LOW-COST PHOTOVOLTAIC ROOF TILE

Static concentrator designs that achieve concentration ratios approach ing the theoretical limit have been developed and demonstrated. Concen tration ratios in excess of 4 : 1 have been predicted although this re duces to 3.6 : 1 for the practical design used for photovoltaic roof t ile applications. A new encapsulant based on ''solid white oil'' has b een evaluated for use in the optical cavity, exhibiting excellent opti cal properties while simultaneously being low cost. Prototype roof til e efficiencies of approximately 15% (not independently confirmed) are well below the expected 17-18%, due primarily to optical losses associ ated with the rear reflector and poor rear surface performance for the Photovoltaic devices. Good progress has been made recently with regar d to the latter, although further work is required to accommodate sola r grade substrates with much shorter diffusion lengths, for the bi-fac ial cells in this application.