years   at   90   %   of   its   rated   power   and   for   up   to   25   years  at  80  %  of  its  rated  power  capacity  [2].  Commonly,  the  lifetime  of  PV  modules  is  assumed   to   be   25   years,   while   the   lifetime   of   inverters   is   15   years   [6].   Factors   that   influence   the   performance   of   a   PV   system   are   geographic   conditions   (weather   conditions,   altitude   and   latitude)  and  designing  factors,  such  as  system  selection,  orientation,  location,  panel  area  and  tilt   angle  [7].  For  example,  it  was  found  that  in  South  Korea  a  PV  module  with  a  slope  of  30  facing  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 7 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

south   resulted   in   the   best   performance   based   on   annual   power   output   and   it   produced   2.5   more   power   than   a   vertical   module   [8].   To   achieve   the   maximum   power   output,   the   direction   and   orientation   of   PV   panels   must   be   ideal.   Efficient   conversion   can   be   achieved   if   the   PV   modules   are  equipped  with  advanced  tracking  and  optical  systems  [2].             PV  panels  are  noiseless,  they  do  not  emit  greenhouse  gas  emissions  and  have  relatively  simple   operation   and   maintenance   [9].   However,   the   manufacturing   process   of   PV   systems   may   involve   toxic  materials  and  chemicals,  as  well  as  solvents  and  alcohols  that  may  have  indirect  impacts  on   the   environment.   In   addition,   PV   may   pose   a   negative   impact   when   integrated   to   the   grid   due   to   output  fluctuations  [10].  It  is  important  to  overcome  any  grid  integration  problems  since  these   may  affect  the  stability  of  the  system.     Today,  there  are  three  generations  of  photovoltaic  cells   [7].  The  1st  generation  involves  single-­‐ junction  crystal  solar  cells  based  on  silicon  wafers  (single  and  multi  crystalline  silicon),  the  2nd   generation   involves   single   junction   devices   and   comprises   CdTe,   CiGS   and   a-­‐SI   to   optimize   material   usage   and   efficiency   and   the   3rd   generation   involves   double   and   triple   junction   and   nanotechnology   for   more   efficient   cells   and   lower   cost.   The   different   PV   cells   and   their   efficiencies  can  be  found  in  Table  1.       Table  1:  Confirmed  cell  and  submodule  efficiencies  under  the  global  AM1.5  spectrum  (1000  W/m2)  at  25  °C   [11].   PV  cells   Silicon  

Classification   Si  (crystalline)   Si  (multicrystalline)   Si  (thin  transfer  submodule)   Si  (thin  film  minimodule)  

Conversion  efficiency  [%]   25.6  ±  0.5   20.8  ±  0.6   21.2  ±  0.4   10.5  ±  0.3  

III-­‐IV  cells  

GaAs  (thin  film)   GaAs  (multicrystalline)   lnP  (crystalline)  

28.8  ±  0.9   18.4  ±  0.5   22.1  ±  0.7  

ClGS  (cell)   ClGS  (minimodule)   CdTe  (cell)   Si  (amorphous)   Si  (microcrystalline)   Dye     Dye  (minimodule)   Dye  (submodule)  

20.5  ±  0.6   18.7  ±  0.6   21.0  ±  0.4   10.2  ±  0.3   11.4  ±  0.3   11.9  ±  0.4   10.0  ±  0.4   8.8  ±  0.3  

Organic  thin  film   Organic  (minimodule)   lnGaP/GaAs/lnGaAs   a-­‐Si/nc-­‐Si/nc-­‐Si  (thin  film)   a-­‐Si/nc-­‐Si  (thin  film  cell)  

11.0  ±  0.3   9.5  ±  0.3   37.9  ±  1.2   13.4  ±  0.4   12.7  ±  0.4  

Thin  film  chalcogenide   Amorphous/microcrystalline  Si   Dye  sensitized   Organic   Multi-­‐junction  devices  

  The   photovoltaic   market   is   dominated   by   mono-­‐   and   multi-­‐crystalline   silicon   solar   cells,   since   these   occupy   about   90   %   of   the   PV   market   [12].   In   2012   multi-­‐crystalline   solar   cells   had   the  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 8 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

highest  share  in  the  PV  market  of  59.9  %,  followed  by  mono-­‐crystalline  solar  cells  with  a  share   of  28.4  %  [13].   PV   installations   for   buildings   can   be   ground-­‐mounted   or   built   on   roofs   or   walls   [2].   Ground-­‐ mounted   or   roof/wall   PV   installations   belong   either   in   the   building-­‐integrated   photovoltaic   (BIPV)   applications   or   the   building-­‐integrated   photovoltaic   thermal   application   (BIPVT)  [7].   In   certain   peak   demand   niche   markets,   BIPV   applications   are   capable   of   delivering   electricity   at   less   than   the   cost   of   grid   electricity.   BIPVT   systems   are   incorporated   within   the   building   structure   and   merge   PV   with   thermal   systems   generating   both   electricity   and   thermal   energy   onsite  [5],  [7].     With   each   doubling   of   installed   capacity   the   cost   of   PV   has   decreased   by   20   %   [4].   The   total   investment  cost  of  PV  was  1.70  €/Wp  in  2013,  and  is  expected  to  be  1.43  €/Wp  in  2017  and  1.19   €/Wp  in  2022  [6].  The  average  PV  module  price  in  2013  was  0.75  €/Wp  and  the  average  inverter   price   0.17   €/Wp.   Engineering,   procurement   and   construction   cost   was   approximately   8   %   of   the   PV   system   cost   and   8   %   of   the   battery   system   cost   (including   inverter).   Operations   and   maintenance   cost   was   1.5   %   of   PV   system   cost   per   year   (incl.   inverter)   and   22   €/kW/year   for   the   battery.   In   addition,   the   balance   of   system1   of   the   PV   system   was   valued   in   2013   at   0.64   €/Wp   and   of   the   battery   at   70   €/kW/year.   In   2013,   the   total   COE   (including   transmission   investment)   from   PV   in   the   USA   was   21.1   cents/kWh   (in   $).   2050   projected   electricity   prices   from  PV  are  5.3-­‐5.7  cents/kWh  and  7.3-­‐7.7  cents/kWh  with  transmission  costs  [4].   CSP  systems  are  based  on  the  concentration  of  solar  irradiation  by  programmed  mirrors  onto  a   receiver   where   the   heat   is   collected   by   a   thermal   energy   carrier,   the   heat   transfer   fluid   (HTF)   [14].   When   compared   to   other   renewables   that   cannot   be   stored   effectively,   CSP   with   thermal   storage   offers   an   reliable   and   stable   alternative   for   energy   generation   [15].   Although   storage   facilities   require   large   surface   areas   and   increase   the   investment   cost   of   a   plant,   it   has   been   shown   that   the   cost   of   electricity   of   a   CSP   with   storage   is   similar   or   even   lower   that   of   a   CSP   without   storage   [16].   CSP   plants   are   composed   of   solar   collectors   (mounted   on   a   solar   tracker   that  keeps  track  of  the  position  of  the  sun  [2]),  a  steam  turbine  and  an  electricity  generator  [17].   CSP   collectors   concentrate   the   sunrays   along   a   focal   line   or   on   a   single   focal   point.   Line-­‐focusing   solar   collectors   have   single-­‐axis   tracking   systems   and   are   parabolic   troughs   or   Fresnel   reflectors,   while   point-­‐focusing   collectors   have   two-­‐axis   tracking   systems   and   are   either   heliostats  (power  tower  plants)  or  parabolic  dishes  [16],  [17].     Parabolic   trough   collectors   are   the   most   widely   used   commercial   technology   worldwide,   associated  with  the  least  possible  risk  when  compared  to  other  alternatives.  In  addition,  they  are                                                                                                                             1  It  includes  all  the  components  of  the  PV  system.  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

associated   with   a   good   land-­‐use   factor.   Parabolic   trough   systems   consist   of   linear   interconnected  parabolic  troughs,  a  steam  turbine  and  a  generator.   For  continuous  function  also   during   the   night   they   are   coupled   with   heat   tanks   that   provide   them   with   the   necessary   thermal   energy   or   gas   as   an   additional   energy   source.   Parabolic   troughs   have   low   heat   losses,   they   are   positioned   toward   the   south,   upright   or   horizontally   and   provide   the   best   land-­‐use   factor   of   any   solar  technology.  CSP  based  on  parabolic  though  collectors  operate  at  temperatures  350-­‐550  °C   with  plant  efficiencies  of  14-­‐20  %  and  annual  solar-­‐to-­‐electricity  efficiency  11-­‐16  %  [16].   Heliostats  are  composed  of  several  flat  mirrors  and  have  mechanisms  of  sun  tracking  along  two   axes.  A  solar  tower  plant  consists  of  heliostats,  a  tower  with  a  receiver  and  the  working  fluid  and   the   generator.   In   a   solar   power   tower   plant,   the   heliostats   concentrate   solar   irradiation   onto   the   receiver   of   the   solar   tower.   This   type   of   plants   is   cost   effective   with   capacities   50-­‐100   MW.   They   require   the   largest   areas   per   unit   of   generated   electricity   and   large   quantities   of   water   and   their   efficiency   depends   on   optical   characteristics   of   the   heliostats,   mirror   cleanliness,   tracking   system  precision,  etc.     Parabolic   dish   systems   are   composed   of   parabolic   reflectors   in   the   form   of   a   dish,   a   Stirling   engine   in   the   focus   of   the   dish   and   a   generator   of   the   electrical   energy   [1].   Parabolic   dishes   have   diameters  of  5-­‐10  m  and  a  surface  area  of  40-­‐120  m2.  The  power  of  parabolic  dish  systems  is  5-­‐ 50  kW  with  an  efficiency  including  the  Stirling  engine  of  30  %.     Solar   power   plants   with   Fresnel   reflectors   consist   of   flat   or   slightly   curved   Fresnel   reflectors,   receivers   of   the   concentrated   irradiation,   a   cylindrical   parabolic   reflector,   a   steam   turbine   and   a   generator.   The   Fresnel   reflectors   reflect   solar   irradiation   to   the   receiver   of   the   cylindrical   parabolic   reflector   that   has   the   form   of   long   tubes.   Fresnel   reflectors   are   cheaper   than   parabolic   mirrors  and  can  have  either  large  or  small  capacity.     Most   of   the   CSP   plants   in   operation   and   under   construction   in   the   world   use   parabolic   trough   systems   and   are   largely   situated   in   Spain   [17].   Some   characteristics   and   costs   of   the   different   CSP  plants  are  shown  in  Table  2  [17]–[19].       Table  2:  Types  of  CSP  plants,  operational  efficiencies  and  costs  (costs  presented  in  €).   Type   of   CSP   plant  

