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Environmental and social impacts vary according to the technology and might hinder development in some cases
As with the economics, the environmental impact of electricity storage is difficult to assess. It is necessary to consider direct and localized impacts, which vary according to the technology used, as well as the impact of the generation source, electricity displaced upon discharging and the increase in generation needed to balance storage energy losses. There is, for instance, no environmental sense in storing low-cost power from coal at night to displace electricity generated during the day from gas or hydro peak power plants.
In terms of individual technologies, pumped hydro storage faces the greatest environmental problems. Due to its low energy density – 1 cubic meter of water over a height of 100 meters gives 0.27 kWh of potential energy – requirements for land and water are high. Closed-cycle plants using two artificial reservoirs reduce water use, but increase the flooded area. Higher elevation differentials and new concepts using seawater and wastewater could mitigate the technology’s environmental impact.
Compressed air energy storage uses very little land, but is the only technology that directly emits greenhouse gases. That said, emissions are very low (equivalent to roughly one third of those of conventional gas turbine) and have been reduced in newer plants where exhaust gas is used to heat up the air. Moreover, emissions will be avoided in adiabatic and isothermal plants. Compressed air energy storage also has high water requirements for the formation of underground salt caverns and for cooling during operation.
Meanwhile, there are concerns over the energy intensity of batteries. According to a recent Stanford University study, over their lifetime batteries store only two to ten times the energy needed to build and operate them. This compares with ratios higher than 200 for pumped hydro storage and compressed air energy storage. The relatively low ratio for batteries results from their cycling life and the materials of which they are made, underlining the need for continuing research to improve durability and investigate new materials. Important safety issues that could compromise public acceptance must be addressed in the case of batteries and hydrogen solutions.
Finally, better communication and education are needed to improve the understanding of electricity storage among energy professionals, policy makers, students and the general public.