In energy systems of developed EU countries, the serious problem is periodic surplus of electricity production, following by deficiencies of electricity. They are particularly important in systems, where renewable energy sources (wind/solar) are significant. These are irregular power sources, depending on season and day time. Power installed in such stations is much less used than power installed in thermal or nuclear power stations. Problem is growing with increase of renewable energy share, in conjunction with the pro-ecological EU policy and continuous support for renewable energy sources. For example, in Germany (in 2011) 20% of produced electricity comes from renewable sources, in 2020 it has to be 35%, and 80% in 2050, because of nuclear plants closing and reducing the CO2 emission. Total power of wind stations there is 29 GW and of solar is 24 GW, despite the unfavorable, as it seems, climate. Germany becomes a world leader in the solar power, and power installed there is similar to total solar plants power in the rest of the world. And plans for 2050 are: 80 GW (wind) and 65 GW (solar). Such a situation in neighboring country, with similar climate, considerably more developed, indicates that similar trends will be present also here. Currently, we are at the beginning - in 2011 total power of wind stations in Poland was 2 GW, and of solar stations – 2 MW. This means the lowest use of both energies among EU, per capita and per 1 km2. In coming years the share of renewable energy sources in Poland must radically increase. Planning in Poland for 2030 is 19% of energy from renewable sources, in comparison with 6% at present (mainly hydro and biomass). Irregularities in electricity production from wind/sun, make this energy still quite expensive. If usage of this energy periodic surpluses would be practically solved, resulting prices would be lower. Problem of electricity storage has not yet been generally solved. There are hydro pumped plants, but they cannot be applied larger, because specific terrain layout is required and the impact on environment is high. Future of surplus electricity storage lies under the ground, in caverns leached in salt deposits, where one can store energy as hydrogen obtained by water electrolysis or as compressed air. This would give much greater density of stored energy than pumped hydro, without the negative environmental impact. In Poland we have appropriate salt deposits, and proven technology of salt caverns building. We already have efficiently working storages in salt caverns: KPMG Mogilno (Cavern Underground Gas Storage - owner PGNiG) and PMRiP Góra (Underground Storage of Oil and Fuels - owner SOLINO/ORLEN). In EU, both such magazines, besides of Poland, are built only in Germany and France. CHEMKOP was the initiator, originator and designer of both Polish underground storages, and specialized computer software for cavern designing, developed in CHEMKOP Sp. z o.o. was purchased (licenses) by 30 leading companies from all over the world. Salt caverns, similar to natural gas storage caverns, after due designing, may be successfully built for hydrogen, and in this form may store the excess energy. Hydrogen will be produced by water electrolysis using excess electricity, stored in salt cavern and afterwards used in different ways: as supplement to natural gas in gas network, as fuel for fuel cells or electro generators or as a raw material in petrochemical industry. The key issue is the salt caverns – they should be located where disposing of brine is possible. Hydrogen storage should be located near potential places of its use. At present, few hydrogen storage salt caverns are existing in UK and USA, but for petrochemical use, not for energy purposes. Special hydrogen pipeline in USA, 300 miles long, connected storage caverns with hydrogen producers and users. The first storage cavern for hydrogen produced from surplus electricity will be built in Etzel (Germany). Pilot peak power stations, working on compressed air from salt caverns are working in Germany (Huntorf) and in USA (McIntosh). Currently most of the research related to hydrogen storage takes place in Germany. It is associated with energy balance of Germany, with large amount of salt deposits and with high level of technologies for underground storage. Matter is urgent, because problem of periodic local energy surpluses in German network is so serious, that Poland and Czech Republic are forced to build special devices on border network connections, to reduce the impact of these irregularities on their own networks. In next few years, as expected, Germany will develop more economical hydrogen electrolysis technology and adequate electrolyzers will be produced. The surface equipment for hydrogen pumping stations will be also available. Poland has periodic surpluses of electricity production even now and very good possibility of salt caverns construction in comparison with others. Most countries do not have appropriate salt deposits, so we can become one of the European champions in storage of hydrogen – the fuel of future. It is necessary, however, to start the research work for such a storage just now. In the authors opinion, the research works should include: • identify the needs for energy storage in Poland, estimate a surplus of energy for storage in hydrogen or compressed air caverns, determine recommendation for hydrogen production by water electrolysis on a wider scale, • define possibility of storage caverns construction for hydrogen in Polish salt deposits, • determine specificity of storage caverns construction for hydrogen: size and shape, working pressures, recommendations for drilling/completion, used materials, • examine geomechanical stability of hydrogen storage caverns in their specific pressure conditions, using special computer model, • examine thermodynamic behavior of hydrogen storage caverns in their specific temperature conditions, using computer model for hydrogen cavern, • compare and evaluate hydrogen storage and compressed air storage technologies for energy surpluses (HYES/ CAES), looking for their usefulness in Polish conditions. Further research work will help to create a sound basis for taking decision to build underground energy storage by specifying: storage policies, applied technology, location of storage caverns and scenarios of their work. Final remarks • Technical and economical problems with proper use of renewable energy sources will be increasing in Poland in nearest future year by year, similarly as currently in Germany. • The problem cannot be solved in other way than storage of energy surplus for use during deficiency periods. • The best solution, at present, is energy storage in salt caverns in the form of hydrogen. • In Poland, we have both appropriate salt deposits and large experience in designing and construction of salt cavern storages. • We are world leaders in computer modeling of development and operation of salt cavern. • Our experience can be extended to the hydrogen storage, provided that relevant research work will start and be performed. • So, there is a chance that Poland will become one of the leading country in storage of hydrogen – a clean fuel of the future.
