4. STEP futures worldwide

Many future WWTPs could be very similar to current WWTPs, but differences would also be likely, notably in terms of head, power or energy per site, cost reduction, environmental impact, pump and turbine optimization. And these stations will also have to adapt to the most readily available sites.

• Demand will also be high in countries with few mountains, and many WWTPs will be able to operate below waterfalls of less than 100 m. The higher cost per kW of such plants can be offset, at least in part, by shorter tunnels between reservoirs. Very low heads are also conceivable, especially for large offshore basins: the Rance tidal power plant in France can pump water from a few meters below sea level.

• Current STEP sites store an average of a few GWh. The unit capacity of many future sites...