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]
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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
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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
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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
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IEF Project GENERGIS 332028 Description, Economics and Environmental Issues of Renewable Energy Technologies
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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
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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
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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.
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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
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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
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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
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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.
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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
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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.
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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
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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
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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
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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.
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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].
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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
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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).
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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
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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
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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].
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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
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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
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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)
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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.
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[years]
3500
of
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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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REFERENCES [1]
International Energy Agency, “Tracking Clean Energy Progress 2014,” 2014.
[2]
V. Devabhaktuni, M. Alam, S. Shekara Sreenadh Reddy Depuru, R. C. Green, D. Nims, and C. Near, “Solar energy: Trends and enabling technologies,” Renew. Sustain. Energy Rev., vol. 19, pp. 555–564, Mar. 2013.
[3]
A. Reza Reisi, M. Hassan Moradi, and S. Jamasb, “Classification and comparison of maximum power point tracking techniques for photovoltaic system: A review,” Renew. Sustain. Energy Rev., vol. 19, pp. 433–443, Mar. 2013.
[4]
W. D. Grossmann, I. Grossmann, and K. W. Steininger, “Solar electricity generation across large geographic areas, Part II: A Pan-‐American energy system based on solar,” Renew. Sustain. Energy Rev., vol. 32, pp. 983–993, Apr. 2014.
[5]
R. S. Kamel and A. S. Fung, “Solar Systems and Their Integration With Heat Pumps: a Review,” Energy Build., vol. 87, pp. 395–412, Nov. 2014.
[6]
J. Hoppmann, J. Volland, T. S. Schmidt, and V. H. Hoffmann, “The economic viability of battery storage for residential solar photovoltaic systems – A review and a simulation model,” Renew. Sustain. Energy Rev., vol. 39, pp. 1101–1118, Nov. 2014.
[7]
L. Shi and M. Y. L. Chew, “A review on sustainable design of renewable energy systems,” Renew. Sustain. Energy Rev., vol. 16, no. 1, pp. 192–207, Jan. 2012.
[8]
J.-‐H. Song, Y.-‐S. An, S.-‐G. Kim, S.-‐J. Lee, J.-‐H. Yoon, and Y.-‐K. Choung, “Power output analysis of transparent thin-‐film module in building integrated photovoltaic system (BIPV),” Energy Build., vol. 40, no. 11, pp. 2067–2075, Jan. 2008.
[9]
S. M. Moosavian, N. a. Rahim, J. Selvaraj, and K. H. Solangi, “Energy policy to promote photovoltaic generation,” Renew. Sustain. Energy Rev., vol. 25, pp. 44–58, Sep. 2013.
[10] R. Shah, N. Mithulananthan, R. C. Bansal, and V. K. Ramachandaramurthy, “A review of key power system stability challenges for large-‐scale PV integration,” Renew. Sustain. Energy Rev., vol. 41, pp. 1423–1436, Jan. 2015. [11] M. A. Green, K. Emery, Y. Hishikawa, W. Warta, and E. D. Dunlop, “Solar cell efficiency tables (Version 45),” Prog. Photovoltaics Res. Appl., vol. 23, pp. 1–9, 2015. [12] M. Hosenuzzaman, N. a. Rahim, J. Selvaraj, M. Hasanuzzaman, a. B. M. a. Malek, and a. Nahar, “Global prospects, progress, policies, and environmental impact of solar photovoltaic power generation,” Renew. Sustain. Energy Rev., vol. 41, pp. 284–297, Jan. 2015.
