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Energy Systems and Technologies for the Coming Century ...

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storage duration4months3weeks2days1hoursCAESpumped hydrohydrogenminutes00,1 1 10 100 GWh1000storage energyFig. 2: Application ranges <strong>for</strong> large scale energy storage optionsThe below sections focus on <strong>the</strong> underground storage options.3.2 Underground storage options – why focus on salt caverns?The storage of natural gas in depleted oil <strong>and</strong> gas reservoirs, in aquifer <strong>for</strong>mations or inman-made salt caverns, has been st<strong>and</strong>ard practise <strong>for</strong> many decades. In Germany <strong>and</strong> inFrance, over 20% of annual consumption is stored underground. And some 100 newcaverns are currently being constructed in Nor<strong>the</strong>rn Germany. Fig. 3 illustrates <strong>the</strong> gasstorage options in underground geological <strong>for</strong>mations including ab<strong>and</strong>oned mines <strong>and</strong>hard rock caverns. Natural reservoirs dominate in terms of amount of gas storedunderground world-wide. However, <strong>the</strong> current enlargements in storage capacities inEurope are concentrated on salt caverns because <strong>the</strong>se storages are much more flexible:having much higher injection <strong>and</strong> withdrawal rates, <strong>and</strong> <strong>the</strong> flexibility to h<strong>and</strong>le frequentcycles. The installation of caverns is naturally dependent on <strong>the</strong> availability of suitablesalt <strong>for</strong>mations, as well as <strong>the</strong> ability to dispose of in an environmentally-compatible way<strong>the</strong> large volumes of brine produced during <strong>the</strong> solution mining of <strong>the</strong> caverns –normally an easy problem to solve when caverns are located close to <strong>the</strong> North Sea.Ano<strong>the</strong>r aspect plays an important role in <strong>the</strong> selection of suitable storage <strong>for</strong>mations <strong>for</strong><strong>the</strong> storage of air <strong>and</strong> hydrogen looked at in this paper: after injection of <strong>the</strong> media, <strong>the</strong>oxygen in <strong>the</strong> air or <strong>the</strong> hydrogen can react with <strong>the</strong> minerals <strong>and</strong> <strong>the</strong> microorganismspresent in natural reservoirs. This can result in a loss of oxygen or hydrogen, productionof hydrogen sulphide as well as <strong>the</strong> blockage of <strong>the</strong> fine pores in <strong>the</strong> reservoir rocks by<strong>the</strong> reaction products. To avoid this, caverns are exclusively used as energy storages inthose regions which have suitable salt <strong>for</strong>mations available. In <strong>the</strong> USA, because <strong>the</strong>regions with large wind resources are often in areas with no suitable salt deposits, <strong>the</strong> useof pore storages <strong>for</strong> compressed air <strong>and</strong> hydrogen are also being analysed. If a means isfound of using <strong>the</strong>se <strong>for</strong>mations, it would make considerable additional storage potentialavailable.Risø International <strong>Energy</strong> Conference 2011 Proceedings Page 411

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