Solar charging, heater or fan

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RJJ

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Hi - many of you were helpful enough to give me some advice on winter afloat without shorepower, but with 300W of solar and 450Ah AGM batteries via a Votronic MTTP regulator.

https://forums.ybw.com/index.php?threads/winter-afloat-keeping-damp-at-bay.547989/page-3

I'm persuaded of the virtue of ventilation. Now I'd like to work out how to power a low-output heater and a fan or two off the 12v; with the absolute requirement never to run down the batteries. Please bear with me as I'm a beginner on this stuff, although I did plug the solar kit in myself so know how that works. I would welcome thoughts on how to do this.

Options seem to be
1. Use the "excess" output from the solar regulator direct to a "winter circuit" including CB, heater and fan. Keeps it simple and away from the batteries, and only works by day.
2. Install some form of voltage relay so the "winter circuit" switches on when the battery is nicely-charged, and off when it goes below 75% (??)or so. This might mean getting more hours, including by night, in the event of a wintry anticyclone with decent sunlight...it also would be an enhancement to have an accurate digital voltage meter which I think can come with the relay.

Pros/cons/other ideas? If option 2, how to go about it?
 
RJJ said:
Hi - many of you were helpful enough to give me some advice on winter afloat without shorepower, but with 300W of solar and 450Ah AGM batteries via a Votronic MTTP regulator.

Winter afloat - keeping damp at bay...

I'm persuaded of the virtue of ventilation. Now I'd like to work out how to power a low-output heater and a fan or two off the 12v; with the absolute requirement never to run down the batteries. Please bear with me as I'm a beginner on this stuff, although I did plug the solar kit in myself so know how that works. I would welcome thoughts on how to do this.

Options seem to be
1. Use the "excess" output from the solar regulator direct to a "winter circuit" including CB, heater and fan. Keeps it simple and away from the batteries, and only works by day.
2. Install some form of voltage relay so the "winter circuit" switches on when the battery is nicely-charged, and off when it goes below 75% (??)or so. This might mean getting more hours, including by night, in the event of a wintry anticyclone with decent sunlight...it also would be an enhancement to have an accurate digital voltage meter which I think can come with the relay.

Pros/cons/other ideas? If option 2, how to go about it?
Click to expand...

How much power do you expect to be generating in a UK winter? I would guess you will be looking at 100w or less from your panels on average. We can just manage in Algarve warm and sunny winter with 300w and 450ah, we have an Eberspacher.

Your best option is to install a drip feed diesel heater which requires no electricity. Next best is to install a low power Chinese forced air diesel heater which will heat and expel damp air at the same time but, likely you still won't have enough power without a generator or, running the engine which is a bad idea.
 
pvb said:
As I said in post 5, a headlamp bulb would be much cheaper, and just as ineffective.
Click to expand...
I'd agree with that and an incandescent bulb will probably be about 95% efficient at converting electricity to heat. I imagine the best you'll get from 300W solar in December/January would be around 140Wh each day, even on the South coast. It isn't much but will keep batteries fully charged without a huge amount to spare. This only works out to a steady output of 6W if left running constantly, even assuming 100% charging efficiency for the battery. Not really much use in heating a boat.

Solar input on the hull will be much greater. I guess you could just run the heater at night and bring output up to 12W or so, still not a lot. Of course the battery charging efficiency would kill that idea anyway. Have you thought about a Tea-light giving about 30-35W (auto-lighting and fire extinguisher extra)? :D:D
 
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Electric heating simply isn't practical. Once the sun goes down, assuming fully charged batteries - unlikely when relying on solar in December in the UK, you have about 200AH left after lighting and stuff That's 2.4kw hours. It'll get you through one night, two if it isn't cold. Now you've got to recharge from solar. If you get 100 watts from the panels, you'll do well. on a cloudy dim day, you'll be lucky to get 20w over about 8 hours. (strictly back of fag packet calculations & guesstimates, and ignoring the little detail that 800w hours into the batteries does not mean 800wh out) 800w at best. That will run a small heater for one hour The dim, dark day will just about run your lights and stuff if you're frugal. By the end of the week, you're running the engine every day, or shopping for new batteries.

I'd look at a Chinese Eber.
 
Stemar said:
Electric heating simply isn't practical. Once the sun goes down, assuming fully charged batteries - unlikely when relying on solar in December in the UK, you have about 200AH left after lighting and stuff That's 2.4kw hours. It'll get you through one night, two if it isn't cold. Now you've got to recharge from solar. If you get 100 watts from the panels, you'll do well. on a cloudy dim day, you'll be lucky to get 20w over about 8 hours. (strictly back of fag packet calculations & guesstimates, and ignoring the little detail that 800w hours into the batteries does not mean 800wh out) 800w at best. That will run a small heater for one hour The dim, dark day will just about run your lights and stuff if you're frugal. By the end of the week, you're running the engine every day, or shopping for new batteries.

I'd look at a Chinese Eber.
Click to expand...
Hi, yes I understand solar heating for human comfort isn't possible; that's not the goal. The goal is to run, when unattended, a very small heat source in/near the bilges; just enough to keep frost at bay and help convection. And for it only to operate when the batteries have sufficicent charge

I have a webasto heater which I can run when on board.
 
RJJ said:
Hi, yes I understand solar heating for human comfort isn't possible; that's not the goal. The goal is to run, when unattended, a very small heat source in/near the bilges; just enough to keep frost at bay and help convection. And for it only to operate when the batteries have sufficicent charge

I have a webasto heater which I can run when on board.
Click to expand...
Unless the whole boat is covered in solar panels I dont think that you will get any 'spares power to run a heater,even if very low power. You might be better off just running a 12 volt fan for an hour each day to move air around if very concerned.
When my boat stays afloat during the winter in a freshwater river, I just rely upon ventilation and the same when ashore. When on board I do use mains electrics to run tubular heaters, etc to make it bearable. On a sunny day most warmth on board is from the sun on a darkish hull.
 
Rather than a bulb why not use a power resistor mounted on a block of aluminium. 100W resistor. This will be less susceptible to overvoltage than a bulb and the block may retain some of the heat. The effect may be minimal but it may just prevent some condensation.
 
Natural ventilation is the answer.
When I collected my boat after completing the purchase she had been closed up as tight as a drum for months and consequently was full of mould. Since then I have always kept the forehatch on its ventilation setting when in the marina, where the boat is normally berthed facing away from the prevailing wind. A gap between the top of the washboards and the sliding hatch allows a through draught which always keeps the mould at bay. The occasional few drops of rainwater on impervious surfaces is a small price to pay.
 
Oh dear me!

If you want to do that buy some 12 volt infra red lamps. The last ones I made were on a classified list and fitted a front line tank.

Also consider that generally you need the heat at night when the solar is not so good. So some batteries will be necessary along with a thermostat and something to prevent the load killing the battery.

Simple 12v 50 watt MR16 halogen lamps will do. They were indifferent light sources but did give off a lot of heat.
 
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