Solar Thermal: A leading technologyThe role of renewables has become more and more important over the past years. The growing dependence on oil and gas imports from politically unstable regions of the world, the foreseeable decline of oil production and the growing evidence of man-made global warming have made renewables an even brighter alternative to coal, oil and gas.
Interestingly, solar thermal has been greatly underestimated for a long time. Looking just at the intermittent renewable energy technologies - i.e. sources whose actual energy output varies with the availability of solar irradiation or wind - most people assume that wind power was the leading technology. However, a direct comparison reveals that solar thermal is larger than either wind power or photovoltaic - both in terms of worldwide installed capacities and in terms of renewable energy produced.
Worldwide installed capacities of different renewable energies
Source: solar thermal data based on IEA-SHC collector statistics, PV and wind power taken from UNDP's World Energy Assessment: Overview 2004 Update (2001 data were taken, because newer worldwide figures were not available for all technologies) Worldwide energy production from different renewable energies
Source: The left column for each technology represents the estimation of the relative European industry association (EPIA for PV, ESTIF for solar thermal and EWEA for wind power); the right columns show the estimations published by UNDP in its World Energy Assessment. How did it come that solar thermal was so underestimated?Several reasons contributed to solar thermal being so underestimated. One key reason was until now: Solar thermal was not measured in the same units as other renewable energies. Statistics for solar thermal were ususally expressed in square meters of collector area. But how much is 100.6 million m2 of collector area compared with e.g. 23.000 GW of installed wind power capacity? To overcome this methodological discrepancy, experts from the International Energy Agency's Solar Heating and Cooling Programme (IEA-SHC) and from major solar thermal trade associations met in September 2004 in Austria to discuss a suitable factor to convert square meters of collector area into MWth (megawatt-thermal) of installed capacity.
The involved associations finally agreed to use one factor of 0.7 kWth/m2 for all collector types, as the differences between flat plate, vacuum tube and unglazed collectors in terms of capacity proved minimal. The underlying methodology is similar to the calculation of MWpeak in photovoltaic and explained in detail in a separate technical note. With the conversion factor it was possible to convert the existing collector statistics of the IEA-SHC Programme from m2 into MWth. Solar thermal installed capacities worldwide - country by country
Source: Data converted from Solar Heating Worldwide: Markets and Contributions to the Energy Supply 2001, IEA-SHC 2004
The conversion of square meters of MWth into energy (MWh) is more complex as different configurations and uses of the same collector area can result in very different energy yields. Several technical experts are working on a proposal for a suitable conversion calculation. The above shown diagram shows the estimates of ESTIF (left column for solar thermal) and the United Nations Development Programme (right column).
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