Operating P2G in a power system with large amounts of PV, wind power ... and solar power have been installed, in addition to the existing hydro power, to.
Operating P2G in a power system with large amounts of PV, wind power and hydro power Jussi Ikäheimo and Juha Kiviluoma VTT Technical Research Centre of Finland Abstract In this article we study of power-to-gas (P2G) plants in the Nordic power hourly market. Plant operation in the whole market is simulated with respect to forecasts of variable generation. We study the case where large amounts of wind and solar power have been installed, in addition to the existing hydro power, to reach a high share of renewable energy. We find that P2G plants find relatively little use in the case studied. Introduction Power-to-gas technology (P2G) has been proposed as one way to overcome the variability of PV and other forms of variable generation (VG). The potential of other energy storages, such as pumped hydro storage and compressed air energy storage, is limited and these technologies are highly location-dependent. In P2G, hydrogen is produced by electrolysis. Hydrogen, together with CO2, may further be converted into synthetic natural gas (SNG) by methanation process. SNG and within certain limits hydrogen may be fed into the natural gas grid to be used in CHP or condensing plants when cheaper forms of production (judged by their variable costs) are not available. In addition, SNG can be consumed in transportation, and waste heat from the production process can be used for district heating. Consequently P2G is not a simple energy storage technology, but can benefit from several possible revenue streams.
We study the possibility to further increase the share of renewables and reduce the combustion of fossil fuels in the energy sector and transportation sector with the help of P2G. The region which was studied was the three countries Finland, Sweden and Norway. These Nordic countries have a large installed base of reservoir hydro power and wind power. Solar conditions are fair and the number of PV installations is growing rapidly. All the three countries have a limited natural gas distribution network, in which SNG could be fed. In Sweden the distribution network is located in the south-western part of the country. In Norway the distribution networks are also located in the south-western part of the country, in addition to the extensive subsea transmission network.
P2G conversion technology is burdened by high capital costs and low efficiency. These problems may be solved to some extent. The cost of P2G conversion technology is expected to fall in the future while the share of variable generation is expected to increase. Thus the business the case for P2G will be more interesting in the medium term. In specific cases P2G may present a sound business case even today but in this article we look 20–30 years ahead. The study looks at the possible operational benefits of P2G. Investment optimization of plant and transmission capacities is not part of this study. Methodology We simulated the hourly operation of the power system in Finland, Sweden and Norway for a period of one year based on certain installed power plant portfolio, hourly power demand, solar irradiation, wind power generation and hydropower inflow. District heating systems were also included in the simulation in an aggregated form. Synthetic natural gas production plants (P2G) with heat recovery were assumed to be present in Finland and southern Sweden. The unit commitment and economic dispatch tool WILMAR joint market model (WJMM) (Meibom et al. 2011) was used to optimize the operation of P2G and power plants subject to certain dynamic constraints as well as power and district heat demand. WJMM is a unit commitment and economic dispatch (UCED) model, which can perform system-wide optimization of power plants scheduling. It optimizes multi-region day-ahead and intra-day power markets constrained by power transmission capacity between regions using net transfer capacities. Figure 1 shows the structure of the simplified power system in WJMM. Different conversion technologies such as condensing and CHP plants and heat pumps are included. In most cases individual plants, except the largest ones, are aggregated into larger units. The tool was supplied with stochastic forecasts of power demand, wind power and solar power.
