Why not use a photovoltaic panel on top of the 'sandwich', so that 10-20% of the sunlight is converted to electricity, and then use the 'sandwich' to heat the fluid with the waste PV layer heat and long wave solar radiation? The result will be electricity and hot water from one panel, thus saving space and cost. The PV panel would also run more efficiently at the reduced temperature.
Why not use a photovoltaic
Why not use a photovoltaic panel on top of the 'sandwich', so that 10-20% of the sunlight is converted to electricity, and then use the 'sandwich' to heat the fluid with the waste PV layer heat and long wave solar radiation? The result will be electricity and hot water from one panel, thus saving space and cost. The PV panel would also run more efficiently at the reduced temperature.