A new transparently insulated, bifacially irradiated solar flat-plate collector

Abstract A new type of transparently insulated flat-plate collector was developed. It reaches higher efficiencies at low irradiation values or high operating temperatures than any other collector type known. Both sides of its absorber are covered with transparent insulation material and both sides are irradiated. Thus, the heat losses of the collector related to the total absorber area are distinctly reduced. An optical efficiency of η0 = 0.72 and a temperature dependent U-value of U(ΔT) = (0.95 + 0.0076 ΔTK−1) W m−2 K−1 were measured with an outdoor test facility. The bifacial-absorber collector is considered to be the best option for the DHW system of the energetically self-sufficient solar house in Freiburg because of its outstanding winter performance.