Figure 1: Schematic structure of the power system simulation model. The dotted lines denote district heat flows, the solid lines electricity flows and dashed lines gas flows. One such illustrated system is built for each region (part of country). Several district heating systems can be included in one region. Assumptions We studied the situation in 20–30 years from now with assumptions that are partly unfavourable for P2G. In Finland all the current nuclear plants will have been shut down and only the Olkiluoto 3 plant, currently under construction, will be operational. Nuclear power capacity in Finland was thus reduced to 1600 MW – a reduction of about 1150 MW compared to the current situation. Coal-fired and peat-fired CHP plants used for district heating were decommissioned. Oil- and coal-fired condensing plants were also decommissioned. In Sweden the nuclear capacity was reduced by one reactor. For SNG production we assumed electricity-to-fuel conversion efficiency of 56 % (based on LHV) and variable operating and maintenance cost ranging from 1 to 10 €/kWhel for different plants. For example Hlusiak and Breyer (2012) use the value 3 €/kWhel. All of the hydrogen produced was converted to SNG. Heat integration of the P2G plants with district heating networks can improve the total efficiency (Lehner, Tichler, Steinmüller, & Koppe, 2014). We assumed that 20 % of the input electricity could be exploited as heat.
One of the most important parameters is the value assumed for SNG. The basis for this parameter is the grid gas price; however, one should add the price of the CO2 emissions avoided. In addition, one may add a subsidy, which is possible for example if SNG is used as renewable transportation fuel. Table 1: Assumptions concerning the factors affecting the value of SNG per energy unit of heating value. value component
value
grid gas price
40 €/MWhLHV
CO2 emissions benefit
12 €/MWhLHV
SNG renewable subsidy
8 €/MWhLHV
In the district heating sector, which is a significant part of the Finnish energy system, a large amount of heat pumps with total heat capacity of 1800 MWth were built for district heating to replace the capacity shortage. These heat pumps could partly be large heat pumps which supply the DH network directly. Depending on local resources they could also be smaller building-integrated heat pumps which use exhaust air as heat source. Among the assumptions which are more favourable for P2G the wind power capacity in Finland was increased to 15 GW and solar PV capacity to 7 GW. These plants would annually generate 32 % and 6 % of demand, respectively, if not curtailed. A low capacity factor of 2000 full-load hours was assumed for wind power. Substantially lower wind power capacity would be required for the same energy penetration if higher (but still realistic) capacity factor was assumed. 500 MW of new NGCC plants and 2000 MW of gas-powered internal combustion engines (ICE) were built for managing peaks in net demand. In addition 2500 MW of gas-fired gas turbines were built. Of course, all of these plants could also be fired by the renewable SNG. Results WJMM produces as result the hourly power (or heat) generation and consumption of each conversion unit and hourly transmission of power between regions. In Figure 2 and Figure 3 power generation in Finland, demand and power exchange with Sweden are shown during two sample weeks. On May 30th a large generation peak consisting of both wind and solar power is shown. However, it can easily be consumed by export and P2G and it is not necessary to ramp down the
nuclear plant, which is three days later shut down for annual maintenance. Curtailment of VG was necessary neither. 20000 18000
IMPORT
16000
NATURAL GAS (OCGT)
14000 12000 10000 MW
8000 6000 4000 2000 0 -2000
NATURAL GAS WOOD HYDRO RESERVOIR HYDRO ROR WIND+SOLAR NUCLEAR INDUSTRIAL CHP MUNICIPAL WASTE SNG HEAT PUMP
-4000
EXPORT
-6000
demand FI_R
-8000
Figure 2: Hourly power generation in Finland by fuel and consumption of some technologies as well as export to and import from Sweden during one week in June when solar power reaches its maximum. The hourly total demand in Finland is also shown. The nuclear plant goes into planned maintenance on June 2nd. Figure 3 shows the peak demand week. Import stays at its maximum level and in some occasions nearly all of the gas-fired power generation capacity is used.
20000 IMPORT NATURAL GAS (OCGT)
15000
NATURAL GAS WOOD HYDRO RESERVOIR
10000 MW
HYDRO ROR WIND+SOLAR NUCLEAR
5000
INDUSTRIAL CHP MUNICIPAL WASTE HEAT PUMP
0
EXPORT demand FI_R
-5000
Figure 3: Hourly power generation in Finland by fuel and consumption of some technologies as well as export to and import from Sweden during the peak demand week in February. The hourly total demand in Finland is also shown. It turns out that P2G is not often profitable with our assumptions. Figure 4 shows the annual power generation by fuel and consumption of some technologies. P2G plants consume only about 2 TWh electricity (corresponding to 1.1 TWh SNG) while the annual consumption of natural gas in the energy sector is more than 6 TWh.
