When size matters
Despite its relatively low profile, small hydropower is an important part of the renewable energy mix.
The use of hydropower has grown over recent decades, led by continuous technical development, and it is currently the second most used renewable energy source in the world, just behind solid biomass. Hydro supplies the vast majority of renewable electricity, generating 16.6 per cent of world supply and 92 per cent of total renewable energy electricity. The normal perception of hydropower is of huge dams, such as Itaipu in Brazil or Guri in Venezuela, but there is a much bigger use of hydropower in smaller installations. There is no real consensus on the definition of small hydropower (SHP), although a capacity of up to 10MW total is becoming accepted by ESHA, the European Commission and UNIPEDE (International Union of Producers and Distributors of Electricity).
Asia, and especially China, is set to become a leader in hydro-electric generation. Present developments in Australia and New Zealand are focusing on small hydropower plants. Canada, a country with a long tradition of hydropower, is developing SHP as a replace-ment for expensive diesel generation in remote off-grid communities. Markets such as South America, the former Soviet Union and Africa also possess great untapped potential. The World Energy Council (WEC) estimates that, under current policies, installed capacity of SHP will increase to 55GW by 2010 with the largest increase coming from China. In the year 2000 the world-installed capacity of SHP was about 37GW. All regions of the world are experiencing significant increases in SHP capacity, with China again showing the greatest increase. SHP schemes generate electricity by converting the power available in rivers, canals and streams. These schemes are mainly run-of-river without any reservoir impoundment. The objective of a hydropower scheme is to convert the potential energy of a mass of water, flowing in a stream with a certain fall (called the 'head'), into electric energy at the lower end of the scheme, where the powerhouse is located. The power of the scheme is proportional to the flow (called the 'discharge') and to the head. SHP contributes towards sustainable development by being economically feasible, respecting the environment and allowing decentralised production for the development of scattered populations. Its fundamental asset is that it is a clean and renewable energy source (the fuel for hydropower is water, which is not consumed in the electricity generation process). The plants are not - if well-equipped with fish ladders - an obstacle for migratory fish and they ensure a minimum flow downstream called the reserved flow (or residual discharge) that guarantees fish life. They have also been proven to assist in maintaining river basins by allowing the recovery of wastes that flow in the river stream. It mobilises financial resources and contributes to the economic development of small scattered populations, ensuring autonomous and reliable energy for the long term. It also assures a high energy payback ratio. For each power generation system, the 'energy payback' is the ratio of energy produced during its normal lifespan, divided by the energy required to build, maintain and feed the generation equipment. If a system has a low payback ratio, it means that much energy is required.
A long history
Before we start heralding this new technology it is worth remembering that hydropower, and in particular SHP, was one of the first energy sources known to man. The first hydro machines appeared about 2,200 years ago in China and the Mediterranean basin. In Europe, before the general electric-networks extension, about 10,000 SHP installations were used in places such as sawmills, tanneries, paper mills and mechanical shops.
Although the number of plants has greatly decreased since the middle of the 20th century, there is now a renewed interest. The sharp increase in the price of crude oil during the 1970s was a great motivator, and the growing ecological sensibility of the 21st century, as well as local and national financial incentives, only serve to fuel the renaissance. SHP also offers some interesting opportunities when combined with drinking water and waste water schemes. The plant at Farebout in France uses aspiration turbines, and the injection of air at the turbine achieves an oxygenation of the river water, which results in improving the water quality downstream from the SHP. The construction in Steinen, Germany, of a hydroelectric facility below the flow of the water in a totally submerged powerhouse inside a residential area has the benefit of ensuring an optimal, economical and non-polluting production of electricity. In plants on the Louros River, Greece, biotopes have been created thanks to the combination of architectural and technical solutions.
But, despite the success and obvious potential, there are numerous barriers for SHP. It is difficult to obtain permission to extract water from rivers; hydro plant is perceived to adversely affect fishing; and it remains difficult to gain affordable connections to the grid. Pressure from a few environmental groups opposed to SHP for its local environmental impact on the river ecosystem, suspends development in many developed countries. However, new technology and improved methods are integrating environmental issues and local population in the planning, design and management process. SHP has huge potential, to allow the EU SHP industry to increase its activities by developing new plants and refurbishing old ones.