Solar panels for charging 12v battery

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sotal
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Solar panels for charging 12v battery

Post by sotal » Sun Nov 14, 2021 10:20 am

Slightly off Bongo topic but I know there is a lot of technical expertise around solar panels in here as lots have installed then on their bongos.

My wife wants lighting in her field shelters. There is no mains power to them at all. There are 3 shelters.

I have 3 x 5w LED strips to start with and a car battery of 96Ah. I don't really want to have to charge the battery so I'm wondering if solar will work for me.

So having all three on would use 1.25A per hour. I might have to double this though if it isn't light enough. So 2.5A at the worst. It is likely to only be used for up to an hour per night. So as I understand it you shouldn't use more than half the capacity of a car battery. So 20 days max. So ideally I'd need to charge it once per fortnight.

That got me thinking that it would be better to put a small solar panel on the roof of over of the shelters to charge the battery. Hopefully in a fit and forget sort of manner.

I've seen the are lots of cheap 100W panels with a cheap controller for around £40. Would these do the job for the relatively small amount it needs charging each day. Are they likely to replenish the 2.5A that is used per evening during the daylight hours over winter?

It wouldn't really be needed during the summer months as they are bright enough inside during daylight, but the solar power could be used to charge up the electric fence batteries, would I just be able to connect another battery in parallel to charge that too? Would there be a possibility of getting enough power in winter to both charge the light battery and the fence battery?

Sorry for all the questions and I know I can read the specifications and work out out from there but I don't really believe the specifications and they are going to be optimistic in the very best of conditions.

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Re: Solar panels for charging 12v battery

Post by g8dhe » Sun Nov 14, 2021 10:30 am

Yes provided you make sure the panels are in the clear and not covered in leaves or moss then that's what the majority of the controllers are designed for, quite a few of the controllers also have built in timers to allow switching of the load terminals according to time so the lights (load) will switch on and off at the pre-set times for you.
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Re: Solar panels for charging 12v battery

Post by sotal » Sun Nov 14, 2021 12:22 pm

Thanks,

So you think the cheap 100W panels with controller would be sufficient for what we require?

I'm not after any fancy features like timers or anything as the time that we are there will vary and we don't really want it out up the rest of the time.

This might sound like a daft question but what happens to the excess energy once the battery is full? Does it overcharge the battery? Does it get dissipated somewhere as heat? Is there any danger in having a panel that is too big?

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Re: Solar panels for charging 12v battery

Post by g8dhe » Sun Nov 14, 2021 12:27 pm

No the controllers which the panels feed into before the battery look after the state of the battery for you. If your looking for the best efficiency then choose a MPPT (Maximum Power Point Transfer) type otherwise there are cheaper PWM (Pulse Width Modulation) controllers but be aware that in the UK they won't perform well in winter lighting conditions.
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Re: Solar panels for charging 12v battery

Post by sotal » Sun Nov 21, 2021 7:39 pm

g8dhe wrote: Sun Nov 14, 2021 12:27 pm No the controllers which the panels feed into before the battery look after the state of the battery for you. If your looking for the best efficiency then choose a MPPT (Maximum Power Point Transfer) type otherwise there are cheaper PWM (Pulse Width Modulation) controllers but be aware that in the UK they won't perform well in winter lighting conditions.
I realise this one is a PWM and I'd prefer MPPT but nothing seems to add up with the specs on this one.

https://www.ebay.co.uk/itm/224382714666

It says it is a 100W panel but the dimensions seem too small.

Also it gives a max amperage of 1.6A at 12V. Which is only just under 20W.

