I fitted a 135 watt solar panel in October last year....clicky here It is doing exactly what I wanted in that on getting to the boat on Friday we had 100% on the smart-gauge. We left the boat at about 70% after the New Year so it has been trickle charging the batteries just perfectly. All we did was run the engine for some hot water, then the stove back boiler kept the water hot via the new Calorifier - it's great when a plan comes together. We were happy to leave the boat at 85% knowing it will be 100% when we are next aboard.
We have to run the engine for an hour to get 10% (on average) into the batteries. I know that our boat uses about a litre of fuel an hour so its in real terms about a quid for every 10% so we are starting to see the return, albeit slowly, on our investment !