Plant  size   [MW]  

Thermal   efficiency  [%]  

Demonstrated   annual   efficiency   [%]  

Levelized   energy  cost   [cent/kWh]  

Land   use   [m2/MWha]  

Capital   cost   [€/W]  

Parabolic   trough  

10-­‐200  

30-­‐40  

10-­‐15  

5.6-­‐9.1  

6-­‐8  

2.99-­‐3.22  

Power  tower  

10-­‐150  

30-­‐40  

8-­‐10  

3.3-­‐5.4  

8-­‐12  

2.40-­‐3.62  

Dish-­‐Stirling  

2.5-­‐100  

30-­‐40  

16-­‐18  

4.0-­‐6.0  

8-­‐12  

2.65-­‐2.90  

 

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

The  cost  of  CSP  is  decreasing  but  slower  than  the  cost  of  PV  [4].  As  an  example,  a  400  MW  PV   installation  in  Spain  will  cost  571  million  dollars  and  the  LCOE  will  be  at  8  cents/kWh.  In  2013,   the   total   COE   (including   transmission   investment)   from   CSP   in   the   USA   was   0.312   $/kWh   [2].   Projected  LCOE  of  CSP  are  €0.05  +  transmission  costs  of  0.015  in  2020  and  €0.04  +  0.01  in  2050   [4].     CPV  use  the  photovoltaic  effect  to  generate  electricity.  The  sunlight  is  concentrated  by  means  of   an  optical  device  (commonly  made  of  plastic  or  glass  material)  onto  a  solar  cell  (in  most  cases,   based  on  multi-­‐junction  solar  cells)  [20].     Multi-­‐junction  cells,  used  as  the  standard  PV  technology  in  space  applications,  recently  entered   the   terrestrial   market   in   CPV   systems   with   several   large-­‐scale   plants   (50   MW   each)   in   operation   or   under   construction   [21].   However,   to   date,   only   a   few   CPV   installations   have   been   commissioned   worldwide,   while   the   initiatives   are   taken   by   a   small   number   of   technology   leaders.  As  reported  by  the  International  Energy  Agency  (IEA),  CPV  represent  less  than  1  %  of   the   market   [21].   CPV   technologies   must   follow   a   steeper   learning   curve   to   have   a   chance   of   becoming  commercially  viable  in  the  long  term  [22].   Based  on  a  report  on  the  status  of  CPV  technology  published  by  the  National  Renewable  Energy   Laboratory  and  the  Fraunhofer  Institute,  the  price  of  CPV  power  plants  with  a  capacity  of  10  MW   (including   installation)   was   estimated   to   lie   between   1,400   €/kWp   and   2,200   €/kWp   [23].   The   large   range   of   prices   results   from   the   different   technological   concepts   and   the   nascent   and   regionally  variable  markets.  Using  various  technical  and  financial  assumptions,  the  levelized  cost   of   electricity   was   found   to   lie   between   0.10   €/kWh   and   0.15   €/kWh   at   locations   with   a   direct   normal   irradiance   (DNI)   of   2,000   kWh/(m²a)   and   between   0.08   €/kWh   and   0.12   €/kWh   with   2,500   kWh/(m²a).   If   installations   continue   to   grow   through   2030,   CPV   could   reach   a   cost   between   0.045   €/kWh   and   0.075   €/kWh   with   system   prices   (including   installation)   between   700  and  1,100  €/kWp.  

  Wind  energy   Wind   energy   constitutes  an   important   electricity   production   technology   in   many   countries   [24].   In  2011,  global  wind  capacity  reached  237  GW  providing  500  TWh  annually,  i.e.,  around  3  %  of   the   global   electricity   consumption.   At   the   end   of   2013,   the   installed   capacity   of   wind   power   reached  318  GW  [25].     Wind  turbines  can  be  classified  into  fixed-­‐speed  and  variable-­‐speed  turbines  based  on  whether   the  rotor  speed  varies  or  not  with  the  wind  speed.  A  comparison  between  the  two  classes  can  be  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

seen  in  Table  3.  The  basic  two  structural  types  of  wind  turbines  are  horizontal  axis  and  vertical   axis   turbines   [26].   Horizontal   axis   wind   turbines   constitute   the   most   common   design   and   are   turbines   with   their   blades   rotating   on   an   axis   parallel   to   the   ground.   For   these   turbines   to   operate   effectively,   they   must   be   pointed   into   the   wind.   In   vertical   axis   turbines,   on   the   other   hand,   the   blades   are   rotated   on   an   axis   perpendicular   to   the   ground   and   do   not   need   to   be   pointed  into  the  wind.     In   a   wind   turbine   generator   blades   capture   the   wind   energy,   which   is   then   converted   into   mechanical  and  then  into  electrical  energy  [27].  The  net  generation  of  a  wind  turbine  is  usually   10-­‐15   %   below   the   theoretical   energy   generation   calculated   based   on   wind   turbine   power   curves  and  wind  regime  [28].  This  is  due  to  array  losses  (shadowing  of  wind  turbines  within  a   farm),   blade   soiling   losses,   electrical   losses   in   transformers   and   cabling   and   wind   turbine   downtime  for  maintenance  or  technical  failure.     The   first   step   to   determine   the   configuration   of   a   wind   farm   is   to   calculate   and   minimize,   if   possible,   array   losses   [24].   After   the   configuration   is   determined   and   the   wind   turbines   are   situated  in  the  area  to  be  studied,  the  wind  energy  production  is  calculated.  To  achieve  this  the   wind   turbine   must   be   selected   and   the   corresponding   power   curve   and   wind   data   collected.   Lastly,   the   generation   cost   of   the   wind   energy   that   can   be   installed   in   the   selected   area   is   calculated.   The  minimum  and  maximum  wind  speeds  with  which  a  wind  turbine  can  function  are  called  “cut   in”   and   “cut   out”   speeds,   and   are   for   most   turbines   are   4   m/s   and   15   m/s,   respectively   [27].   The   recommended   speed   for   wind   turbines   is   7-­‐10   m/s.   For   small   wind   generators   of   20-­‐100   W   annual   average   wind   speeds   of   3-­‐4   m/s   can   be   adequate   [2].   The   full   load   hours   for   onshore   applications  are  between  1,700-­‐3,000  h/year  [28].  The  average  load  hours  in  Spain  are  2,342,  in   Denmark  2,300  and  in  the  United  Kingdom  2,600.     Table  3:  Comparison  of  fixed  and  variable  speed  wind  turbines  [27].      

Strengths  

Weaknesses  

Constant  speed  

Doubly  fed  

Direct  drive  

Simple  and  robust  

Less  mechanical  stress    

Less  mechanical  stress    

Less  expensive  

Less  noisy  

Less  noisy  

Standard  generator  

Aerodynamically  efficient  

Aerodynamically  efficient  

Standard  generator  

No  gearbox  

Small  converter  suffices  

 

Aerodynamically  less  efficient  

Electrically  less  efficient  

Electrically  less  efficient  

Gearbox  included  

Gearbox  included  

Large  converter  necessary  

Mechanical  stress  

Expensive  

Expensive  

Noisy  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

Heavy,  large  and  complex  generator  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

