3. Existing or planned WWTPs

Worldwide, more than 400 WWTPs are currently in service or under construction, with a total capacity of over 150 GW, i.e. 15% of the capacity of hydroelectric power plants, or a third of the capacity of all the world's reactors.

Around 1970, the economic interest in STEPs was fairly low, for easily modulated electricity based mainly on inexpensive, storable fossil resources or on hydroelectric generation. The first major development of STEPs in the 1980s accompanied the higher cost of oil and the rapid development of nuclear power, which was not very flexible. After 1990, the lower cost of oil and the halt in nuclear investment led to a significant reduction in STEP investments, which are now resuming (except in France) at a high rate, linked to the cost of fossil fuels and the development of intermittent energies, particularly wind power.

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