Making Solar PV Tiles By Integrating / Laminating Amorphous Silicon Onto Existing Roofing Profiles...

1. INTRODUCTION

With the assistance of the Japanese Government's subsidy policy, the grid-connected residential PV system is about to take off in Japan. Integration of PV into roof covering materials must be the ideal combination, but actually few products have been successful in the past. Different from a conventional glass covered solar modules, Canon's module has resin film lamination structure which leads to unique features as hybrid roofing material with synergy effect. Canon's triple stacked amorphous silicon(a-Si) solar cell[1] is flexible, since the a-Si layer is formed on the thin stainless steel substrate. (Fig.1 left) Flexible cell is embedded in the thermoplastic adhesiveresin between metal back plate and fluoro resin film. (Fig.1 right) Having this module structure Canon's module can be bent into the same designs as existing metal roof element for example[2]. The advantage in this case is that basic roof performance such as water tightness and wind resistance is assured at the same level as existing metal roof, secondly the PV roof module can be sheathed mixed together with normal metal roof element without PV side to side and thirdly a-Si solar cell is expected to perform better under higher temperature like rooftop[3]. This paper reports the primary features of Canon's PV roof module and its installation examples.

Two major materials which constitute this module are the resin lamination and steel back plate. The resin lamination has shown an excellent weather resistance in accelarated weathering tests so far. The laminated test samples were subjected to outdoor exposure test (EMMAQUA) at DSET laboratories Inc. in Arizona. Eight times concentrated solar irradiation has been irradiated to the samples for about a year whcih corresponds to about 10 years stress in Tokyo. Another test is accelarated UV irradiation in the laboratory test chamber which is equivalent to 30 years stress in Tokyo. The samples were evaluated in terms of discoloration, peeling, electrecal insulation and power generation efficiency in both tests. No anomaly results was obtained in any test so far.

Fig 3 shows the result of acid rain corrosion test conducted on steel sheet samples. Laminated steel plate has shown a noticeable improvement of surface corrosion resistance thanks to the fluoro resin film lamination. Commercially availble steel roof plate with and without lamination were subjected to the cycle of acid spray and dry up for 48 days whcih is estimated equivalent to 15 to 30 years of outdoor exposure in Tokyo. Standard galvanized steel sheet without lamination showed heavy white rust and red rust over whole surface, whereas the laminated surface showed no corrosion except edge corrosion. 55% aluminum-zinc alloy plated steel sheet showed less white rust even on inside surface. No corrosion was observed on laminated surface either and edge corrosion was also observed.

2-3 Reduced Noise

It is often said that metal roof is noisy when rain drops. Small stell ball with 8mm in diameter was fallen on to a conventional metal roof and on the PV roof to measure the magnitude of noise level. Result shows that PV roof generated about 93dB whereas metal roof did 103dB in terms of "A characteristics" which corresponds to human ears' sound sensitivity. It is commonly understood that 10dB difference corresponds to two times in magnitude.

4-1 Electrical Insulation

Since the surface of the module is covered by resin film, strength against surface scratch is inevitable concern in terms of electrical insulation. UL (Underwriters Laboratories Inc., USA) 1703 stipulates the test procedure for surface cut susceptivility for solar module. The surface of the module is cut by knife edge and evaluated by measuring leak current under wet condition and high voltage application. The module has been proved to well exceed the criterion.