Well, we’ve just completed our first three days of evaluating how solar panels have and will change our cruising life. Chose one or all of the following — delightfully, dramatically, significantly. Basically, no fossil fuel consumption was required other than the gallon or so of diesel required to get us out where the wind was. I think we are going to like this. The supply-demand picture looks like this.
Daily, we had low clouds in the morning, drifting cumulus in the early afternoon, and otherwise clear. One shower crossed us for about half an hour one afternoon. We had an average of 15 hours of sun a day. For charge controller purposes, that was more like 13 useful hours.
Underway, the radar, chartplotter, instruments, autopilot, radio, and refrigeration were all operating (the freezer was not).
Anchored, we had the refrigeration, stereo, anchor lights (LED), reading lights (LED), inverter, television, microwave and fans on according to their normal usage.
Water temperature was 78 deg F, and the air temp was in the mid to upper 80s down to upper 60s, so the refrigeration was working for a living, but not in tropical mode (nearly constant).
The bottom line.
Starting from zero deficit, the deepest we went into the 660 Ah battery bank was -39 Ah. This deficit was reduced to -5 Ah by 1100-1200 each day at which point the controller went to “Float.”.
On the return trip we averaged a net -1.5 A per hour with 100% autopilot use under sail.
And the solar panels shading the bimini made it cooler and more comfortable in the cockpit.
I had grinning cramps.
- add an estimate for the freezer consumption
- adjust for statistical cloudiness
- adjust for shorter days and lower solar incidence angles
- adjust for warmer water and warmer days and nights
- and recognize the hot water heater and air conditioning will always require the main engine or genset
It looks as if the daily deficit at anchor will run to around -60 Ah. This should be recovered by around 1500 each day. Absent the want of hot water and air conditioning this would take our diesel consumption for electricity production at anchor to zero. Since we were paying about -$2.50 a day for genset operation (just for recharge) this alone gives a payback on the capital expense for solar of 2.7 years.* Reduced wear and tear on the genset will improve this a bit. Vagaries in the weather will push it the other direction
The underway consumption looks to go up to around a net of -3 A per hour during the hours of useful sunlight. We need a couple of 24 hour runs to see how this plays out as to consumption during the hours of darkness. Right now, if we assume we start the evening down by -36 Ah, then at solar useful dawn (my term) we might be down to -100 Ah. The panels may not be able to service this deficit since the daylight hours already include a 3 A per hour net consumption. This would indicate the need to run the genset for three hours every 48. We’ll see…
*Unfortunately quite a few marinas charge you for electric whether you hook up or not. When in Florida (2008-09), we had it happen to us more than once.