Managing solar power as a liveaboard

[Tessellate]

Now that we have solar and are liveaboards, it would seem the obvious thing to do is turn off the shore charger and power 12v loads from solar as much as possible, turning on the shore charger only say once a week.

But I've realized while solar is a pure win while cruising, it's not clearly superior to using a shore power charger while living aboard (in a marina). Using solar instead of a shore charger you're basically trading potentially shorter battery life for lower shoreside electrical usage. Electricity is cheap and relatively earth friendly here (hydro-electric), and my batteries are also relatively cheap - but a hassle to replace. So it's not clear which to favor, and I'm wondering what approach others have taken.

- Solar only: batteries cycle between partially discharged and fully charged states.
- Shore charger + solar: batteries are happiest, fully charged all the time (equivalent to non-solar liveaboard situation), but we'll pay a bit more for electricity and won't be as earth friendly.

If we do solar only, each night the batteries may discharge to about 90% (the fridge is our only significant DC usage) and get charged to 100% the next day. But, if there's an overcast day, we may have some 90% -> 95% -> 85% -> 100% cycles, and my understanding is those shallow recharges are what can reduce a battery's capacity pretty quickly.

We're already used to timing our fridge use manually - we turn it up while motoring, and super-chill it at dock prior to a cruise. Our ice box is pretty efficient and the fridge only needs to run about every 4-6 hours - but by cooling it more to a higher setting we can forestall the next cooling cycle to 8-10 hours.

So even while cruising, there's still a solar management question - should we time when our fridge runs to be during the daytime (and sunny)? Does anyone else do that or do you feel it's not worth the effort? I suppose I could make it easier by hooking a timer device into the switch.

[john61ct]

Your solar should be sized to minimize sacrifices while at sea.

Shore power, if not expensive, eliminates all such sacrifices, and should be used to keep the expensive bank from using up it's limited life cycles.

[Tessellate]

Originally Posted by john61ct

Your solar should be sized to minimize sacrifices while at sea.

Shore power, if not expensive, eliminates all such sacrifices, and should be used to keep the expensive bank from using up it's limited life cycles.

Sounds like one vote for shore + solar charging while living aboard in a marina. Anyone else? The reason I asked this is I think there's no one right answer, rather I want to hear the consensus or diversity of opinions.

[smac999]

Turn the charger on at night. And off during day?...

[JstaRebel]

You say your shore power is cheap so use it. Here in the Caribbean electricity isn't so cheap, so we tend to use our solar anyway. But keep in mind that we don't usually tie up to a dock as a general rule. Most liveaboards on dock in St.Thomas pay like $200.00 a month for power. Add that to slip rental and water at $.14 per gallon and you may as well live ashore IMO.

[Tessellate]

Originally Posted by smac999

Turn the charger on at night. And off during day?...

A simple suggestion, and one that reveals my imperfect understanding of battery health. I can certainly do that, but does the shore charger cycling on every night (in bulk) with the solar cycling into bulk in the morning do no harm to the batteries?

All chargers start out in bulk, switch to absorbtion for some period and then float. With 1 charging source and fully charged batteries, bulk will be a short duration. With 3 charging sources (counting alternator) that you switch between, bulk on full batteries could be many hours more in a day. So going into bulk multiple times per day seems it would be a stress. Otherwise why do chargers not just remain in bulk all the time?

[john61ct]

I think you mean Absorb, Bulk means before voltage setpoint is reached.

All depends on your charge sources. Good ones let you adjust the algorithm to suit your situation rather than just using a static egg-timer for minimum Absorb.

In any case as long as voltage is set correctly, little harm will come to AGM, and none at all to FLA, just need to add a bit more water.