by Amanda Chiu/ August 20, 2009
Solar thermal heating worldwide expanded by 19 gigawatts of thermal equivalent (GWth) with the highest annual growth rate since 1995 to reach 147 GWth (210 million square meters (m2)) of capacity in 2007.1 (See Figures 1 and 2 on solar water heating-a subset of solar thermal heating applications.) Water heating for domestic uses accounts for 126 GWth (180 million m2), or 86 percent of all installations, while space heating, swimming pool heating, and industrial processes account for the remaining 21 GWth (30 million m2).2 Preliminary estimates for global solar thermal heating suggest additions of between 18 and 19 GWth in 2008, mostly in China.3
The most mature of solar technologies, solar thermal heating harnesses the sun's energy for domestic water heating, space heating, swimming pool heating, and drying and other industrial processes. Solar thermal systems can also meet cooling needs by fueling a compressor driven by heat rather than by traditional mechanical energy. It is one of the most widely used renewable heating technologies and the only one to produce energy at levels comparable to renewable power, second only to wind in terms of energy produced annually.4 Solar thermal heating produced enough energy globally in 2007 to meet the equivalent heating needs of 15 percent of U.S. households.5
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 percent of newly installed systems in 2007.6 (See Figure 3.) Solar water heating in single-family homes accounts for nearly half of all uses and 97 percent of new installations.7 The remaining applications are split between multi-family homes and hotels, where the other 3 percent of new installations took place.8
The contributing factors to Chinese dominance include a lack of natural gas access in most homes, low cost, and government support of research and development.9 In the coastal city of Rizhao, where about 99 percent of all households use solar water heating, the initial capital costs for solar water heaters are on a par with conventional electric systems, while lifecycle costs demonstrate annual savings of 3-6 percent of the average 2006 household income.10 Although national policies have so far not been the driving force behind solar thermal heating in China, spring 2009 saw the launch of the first national rebate program, which targets rural areas.11
The market in Turkey, second behind China, peaked in 2004 and reached an annual installation plateau of 490 MWth (700,000 m2) in 2006 and 2007.12 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.13
Germany remains the market leader in Europe, with 660 MWth (940,000 m2) of new installations, despite a substantial 37-percent decrease between 2006 and 2007.14 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.15 In 2008, the state of Baden Württemberg enacted Germany's first renewable energy heating law, which required new buildings to meet 20 percent of their space and water heating needs with renewables and gave existing buildings two years to transition to 10 percent renewables.16 A similar law went into effect at the national level in 2009, requiring new residential buildings to use renewable resources for 14 percent of their space and heating needs by 2020, with a two-year transition period and a lower 10 percent target for existing buildings.17
The European market experienced its first slowdown in five years in 2007, with 10 percent fewer new installations than in 2006.18 Germany had the largest decline in annual installations, but Denmark (down 21 percent compared with 2006), Sweden (11 percent), and Austria (4 percent) experienced similar dips, whereas markets in Hungary and Italy soared-with growth rates of 700 percent and 200 percent, respectively.19 Early estimates for 2008 show a market recovery in Europe, with accelerated growth in the Mediterranean region and a strong rebound in Germany of more than double 2007 annual installations following readjustments in investment subsidies.20
Europe maintains the most comprehensive portfolio, with significant levels of applications in hot water and space heating for residential buildings and hotels, district heating, space cooling, and industrial processes. Just under half of new installations in 2007 were used for water heating in single-family homes.21 In late 2008, the European Union passed a renewable energy directive that includes heating and cooling for the first time, and markets are expected to respond positively.22
In Israel, the fifth largest market, new installations (49.7 MWth, 71,000 m2) plummeted by two thirds in 2007 compared with 2006.23 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.24 Solar thermal heating is now a mainstream technology and meets 4 percent of the country's total energy demand.25 Similar laws have since been enacted in Portugal, Ireland, Italy, and Spain.26
In the United States, new installations (100 MWth, 150,000 m2) increased by 28 percent to reach a cumulative total of 1.7 GWth.27 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 2009.28 Hawaii leads the U.S. market, with 37 percent of new installations nationally in 2008, and has enacted a law requiring solar water heating systems in new single-family homes starting in 2010. 29 The largest solar water heating program in the country was approved in California in 2007, and 11 other states include renewable heating and cooling in state renewable electricity targets.30
Cyprus has the highest solar thermal heating use per capita in the world (0.67 kWth per capita), followed by Israel (0.52 kWth per capita) and Austria (0.25 kWth per capita).31 Mediterranean countries like Cyprus and Greece (0.23 kWth per capita) benefit from mild climates, where cheaper, less weatherized systems are economical options.32 Germany ranks eighth with 71 Wth per capita, China steps in at ninth (61 Wth per capita), and the United States lags far behind at thirty-first (6 Wth per capita).33
Integration of solar thermal heating systems into architectural designs is becoming more prevalent and provides additional benefits, including shading and thermal insulation.34 The best commercially available solar thermal heating systems demonstrate efficiencies of nearly 70 percent.35
Worldwide, 200,000 jobs support the production, installation, and maintenance needs of solar thermal heating systems.36 In the European Union, more than 30,000 people are employed directly or indirectly in the industry, and the German industry alone is responsible for half of these jobs.37
Heating accounts for more than two thirds of total energy use in buildings, which emit 30-40 percent of global greenhouse gases.38 In 2005, nearly 55 percent of energy use in buildings went toward space heating and another 16-17 percent to water heating.39 Renewable heating resources like solar thermal energy displace conventional heating fuels, primarily natural gas and electricity.
The International Energy Agency estimates that residential solar water heating could displace 60-70 percent of the natural gas and electricity that would otherwise be used in these buildings.40 In the United States, water heating accounts for 20 percent of total household energy use.41 By using solar water heating, residential and commercial customers could reduce their heating fuel use by one third and displace the equivalent of 1 percent of the country's total energy use or one third of its natural gas-powered electricity.42 These improvements would reduce greenhouse gas emissions by 50-75 million tons per year in the United States alone.43
In Europe, half of total energy demand is from heating and cooling in buildings and industrial processes. Through efficiency improvements and new technologies, the solar thermal heating industry estimates that Europe could reduce energy demand for heating and cooling by 40 percent and meet half of the remaining low and medium temperature demand with solar heating by 2050.44 Solar thermal heating technologies also have the potential to provide the industrial sector with up to 125 GWth of thermal fuel, enough for 4 percent of its heating needs.45
Solar thermal heating markets were inconsistently affected by the economic downturn in 2007, with major markets stumbling while emerging markets surged forward. In displacing fossil fuels, solar thermal heating provides stability in an era of volatile energy prices and supply while also reducing greenhouse gas emissions.
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Solar Thermal Figures:
