A large number of technologies have been developed, at least at a development scale, to offer solutions to this problem, addressing the need for both electricity generation and direct heating. They include geothermal, various biomasses, hydropower, wave, solar (both photovoltaic (PV) and thermal collectors) and wind. Development of the various technologies is in different states of maturity, for instance, hydropower has been in existence for many years, uses mature technology and has the largest installed capacity. Conversely, wave and other ocean based generation systems are still really in heir infancy and may not be fully commercially viable until the next decade. Although hydropower is well established environmental concerns over the vast tracts of land that have to be submerged mean that hydropower projects are not now the most popular solution to the problem, but there is certainly scope for upgrading and updating existing equipment with more efficient plant. Grid connected solar PV is the fastest growing sector of the renewable energy market, achieving 50% capacity growth in 2006 and in 2007 reaching about 7.7GW installed capacity, whilst wind power is the largest single component of renewable energy production, at around 95GW at the end of 2007.