The theoretical size of worldwide hydropower is about 3,000 GW, four times greater than the capacity that has already been exploited. However, the actual amount of electricity that is likely to be generated by hydropower will probably be much lower than the theoretical potential because of environmental concerns and economic constraints.
Hydropower has reached its potential capacity limit in most OECD countries. Much of the remaining hydro potential in the world exists in the developing countries of Africa and Asia and is considerable in these regions. In North America, an estimated 72% of potential has been exploited and in OECD Europe 63%. The highest level of exploitation after that is in Asia, with 45%. The Pacific and non-OECD Europe follow with 25% and 21% respectively. However, in the developing countries exploitation ranges from 6-12%, indicating a huge theoretical potential for hydropower development.
Harnessing this resource would require massive expenditure because of the high construction costs of hydroelectric facilities. In the past, the World Bank has spent billions of foreign aid dollars on huge hydroelectric projects in the developing world. Opposition to hydropower from environmentalists and local populations, as well as new environmental assessments at the World Bank, will restrict the amount of money spent on hydroelectric power construction in the developing countries. There is also a trend in thinking towards smaller projects serving local areas, which are easier to manage and finance.
A large percentage of hydropower potential has already been developed in North America and Europe. As in the developing countries, public opposition to large hydro schemes will probably result in very little new development of big dams and reservoirs.
The development of distributed generation will offer opportunities for development of small scale hydro plants. There is already a large amount of small hydro in the industrial countries and small scale and low head hydro capacity will probably increase in the future as research on low head turbines and standardised turbine production lowers the costs. New computerised control systems and improved turbines may allow more electricity to be generated from existing facilities in the future. Many small hydroelectric sites were abandoned in the 1950s and 60s when the price of oil and coal was very low and the environmental impacts of fossil fuels were unrealised. Increased fuel prices in the future could result in these facilities being refurbished.
