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Solar thermal systems produce hot water whether the system is installed in Sweden, Germany, India, Tunisia or South America. The annual yield depends on the application (domestic hot water, pool heating, space heating), the local climatic conditions and system dimensioning (high or low solar fraction). The annual collector yield per square metre of collector area lies around 250 kWh/m2 for unglazed pool heating systems, 400 kWh/m2 for solar combi systems for hot water production and space heating in northern regions, and up to 700 kWh/m2 for installations in southern European regions used only for hot water preparation.
Flat plat collectors are made of metal, glass, insulating and joining materials. Typically copper, steel or aluminium is used for the absorber configuration. The sides and bottom of the collector are usually metal and insulated with mineral wool to minimize heat loss. The glass top is made of special glass to resist facture and maximise transmission of energy. In the future, a variety of materials and combinations of materials including plastics may be used to improve cost benefits ratios, higher temperature ranges and systems performance.
Vacuum tubes collectors are made of a borosilicate glass. Mostly the absorber layer is coated on the inner tube and no metal is required. But there are also tubes with an inner metal fin absorber.
For swimming pool heating, plastic or rubber are used to make low-temperature absorber plates.
The solar collector is usually mounted on the roof and is connected to a circuit containing water with propylene glycol anti-freeze added. The tank is also made of metal, partly stainless steel, partly enamelled steel or copper.
There is a wide variety of applications for solar thermal technology. The most common application is the heating of pool water, the heating of domestic hot water and space heating. Not very wide spread yet are solar cooling systems, because of the complexity of the technology and the high initial investment costs. Also, process heat applications such as in breweries or car washes, as well as in the food and textile industries, are still in their infancy. You can search for all these different kinds of applications in the filter section market sectors on the right hand side of the page.
What is the difference between vacuum tube collectors and flat plate collectors? With flat plate glazed collectors the absorbers are fitted in a box closed by a pane of glass (90 % market share in 2009 in Europe). Vacuum tube collectors – which are the dominating technology in China (96 % market share in 2008) – have the absorber coating on the outside of the inner tube in placed within an evacuated glass tube. Generally speaking, the advantage of vacuum tubes is a higher efficiency (less space required for the collector on the roof) and higher temperatures (necessary for process heat and some solar cooling technologies).
The disadvantage: The vacuum tubes produced in Europe are more expensive than the flat plate collectors but in some incentive schemes like in Germany they receive the same grants as the flat plate collectors. In China, some locally produced vacuum tube collectors have a poor quality performance, flat plate collectors are seen as high-quality products.
Solar thermal systems most probably have higher "first costs" than other kinds of heating systems. Also, the energy is not available 24 hours a day and not sufficiently during all seasons of the year. That means that storage systems like water tanks and backup systems are a must in all solar thermal installations.
“Replacing imported fuels with local jobs”, this slogan of the European Solar Thermal Industry Federation (ESTIF) sums up perfectly the advantages of solar thermal technology for a national economy. The six biggest solar thermal markets in Europe – Germany, Austria, Italy, Spain, Greece and France – already exceeded 34,000 full time jobs in 2007 (check related article here). With an annual average growth rate of 20 % that is 6,800 jobs more each year. In the boom year 2008 in Europe this calculation results in 116,000 full-time jobs.
Furthermore solar thermal technology is an export trigger. In mature markets solar thermal industry is reaching high export rates. In 2007, Austria produced four times as many collectors as were newly installed in the country. In Greece, for the first time in 2008, the export will exceed local sales. Further Information: “Solar Thermal Action Plan for Europe” by the European Solar Thermal Industry Federation (ESTIF) http://www.estif.org/policies/st_action_plan/
Most importantly: The energy of the sun is endless, sufficient and free of charge. Using solar water heating technology makes you independent of the rapidly increasing fossil fuel prices. It saves customers energy, money, is clean and safe and it is a long-living technology with life cycles of 25 years and more.
In the summer your system can provide 100 % of your hot water demand for showering and bathing. To make sure that you do not run out of hot water, there is always a backup system for the times the solar system cannot provide all your needs. In sunny regions such as Southern Europe and Northern Africa solar water heaters can provide almost 100 % of the hot water demand of a family.
The ambitious scenario of the European Solar Thermal Industry Federation (ESTIF) expects Europe will reach 0.7 kWth (1 m2 of collector area) per European in 2020, equivalent to a total capacity in operation in the EU by then of 320 GWth. To reach this target, a suitable support framework will be required and solar will then be widely used for both cooling and supplying process heat, though the majority of this capacity will still supply domestic hot water and space heating. The average yearly growth rate of the EU market necessary to reach this target is 31 % – less than the rate achieved in 2006 and only 7 % above the 2002 to 2006 average. This scenario requires – supposing a linear growth – an installation of 12.2 GWth (17 million m2) in the year 2020, six times more than in 2007, when 2.1 GWth (3 million m2) were newly installed in Europe as a whole. Further Information: “Solar Thermal Action Plan for Europe” by the European Solar Thermal Industry Federation (ESTIF) http://www.estif.org/policies/st_action_plan/
The international solar thermal market is growing constantly but with ups and downs. According to the annual study "Solar Heat Worldwide" the newly installed collector area globally grew accordingly:
2004: 12.6 %
2005: 10.3 %
2006: 22 %
2007: 8.7 %
The future perspective depends very much on the market development in China. In the last seven years the solar thermal market in the People’s Republic increased at an average rate of 21 % per year.
Further information: Solar Heat Worldwide, a study from the IEA Solar Heating & Cooling Programme, May 2009 (http://www.aee-intec.at/0uploads/dateien648.pdf)
By far the largest solar thermal market in the world according to newly installed solar thermal capacity per year is China. In 2008, around 21 GWth (30 million m2) were sold in China, which was around 80 % of the world global solar thermal market.
In Europe, Germany – the second biggest market in the world – is dominating. With its newly installed capacity of 1.13 GWth (1,615,000 m2) in 2009, the country reached a market share of 38 % within Europe.
Position three is held by Turkey, a dynamic solar thermal market which is estimated at 785 MWth ( 1,120,000 m2).
Besides these front-runners, India, Brazil, Israel, Austria, Greece, USA, Japan, France, Italy, Spain and Australia are countries which reached a market volume of greater than 70 MWth (100,000 m2) in 2007.
Solarenergie 2007, Study by the Swiss bank Sarasin, November 2008 (Only available in German)
Solar thermal Markets in Europe. Trends and Market Statistics 2009, Study by European Solar Thermal Industry Federation (ESTIF), June 2009 (see the following link)