There   are   three   main   types   of   generators   that   can   be   coupled   with   wind   turbines:   (1)   the   squirrel   cage   induction   generator   for   fixed   speed,   (2)   the   doubly   fed   induction   generator   for   variable   speed   and   (3)   the   permanent   magnet   synchronous   generator   for   variable   speed   [27].   The  latter  is  preferred  for  variable  speed  due  to  its  higher  efficiency,  minimal  maintenance  cost   and  lower  weight  (it  does  not  have  external  rotor  current  and  gearbox).     The   main   drawback   of   wind   energy   is   its   dependence   on   the   weather.   Output   fluctuations   in   the   time   range   of   a   minute   for   wind   generators   can   cause   frequency   and   voltage   variations   [29].   Combining  an  energy  storage  system  with  a  wind  turbine  can  minimize  the  challenges  present   and  mitigate  the  effects  of  power  fluctuations  [27],  [29].  Batteries  (excluding  conventional  lead-­‐ acid  batteries),  flow  batteries  and  short  time  scale  storage  like  supercapacitors  with  fast  power   modulation  and  continuous  operation  are  suitable  for  managing  output  fluctuations.  In  addition,   reliable   wind   power   forecasting   plays   a   very   important   role   in   balancing   supply   and   demand   [30].   Flywheels  and  superconducting  magnetic  energy  storage  and  compressed  air  energy  storage  can   serve  this  purpose  well  [27],  [29].  Economic  viability  is  also  an  important  factor  when  choosing   a   storage   technology.   Although   hydrogen   storage   provides   great   potential   for  long-­‐term   storage,   the   economic   viability   of   the   method   is   associated   with   rather   high   uncertainty   [29].   More   information  on  storage  options  can  be  found  in  the  Section  “Storage  technologies”.   Although   wind   energy   provides   an   alternative   solution   to   the   global   energy   problem,   it   can   create  issues  in  a  habitat  community  [31].  Some  problems  than  can  be  caused  by  the  installation   of   wind   turbines   are:   effects   on   animals   (mortality   and   disturbance   of   birds,   bats   and   marine   species   in   the   case   of   offshore   projects),   deforestation   and   soil   erosion,   noise,   visual   impact,   reception   of   radio   waves   and   weather   radar   and   local   weather   and   regional   change   impact   [31].   Such  environmental  and  social  issues  must  be  accounted  for  in  wind  energy  projects.   The  capital  costs  of  a  wind  turbine  project  include  wind  turbines,  foundation,  road  construction   and   grid   connection   and   can   be   close   to   80   %   of   the   total   cost   of   the   project   over   its   entire   lifetime   [28].   The   variable   costs   of   such   a   project   (dominated   by   the   operation   and   maintenance   costs,   O&M,   and   also   including   land   rental,   insurance,   taxes,   etc.)   are   10-­‐20   %   of   the   total   investment.  The  variable  costs  are  not  as  easy  to  calculate  as  capital  costs.  The  current  trend  of   wind  turbine  manufacturers  is  to  lower  the  variable  costs  by  new  turbine  designs  that  require   fewer   service   visits   and   have   better   productivity.   The   cost   of   the   electricity   of   a   wind   turbine   depends  on  the  capacity  factor  (the  percentage  of  the  time  the  wind  farm  generates  electricity   during  a  year).  The  discount  rate  and  economic  lifetime  of  the  investment  reflect  the  perceived   risk,  regulatory  climate  in  a  country  and  profitability  and  alternative  investments.    

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

For   offshore   turbines   the   wind   turbine   costs   represent   approximately   50   %   of   the   overall   project   [32].   The   foundation   costs   (included   in   the   civil   works)   increase   from   4-­‐6   %   in   the   onshore  case  to  21  %  [28].  O&M  costs  can  constitute  up  to  30  %  of  the  overall  costs.  For  offshore   projects  a  range  between  1,800-­‐2,500  €/kW  can  be  assumed,  which  results  in  generation  costs   of  6-­‐11.1  cent/kWh.   Between  2002  and  2008,  wind  turbine  prices  in  the  USA  increased  by  more  than  100  %  (from   700  to  1,500  $/kW)  due  to  the  strong  demand  in  wind  turbines,  turbine  and  component  supply   shortages,   increased   material,   energy   and   labor   prices,   etc.   [24].   Since   2008   wind   turbine   prices   have  decreased  due  to  the  reversal  of  some  of  these  factors  and  increased  competition.  In  2009   the  capital  costs  of  a  wind  energy  project  in  Europe  were  1,100-­‐1,400  €/kW  (in  2010  in  Spain  an   installed  wind  turbine  cost  1,490  €/kW)  [28].  Of  this  cost,  71  %  was  associated  with  the  turbine   itself,   12   %   with   the   grid   connection,   9   %   with   civil   works   (foundations,   road   construction,   buildings)   and   8   %   with   other   capital   costs   (development   and   engineering   costs,   land   costs,   licensing   procedures,   consultancy   and   permits,   monitoring,   etc.).   Ref.   [24]   presents   the   cost   breakdown  in  Spain  as:  74  %  for  the  turbine,  12  %  for  the  grid  connection,  9  %  for  civil  works   and   5   %   for   other   capital   costs   and   in   the   USA   as:   80   %   for   the   turbine,   11   %   for   the   grid   connection,   5   %   for   the   civil   works   and   4   %   for   other   capital   costs.   According   to   the   Strategic   Energy   Review   of   the   European   Commission,   the   capital   cost   of   wind   energy   is   likely   to   fall   to   826  €/kW  in  2020,  788  €/kW  in  2030  and  762  €/kW  in  2050  [28].   According  to  Ref.  [24],  for  a  2  MW  turbine  with  a  capital  cost  of  1,100-­‐1,400  €/kW,  O&M  costs  of   1-­‐1.5   cent/kWh   over   the   lifetime   of   the   turbine   (1.5-­‐2.0   %   of   the   capital   cost),   20   years   of   lifetime,   an   80/20   debt/equity   ratio,   a   7   %   discount   rate   to   be   repaid   over   20   years,   a   3   %   inflation  rate  and  1,700-­‐3,000  working  hours,  the  COE  was  found  to  be  4.5-­‐8.7  cent/kWh  [24],   [28].      

Hydropower   Hydropower   is   generated   by   converting   the   potential   energy   of   water   into   kinetic   energy   of   running   water   and   then   into   electrical   energy   via   turbines.   In   2010   3,300   TWh   of   electrical   energy  was  generated   through  hydropower  globally,  i.e.,  90  %  of  the  renewable  energy  or  16  %   of   the   total   electric   energy   worldwide   [33],   [34].   In   2012,   hydropower   accounted   for   18   %   of   power  generation  worldwide  and  11.7  %  of  the  net  electricity  generation  in  Europe  [35],  [36].     The  turbines  used  in  hydropower  can  be  separated  into  impulse  (Pel,  Cross-­‐flow  and  Turgo)  and   reaction   turbines   (Propeller,   Francis   and   Kinetic)   [37],   [38].   Submerged   turbines   can   generate  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

power   from   ocean   or   river   currents   without   generating   greenhouse   gas   emissions   and   with   relatively  low  operating  costs.     Hydrostatic   and   hydrokinetic   are   the   two   methods   to   harness   energy   from   water   [35].   Hydrostatic  requires  storage  of  water  in  reservoirs  to  create  a  pressure  head,  while  hydrokinetic   converts  the  kinetic  energy  of  flowing  water  into  electricity  in  relatively  small-­‐scale  turbines.     Although  hydropower  is  the  most  efficient  way  to  generate  electricity,  the  efficiency  decreases   with  size.  High  quality  professional  systems  of  hydrokinetic  turbines  can  only  reach  an  efficiency   of  50  %  [35].  Two  other  drawbacks  of  hydrokinetic  turbines  are  cavitation  and  degradation  in   harsh  marine  environments.  However,  when  compared  to  a  wind  turbine,  the  power  density  of  a   hydrokinetic  turbine   operating  at  2   m/s   stream   velocity   is   similar   to   a   wind   turbine   operating   with  a  wind  speed  of  16  m/s.     Small-­‐scale  hydro  are  mainly  run-­‐of-­‐river  projects  that  do  not  involve  complex  construction  or   large   dams   with   little   or   no   water   stored   and   can   be   installed   as   multi-­‐unit   arrays   like   wind   farms   [35],   [39].   Low-­‐head   micro-­‐hydropower   stations   are   also   a   small-­‐size   alternative   and   a   promising  choice  for  electricity  generation  in  rural,  remote  and  hilly  areas,  where  fuel  prices  are   higher   [38].   Most   low-­‐head   micro-­‐hydropower   plants   produce   less   than   100   kW,   although   there   are  classifications  involving  plants  of  up  to  500  kW.     Positive   aspects   of   hydropower   include   the   wide   availability   of   resources,   efficient   energy   conversion   with   proven   technology,   relatively   low   operating   and   maintenance   costs   (although   with   high   capital   cost)   and   a   long   life   span.   Hydropower   is   also   a   renewable   energy   resource   without   fluctuations   and   can   be   used   for   irrigation   and   flood   control.   However,   large   hydropower  projects  may  cause  social  and  environmental  problems.  Some  examples  are  people   relocation,   modification   to   local   land   use   patterns   and   limitation   of   biodiversity   [33],   [39].   Spatial   optimization   accounting   for   social   and   environmental   aspects   is   necessary   before   the   construction   of   large-­‐scale   projects   [40].   Very   small   hydro   plants,   on   the   other   hand,   do   not   suffer   from   such   problems   due   to   the   much   smaller   technology   scale   and   the   smaller   water   storage  required.  Some  advantages  and  disadvantage  of  hydropower  are  shown  in  Table  4  [37].   The  installation  costs  of  hydropower  projects  depend  on  the  location,  existing  infrastructure  and   installation   capacity   [37].   In   general,   the   equipment   of   low-­‐head   plants   cost   more   than   higher   head   plants   for   the   same   output,   while   low   output   equipment  is   also   more   costly.   The   electro-­‐ mechanical   equipment   costs   account   for   about   30-­‐40   %   of   the   total   small   hydropower   plant   budget,  while  operation  and  maintenance  costs  are  estimated  to  3-­‐4  %  of  the  total  capital  cost.        

