Outdoor testing of solar concentrators depends on the season and on the daily weather. The sun intensity in Trondheim during summer time is quite good (often 900 W/M2), as the air is most often clean and dry. The limiting factor is the low number of sun-hours, we often have cloudy weather and the winter is dark.
Heat storages, and some heat transfer methods can be tested with artificial heating indoors. For absorber testing, a solar simulator is needed. An assembly of 7 lamps have been constructed, similar to a setup from Massachusetts Institute of Technology, but with stronger lamps:
A simple cone shaped concentrator can be attached, made of flat MIRO panels (95% reflectance, to provide some reflection effects onto a small area (40 cm diameter). Intensity measurements have been estimated with a thermal method. The intensity is largest at the centre (about 70 kW/m2) and decreases towards the rim (about 50 kW/m2).
An indoor sun in the form of several high power lamps has been constructed
Flux intensities on the cross section.
Green < 55 kW/m², Yellow [55-60]kW/m²,
Orange [60-65]kW/m², Red ]65-70]kW/m², Dark Red > 70 kW/m²
(Student project, Grouillon Florence, 2014)
A visiting PhD researcher from Eduado Mondlane University, Mozambique, used the lamps to test a concept for a solar dryer (Amos Veremachi 2014). The lamps are now in place of a Scheffler reflector, which is positioned to focus on a cavity of a rock bed container. Natural circulation of air provides a continuous stream of air through the container. The rock bed stores a large amount of energy, so the air stream out of the container continuous to be hot after sunset.
Solar dryer tests (Amos Veremachi, Azer Zia, 2014)
Volumetric absorbers for air are difficult to design. A fibre based solution has been proposed by prof. Em. Jorgen Løvseth and outdoor tests with dish concentrators have been made with promising results. Outdoor tests require a complete system with solar tracking. The solar simulator allow for indoor analysis of absorber solutions in point focusing systems.
Outdoor test with air absorber (Trygve Veslum 2012)
We are testing solutions for a direct fryer for the Ethiopian bread Injera. An anodized aluminium plate, which is thick enough to store sufficient energy to bake a few Injeras, has been fitted to for tests with the standard SK14 reflector. The surface becomes illuminated from both sides. Ray tracing shows that a perfectly smooth reflector can give potentially damaging localized heating of the plate, compared with the tiled SK14 reflector. Tests on Injera baking can be made with the plate heated by the solar lamps (pending injera baking expert).
Measurements on frying pan in an SK14 concentrator (Asfafaw Tesfay 2015)
We have tested a heat battery charged by a double reflector system, in order to charge a Solar Salt latent heat battery from the top. The battery can then be used for cooking or for heating purposes. A side illuminated battery (e.g. from a Scheffler reflector) will demand a more careful design of the internal heat conductors. This can be studied using the solar lamps.
Heat battery charged with a double reflector (Amos Veremachi, 2014)