110
demand Net import RU & EE
90
TWh
70
Import NATURAL GAS WOOD WATER WIND+SOLAR
50
NUCLEAR INDUSTRIAL CHP
30
MUNICIPAL WASTE Export
10
SNG HEAT PUMPS
-10
Figure 4: Total annual electricity generation grouped by fuel and consumption grouped by technology.
Discussion The results show that with 22 GW of variable generation the hourly power balance in Finland was maintained when 5 GW of gas-fired condensing power plants and 5 GWe of P2G plants were built. It did not even require curtailing VG. However, the flexibility of the Swedish and Norwegian hydro power assets left little room for P2G and synthetic natural gas. The increased variability, decrease in capacity of baseload and middle-merit plants as well as increased penetration of heat pumps was mainly balanced by imports. Consequently occasions when P2G was profitable were not many and mainly correlated with peaks in solar PV production. Higher demand periods were mainly met with condensing plants. P2G was able to prevent curtailment of VG and ramping down the nuclear plant was necessary neither. We also see that P2G can be run at times of both large export and large import. Parameters which greatly affect the P2G operation include grid gas price, capacity of P2G, capacity of VG, efficiency of heat recovery, hydropower situation, import and export capacity, possible subsidies, ancillary service markets and power market situation in neighbouring countries. These need to be further studied before conclusions about the possible profitability of P2G. Conclusion P2G can play an important role in balancing VG and producing transportation fuels. Its advantage is the almost unlimited storage capacity but it is encumbered by low efficiency and a relatively large initial investment. In our case Finland suffered from capacity shortage and was dependent on power import. There was little excess power which could be profitably fed into P2G plants.
References Hlusiak, M., & Breyer, C. (2012). Integrating End-User and Grid Focused Batteries and Long-Term Power-to-Gas Storage for Reaching a 100 % Renewable Energy Supply. In 7th International Renewable Energy Storage Conference. Berlin. Lehner, M., Tichler, R., Steinmüller, H., & Koppe, M. (2014). Power-to-Gas: Technology and Business Models (p. 93). Cham: Springer International Publishing. doi:10.1007/978-3-31903995-4
Meibom, P., Barth, R., Hasche, B., Brand, H., & O’Malley M. (2011). Stochastic optimisation model to study the operational impacts of high wind penetrations in Ireland. IEEE Trans. Power Syst., Vol. 26, Iss. 3, pp. 1367–1379, 2011. Jussi Ikäheimo, Jussi Ikäheimo received his M.Sc. degree in engineering physics from Helsinki University of Technology in 1999. Since 2000 he has worked with Technical Research Centre of Finland (VTT), with energy efficiency, wind and solar power, district heating, power markets, demand response, and integration of demand response with distributed generation, energy storages and smart grids. He has worked in international, European and national research and development projects. He has acted as the Operating Agent of IEA DSM Task 17. Dr Juha Kiviluoma, Juha Kiviluoma obtained his PhD degree in engineering physics at Aalto University in 2013. Juha has 11 years of research experience and is currently Senior Scientist in Smart Energy and Systems Integration research area at VTT Technical Research Centre of Finland. He has developed and used several energy system models and algorithms including WILMAR and Balmorel. His PhD thesis compared flexibility options for power systems with large amounts of variable generation. He has co-authored approximately 50 publications including 7 journal articles. Juha’s main research interest is in modelling energy systems with qualifications in problem formulation, model formulation, programming, generation planning, unit commitment and dispatch, power system reserves, capacity adequacy, and energy resources.
