According to the World Watch Institute, water heating for domestic use through solar thermal means accounts for 126 giga watt (180 million m2), or 86% of all installations, while space heating, swimming pool heating and industrial processes account for the remaining 21 gw of thermal equivalent (GWth) or 30 million m2. Preliminary estimates for global solar thermal heating suggest additions of anything between 18 and 19 GWth in 2008, mostly in China .
Solar thermal heating worldwide has expanded by 19 GWth, with the highest annual growth rate since 1995 to reach 147 GWth (210 million square meter) of capacity in 2007. In India , the estimated potential is 140 million square metre collector area. However, by 2007, only 2.15 million sq metre collector area was achieved, with only 6.17 lakh solar cookers.
China , by far the largest market, has two thirds (79.9 GWth, 114.1 million m2) of global capacity and, despite a one-third decrease in new installations to 16 GWth (22.9 million m2) in 2007 compared with 2006, accounted for 80% of newly installed systems in 2007. Solar water heating in single-family homes accounts for nearly half and 97% of new installations. The remaining applications are split between multi-family homes and hotels, where the other 3% of new installations took place.
The market in Turkey , second only to China , peaked in 2004 and reached an annual installation plateau of 490 mwth (700,000 m2) in 2006 and 2007. The slowdown can be traced to increased access to new gas pipelines (which has affected cost competitiveness in some regions), a high value-added tax, and little government support.
Germany remains the market leader in Europe , with 0.66 GWth (9,40,000 m2) of new installations, despite a substantial 37% decrease between 2006 and 2007. This decline has been attributed to reductions in subsidies, a maturing heating market, the economic slowdown, an increase in the value-added tax and a mild winter.
In Israel , the fifth largest market, new installations (49.7 mwth, 71,000 m2) plummeted by two thirds in 2007 compared to 2006. Despite this, Israel has a long history of promoting solar thermal heating, dating back to 1980 when it became the first country to implement a solar thermal heating law. Solar thermal heating is now a mainstream technology and meets 4 % of the countrys total energy demand. Similar laws have since been enacted in Portugal , Ireland , Italy , and Spain .
In the US, new installations increased by 28% to reach a cumulative total of 1.7 GWth. Solar water heating received a supporting hand in late 2008 with the extension of the federal investment tax credit to 2016 and with the removal of a tax credit cap in early 2009.
The International Energy Agency estimates that residential solar water heating could displace 60-70% of the natural gas and electricity that would otherwise be used in these buildings.
Integration of solar thermal heating systems into architectural designs is becoming prevalent and provides additional benefits, including shading and thermal insulation. The best commercially available solar thermal heating systems demonstrate efficiencies of nearly 70%.