The possibility to use photovoltaic (PV) modules under a water layer has been explored under different forms: submerged, covered by a water layer, and under a transparent box that contains water. All these test conditions have in common the use of water as a filter for solar radiation to reduce the warming of the PV cells. The effect of the change of the solar spectrum impinging on the PV cells depends highly on the PV technology. A numerical analysis to evaluate the photoelectric efficiency of different PV cells under water is given. Further indoor experimental measurements of PV cells stroked by the artificial light of a halogen lamp that passes through the water-flow-lens (WFL) system are also presented. The connection between the band gap, intensity of light, and distribution of light for a different approach for filtering solar radiation is discussed. The influence of light intensity, halogen spectrum, as well as the WFL system used and their influence on the short-circuit current ( I SC) and the open-circuit voltage ( V OC) are also investigated.