After waiting a day for the painted baseboard to dry, I fitted the solar cells to the board today and soldered interconnecting wires to join them all together in series. Under artifical light the output from the panels was 13.5 volts and once the silicone sealant is dry I will be able to take the panel outdoors to try a test under sunlight!

Half of the cells fitted to the base board:

All cells fitted, interconnecting wires fitted and fixed in place with silicone sealant.