To obtain cost-effective photovoltaic modules, we have developed static prism-array concentrator modules consisting of prism concentrators about 4 mm thick assembled unidirectionally under a 3.2-mm-thick cover glass. Calculating the optical collection efficiency for the annual solar irradiation in Tokyo, we found that the theoretical efficiency of the modules is 94.4% when the geometrical concentration ratio is 1.88 and that it is 89.1% when that ratio is 2.66, respectively. Fabricating prism-array-concentrator modules with a geometrical concentration ratio of 2.66, we obtained a maximum optical collection efficiency of 82% with a flat reflector and 81.7% with a V-grooved reflector. (C) 2001 Elsevier Science B.V. All rights reserved.