Directional-hemispherical solar transmittance data for plastic honeycomb-type structures

The directional-hemispherical (also sometimes called direct-diffuse) solar transmittance for several different honeycomb-type structures has been measured with an indoor solar simulator and a 40 cm diameter integrating sphere for incidence angles up to 70 degree. The samples have been fabricated by commercial companies from different plastics, with cell wall thicknesses between 15 and 70Mym and have approximately square or circular cell cross sections. After a discussion of the measurement errors and problems associated with a limited number of nonideal samples, a fit procedure based on a physically based transmittance model is presented and applied to the data. The resulting coefficients describe the angular and thickness dependence of the solar transmittance for each type of material. They may be used in order to feed data easily and flexibly into simulation models for solar collectors, windows or building.