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

 

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

Table  4:  Advantages  and  disadvantages  of  hydropower   Advantages  

Disadvantages  

Economic  aspects   -­‐  Low  operating  and  maintenance  cost  

-­‐  High  capital  cost  

-­‐  Long-­‐lasting  and  robust  technology,  systems  can  last  for   50-­‐100  years  or  more  without  major  new  investments  

-­‐  Requires  multidisciplinary  involvement    

-­‐  A  reliable  source  of  energy  

-­‐  Precipitation  (availability  of  water)   -­‐  Long-­‐term  planning  is  required  

-­‐  Includes  proven  technology  

-­‐  Long-­‐term  agreement  is  required  

-­‐  Promotes  regional  development  

-­‐  Requires  outsourcing  of  contractors  and  funding  

-­‐  Technology  with  high  efficiency   -­‐  Generates  revenues  to  sustain  water   -­‐  Creates  employment  opportunities  and  saves  fuel   Social  aspects   -­‐  Improves  standard  of  living  

-­‐  May  lead  to  resettlement    

-­‐  Leaves  water  available  for  other  uses  

-­‐  Limits  navigation  

-­‐  Frequently  provides  flood  protection  

-­‐   Damming   of   large   area   reduces   public   access   to   areas.  This  affects  outdoor  recreation  activities  

-­‐  May  enhance  navigation  conditions  

-­‐  Requires  checking  of  waterborne  disease  vectors  

-­‐  Enhances  recreation   -­‐Enhances  accessibility  of  the  territory  and  its  resources  

-­‐  The  power  lines  can  change  the  landscape   -­‐  Management  of  competing  water  uses  is  needed  

Environmental  aspects   -­‐   Produces   no   atmospheric   pollutant   and   only   some   greenhouse  gas  emissions   -­‐  No  waste  is  produced  

-­‐  Barriers  for  fish  migration  and  fish  entrainment     -­‐  Involves  modification  of  aquatic  habitats   -­‐  Requires  management  of  water  quality  

-­‐  Avoids  depleting  non-­‐renewable  fuel  resources   -­‐   Creates   new   freshwater   ecosystems   with   increased   productivity   -­‐  Enhances  skill  development    

-­‐   The   methyl   mercury   introduction   into   the   food   chain  requires  close  monitoring/management     -­‐  The  populations  may  need  to  be  monitored   -­‐  Damming  areas  rich  in  biodiverse  flora  results  in   carbon  emissions  

-­‐  Slows  down  climate  change  

 

Geothermal     Table  5:  Global  energy  savings,  carbon  and  greenhouse  gases  of  geothermal  energy  (incl.  geothermal  heat   pump  cooling).  (Numbers  in  millions  in  terms  of  tonnes  of  oil  equivalent,  TOE).     As  electricity   As  direct  heat  

Fuel  oil   TOE   37.5   18.8  

Carbon   TOE   33.2   16.6  

CO2   TOE   106.9   53.4  

SOX   TOE   0.74   0.37  

NOX   TOE   0.022   0.011  

   

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

 

                   Page 16 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

Table  6:  Positive  and  negative  impacts  of  geothermal  energy.   Topic  

Poverty  

Positive  impacts  

Negative  impacts  

-­‐Increased  income  per  capita  

-­‐  Rising  property  prices  

-­‐  Increase  in  salaries  

-­‐  Community  displacement  

-­‐  Social  development  initiatives  

 

-­‐  Affordable  energy  supply   -­‐  Higher  living  standards   -­‐  Improved  food  security   -­‐  Access  to  drinking  water  

Health  

Education  

-­‐  Improved  sanitation  

-­‐  Odors    

-­‐  Improved  medical  facilities  

-­‐  Toxic  gas  emissions  

-­‐  Lower  indoor  air  pollution  

-­‐  Water  contamination  risk  

-­‐  Therapeutic  uses  

-­‐  Noise  pollution  

-­‐  Improved  education  facilities  

Sudden   or   cultural  change  

-­‐  Improved  school  attendance    

Natural  hazards  

unprecedented  

-­‐  Induced  seismicity   -­‐  Subsidence   -­‐  Hydrothermal  eruptions  

Demographics  

-­‐  Positive  social  change  

-­‐  Negative  cultural  impacts  

-­‐  Increased  tourism  

-­‐  Resettlement   -­‐  Livelihood  displacement  

Atmosphere  

Displacement   of   greenhouse   gas   emissions   from  other  energy  sources  

-­‐  Greenhouse  gas  emissions   -­‐  H2S  pollution   -­‐  Toxic  gas  emissions  

Land  

Small   land   requirements   relative   to   other   energy  sources  

-­‐  Habitat  loss   -­‐  Soil  compaction   -­‐  Conflict  with  other  land  uses  

Forests  

Freshwater  

Replacement  of  traditional  biomass  

-­‐  Deforestation     -­‐  Ecosystem  loss  

Low  lifecycle  water  consumption  relative  to   other  energy  sources  

-­‐  Conflict  with  other  energy  uses  

 

-­‐  Habitat  loss  or  disturbance    

Biodiversity  

-­‐   Contamination   of   shallow   aquifers  and  other  water  bodies  

-­‐   Loss   of   rare   geothermal   ecosystems   -­‐  Increased  energy  security  

Limited  direct  long-­‐term  jobs  

-­‐  Low  climate  dependence     Economic  development  

-­‐  High  capacity  factor   -­‐   Direct,   indirect   and   induced   economic   activity  and  employment   Waste  heat  can  be  cascaded  or  recaptured  

Consumption   and   production  patterns  

-­‐  Waste  may  cause  environmental   contamination   -­‐  Risk  of  overexploitation     -­‐   High   cost   of   turbines   may   compromise  efficiency  

 

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 17 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

The  development  in  geothermal  for  direct  use  has  been  relatively  slow  in  most  countries   [41].   The   IEA   reported   that   geothermal   energy   could   contribute   approximately   3.5   %   of   the   annual   global  electricity  production  and  3.9  %  of  the  required  energy  for  heat  (excluding  ground  source   heat   pumps)   by   2050.   In   2012,   geothermal   energy   contributed   0.2   %   of   the   total   net   production   in   the   EU-­‐27   countries   [42].   In   2010,   geothermal   (ground-­‐source)   heat   pumps   had   the   largest   installed   capacity   among   geothermal   technologies   with   a   share   of   68.3   %   worldwide.   Between   2005   and   2010,   the   installed   capacity   of   geothermal   applications   for   space   heating   and   greenhouse  heating  has  increased  by  24  and  10  %,  respectively.   The   worldwide   savings   in   energy,   carbon   and   greenhouse   gases   with   geothermal   energy   are   shown  in  Table  5  [41].   Geothermal   developments   may   present   both   positive   and   negative   impacts   that   must   be   managed  to  result  in  an  overall  positive  outcome.  A  summary  of  geothermal  sustainability  issues   are  seen  in  Table  6  [43].    

Biomass  for  bioenergy     It   is   expected   that   bioenergy   will   play   a   key   role   in   the   long-­‐term   energy   strategy   of   the   European   Union   for   many   applications,   with   an   emphasis   on   the   transport   sector   [32].   It   is   foreseen  that  by  2020  bioenergy  will  contribute  up  to  14  %  of  the  EU  energy  mix  and  up  to  10  %   of  energy  demand  in  transport.  There  are  strong  indications  that  bioenergy  will  cover  30  %  of   the  global  energy  demand  by  2050  [44].   Biomass  is  the  only  renewable  resource  that  can  address  the  dependence  of  the  transportation   sector   on   foreign   oil   without   having   to   replace   the   vehicle   fleet   [45].   A   challenge   of   biomass   feedstock  is  the  seasonal  nature  of  biomass  supply,  since  it  is  based  on  plant  matter  that  must  be   planted,  cultivated  and  harvested.  Wood  residues  are  less  seasonal  compared  to  crop  residues,   since  they  grow  over  multiple  years.  Another  alternative  that  permits  several  harvests  in  a  short   timeframe   is   aquatic   biomass,   from   microscopic   (microalgae   and   cyanobacteria)   to   large   seaweeds  (macroalgae).     Storage   is   an   issue   that   must   be   accounted   for   when   planning   biomass   applications.   There   are   various  choices  of  biomass  storage  [45].  The  cheapest  option  is  ambient  storage  that  may  lead,   however,   to   biomass   degradation   and   1   %   material   loss/month.   To   reduce   this   loss   to   approximately   0.5   %,   covered   storage   in   pole-­‐frame   structures   can   be   applied.   In   the   case   that   a   higher   quality   of   biomass   is   required,   closed   warehouses   with   hot   air   drying   can   be   used.   In  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 18 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

