A detailed numerical model for flat-plate solar thermal collectors based on one-dimensional finite volume techniques was recently presented, see Cadafalch (2009). The model considers a solar thermal device as a pile of components represented by one or several layers characterized by thermal inertia, internal energy generation and heat transfer to neighboring layers. A multi-layer model is then used to evaluate the full flat-plate solar thermal device. The model permits to investigate any configuration and material by combining appropriate layers. Standard components as opaque insulation, absorbers, air-gaps and glasses were addressed in Cadafalch (2009).Here, a numerical model to evaluate honeycomb-like transparent insulation material in the covers as a component of the multi-layer model is discussed in detail. The honeycomb is evaluated coupling radiation, convection and conduction phenomena. The discret ordinate method is used to evaluate media participation in thermal radiation.A comparison of numerical and experimental results is presented and discussed in order to show evidence of the model credibility.

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