S/V Hello World's Travel Log

the gallant fox - energy neutral

Continued from here.

Do you guys use refrigeration on board? Do you have to run the engine to charge up the batts? We really want to be energy neutral with solar power and possibly a (quiet) wind generator if we can. Pipe dream?

Gallant Fox:
Doable. We have refrigeration on board & as the water warms up & the sun gets brighter, it runs 24/7 & frosts up a lot. So, you defrost more & shade the outside of the hull (by hanging one of those reflective auto dashboard sun shades over the side of your hull where the fridge is).

In warm climates, our fridge & our watermaker are the greatest energy draws. GB's explaining to me that our fridge uses salt water to cool the condenser via a cooling ring that attaches to the thru-hull (Isotherm) as opposed to the type that uses salt water in a pump configuration like Glacier Bay uses; or an air fan to cool it. Whatever your design, insulate the box by filling the voids all around it with that spray-expand-o insulation stuff. That's the best work you can do to keep the fridge running its most efficiently. Whatever your fridge draws now in energy, GB sez expect it to increase at least 50% when you get down to the tropics.

We have a KISS wind generator that's as quiet as they come, and works great when the wind blows; & 2 solar panels giving us 180 watts - but we actually need 300 if we depended exclusively on solar. The solar actually works better on more days than the wind generator does, though we've found both are useful for keeping the batteries topped off. But if there's no wind, our 2 solar panels allow us to stay at anchor without running the engine for 3 or 4 days. So, if we could find space for 2 more solar panels, we'd put 'em up - other boats our size with 4 solar panels can spend more time at anchor than we can, especially if the wind's calm. Although, we've only needed to run the engine a few times to recharge our batteries, over the course of 3 months cruising the Sea of Cortez. I think I saw you have a stern arch, so you might want to fill it with solar if you haven't already. Solar panels are rare and expensive down here, so make sure you have all the panels & replacement parts you need before you head down here. We don't have a generator on board & don't especially need one for the type of cruising we do here in Mexico for now - but if we ever change our minds, or start spending weeks at a time in one anchorage, a generator is something that's more available down here (though about 40% more expensive than in the US).

Batteries: our boat came with 2 wet-cell batteries (360 amp hours in the house bank) which was inadequate for 4-season cruising. GB replaced them with 3 4D gels, which gave us 520 amp hours (fast acceptance & discharge rate, but still minimum for our usage). But our batteries have held up nicely because they're in balance with our charging system, an Ample Power high-output alternator that's externally regulated. GB's telling me that what you want to aim for is a house bank that covers your energy draw (fridge, lights, watermaker, whatever), taking into consideration how long you might want to spend at any one spot. Also, GB sez your alternator's output should be about 20-25% of the total in your house bank (we have 520 amp hours, & our alternator puts out 80 to 90 amps, which is close enough). Aim for an externally-regulated alternator that goes through a 3-stage charge (bulk, absorption & float). Go to Ample Power & pick their brains - they're cool guys. Finally make sure the output wire going from your alternator to the battery bank is large enough to handle the flow without burning itself (and ultimately, the boat) up.

Bottom line: your energy/battery recharging plan may need some tweaking as you go, but with the right number & kind of batteries, the proper size alternator & output wire, & the right number of solar panels & possibly a wind generator, you can bring your energy system into balance. Balancing will take a long while.

That's it for batteries - hope some of it makes sense...