PVA’s work best under direct sunlight but only at about 14%. Additionally, not all types of light produce electricity from a PVA at the same level. Since backscatter from water is lower in intensity, lacks some of the full spectrum, and is less focused, it adds little to the total from the cells. Better to add silvered reflectors or a rotation system to keep the cells under full intensity for longer each day.
NREL has already shown a cell with 40.8% efficiency but requires special manufacturing and handling steps so, RSN (real soon now). As an aside, it splits the incoming EMS into 3 parts and produces an electron from each of the partial photon making 3 electrons from 1 photon instead of 1 electron from 1 photon.