Hydrogen Energy Storage

Executive Summary

Electricity can be converted into hydrogen by electrolysis. The hydrogen can be then stored and eventually re-electrified. The round trip efficiencyThe amount of energy that a storage system can deliver relative to the amount of energy injected into the system during the immediately preceding charge. (Also referred to as efficiency.) today is as low as 30 to 40% but could increase up to 50% if more efficient technologies are developed. Despite this low efficiency the interest in hydrogen energy1. Energy is the potential of a physical system to perform work. (A common unit of work is foot-pound—the amount of energy needed to lift one pound up a distance of one foot.) Energy exists in several forms such as electromagnetic radiation ... storage is growing due to the much higher storage capacityThe rate at which equipment can either generate, convert or transfer energy. compared to batteries (small scale) or pumped hydro and CAES (large scale).

Discussion

Hydrogen Production

Alkaline electrolysis is a mature technology for large systems, whereas PEM (Proton Exchange Membrane) electrolyzers are more flexible and can be used for small decentralized solutions. The conversion efficiency for both technologies is about 65%~70% (lower heating value). High temperature electrolyzers are currently under development and could represent a very efficient alternative to PEM and alkaline systems, with efficiencies up to 90%.

Hydrogen Storage

Small amounts of hydrogen (up to a few MWh) can be stored in pressurized vessels at 100~300 bar or liquefied at 20.3K (-423 deg F). Alternatively, solid metal hydrides or nanotubes can store hydrogen with a very high density. Very large amounts of hydrogen can be stored in man made underground salt caverns of up to 500,000 m3 at 200 bar (2,900 psi), corresponding to a storage capacity of 167 GWh hydrogen (100 GWh electricity). In this way, longer periods of flaws or of excess wind / PV energy production can be leveled. Even balancing seasonal variations might be possible.

Hydrogen Re-Electrification

Hydrogen can be re-electrified in fuel cells with efficiencies up to 50%, or alternatively burned in combined cycleOne sequence of storage charging and discharging. Also known as charge-discharge cycle. gas powerThe rate at which energy is generated, converted, transmitted, distributed or delivered. plants (efficiencies as high as 60%).

Other Uses of Hydrogen

Because of the limited round trip efficiency, direct uses of green hydrogen are under development, e.g. as feedstock for the chemical and the petrochemical industry, as fuel for future fuel cell cars or blending with natural gasA mixture of hydrocarbon gases occurring with petroleum deposits, mainly combining methane with varying quantities of ethane, propane, butane and other gases. Used as a fuel and for manufacturing organic compounds. This type of gas generates about 38... of up to 5 to 15% in natural gas pipelines. Electrolytic hydrogen can also be used for the production of synthetic liquid fuels from biomass, thereby increasing significantly the efficiency of the biomass utilization.

Deployment Status

Several European and American companies offer integrated hydrogen solutions for the supply of electricAn adjective meaning “needing electricity to operate” such as electric motor or wire. IEEE: Containing, producing , arising from, actuated by or carrying electricity. power to small isolated sites or islands. Demonstration projects have been performed since 2000 in Europe and the USA and commercial products are available. Large scale hydrogen storage in salt cavern is standard technology. To date there are two full size hydrogen caverns in operation in Texas, USA, a third one is under construction, three older caverns are operating at Teesside, UK.