Thanks Mark for giving us the chance to chip in on a favorite topic for boat owners (rivaled only by discussions about anchors). I’d like to argue for balancing your budget with your needs.
Some people day sail only, some stay attached to shore power 5 days a week, then cruise on weekends, some (like myself) live on the hook 7x365 and almost never get to shore power. It makes no sense for one-size-fits-all advice for such diverse needs.
Unless you abuse your batteries (by draining to 11.5), the #1 cause of short life is sulphation. You must have a way to desulphate (also called equalize). But you may have three choices (alternator charge control, shore charging control, solar/wind panel control) for how to accomplish it. You only need one of those three. You may have a 4th choice if someone at the marina has a portable charger with equalize that you can borrow, or share. But if your boat floats on shore power 5 days a week, and you sail 2 days, then sulphation builds up only 2/7 as fast, so you need the equalization only 2/7 as often.
Match the amp rating of your shore power and your alternator to your use pattern. If you stay on shore power for 24 hours or more at a time, or if you run your engine 8 hours or more at a time, then you don’t need so many amps.
Solar panels today are twice as good (in watts/ft^2 and in $/watt) than 3 years ago. They are expected to double again in the next 3 years. Therefore, I cannot get excited about spending a lot of money to find the best brand. In my plans, anything I buy today, I’ll junk and replace within 4 years.
One thing that improved particularly well in the past couple of years are roll-up flexible panels that you can simply plug in when you need them, then roll up for storage when you don’t. That would be great for occasional weekend sailors. You should look into that.
Controllers: If your panel puts out less than 2 amps max, then you need no controller at all. If it makes 2-8 amps, then West Marine’s cheapest $19 charge controller is all you need. A 40A non-MPPT controller can be had for about $120. Fully MPPT controllers maximize the efficiency of the system for $100-$200 more. But since the $/watt of panels is so low today, I think it makes more sense to buy more watts than to buy MPPT. Remember, in 4 years, you’ll have still more efficient panels, making the MPPT controller benefits even less. Once your system can fully recharge your batteries in typical weather, then there is no benefit to added efficiency.
So, what do I actually have on Tarwathie?
2x group 31 batteries. I pay about $110 each for them. Trojan batteries cost twice as much but their warranty is identical to the cheap ones. I will not spend twice as much until Trojan backs up their claims of higher quality in a written warranty.
50A alternator with old-fashioned dumb control.
2x80 plus 1x50 solar panels (205 watts total).
40A solar/wind controller with 3-stage and equalize cycles. I leave it set to equalize automatically every 30 days. Last year I left the boat for 5 months, with the fridge turned on, and powered by the panels. (My fridge has gone 6 years with zero coolant leak, but if I turn it off the coolant leaks out in a week.) When I came back, the water in the battery cells was very low (because of the 5x equalize cycles with no replenishment of water.) It would be nice to have a programmable controller where you can set the equalizing frequency, duration and voltage yourself.
On sunny days, my batteries are fully recharged by 1100. On mostly cloudy days they are recharged by 1700. Given two or more consecutive days with thick clouds, I need to run my engine. I like to run the engine at least once every 15 days in any case.
Next year, I plan to replace those three panels with a single 240 watt panel. 4-5 years from now, I’ll junk the 240 and replace it with another 240 half the size.
An 8A Genius shore power charger with 3-stage and equalize.
On my wish list is a battery watering system.
Hope this helps Mark. Thanks for asking the question.
