However, these forms of energy are irregular and unstable. One of the challenges that scientific research must quickly resolve is how to store the electricity they produce when conditions are favourable more efficiently and more economically for use when conditions are less favourable.
Various ways of storing energy already exist. Surplus electricity can, for example, be used to move water from a low reservoir to a high reservoir or to electrolyse water with hydrogen and oxygen, which can then be burned or used in a fuel cell, or to compress gases (such as nitrogen) to their liquefaction point. One major area of development will, however, be that of rechargeable batteries.