Dr.-‐Ing. Fontina Petrakopoulou, E-‐mail:
[email protected]
Page 31 of 35
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[13] European Union, “EU PV Platform: Fact sheets,” 2012. [Online]. Available: http://www.eupvplatform.org/publications/fact-‐sheets.html. [Accessed: 03-‐May-‐ 2015]. [14] K. Vignarooban, X. Xu, a. Arvay, K. Hsu, and a. M. Kannan, “Heat transfer fluids for concentrating solar power systems – A review,” Appl. Energy, vol. 146, pp. 383– 396, May 2015. [15] J. Rawlins and M. Ashcroft, “Small-‐scale Concentrated Solar Power A review of current activity and potential to accelerate deployment,” 2013. [16] IRENA -‐ International Renewable Energy Agency, “Concentrating Solar Power -‐ Renewable Energy Technologies: Cost analysis series,” 2012. [Online]. Available: http://www.irena.org/documentdownloads/publications/re_technologies_cost_a nalysis-‐csp.pdf. [Accessed: 05-‐Jun-‐2015]. [17] T. M. Pavlović, I. S. Radonjić, D. D. Milosavljević, and L. S. Pantić, “A review of concentrating solar power plants in the world and their potential use in Serbia,” Renew. Sustain. Energy Rev., vol. 16, no. 6, pp. 3891–3902, Aug. 2012. [18] M. Z. A. Ab Kadir, Y. Rafeeu, and N. M. Adam, “Prospective scenarios for the full solar energy development in Malaysia,” Renew. Sustain. Energy Rev., vol. 14, no. 9, pp. 3023–3031, Dec. 2010. [19] K. Kaygusuz, “Prospect of concentrating solar power in Turkey: The sustainable future,” Renew. Sustain. Energy Rev., vol. 15, no. 1, pp. 808–814, Jan. 2011. [20] B. García-‐Domingo, C. J. Carmona, A. J. Rivera-‐Rivas, M. J. del Jesus, and J. Aguilera, “A differential evolution proposal for estimating the maximum power delivered by CPV modules under real outdoor conditions,” Expert Syst. Appl., vol. 42, pp. 5452– 5462, 2015. [21] International Energy Agency, “Technology Roadmap Solar Photovoltaic Energy,” 2014. [22] J. Leloux, E. Lorenzo, B. García-‐Domingo, J. Aguilera, and C. A. Gueymard, “A bankable method of assessing the performance of a CPV plant,” Appl. Energy, vol. 118, pp. 1–11, 2014. [23] Fraunhofer Institute for Solar Energy Systems and National Renewable Energy Laboratory, “Current status of concentrator photovoltaic (CPV) technology,” 2015. [24] J. Schallenberg-‐Rodriguez, “A methodological review to estimate techno-‐ economical wind energy production,” Renew. Sustain. Energy Rev., vol. 21, pp. 272–287, May 2013. [25] Global Wind Energy Council, “Global wind energy outlook 2014,” 2014.
Dr.-‐Ing. Fontina Petrakopoulou, E-‐mail:
[email protected]
Page 32 of 35
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[26] Iowa Energy Center, “Basic Designs of wind turbines,” 2015. [Online]. Available: http://www.iowaenergycenter.org/wind-‐energy-‐manual/wind-‐energy-‐ systems/basic-‐designs/. [Accessed: 03-‐May-‐2015]. [27] N. S. Hasan, M. Y. Hassan, M. S. Majid, and H. A. Rahman, “Review of storage schemes for wind energy systems,” Renew. Sustain. Energy Rev., vol. 21, pp. 237– 247, May 2013. [28] M. I. Blanco, “The economics of wind energy,” Renew. Sustain. Energy Rev., vol. 13, pp. 1372–1382, 2009. [29] F. Díaz-‐González, A. Sumper, O. Gomis-‐Bellmunt, and R. Villafáfila-‐Robles, “A review of energy storage technologies for wind power applications,” Renew. Sustain. Energy Rev., vol. 16, no. 4, pp. 2154–2171, May 2012. [30] D. H. W. Li, L. Yang, and J. C. Lam, “Zero energy buildings and sustainable development implications – A review,” Energy, vol. 54, pp. 1–10, Jun. 2013. [31] K. Dai, A. Bergot, C. Liang, W.-‐N. Xiang, and Z. Huang, “Environmental issues associated with wind energy – A review,” Renew. Energy, vol. 75, pp. 911–921, Mar. 2015. [32] European Wind Energy Technology Platform, “Strategic Research Agenda / Market Deployment Strategy,” 2014. [33] Darmawi, R. Sipahutar, S. Masreah, and M. Sodik, “Renewable energy and hydropower utilization tendency worldwide,” vol. 17, pp. 213–215, 2013. [34] S. Chen, B. Chen, and B. D. Fath, “Assessing the cumulative environmental impact of hydropower construction on river systems based on energy network model,” vol. 42, no. 19, pp. 78–92, 2015. [35] M. I. Yuce and A. Muratoglu, “Hydrokinetic energy conversion systems: A technology status review,” Renew. Sustain. Energy Rev., vol. 43, pp. 72–82, Mar. 2015. [36] European Commision, “Hydropower -‐ Eurostat,” 2012. [Online]. Available: http://ec.europa.eu/eurostat/web/environmental-‐data-‐centre-‐on-‐natural-‐ resources/natural-‐resources/energy-‐resources/hydropower. [Accessed: 03-‐May-‐ 2015]. [37] D. K. Okot, “Review of small hydropower technology,” Renew. Sustain. Energy Rev., vol. 26, pp. 515–520, 2013. [38] a. H. Elbatran, O. B. Yaakob, Y. M. Ahmed, and H. M. Shabara, “Operation, performance and economic analysis of low head micro-‐hydropower turbines for rural and remote areas: A review,” Renew. Sustain. Energy Rev., vol. 43, pp. 40–50, Mar. 2015.
