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Will solar panels keep my batteries topped up over winter?


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I am about to take my boat back to a marina for the winter months.

 

I have 2 x 100w solar panels with an MPPT controller. Will this be enough to keep the batteries topped up or do I need to connect the battery charger via the electric hook up?

 

The only use of power will be an automatic bilge pump.

 

Many thanks

 

 

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My guess is yes, as i survived last winter with 2 x 100w solar panels as my ONLY source of battery charging (no alternator or mains charging), and that was living aboard week on week off.

 

I would try and arrange regular visits to ensure all is still working ok though if i were you.

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My guess is yes, as i survived last winter with 2 x 100w solar panels as my ONLY source of battery charging (no alternator or mains charging), and that was living aboard week on week off.

 

I would try and arrange regular visits to ensure all is still working ok though if i were you.

 

Thanks Junior. Yes, I will be popping back from time to time to check that everything's okay.

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Should do without any problems. I have a 5W panel on a 400 ah bank that is enough to prevent self discharge problems. A lot does depend on the quality of the batteries and their condition.

Hi Chalky, is 5W a typo? I calculated 50W should do my bank of 4x135's (maybe only 450Ah by now) over the winter months @ 5% discharge per month, using worst case scenario.

 

What do others think? Should I go back to the drawing board?

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I am about to take my boat back to a marina for the winter months.

 

I have 2 x 100w solar panels with an MPPT controller. Will this be enough to keep the batteries topped up or do I need to connect the battery charger via the electric hook up?

 

The only use of power will be an automatic bilge pump.

 

Many thanks

 

 

 

 

Id say yes, especially as the automatic bilge pump ought never to run!

 

I have two solar panels too, and they kept the fridge running all summer until about late September when the domestic batteries ran flat.

 

Even if your boat's stern gland is leaking a bit and some rain is getting in I doubt a bilge pump clearing the water would use even 10% of the electricity a fridge uses, so should be fine.

 

Don't blame me if the boat sinks though ;)

 

MtB

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Oasis

 

Lead acid batteries self discharge at (approx) 5% per month so a 540 amp.hr bank will lose 27 amp.hrs

 

That is equivalent to 1 amp.hr a day (approx)

 

A 5w panel would in ideal conditions 'supply' 0.4 amps (approx) so it would need to be working in ideal conditions for two+ hours.

 

So a 5w panel should be OK but fitting a larger (watts) would be a good idea because when actually using the boat in the summer it will probably reduce engine running for battery charging.

 

Essbee

 

Your panels will be perfect, well not perfect as they will be OTT for just keeping the batteries topped up.

 

 

 

It would be a good idea to ensure the batteries were fully charged before leaving the boat in both (all) cases.

Edited by bottle
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Oasis

 

Lead acid batteries self discharge at (approx) 5% per month so a 540 amp.hr bank will lose 27 amp.hrs

 

That is equivalent to 1 amp.hr a day (approx)

 

A 5w panel would in ideal conditions 'supply' 0.4 amps (approx) so it would need to be working in ideal conditions for two+ hours.

 

So a 5w panel should be OK but fitting a larger (watts) would be a good idea because when actually using the boat in the summer it will probably reduce engine running for battery charging.

 

Essbee

 

Your panels will be perfect, well not perfect as they will be OTT for just keeping the batteries topped up.

 

 

 

It would be a good idea to ensure the batteries were fully charged before leaving the boat in both (all) cases.

 

 

 

But bear in mind winter is the opposite of the ideal conditions Bottle speaks of above.

 

To starkly illustrate the point, his 5W solar gives 0.4 Amps in ideal conditions. When I last checked my solar panel controller on Sunday afternoon, yes you probably guessed it, my 200w of solar was also delivering 0.4 Amps

 

It was into quite heavily discharged batteries (60% SOC) too, but granted into 24v though, but you'll get my point. Winter solar performance reduces phenomenally.

 

 

MtB

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So we know the boat is not a cruiser stern with leaky deck boards then

Thats good.

 

personally if a hookup were available and the boat were left unattended for long periods I would definitely have a small charger on regardless of any solar.

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Hi Chalky, is 5W a typo? I calculated 50W should do my bank of 4x135's (maybe only 450Ah by now) over the winter months @ 5% discharge per month, using worst case scenario.

 

What do others think? Should I go back to the drawing board?

 

No, its not a typo however these are not your usual lead acid batteries. As a test I charged one and left it unused for 2 years (actually used as ballast!) It registered 12.5 V and started the engine without difficulty after this time.

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Thanks for the input everyone.

 

Actually I left my inverter on while I was away for 4 days (coupled with my solar on, and mains incoming, 12V systems switched off) and my soc dropped to 77% so a shore powered trickle charge through my inverter is not an option, at least not for 7 months away from the boat. Anything can happen to the shore power.

 

I have done some tests during the day with everything off and solar going to batteries (yes dear, the power will be on soon dear) and it performs well in overcast conditions. I know winter will be different but I should get about 7 ah a week - surely.

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The op has mains umbillical available anyway. My mains costs nothing unless it is used. Thats CRT resi mooring. Maybe marinas are different?

I can't really see why not to put a small charger on as long as it is a proper one which won't dry the batteries.

Or maybe they charge for electric even if you don't use it :unsure:

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Thanks everyone.

 

I have a trad stern and water doesn't get in unless I forget to clear out the gulley round the rear hatch.

 

MtB you were right, the automatic bilge pump is for the stern gland. However, I have recently tightened it and it doesn't drip hardly at all now smile.png so maybe the pump won't be coming on anyway. By the way, if I turn off the battery isolator switches, would the automatic pump still work?

 

 

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Thanks everyone.

 

I have a trad stern and water doesn't get in unless I forget to clear out the gulley round the rear hatch.

 

MtB you were right, the automatic bilge pump is for the stern gland. However, I have recently tightened it and it doesn't drip hardly at all now smile.png so maybe the pump won't be coming on anyway. By the way, if I turn off the battery isolator switches, would the automatic pump still work?

 

 

 

It depends how the boat is wired, but one would hope that the auto bilge pump was installed with a fuse then directly to the battery, rather than via the isolation switch. It is one of the devices which is "allowed" to be connected directly to the battery (others need to via isolation switch).

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