addition   to   the   direct   storage   of   biomass,   pretreatment   to   reduce   moisture   and   improve   feedstock  quality  may  also  be  adopted.   First  generation  biofuels  include  corn  grain,  sugarcane,  soybean,  oil  seed  etc.  and  may  compete   with   and   influence   the   prices   and   production   of   animal   feed   and   human   food   [44],   [45].   Currently   most   biofuels   are   produced   by   these   feedstocks   mainly   due   to   their   technological   maturity  and  lower  unit  production.  To  overcome  the  problems  of  the  first-­‐generation  biofuels,   second-­‐generation   biofuel,   i.e.,   non-­‐starch,   non-­‐edible,   non-­‐food   feedstocks   based   on   cellulosic   biomass,  such  as  forest  and  agricultural  residues,  food  processing  waste,  dedicated  energy  crops   (e.g.,  poplar,  switchgrass)  and  others  are  being  explored.     Biofuels  have  been  produced  and  used  over  the  last  15  years  in  solid,  liquid  and  gaseous  form   [44].   Solid   biofuels   (biomass)   include   firewood,   wood   chips,   wood   pellets   and   wood   charcoal,   liquid   biofuels   include   bioethanol,   biodiesel,   pyrolysis   bio-­‐oil   and   transportation   fuels,   while   gaseous  include  biogas  and  syngas.   Wood   and   plant   oil   were   the   dominant   fuels   for   cooking,   heating   and   lighting   before   the   19th   century.  In  the  last  13  years  the  global  consumption  in  firewood  has  increased  by  3  %,  while  its   share  in  the  overall  energy  consumption  has  decreased  [44].  Approximately  40  %  of  the  global   population  relies  on  firewood  for  cooking  and  heating.  Firewood,  however,  is  bulky  and  cannot   be  used  in  small,  automated  heating  systems  with  controlled  fuel  value.     Wood  chips,  on  the  other  had,  are  small  pieces  of  biomass  and  have  been  used  for  heating  and   electricity   generation   since   the   beginning   of   the   21st   century.   They   have   also   been   used   in   co-­‐ firing   projects   with   coal   (15-­‐30   vol%   mixtures)   to   generate   electricity   with   overall   conversion   efficiencies   of   33-­‐37   %   [44].   Compared   to   coal,   wood   chips   emit   less   SOX   and   NOX   when   combusted,   but   may   lose   significant   dry   matter   and   energy   value   during   storage.   The   global   electricity  generation  from  wood  chips  is  expected  to  double  from  70  GW  in  2010  to  145  GW  in   2020  [44].   Wood   pellets   are   more   processed   than   wood   chips   with   lower   moisture   content   and   a   high   packing   density   but   they   are   more   expensive.   They   can   also   be   produced   from   grasses,   crop   residues  and  nutshells.  Their  small  size  if  offered  for  use  in  automatic  stoves  at  fine  calibration   with  energy  efficiency  70-­‐83  %.  The  current  price  of  wood  pellets  in  the  USA  is  $250  per  tonne   [44].  The  global  production  of  wood  pellets  is  expected  to  increase  from  15.4  million  tonnes  in   2010  to  45.2  tonnes  in  2020  [44].   Charcoal   is   a   carbon-­‐enriched,   porous   solid   produced   through   the   pyrolysis   of   wood.   Good   quality  charcoal  has  an  energy  content  of  approximately  28-­‐33  MJ/kg  and  it  gives  a  combustion   temperature  as  high  as  2,700  °C.    

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 19 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

Bioethanol  is  a  liquid  fuel  that  can  be  produced  through  the  fermentation  of  vegetative  biomass   (simple  sugars,  such  as  glucose,  fructose  and  other  monosaccharides).  The  most  important  use   of   ethanol   is   as   a   substitute   of   gasoline   in   power   petrol   engines.   Bioethanol   has   an   energy   density   equal   to   67   %   that   of   gasoline.   The   global   consumption   of   bioethanol   increased   from   4.5   billion   gallons   in   2000   to   21.8   billion   gallons   in   2012   [44].   Bioethanol   can   be   blended   with   gasoline  in  any  combination.  In  the  USA  it  is  currently  approved  as  a  10  %  blend  for  all  vehicles   and  as  85  %  blend  for  flex-­‐fuel  vehicles.  Most  of  the  cost  of  lignocellulosic  bioethanol  production   is  associated  with  the  conversion  of  cellulosic  components  into  fermentable  sugars.   Diesel  is  used  in  diesel  engines,  heavy-­‐duty  vehicles  and  machines  and  in  home-­‐heating  facilities   in   developing   countries.   Biodiesel   (fatty   ethyl   methyl   esters,   FAME)   is   generated   from   vegetable   oil,   animal   fats,   algal   lipids   and   waste   grease   through   trans-­‐esterification   in   the   presence   of   alcohol  and  alkaline  catalysts.  Biodiesel  has  90  %  the  energy  density  of  petrol  diesel  and  it  can   be   blended   with   diesel   at   any   combination   [44],   [45].   The   global   consumption   of   biodiesel   increased   from   213   million   gallons   in   2000   to   5,670   million   gallons   in   2012   [44].   Due   to   problems  like  lower  stability,  cleaning  effects  and  high  oxygen  content  of  FAME,  when  compared   to  diesel,  it  is  typically  limited  by  vehicle  warranties  to  a  blending  of  5  %  [45].     Bio-­‐oil  is  one  of  the  three  products  of  biomass  pyrolysis  (together  with  biochar  and  syngas)  in   the   absence   of   air.   To   be   able   to   use   the   liquid   as   a   petrol   distillate   fuel   alternative,   significant   upgrading   (hydroprocessing)   is   needed,   in   order   to   decrease   its   moisture   content   and   acidity   and  improve  its  heating  value  and  storage  stability  [44],  [45].     Bioethanol  and  biodiesel  have  higher  oxygen  content  and  dissolution  capability  than  petrol  fuels   and   are   thus   more   corrosive   to   engines,   fuel   storage   and   distribution   equipment.   Drop-­‐in   biofuels,   i.e.,   biomass-­‐derived   liquid   hydrocarbons   that   follow   the   existing   petrol   distillate   fuel   specifications  can  be  ready  to  “drop-­‐in”  to  the  existing  fuel  supply.  These  fuels  include  butanol,   liquefied   biomass,   sugar   hydrocarbons   and   others   and   they   are   generated   through   different   pathways.   Biogas  is  an  alternative,  renewable  fuel,  to  natural  gas  that  is  generated  through  the  anaerobic   digestion   of   organic   wastes.   Typically   one   tonne   biowaste   (dry   weight)   can   yield   120   m3   of   biomethane  that  can  potentially  produce  200  kWh  of  net  electricity  [44].   Syngas  is  generated  from  the  gasification  or  pyrolysis  of  plant  materials.  It  can  be  used  directly   to   generate   electricity   or,   most   commonly,   purified   to   synthesize   transportation   fuels,   such   as   methanol,   ethanol,   methane   and   others.   Through   the   Fischer-­‐Tropsch   process   purified   syngas   has  been  converted  to  diesel.   Advantages  and  disadvantages  of  the  different  biofuels  are  seen  in  Table  7  [44].  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 20 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

Table  7:  Advantages  and  disadvantages  of  the  different  types  of  biofuels.   Biofuels  

 

Advantages  

Disadvantages  

Firewood  

Renewable,  readily  available,  cheap,  most   energy  efficient  

Bulky,  low  in  energy  density;  high   hazardous   emissions   from   incomplete   combustion;   unsuitable  for  automated  burners  

Wood  chips  

More   convenient   to   transport,   handle   and   store   than   firewood;   lower   SO2,   NOX   emissions  than  coal  when  combusted  

Involves   chipping   cost;   tends   to   decay   during   storage;   bulkier   and   lower   energy   density   than   coal;   ash   slagging   and   boiler   fouling;   unsuitable  for  precise  combustion  

Wood  pellets  

Convenient   to   transport,   handle   and   store;   low   SO2   and   NOX   emissions;   suitable  for  precise  combustion  

Higher   processing   cost;   lower   energy   content   than   coal;   only   for   solid  fuel  burners  

Charcoal  

Stable,  high  energy  content,  clean  burning  

High   production   cost;   bulk,   inconvenient   for   transport;   cannot   be   used   in   liquid   fuel   and   gas   burners  

Corn/sugar  ethanol  

Renewable   substitute   for   gasoline;   low   combustion  emissions;  existing  feedstock   production  systems  

Low   net   energy   efficiency;   corrosive   to   existing   gasoline   fouling   devices;   competing   with   food  and  feed  for  source  materials  

Cellulosic  ethanol  

A   gasoline   alternative   from   non-­‐food   biomass  

Low   net   efficiency;   not   cost-­‐ effective  

Biodiesel  

Renewable   substitute   for   petrol   diesel;   existing  feedstock  production  systems  

Competes   with   food   production;   feedstock   is   limited   to   lipids;   corrosive  to  existing  diesel  fueling   devices;   substantial   processing   cost  

Pyrolysis  bio-­‐oil  

Renewable   feedstock;   simple   conversion   technology  

Upgrading   is   needed   prior   to   fuel   uses;   immature   upgrading   techniques  

Drop-­‐in  fuels  

Renewable  feedstock;  gasoline  substitute;   compatible  with  existing  fueling  systems  

Immature,   complicated   conversion  technology;  high  cost  

Biogas  

From   organic   waste   and   residues;   wide   feedstock   sources;   fits   the   existing   natural  gas  grid    

Usually   in   rural   areas;   requires   intensive   feedstock   collection   and   waste  disposal  

Syngas  

Mature   production   technology;   feedstock   for  industrial  chemicals  

Char   and   bio-­‐oil   as   byproducts;   stringent   requirements   for   feedstock  

Solid  

Liquid  

Gaseous  

   

Municipal  organic  waste   Another  specific  category  of  biomass  is  municipal  organic  waste  and  especially  household  food   discharged  from  various  food  processing  plants  and  domestic/commercial  kitchens  or  lost  along   the   food   supply   chain   [46].   The   quantities   of   food   waste   are   continuously   increasing,   while   their   disposal  can  cause  environmental  issues,  such  as  gas  emissions  contributing  to  the  greenhouse   effect   and   water   contamination.   Food   waste   can   be   incinerated   with   other   municipal   waste   to   generate  heat  or  energy.  However,  food  waste  is  characterized  by  high  levels  of  moisture,  while   its   incineration   can   cause   air   pollution   or   loss   of   its   chemical   values.   Fuel   applications   of   food   waste   usually   create   more   value   (200-­‐400   $/t   biomass)   when   compared   to   electricity  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 21 of 35  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

generation   applications   ($60-­‐150/t   biomass)   [46].   In   addition,   food   waste   can   be   used   to   produce   high-­‐value   materials   (e.g.,   organic   acids,   biodegradable   plastics,   etc.)   with   a   reported   approximate   value   of   1,000   $/t   biomass.   However,   the   market   demand   of   such   chemicals   is   much   smaller   than   that   for   biofuels.   Ethanol,   hydrogen,   methane   and   biodiesel   are   some   alternative  biofuels  that  can  be  produced  from  food  waste.  

