--------

---------------

In the autumn of 2005, Navitron took the decision to have a range of solar panels tested for the BS EN 12975 standard. Unfortunately, we were forced to choose a European company from the 'approved testing house' list. Having spoken to a number of testing houses, we opted to use SPF in Switzerland, a Solar Keymark Company, due to their extensive industry experience, and the level of their professionalism and help in dealing with our enquiry. The European standard is mainly about documenting the performance of a panel - hence even flat plate collectors are able to achieve the standard - although political decision-makers assume that the standard indicates a 'quality' product, and therefore it is frequently specified as a requirement to qualify for certain grants, subsidies or for inclusion on various 'approved product' lists.  Hence our decision to have our panels tested.

No CE label for solar collectors

Weather

Unfortunately, the Swiss climate does not permit suitable sunlight conditions for testing during the winter months, so the tests had to be called off until April at which point solar irradiation levels are sufficient to continue testing. The tests are exhaustive, and therefore take some time to complete. Due to the reliance on weather conditions, it is impossible for SPF to provide an accurate date for completion of the tests, but we are anticipating that testing should be complete by mid-summer.

About SPF

The Institut für Solartechnik SPF is part of the Hochschule für Technik Rapperswil HSR. The Institute has been engaged in applied research and development on thermal solar technology since 1981. Around 20 members of staff (engineers, physicists and technicians) are occupied in the following areas:

• Materials and components (absorber coatings, substrates, covers, pumps, compensators)
• Collectors (flat-plate and tubular collectors, liquid and gaseous heat transfer media, concentrating configurations)
• Systems (solar domestic hot water systems, combined systems for space heating and hot water, solar cooling)
• Information technology (Software ""Polysun"" to calculate and optimize collector systems)

SPF is involved in technology transfer between research and development centres on the one hand, and trade and industry on the other. In doing so, SPF acts as a link between users, investors, educational institutions, manufacturers and installation tradespeople.

• SPF's expertise is officially confirmed by accreditation (Schweizer Akkreditierungsstelle (SAS))
• SPF test reports are recognized internationally without restrictions
• Outdoor testing guarantees realistic results
• SPF have 25 years of experience
• All existing standards will be taken into account if required
• Navitron test results will be published on SPF's CD-ROM and on their Internet
• Navitron data will be included in the Polysun collector data base

 

SPF Performance test

THE BS EN TESTING FACILITIES:

Optical Measurements
Several instruments are available to determine the various optical properties that are important in the thermal use of solar energy. These include an FTIR spectrometer with integrating spheres and a spectral range from UV to MIR, an IAM measurement stand to determine the angle-dependent transmittance and a spectroradiometer to measure the spectral radiation.These instruments can be used for many different measurement tasks. Some measurement procedures and tests have been standardized, so that the most relevant materials properties for the thermal use of solar energy can be determined as inexpensively and quickly as possible:
Absorber The absorptance and emittance of absorbers is determined on the basis of a spectral, direct/hemispherical reflectance measurement. The sample is irradiated with a parallel ray (Ø 25 mm) with an incidence angle of 10° relative to the sample normal. The hemispherically reflected radiation is measured using an integrating sphere. The solar absorptance is calculated from these measured data by integration, with the AM1.5 spectrum (ISO 9845-1) as the weighting spectrum. The thermal emittance is obtained from weighted integration with the spectrum of a blackbody at a temperature of 100 °C (373K). If desired, other weighting functions (for instance, the blackbody spectrum for another temperature than 100 °C (373K)) can be used to calculate the integrated values. Further, the standard measurement spectral range (0.3 µm - 18 µm) can be extended or restricted.
Spectral measurement of the specular/hemispherical reflectance in the range from 0.3 µm to 18 µm. Calculation of the solar absorptance a (AM1.5) (other spectra possible). Calculation of the emittance e (373K) (other temperatures possible)	Fig.2: Result of an spectral reflection measurement
Cover glazing The transmittance of a sample is determined with a direct/hemispherical spectral measurement. The sample is irradiated with a parallel ray (Ø 25 mm) with an incidence angle of 10° relative to the sample normal. The hemispherically transmitted radiation is measured using an integrating sphere. The solar transmittance is calculated from these measured data by integration, with the AM1.5 spectrum (ISO 9845-1) as the weighting spectrum. The visible transmittance is obtained from weighted integration with the product of the radiation function for the standard light source D65 and the photopic spectral response of the human eye (DIN 67 607). If desired, other weighting functions can be used to calculate the integrated values. Further, the standard measurement spectral range (0.29 µm - 2.5 µm) can be extended or restricted. The latter can be an interesting option, if measurements in the UV and or NIR are not required.
Spectral measurement of the direct/hemispherical transmittance in the range from 0.29 µm to 2.5 µm. Calculation of the solar transmittance t(AM1.5). (other spectra possible) Calculation of the visible transmittance t(D65). (other spectra possible) Sample dimensions at least 5 cm x 5 cm.	Fig.3: Result of an spectral transmission measurement
Incident angle modifier The sun is not always located perpendicular to the collector plane; the incidence angle generally changes both during the course of a day and throughout the year. The transmittance of the cover glazing for the collector changes with the incidence angle. The relationship between the incident angle and the transmittance can be calculated for materials with smooth surfaces.However, usually at least one surface of the cover used for a solar collector is structured, which means that the angle-dependent transmittance can no longer be easily calculated. For this reason, we have set up a special test stand to determine this quantity.To be precise, the angle-dependent transmittance is not determined absolutely with this test stand, but its variation with respect to that at normal incidence. This is the definition of the incident angle modifier (IAM) for transmittance. However, an additional transmittance measurement for normally incident radiation can be made. From the measurement technology, this does not achieve the same absolute accuracy as a measurement with the Fourier spectrometer (see above), but it is usually adequate for comparison purposes.
Determination of the IAM in the range between 30° and 70° in 10° steps (measurement geometry depending on the sample)   Spectral measurement of the direct/hemispherical transmittance in the range from 0.3 µm to 1.7 µm and calculation of the transmittance (basic glazing package II)   Sample size up to collector dimensions.	Fig.4: Result of an incident angle modifier measurement

Durability of Materials for Solar Systems
Absorber coatings The optical properties of the selective coating are decisive in determining the efficiency of the collector and thus the system yield. These should not decrease with time due to degradation of the absorber coating. In order to guarantee this, in principle a newly developed absorber coating would have to withstand 25 years of use without damage, before marketing could begin. Clearly, this condition cannot be met. Thus, we have co-operated internationally with other institutes to establish a method which allows the aging performance of such coatings to be determined in the laboratory within a short time.	Fig.1: Condensation test of new absorbers
Fig.2: Test of the fin - tube bond	Climatic chambers Many materials tests demand that the testing climate be accurately specified and controlled. To achieve this, we use climatic chambers, in which the air humidity and temperature can be exactly controlled within wide ranges. In addition, the sample can be subjected to simulated solar radiation or UV-enhanced radiation. A precisely controlled, circulating-air oven can be used for higher temperatures. If the surrounding atmosphere is disturbing, the high temperatures can also be applied under vacuum.