Development of a Thermally Improved Prototype

The second prototype built in 1994 had a much larger water tank which served also as the module’s foundation, its stand and mounting structure (TEPVIS – Thermal Enhanced PV module with Integrated Standing). It was tested with an M55 in Berlin (see Figures 10.17, 10.18, and 10.19) and showed an energy gain of up to 12%, and with PQ 10/40 devices in Bulawayo, Zimbabwe and proved an increase of 9.5%. The gain in Zimbabwe was lower due to reduced water circulation and more stratification (the upper part of the tank got considerably warmer than the lower one). The inclination of the module plane in Zimbabwe was much lower (20 degrees, according to the latitude of Bulawayo), thus reducing the thermo-siphon effect. The device in Berlin was also equipped with an additional plate inside the tank, in parallel to the module at a distance of 12 cm, forming a kind of chimney and thus enhancing circulation (“Onneken’s separator”). Nevertheless, the

PV conversion efficiency of the cooled module was noteworthy above the reference module during at least 95% of the day.

To eliminate possible measurement errors which may have been caused by the differing electrical properties of the systems, all modules (reference and cooled ones) were interchanged and retested. The modules had been operated continuously at the Maximum Power Point (MPP) by manual tracking of an ohmic load together with power metering. The application for the new I-SHS was carried during the first quarter of 2002.

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Fig. 10.17. TEPVIS (Thermal Enhanced PV with Integrated Standing): “Proof-of-principle” prototype made of acrylic showed a gain in electricity yield of 11.6% (Berlin, Germany, 1995).

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Fig. 10.19. PV power output of TEPVIS in comparison to a conventional M55 with conventional mounting, both operated at MPP (same test conditions as above). The gain in electrical energy yield is 11.6%.

 

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