  Cooling  and  heating  applications   In   this   Section,   cooling   and   heating   measures   refer   to   applications   in   buildings   for   the   improvement  of  the  building’s  energy  performance.  The  measures  that  can  be  taken  to  improve   the  energy  performance  of  a  building  can  be  separated  into  energy  efficiency  measures  (EEMs)   and  the  adoption  of  renewable  energy  and  other  technologies  (RETs)  [30].     EEMs  involve  measures  related  to  the  building  envelope  (thermal  insulation,  windows/glazing,   reflective/green  roofs,  thermal  mass),  internal  conditions  (indoor  design  conditions  and  internal   heat   loads   due   to   lighting   and   appliances)   and   building   services   systems   (heating,   ventilation   and   air   conditioning,   HVAC,   electrical   services   and   vertical   transportation,   i.e.,   lifts   and   escalators).   Thermal   insulation   is   less   effective   in   cooling-­‐dominated   buildings   that   have   large   internal   heat   loads   in   warmer   climates   and   over-­‐insulation   that   may   increase   energy   requirements   for   space   cooling   should   be   avoided.   Reflective/green   roofs   present   conflicting   space   requirements   with   RETs.   Daylighting   and   new   lighting   technologies   show   great   energy-­‐ saving   potential.   Alternative   solar-­‐based   energy   systems   for   buildings   are   solar   chimneys   [7].   Solar   chimneys   include   a   solar   air   heater   (collector)   and   a   chimney   and   are   classified   into   vertical  solar  and  roof  solar  chimneys.  Factors  that  affect  the  performance  of  a  solar  chimney  are   height,  width  and  depth  of  cavity,  glazing  type,  the  type  of  the  absorber,  location,  climate,  etc.   Thermal   cooling   systems   can   be   used   for   heating   or   cooling   purposes   and   may   have   small   to   large  capacities  [47].  However,  their  use  has  been  limited  due  to  low  efficiencies  and  high  cost.   Thermal   cooling   systems   can   be   coupled   with   renewable   energy   sources   (e.g.,   solar   thermal   energy)  and  they  are  separated  into  absorption,  adsorption,  desiccant  systems  using  solids  and   liquids,  Rankine  cycle,  Stirling,  ejector-­‐compression  systems  and  hybrid  systems  [47],  [48].     Water/lithium  bromide  absorption  systems  at  single  and  double  effect  are  the  most  promising   systems   in   small   and   medium   size   capacities   [47].   Air-­‐cooling   with   this   mixture   or   ammonia/lithium   nitrate   can   be   used   in   air   conditioning   applications   where   water/lithium   bromide  requires  a  water-­‐cooling  tower  but  with  a  lower  coefficient  of  performance  (COP)  (i.e.,   the  ratio  of  the  amount  of  energy  provided  by  the  heat  pump  to  the  electrical  energy  consumed).  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

Hybrid   systems   such   as   the   combination   of   ejectors   with   absorption   cooling   systems   and   ejectors   with   mechanical   vapor   compression   show   good   potential.   The   combination   (hybridization)  of  desiccant  systems  with  absorption  systems  shows  promising  power  savings.   Some  advantages  and  disadvantages  of  these  thermal  processes  are  seen  in  the  following  table   [48].     Table  8:  Advantages  and  disadvantages  of  thermal  processes.   Thermal  processes  

Absorption  systems  

Advantages  

Disadvantages  

-­‐  Operate  silently   -­‐  High  reliability  

-­‐   High   installation   cost   and   large   installation   area   in   case   of   continuous   system  

-­‐   No   auxiliary   energy   for   operation   of   a   small   system  

-­‐   Quite   complicated   system   that   requires   knowledge  for  maintenance  

-­‐  Simpler  capacity  control  mechanism  

-­‐  High  heat  release  to  the  environment  

-­‐  Easier  implementation   -­‐  Low  temperature  heat  supply   -­‐  Low  maintenance  cost   -­‐  No  moving  parts   -­‐  Low  heat  source  temperatures   Adsorption  systems  

-­‐   Poor   thermal   conductivity   of   the   adsorbent   -­‐  Very  sensitive  to  low  temperature  during   night  time   -­‐  Low  COP   -­‐  Intermittent  in  basic  system   -­‐  Bulky  machine  

-­‐   Uses   water   as   a   working   fluid   which   is   environmentally  safe   Desiccant  systems  

-­‐  Can  be  integrated  with  a  ventilation  and  heating   system   -­‐  Low  heat  release  to  the  environment  (in  the  case   of  liquid  desiccant  system)  

-­‐   Difficult   design   for   small   applications   and   complex   control   strategy   especially   in   humid  areas   -­‐   Crystallization   risk   in   liquid   desiccant   systems   -­‐  Require  dehumidifier   -­‐  Rotating  elements  need  maintenance  

Ejector  systems  

-­‐  Low  temperature  heat  can  be  used  

-­‐  Low  COP  

-­‐  Low  operating  cost  

-­‐  Complex  design  of  the  ejector   -­‐   Specific   ambient   temperature   ranges   are   required  

    Configurations   implemented   in   different   climatic   zones   in   Europe   show   energy   savings   of   29-­‐55   %  for  adsorption,  25-­‐52  %  for  absorption  and  16-­‐56  %  for  desiccant  cooling  systems  [48].   RETs  involve  photovoltaic,  BIPV,  wind  turbines,  heat  pumps,  solar  thermal  (water  heaters)  and   district  heating/cooling.  Most  of  these  technologies  are  well  established.     PV  is  one  of  the  most  promising  and  applied  technologies.  BIPV  increases  the  power  per  unit  of   floor  area.  A  solar  cell  has  a  solar-­‐to-­‐electric  efficiency  of  9-­‐18  %.  80  %  of  the  solar  radiation  that   is   not   converted   or   reflected   increases   the   working   temperature   of   the   solar   cell   that   lowers   the   efficiency   [30].   Hybrid   photovoltaic-­‐thermal   (HPVT   or   PV/T)   systems   were   conceived   in   the  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

1970s   [5].   In   such   applications   a   solar   collector   is   combined   with   a   photovoltaic   panel,   generating   both   electrical   and   thermal   energy.   The   collector   has   the   goal   to   reduce   the   temperature   of   the   cells   (improving   their   electrical   efficiency)   and   to   use   excess   heat   in   low-­‐ temperature   applications,   such   as   water   preheating,   space   heating   and   natural   ventilation.   A   properly   designed   PV/T   hybrid   solar   system   can   result   in   thermal   and   electrical   efficiencies   comparable   to   and   even   better   than   those   of   conventional   solar   thermal-­‐only   systems   and   PV   modules  [5],  [49].   Unglazed   and   glazed   PV/T   collectors   were   found   to   have   31   %   and   35   %   lower   cost   payback   times,   respectively,   when   compared   to   standard   PV   systems   [5].   The   payback   period   for   PV/T   hybrid   solar   systems   is   equivalent   to   that   of   side-­‐by-­‐side   configuration   of   the   technologies.   In   addition,   PV/T   solar   systems   improve   the   energy   performance   per   unit   area,   an   aspect   very   important  for  urban  areas  [5],  [49].  The  working  fluid  in  these  systems  can  be  either  liquid  or  air   depending   on   local   parameters   and   design   configuration.   Air   is   preferred   in   indoor   space   air-­‐ conditioning   and   agriculture   applications.   In   general,   PV/T   systems   have   potential   for   single-­‐ family  or  multi-­‐family  buildings  because  they  provide  direct  space  heating.     PV  systems  with  air-­‐cooling  offer  minimal  material  use  and  low  operating  costs  [50].  Forced  air   enhances  heat  extraction  when  compared  to  natural  ventilation  at  the  expense  of  some  parasitic   losses.   Liquid   cooling   offers   a   more   efficient   alternative   when   compared   to   air-­‐cooling.   Moreover,   the   replacement   of   the   most   common   liquid   cooling   material,   water,   with   phase-­‐ changing  materials  make  the  PV  cooling  application  more  attractive  due  to  better  heat  transfer   rates  and  heat  absorption  due  to  latent  heating.       Table  9:  Characteristics  of  solar  thermal  collectors  available  in  the  market.   Motion  

Stationary  

Single-­‐axis  tracking  

Two-­‐axes  tracking  

Collector  type  

Concentration   ratio  

Temperature  range  [°C]  

Flat  plate  collector  

1  

30-­‐200  

Evacuated  tube  collector  

1  

50-­‐200  

Compound  parabolic  collector  

1-­‐5  

60-­‐300  

Linear  Fresnel  reflector  

10-­‐40  

60-­‐250  

Parabolic  trough  collector  

15-­‐45  

50-­‐400  

Cylindrical  trough  collector  

10-­‐50  

60-­‐300  

Parabolic  dish  reflector  

600-­‐2,000  

100-­‐1,500  

Heliostat  field  collector  

300-­‐1,500  

150-­‐2,000  

  Solar   thermal   is   very   important   in   the   residential   sector.   The   thermal   energy   from   a   solar   collector   can   be   used   in   space   heating,   water   heating,   steam   generation   or   stored   in   thermal  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

storage   for   later   use.   Depending   on   solar   intensity   and   location,   it   is   expected   that   the   cost   of   solar  thermal  energy  will  fall  from  61-­‐122  $/MWh  in  2007  to  22-­‐44  $/MWh  in  2050  [5].  Some   characteristics  of  solar  thermal  collectors  based  on  their  motion  are  shown  in  Table  9  [48].    

