Solar Power for Marine Propulsion - What is stopping us?

Background, Description, Delivery and Learning Objective Growing environmental concerns and depleting fossil fuels are forcing us to look at using non-conventional, renewable energy sources for power generation on board ships.
Why not Main Propulsion? We can have electric propulsion with power drawn from the sun’s energy through photo-voltaic cells replacing diesel engines. With the presently available conversion efficiency of almost 20% with solar cells sprayed on the exposed areas of the ships in the form of paint, the power generated can be as high as 40% of today’s Diesel Engines MCR giving 60-70% of the maximum speed, satisfying today’s slow-steaming requirements. It also substantially reduces fuel cost which constitutes about 50% of a ship’s operational cost.
Today, Solar power is being used for lighting of crews’ onboard living area having been unjustifiably considered unviable and uneconomical for main propulsion. It offers an out-of-the-box solution to the problems facing the marine industry and the world at large.
The area available on the deck and the shipside above the waterline can be utilized to generate power from the solar energy. Fuel constitutes about 50% of the operational cost of a ship. Dispensing away the diesel engines and the associated fuel storage systems, would make it much more economical to run ships than it is today with fossil fuels. We also save on the deadweight and volumetric cargo space giving us more cargo carrying capacity. There is a substantial saving on manning costs.