Electrical energy generated by photovoltaic modules mounted inside the roof of a north–south oriented greenhouse

Four amorphous-silicon photovoltaic (PV) modules were arranged in an arch formation at the northern end of the Gothic-arch style roof of a north–south oriented greenhouse. Two were attached to the inner surface of the east roof with tilt angles of 20° (PV1) and 28° (PV2). The other two were attached to the inner surface of the west roof with tilt angles of 20° (PV3) and 28° (PV4). Each module (832 mm × 412 mm) was lightweight (0.42 kg) and flexible with rated power of 24 W and the efficiency of 7%. The total area of PV1–PV4 was 1.7 m2, which corresponded to 1.5% of the roof area. During seven months, PV1–PV4 generated 71.6 MJ in total. Modules with lower tilt angle generated more energy. West-roof mounted modules generated more energy than was generated by east-roof mounted modules because the greenhouse was oriented 7.03° from true north–south. Yearly generated energy was calculated by assuming cloudless skies. The PV3 unit generated the maximum energy of 119.4 MJ y−1. These results show that the low tilt-angle module generates more electrical energy when it is mounted inside the roof of a north–south oriented greenhouse.