As a test case we fitted a 200W system along with an advanced controller to a new barge style cruiser for a week to check to usefullness of solar power against the designed option of running a large 90HP engine for up to 6 hours per day. The owners were keen to discover the potential cost gains they would make by using a solar system.

The barge was built with a bank of 5 x 110 Amp Hour leisure batteries which were around 2 years old at the time of the trial - so about two thirds of their way through their useful life. These are charged by by an alternator from the main engine - typically requireing approx 6 hours to bring them back from a 'flat' condition. There is a further bank of two 110 Amp Hour batteries for starting the engine and running the diesel heating which only charge from a separate alternator on the engine.

The 12v equipment consists of a Shoreline 12v fridge, Jabsco water pump and 29 lights - three of which are still using halogen bulbs (2 of these are to be retained as halogen), 3 are filament type bus bulbs (which will be replaced shortly) - the rest of them are LED.

The inverter is a Mastervolt 4000W Combi - which also includes a 3 step mains battery charger. It has an automatic transfer switch to seemlessly move between mains and inverter power. This inverter is a little large for the load it services and uses 3 - 4 amps when idle so it is only used when boating in the evenings or when it's required for other purposes.

The TV is quite old and power hungry, and we have it linked to a HD recorder, DVD player and stereo. When these are in use we seem to draw 10 - 12 Amps, sometimes a little more when the laptop is charging as well.

Even with sparing use - we would need to run the engine for charging for around 24 - 30 hours per week without the solar. With the solar, and reasonably good weather - we could most likely half that - maybe even less, which is probably the best we could hope for.

This graph shows the percentage of battery charge over the week. The trial was conducted in June 2013 so the days were long. The 3rd day of the trial was overcast whereas the rest of the week was sunny. None the less, the 200W system managed to maintain a battery charge level of over 60% throughout - which is about the point where we would be starting the engine.
Battery Power Drain Over Time

The second graph displays the actual power input (in Amps) from the solar panels over the same time period. The overcast day is plainly shown - and note that readings were taken at longer intervals during towards the end of the trial which is why the peaks are shown as narrower.
Battery Power Drain Over Time

The trial resulted in a successful sale.