Hydro power is much more significant as a generator of electricity. At 15.9% hydro power currently has a larger share than nuclear power which has 13.5%. Hydro power is the most important renewable energy source for the generation of electricity.
The theoretical size of worldwide hydropower is about 3,000 GW, four times greater than what has already been exploited. The actual amount of electricity which will ever 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 and much of the remaining hydro potential in the world exists in the developing countries of Africa and Asia, and it 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. But 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 hydro-electric facilities. In the past, the World Bank has spent billions of foreign aid dollars on huge hydro-electric projects in the third 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 hydro-electric 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 to finance. However, the World Bank has recently had a change of heart in its view of hydro projects and is financing the sector.
In North-America and Europe, a large percentage of hydropower potential has already been developed. As in the developing countries, public opposition to large hydro schemes will probably result in very little new development of big dams and reservoirs.