Solar Panel size for winter top up

[rjs]

I have a domestic battery bank of approxiamaely 400 Ah. I wish to keep them in good condition over winter without running the engine. ( I can take to starter battery home to top up).

 

What rating in Watts for a Solar panel would I need to keep the domestic batteries topped up when the temperature will drop below freezing and winter sun is weak?

 

Richard

[Bobbybass]

I have a domestic battery bank of approxiamaely 400 Ah. I wish to keep them in good condition over winter without running the engine. ( I can take to starter battery home to top up).

 

What rating in Watts for a Solar panel would I need to keep the domestic batteries topped up when the temperature will drop below freezing and winter sun is weak?

 

Richard

I have two 120w panels whcih I am very pleased with during my summer cruising (as long as the sun is out !!)

I leave the boat for 6 months over winter and when I return the batteries are totally up and ready to go. The batteries seem to last very well...as...when I stop the engine...they carry on 'drip charging' (my expression..I like that...drip charge)...

 

bob

[rjs]

Bob,

Thank you for your reply, I was hoping to find out what would be the minimum wattage which would keep the batteries in good condition while I am away from the boat during the winter. Any boost during the Summer cruising would be a bonus.

 

Richard

[Justme]

It is simply impossible to say what the absolute minimum will be.

 

Battery condition & self discharge

static loads

installation position, angle, direction, shading

weather

 

What would work for summer could need to be 20 times bigger for winter. Its even possible that no matter how big it is it still would not work for long periods say when snow covered or just plain bad weather. I have 1200watts & last December had 14 days in a row of no power at all (so even if I had 20kW I would still not make any power) & the remaining days only made 2.4kWh (or 200Ah @ 12v nominal if you prefer). Using that as a base then 100 watts would make 200Wh or 16Ah. That should cover self discharge on a boat sized bank I think.

 

 

You could size it up by accepting that for most of the time it will be too large & for the rest to small & that some cycling of the bank will happen.

[Proper Job]

It's a bit of a 'how long is a piece of string' question.

 

I'd have though a panel of around 80W would be more than enough (and some) to cover self discharge over the Winter months.

[steve hayes]

We have a 45 watt panel and 550Ah of batteries and the difference it made is enormous. Even in the winter the batteries are nicely maintained.

[Chalky]

I have a 5 watt solar that I use to keep the domestic batteries (400 ah) topped up in the summer. I aim to leave them fully charged so I only have to overcome the self discharge. In the winter the batteries live in the garage at home and are cycled through a smart charger every couple of weeks.

[smileypete]

I have a domestic battery bank of approxiamaely 400 Ah. I wish to keep them in good condition over winter without running the engine. ( I can take to starter battery home to top up).

 

What rating in Watts for a Solar panel would I need to keep the domestic batteries topped up when the temperature will drop below freezing and winter sun is weak?

 

IF the batts are standard non sealed leisure ones in reasonable condition, you could try a 10W panel directly connected to the batts (via blocking diode and fuse at + batt post) and angled towards the sun.

 

If that isn't enough try another 10W panel but check the batt voltage doesn't go much above 14.4V on a sunny cold winters day.

 

If the batts are sitting on a cold surface, try putting a 1/2" sheet of polystyrene under the them to minimise the chance they'll 'stratify' which may increase self discharge.

 

cheers,

Pete.