>Well let's run the numbers

Ok i prefer to keep it metric... so if 4kW makes 5kts, a 12 hour day electro-motoring will consume 48kWh. If we had sunshine that day perhaps we could capture 12kWH with 2kW of panels, so the remaining 36kWh could be recharged with less then 2 hours of 20kW genset run time.

At 300g / kWh we'd use 10.8kg or about 13 litres of diesel. So about 3 gallons to cover 60 nautical miles in 12 hours.

But to me the real value is measured in 10 hours of silence vs 12 hours of noise.