Dr.-‐Ing. Fontina Petrakopoulou, E-‐mail:
[email protected]
Page 33 of 35
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[39] J. Liu, J. Zuo, Z. Sun, G. Zillante, and X. Chen, “Sustainability in hydropower development — A case study,” vol. 19, pp. 230–237, 2013. [40] H. I. Jager, R. a. Efroymson, J. J. Opperman, and M. R. Kelly, “Spatial design principles for sustainable hydropower development in river basins,” Renew. Sustain. Energy Rev., vol. 45, pp. 808–816, May 2015. [41] J. W. Lund, D. H. Freeston, and T. L. Boyd, “Direct utilization of geothermal energy 2010 worldwide review,” Geothermics, vol. 40, no. 3, pp. 159–180, Sep. 2011. [42] European Commission, “Geothermal energy -‐ Eurostat,” 2012. [Online]. Available: http://ec.europa.eu/eurostat/web/environmental-‐data-‐centre-‐on-‐natural-‐ resources/natural-‐resources/energy-‐resources/geothermal-‐energy. [Accessed: 03-‐May-‐2015]. [43] R. Shortall, B. Davidsdottir, and G. Axelsson, “Geothermal energy for sustainable development : A review of sustainability impacts and assessment frameworks,” vol. 44, pp. 391–406, 2015. [44] M. Guo, W. Song, and J. Buhain, “Bioenergy and biofuels: History, status, and perspective,” Renew. Sustain. Energy Rev., vol. 42, pp. 712–725, Feb. 2015. [45] D. Yue, F. You, and S. W. Snyder, “Biomass-‐to-‐bioenergy and biofuel supply chain optimization : Overview , key issues and challenges,” Comput. Chem. Eng., vol. 66, pp. 36–56, 2014. [46] E. Uçkun Kiran, A. P. Trzcinski, W. J. Ng, and Y. Liu, “Bioconversion of food waste to energy: A review,” Fuel, vol. 134, pp. 389–399, Oct. 2014. [47] R. Best and W. Rivera, “A review of thermal cooling systems,” Appl. Therm. Eng., vol. 75, pp. 1162–1175, Jan. 2015. [48] a. Allouhi, T. Kousksou, a. Jamil, P. Bruel, Y. Mourad, and Y. Zeraouli, “Solar driven cooling systems: An updated review,” Renew. Sustain. Energy Rev., vol. 44, pp. 159–181, Apr. 2015. [49] O. Ibrahim, F. Fardoun, R. Younes, and H. Louahlia-‐Gualous, “Review of water-‐ heating systems: General selection approach based on energy and environmental aspects,” Build. Environ., vol. 72, pp. 259–286, Feb. 2014. [50] A. Makki, S. Omer, and H. Sabir, “Advancements in hybrid photovoltaic systems for enhanced solar cells performance,” Renew. Sustain. Energy Rev., vol. 41, pp. 658– 684, Jan. 2015. [51] R. Shukla, K. Sumathy, P. Erickson, and J. Gong, “Recent advances in the solar water heating systems: A review,” Renew. Sustain. Energy Rev., vol. 19, pp. 173– 190, Mar. 2013.
Dr.-‐Ing. Fontina Petrakopoulou, E-‐mail:
[email protected]
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[52] M. K. A. Sharif, a. a. Al-‐Abidi, S. Mat, K. Sopian, M. H. Ruslan, M. Y. Sulaiman, and M. a. M. Rosli, “Review of the application of phase change material for heating and domestic hot water systems,” Renew. Sustain. Energy Rev., vol. 42, pp. 557–568, Feb. 2015. [53] I. Sarbu and C. Sebarchievici, “General review of ground-‐source heat pump systems for heating and cooling of buildings,” vol. 70, pp. 441–454, 2014. [54] T. Kousksou, P. Bruel, a. Jamil, T. El Rhafiki, and Y. Zeraouli, “Energy storage: Applications and challenges,” Sol. Energy Mater. Sol. Cells, vol. 120, pp. 59–80, Jan. 2014. [55] IRENA -‐ International Renewable Energy Agency, “Thermal Energy Storage -‐ Technology Brief,” 2013. [56] A. H. Abedin, “Thermochemical Energy Storage Systems: Modelling, Analysis and Design,” University of Ontario Institute of Technology, 2010. [57] P. Pardo, a. Deydier, Z. Anxionnaz-‐Minvielle, S. Rougé, M. Cabassud, and P. Cognet, “A review on high temperature thermochemical heat energy storage,” Renew. Sustain. Energy Rev., vol. 32, pp. 591–610, Apr. 2014. [58] International Renewable Energy Agency, “Electricity Storage -‐ Technology Brief,” 2012. [59] International Energy Agency, “Technology Roadmap -‐ Energy storage,” 2014. [60] Fraunhofer Institute for Solar Energy Systems, “Recent Facts about Photovoltaics in Germany,” 2015. [61] Renewables Insight -‐ Energy Industry Guides, “PV Power Plants 2014 -‐ Industry Guide,” 2014. [62] A. Chauhan and R. P. Saini, “A review on Integrated Renewable Energy System based power generation for stand-‐alone applications: Configurations, storage options, sizing methodologies and control,” Renew. Sustain. Energy Rev., vol. 38, pp. 99–120, Oct. 2014.
Dr.-‐Ing. Fontina Petrakopoulou, E-‐mail:
[email protected]
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