The theoretical size of the worldwide hydro power is about four times greater than that which has been exploited at this time. The actual amount of electricity which will ever be generated by hydro power will be much less than the theoretical potential. This is due to the environmental concerns outlined above, and economic constraints. Much of the remaining hydro potential in the world exists in the developing countries of Africa and Asia. Harnessing this resource would require billions of dollars, because hydro-electric facilities generally have very high construction costs.

In the past, the World Bank has spent billions of foreign aid dollars on huge hydro-electric projects in the third world. Opposition to hydro power from environmentalists and native people, 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 of the world. In North-America and Europe, a large percentage of hydro power potential has already been developed. Public opposition to large hydro schemes will probably result in very little new development of big dams and reservoirs. Small scale and low head hydro capacity will probably increase in the future as research on low head turbines, and standardized turbine production, lowers the costs of hydro-electric power at sites with low heads.

New computerized control systems and improved turbines may allow more electricity to be generated from existing facilities in the future. As well, many small hydro electric sites were abandoned in the 1950's and 60's when the price of oil and coal was very low, and their environmental impacts unrealized. Increased fuel prices in the future could result in these facilities being refurbished. Low fossil fuel prices continue to constrain development of the world's renewable energy sources. While the costs of installing and generating electricity with renewable resources continue to decline and technological advances improve generating efficiencies. The potential for growth of hydroelectricity and other renewable sources is higher in parts of the developing world. Renewables are projected to grow by almost 5 percent annually in developing Asia between 1995 and 2015, for the most part because large-scale hydroelectricity projects are still being constructed there. On the other hand, the particularly strong annual growth of renewables in India almost 7 percent per year will result from increased use of alternative energy sources, including primarily wind, some photovoltaic, and some hydro-electric power development.

As in Western Europe, India's government programs and incentives for installing renewables have resulted in strong growth. Further, there are signs that some large energy companies, such as Enron Corporation, Royal Dutch/Shell, and British Petroleum (BP), are expanding their interest in renewables. In 1997 Enron Corporation acquired the American wind power developer, Zond Corporation, and German wind turbine manufacturer, Tacke Windtechnik GmbH. BP announced plans to increase its solar technology sales to $1 billion within 10 years, including plans to invest $6.5 million (U.S.) in its solar photovoltaic cell production plant in Madrid, Spain, in an effort to double production of solar photovoltaic cells. BP also pledged to reduce the company's greenhouse gas emissions by 10 percent relative to 1990 levels. Royal Dutch/Shell announced a similar objective to be achieved by 2002.