Water  heating   Water  heaters  in  the  residential  sector  can  be  classified  into  storage-­‐type  gas/oil,  wood  water,   heat   pumps,   storage-­‐type   electric,   solar   water-­‐heating   systems   and   instantaneous   water   heaters   [49].   All   of   these   choices   have   advantages   and   disadvantages.   Instantaneous   water   heaters   operate   on   demand   and   use   an   energy   source   (gas/oil/electricity)   when   hot   water   is   required   without  incorporating  hot-­‐water  storage.  Instantaneous  heating  energy  is  needed  to  provide  the   required   hot-­‐water   temperature.   Electric   heaters   require   a   continuous   electricity   supply   and   may   be   problematic   in   areas   where   the   electrical   supply   is   inconsistent.   Wood,   oil   and   gas   domestic   storage-­‐type   water   heaters   constitute   alternatives   to   insufficient   electrical   energy   supply.  However,  such  heaters  pollute  and  may  be  harmful.   Solar   water   heating   systems   (SWHSs)   can   be   separated   into   passive   and   active   systems   [51].   Passive  systems  use  convection  to  circulate  the  heating  fluid  of  the  system  (integrated  collector   storage  and  thermosyphon  systems),  while  active  solar  water  heating  systems  use  one  or  more   pumps  to  circulate  the  working  fluid.  New  developments  in  solar  water  heaters  (SWHs)  include   a   low-­‐profile   integrated   collector   storage   hot   water   system,   an   SWH   using   a   solar   water   pump,   a   two-­‐phase   thermosyphon   with   a   higher   efficiency   than   conventional   SWHs,   an   SWH   with   a   V-­‐ trough   collector   and   a   solar   combisystem   generating   hot   water   and   fulfilling   space   heating   requirements   [30].   From   the   utilization   point   of   view,   thermosyphon   SWH   occupies   a   good   amount   of   domestic   applications   because   it   is   easy   to   operate   and   it   does   not   require   external   energy.  SWHSs  with  electrical  back  up  have  no  local  pollution  impact  [49].  The  performance  of   two-­‐phase  thermosyphons  SWHSs  is  better  than  that  of  single-­‐phase  systems.  It  was  found  that   the  payback  time  for  solar  water  heater  systems  was  less  than  half  year,  while  for  conventional   electrical  water  heating  systems  it  was  between  4-­‐12  years,  depending  on  the  location  [5].   The  storage  tank  is  an  important  part  of  the  solar  water  heating  system,  generally  constructed   using   steel,   concrete,   plastic,   fiber   glass   or   other   materials   [51].   Phase-­‐changing   materials   can   reduce  the  thermal  energy  loss  in  either  pipe  or  duct  networks  and  the  initial  cost  because  they   do   not   need   insulation   and   storage   tanks   and   thus   save   space   [52].   For   SWHSs   smart   solar   storage  tanks  are  preferred  [49].    

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

Heat   pumps   can   recover   heat   from   various   energy   sources   and   they   are   used   in   different   building   applications   [30].   Heat   pump   water   heaters   (HPWHs)   are   energy   efficient   systems   without  local  pollution.  The  COP  of  heat  pumps  is  between  3  and  5.     Air-­‐source   heat   pumps   (ASHPs)   have   a   COP   close   to   the   lower   end   and   can   be   improved   by   incorporating   solar   collectors   for   energy   supply   into   the   evaporator   at   a   temperature   higher   than  that  of  the  environment.  To  avoid  possible  damage  from  inconsistent  solar  radiation,  solar   heat   pumps   are   preferred   to   include   thermal   storage   [5].   Conventional   air-­‐source   heat   pumps   water  heaters  (ASHPWH)  should  be  preferably  installed  in  areas  with  an  ambient  temperature   above  4.4  °C  throughout  the  year.     Ground-­‐source  heat  pumps  (GSHPs)  work  better  when  the  heating  and  cooling  requirements  of   a   building   are   balanced   over   the   year.   To   avoid   a   temperature   increase   in   the   ground   due   to   temperature  rejection  from  a  GSHP  (especially  in  heating-­‐dominated  climates  [53]),  a  GSHP  can   be  coupled  with  solar  collectors  (hybrid  GSHP).  Compared  to  conventional  heating  and  cooling   systems,  GSHPs  have  been  shown  to  reduce  primary  energy  consumption  by  60  %  [7].  A  factor   that  limits  the  wide  application  of  GSHP  is  the  limited  availability  of  groundwater  and  the  high   maintenance  cost  due  to  foiling,  corrosion  in  pipes  and  equipment.  Compared  to  ASHPs,  GSHPs   have   lower   operating   costs,   usually   no   outdoor   units,   longer   life   and   better   reliability   [30].   Nevertheless,   the   cost   of   GSHPs   is   higher   than   that   of   ASHPs   [5].   Ground-­‐source   heat   pump   water  heaters  (GSHPWH)  are  always  energy  efficient  and  applicable,  independent  of  climate.     PV/T  HPWH  systems  constitute  another  alternative  for  water  heating  applications.  Such  systems   can  improve  the  energy  performance  per  unit  area,  the  electrical  efficiency  of  PV  modules  and   the  COP  of  heat  pumps.   Lastly,   gas   engine-­‐driven   heat   pumps   (GEHPs)   are   novel,   efficient   systems   and   become   more   efficient  when  they  are  used  for  both  water  and  space  heating  [49].    

  Storage  technologies   Storage   technologies   can   be   classified   into   thermal   energy   storage   (TES)   and   electrical   energy   storage   systems   [54].   Storage   increases   the   cost   of   a   structure   but   it   allows   higher   capacity   factors.   Also,   the   incorporation   of   storage   decreases   the   operating   and   maintenance   costs   by   decreasing  the  costs  of  service  staff  [55].   TES   technologies   must   be   able   to   retain   the   energy   absorbed   for   at   least   a   few   days;   they   can   be   separated   into   high-­‐   and   low-­‐temperature   storage   systems.   Low-­‐temperature   storage   systems  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

are   used   more   in   building   heating   and   cooling   and   applications,   solar   cooking,   solar   water   boilers   and   air-­‐heating   systems,   while   high-­‐temperature   storage   systems   are   more   used   in   renewable   energy   technologies   and   waste   heat   recovery   [54].   They   can   also   be   divided   into   short-­‐   and   long-­‐term   systems   and   sensible   heat,   latent   heat   and   thermochemical   heat   storage   systems.     Sensible   storage   systems   (advanced   stage   of   development)   store   energy   by   changing   the   temperature  of  the  storage  means  (liquid  or  solid  media).  Thus,  this  type  of  storage  is  based  on   the   heat   capacity   of   the   storage   medium.   Two   disadvantages   of   the   technology   are   the   large   storage   size   required   and   the   created   temperature   swing   from   the   sensible   addition   and   extraction   of   energy.   The   large   size   storage   requirement   is   also   linked   to   large   thermal   losses   and  costs.     Indirect   systems   use   a   heat   transfer   fluid   (HTF)   and   a   storage   fluid,   while   direct   systems   use   the   same   fluid   to   transfer   and   store   the   heat.   Sensible   thermal   energy   storage   has   typically   a   capacity  factor  of  80  %  and  storage  capacities  of  10-­‐50  kWh/t  [55].     The  HTF  of  a  CSP  system  can  directly  drive  a  turbine  to  generate  power  or,  most  commonly,  be   combined   with   a   heat   exchanger   and   a   secondary   cycle   to   generate   steam   [14].   HTFs   can   be   classified   into   (1)   air   and   other   gases,   (2)   water/steam,   (3)   thermal   oils,   (4)   organics,   (5)   molten-­‐salts   and   (6)   liquid   metals.   Each   HTF   has   different   properties.   Water   is   one   of   the   best   storage   liquid   media   for   low-­‐temperature   ranges.   However,   it   is   corrosive   and   its   lifetime   is   about  10  years.  Water  has  been  mainly  used  in  smaller  plants  or  in  intermediate  tanks  [4].  There   is  a  trend  in  developing  HTFs  that  can  operate  over  a  wider  temperature  range  and  with  more   stability.   For   intermediate-­‐   and   high-­‐temperature   ranges   pressurized   or   unpressurized   fluids   can   be   considered.   Unpressurized   organic   liquids   can   be   considered   for   intermediate   temperature   ranges,   while   pressurized   water   at   140   bar   (temperatures   up   to   300   °C),   molten   salts,   oil   and   liquid   metals   for   high-­‐temperature   ranges.   Molten   salts   have   a   relatively   low   melting  point  and  can  operate  at  relatively  high  temperatures  (up  to  800  °C).  In  addition,  they   are  widely  used  in  power  tower  systems  being  non-­‐toxic  and  non-­‐flammable,  liquid  at  ambient   pressure;   a   relatively   efficient   and   low-­‐cost   alternative.   Most   of   the   molten   salts   are   based   on   nitrates/nitrides  but  because  their  annual  production  is  limited,  chloride-­‐based  salts  have  been   proposed  and  are  currently  being  studied.  Potential  hazardous  heat-­‐transfer  fluids  may  require   handling  and  appropriate  disposal  [2].       Latent   storage   systems   are   developing   systems   where   the   thermal   medium   changes   phase   (phase-­‐changing   materials,   PCMs).   Since   the   latent   heat   is   much   higher   than   the   sensible   heat,   much  smaller  storage  volumes  are  required.  In  addition,  the  temperature  variation  is  restrained,   since   the   phase   change   occurs   at   approximately   constant   temperature.   Some   difficulties   arise  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

