Solar collectors — EN 12975 Part 1 and 2
With regard to the standard series EN 12975 for solar thermal collectors, a major change undertaken during this revision process was e. g. the presentation of the thermal performance by means of the so-called “power curve” instead of the efficiency curve previously used. An example of a power curve is shown in Figure 1.
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Table 3: Titles of European solar thermal standards at present
* expected year of publication. |
The power curve describes the thermal power output per collector module or unit respectively as a function of the temperature difference between mean collector temperature tm [°C] and the ambient temperature ta [°C]. Since the power curve depends on the hemispherical solar irradiance G* used for its calculation the corresponding value of G* has to be mentioned together with the power curve. According to EN 12975-2:2006 a value of G* = 1000 W/m2 has to be used.
In comparison to the previously used collector efficiency curve the major advantage of the power curve is that the presentation of the collector output is not related to a certain area anymore. Hence the discussions about gross, aperture and absorber area become obsolete.
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Fig. 1. Example of a solar thermal collector “power curve” |
An other important modification made during the revision of the EN 12975 series is related to the mechanical load tests. The procedure was changed in such a way that the supporting frame is no longer subject of the standard. However the interface between supporting frame and collector is
used to fix the collector on the respective test rig. The load during the test is increased until the collector fails.