due  to  density  changes,  stability  of  properties  under  cycling,  phase  segregation  and  supercooling   of  the  phase-­‐changing  materials.  In  addition,  the  power  that  can  be  extracted  may  be  limited  by   low  thermal  conductivity  of  the  phase-­‐changing  materials.     PCMs  can  be  separated  into  organic  (paraffins  and  non-­‐paraffins),  inorganic  (salt  hydrates,  salts,   metals  and  alloys)  and  eutectic  PCMs  (mixture  of  PCMs,  either  organic  or  inorganic).  PCMs  such   as  salt  hydrates,  paraffins,  non-­‐paraffins,  eutectics  and  solid  state  PCMs  have  good  potential  for   low-­‐temperature  thermal  energy  storage  applications.   Thermochemical  storage  can  be  separated  into  thermochemical  reactions  (using  collected  heat   to   cause   an   endothermic   chemical   reaction   that   can   be   reversed   usually   by   adding   a   catalyst)   and   sorption   processes   (capture   of   a   gas   or   vapor   called   sorbate   by   a   substance   in   condensed   state   called   sorbent)   [4].   Suitable   materials   with   good   thermal   stability   and   low   cost   must   be   researched  and  identified.         Table  10  presents  a  comparison  of  the  different  types  of  TES  technologies  [54],  [56].     Table  10:  Comparison  of  different  TES  technologies.     Performance   parameter  

Temperature   range  

Type  of  thermal  energy  storage   Sensible  TES  

Latent  TES  

Chemical  TES  

Up  to:  

-­‐  20-­‐40  °C  (paraffins)  

20-­‐200  °C  

-­‐  110  °C  (Water  tanks)  

-­‐  30-­‐80  °C  (salt  hydrates)  

-­‐   50   °C   (aquifers   and   ground   storage)   -­‐  400  °C  (concrete)  

Storage   density  

Low   (with   high   temperature   interval)   0.2   GJ/m3   (for   typical   water  tanks)  

Moderate   (with   low   temperature   interval)  0.3-­‐0.5  GJ/m3  

Normally   high   0.4-­‐3.0   GJ/m3  

Long  

Often   limited   due   to   storage   material   cycling  

Depends   on   reactant   degradation   and   side   reactions  

Available  commercially  

Available   commercially   for   some   temperatures  and  materials  

Generally   not   available   but   undergoing   research   and  pilot  project  tests  

-­‐  Low  cost  

-­‐  Medium  storage  density  

-­‐  High  storage  density  

-­‐  Reliable  

-­‐  Small  volumes  

-­‐  Low  heat  losses  

-­‐  Short  distance  transport  possibility  

-­‐  Long  storage  period  

Lifetime  

Technology   status  

Advantages  

-­‐   Long   distance   transport   possibility  

Disadvantages  

-­‐   Significant   heat   loss   over   time   (depending   on   level   of   insulation)  

-­‐  Low  heat  conductivity    

-­‐  High  capital  costs  

-­‐  Corrosiveness  of  materials  

-­‐  Technically  complex  

-­‐  Large  volume  needed  

-­‐   Significant   heat   losses   (depending   on   level  of  insulation)  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 28 of 35  

IEF  Project  GENERGIS  332028        Description,   Economics   and   Environmental   Issues   of   Renewable   Energy   Technologies   Table  11:  Comparison  of  energy  storage  systems.    

Form   of   storage  

Efficiency     Capacity    

Capital    

[MW]  

Energy   density   [Wh/kg]  

Storage   duration    

Response   time  

Lifetime    

[%]  

TES  

Thermal  

PHS  

Mechanical  

30-­‐60  

0-­‐300  

80-­‐250  

75-­‐85  

100-­‐5,000  

0.5-­‐1.5  

200-­‐300,  3-­‐50  

 

 

5-­‐40  

600-­‐2,000,  5-­‐100  

Long  

Fast  

40-­‐60  

CAES  

Mechanical  

50-­‐89  

3-­‐400  

30-­‐60  

400-­‐2,000,  2-­‐100  

Medium  

Fast  

20-­‐60  

Flywheel  

Mechanical  

93-­‐95  

0.25  

10-­‐30  

350,  5,000  

Short  

Very  fast  

~15  

Pb-­‐acid  battery  

Chemical    

70-­‐90  

0-­‐40  

30-­‐50  

300,  400*  

Medium  

Fast  

5-­‐15,  1200-­‐1800   cycles  

Ni-­‐Cd  battery  

Chemical  

60-­‐65  

0-­‐40  

50-­‐75  

500-­‐1,500,  800-­‐1,500  

Medium  

Fast  

10-­‐20,   more   than  3500  cycles  

Na-­‐S  battery  

Chemical  

80-­‐90  

0.05-­‐8  

150-­‐240  

1,000-­‐3,000,  300-­‐500  

Medium  

Fast  

10-­‐15  

Li-­‐ion  battery  

Chemical  

85-­‐90  

0.1  

75-­‐200  

4,000,  2,500  

 

Fast  

5-­‐15,   cycles  

Fuel  cells  

Chemical  

20-­‐50  

0-­‐50  

800-­‐10,000  

500-­‐1,500,  10-­‐20  

Medium  

Good  

5-­‐15,   more   than   20,000  cycles  

Flow  battery  

Chemical  

75-­‐85  

0.3-­‐15  

10-­‐50  

600-­‐1,500,  120-­‐1,000  

Medium  

Very  fast  

5-­‐15  

Capacitors  

Electrical  

60-­‐65  

0.05  

0,05-­‐5  

400,  1,000  

 

Very  fast  

~5  

Supercapacitors  

Electrical  

90-­‐95  

0.2  

2.5-­‐15  

300,  2,000  

Short  

Very  fast  

20+  

SMES  

Electrical  

95-­‐98  

0.1-­‐10  

0.5-­‐5  

300,  10,000  

Short  

Very  fast  

20+,   tens   thousands   cycles  

[$/kW,  $/kWh]  

In   Ref.   [6],   the   investment   cost   of   a   5   kWh   storage   (lead-­‐acid   battery)   for   annual   PV   electricity   equal   to   3,908   kWh   annually   (three-­‐ person  household  in  Germany)  was  found  to  be  2,325  euro  in  2013,  1,813  in  2017  and  1,327  in  2022.  The  investment  cost  of  lead-­‐ acid  battery  in  2013  was  171  euro/kWh  +  172  euro/kWh  (energy  +  power  costs)  with  a  battery  investment  cost  decrease  of  7.6  %   /year.   Abbreviations:   TES:   Thermal   energy   storage;   CAES:   Compressed   air   energy   storage;   PHS:   Pumped   hydro   storage;   SMES:   Superconducting  magnetic  energy  storage.  

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

                   Page 29 of 35  

[years]  

3500  

of  

IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

The  energy  density  of  a  thermochemical  TES  system  (approximately  500  kWh/m3)  is  5-­‐10  times   higher   than   latent   and   sensible   heat   storage   systems,   respectively   [57].   Thermochemical   TES   systems   appear   to   be   the   most   promising   way   to   store   solar   thermal   energy   for   a   long   period   because  there  are  no  thermal  losses  since  the  products  can  be  stored  at  ambient  temperature.   Hydrogen   storage   is   an   alternative   for   long-­‐term   storage   in   energy   systems.   In   such   storage   systems  electricity  is  converted  into  hydrogen  and  stored.  When  it  is  needed  the  hydrogen  can   be  re-­‐converted  into  electricity.  Although  such  technologies  are  very  promising,  high  costs,  low   conversion   of   electricity-­‐hydrogen-­‐electricity   and   other   concerns   limit   their   further   development   and   wider   use   [58],[59].   Nevertheless,   they   have   good   potential   for   implementation  in  large-­‐scale  applications.     Lastly,   electrical   energy   can   be   stored   directly   or   indirectly   with   various   methods   [54]:   mechanically   by   pumping   water,   compressing   air,   or   increasing   the   rotational   speed   of   electromagnetic   flywheels,   chemically   by   producing   or   converting   components   in   chemical   systems   like   batteries   and   by   modifying   electrical   or   magnetic   fields   in   capacitors   or   superconducting   magnets.   Pumped   hydro   is   the   only   well-­‐developed   and   reliable   technology,   the   main   problem   of   which   is   to   find   sites   suitable   for   two   reservoirs   with   a   height   difference   of   at  least  100  m  [54].  To  date,  centralized  and  large-­‐scale  storage  system  exist  only  in  the  form  of   pumped  storage  [60].  Among  various  storage  technologies,  battery  storage  is  the  most  flexible,   reliable  and  responsive  for  integrated  RES  in  stand-­‐alone  applications  [6].  Since  storage  is  still   expensive,   only   pilot   applications   exist   currently.   These   applications   use   mainly   lead-­‐acid   batteries  due  to  their  lower  cost  [61].   A  comparison  of  TES  systems  and  systems  for  storing  electrical  energy  can  be  seen  in  Table  11   [27],  [29],  [54],  [62].  Similar  information  on  different  options  for  electricity  storage  can  be  found   in  Ref.  [58].    

 

 

Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

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[3]  

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[4]  

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[6]  

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Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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IEF  Project  GENERGIS  332028        Description,  Economics  and  Environmental  Issues  of  Renewable  Energy  Technologies  

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Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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Dr.-­‐Ing.  Fontina  Petrakopoulou,  E-­‐mail:  [email protected]  

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