Am I missing something or in reality is this just a 20W panel?
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Re: Solar panels for charging 12v battery

Post by g8dhe » Sun Nov 21, 2021 10:11 pm

That spec is just rubbish - avoid - it makes no sense and as you say it equates and looks like a 20 Watt device, also the 12 volt out connection is via a tiny co-ax power plug which won't be capable of handling 8+ Amps needed for a 100 Watt output.
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Re: Solar panels for charging 12v battery

Post by Bob » Sun Nov 21, 2021 10:17 pm

I rather liked the bottom graphic showing the panel, controller, battery, then an inverter running a washing machine. :shock:
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Re: Solar panels for charging 12v battery

Post by sotal » Mon Nov 22, 2021 4:21 pm

Bob wrote: Sun Nov 21, 2021 10:17 pm I rather liked the bottom graphic showing the panel, controller, battery, then an inverter running a washing machine. :shock:
And a TV, a computer and a fridge freezer :lol:

I also like the picture with it on the roof of a camper van. It takes up a good portion of the roof, given the dimensions the campervan must be tiny!
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Re: Solar panels for charging 12v battery

Post by sotal » Mon Nov 22, 2021 4:22 pm

g8dhe wrote: Sun Nov 21, 2021 10:11 pm That spec is just rubbish - avoid - it makes no sense and as you say it equates and looks like a 20 Watt device, also the 12 volt out connection is via a tiny co-ax power plug which won't be capable of handling 8+ Amps needed for a 100 Watt output.
Thanks, I think it is all going to cost a little more than I'd planned but I might as well get something that will work.
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Re: Solar panels for charging 12v battery

Post by g8dhe » Mon Nov 22, 2021 5:47 pm

If you want quality and reliability then take a look at Rogers stuff here https://www.solarcampersolutions.co.uk/ yes its not cheap, but you only have to see the reports from people who have tried to put together a cheap package and found the problems the hard way. also see a previous post I did a while ago but the situation hasn't changed :-( https://www.igmaynard.co.uk/bongo/forum ... =1&t=72346
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Re: Solar panels for charging 12v battery

Post by sotal » Mon Nov 22, 2021 6:45 pm

I'd love to say that I want quality and reliability (of course I do want these) but budget and not wanting to leave stuff that is too expensive in the middle of nowhere is the overriding factor.

It is also quite a different scenario to the campervan roof. Size doesn't matter, shape doesn't matter, and I'm wanting a really comparative output compared to a campervan.

My initial output is only 15W for perhaps one hour 7 times per week. I think I will probably add an LED floodlight of perhaps 30W to light the yard area but still it isn't a huge draw, or a huge amount of time.

I've found some decent looking panels that look worth a gamble. They are only 80W but an hour at anywhere near that would do me for the day, so hopefully the full light averaged out over the day will be enough, and bright days will make up for dull days.

So I just need to find a good enough controller now to go with it. I'm after a 30A MPPT. I thought I'd found a couple but after a bit of research they appear to be PWM with MPPT just printed on the case :roll:

I don't want to spend a fortune so might have to risk a PWM and hope it is good enough to work for what I need.
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Re: Solar panels for charging 12v battery

Post by g8dhe » Mon Nov 22, 2021 10:05 pm

Ah yes, its the non-Bongo install, forgot that!
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Re: Solar panels for charging 12v battery

Post by sotal » Mon Nov 22, 2021 10:47 pm

I've ordered all the bits I can think of. It has come to about £100 for all the bits so I hope the gamble pays off.

80W panel
A charge controller that says it is MPPT but I'm not convinced
2m mc4 cable
2gang weatherproof switch
20m of 12v cable

I've already got a few bits like the battery connectors. I've got 4 lights now too. 3*5W strip lights plus a 30W flood light.

I'll see how it all goes. I'm going to replace the AGM battery in the Freelander (works fine for general use but start stop doesn't work any more as the battery management system shows it has dropped below 75% health) - so the old battery will be the lights battery. Or that is the plan anyway!
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Re: Solar panels for charging 12v battery

Post by sotal » Thu Dec 30, 2021 8:47 am

Just wanted to update to say it is all setup and working now.

The wife is very happy with it as she can see what she is doing without just using the light of a head torch!

Time will tell how well the solar panel works.

I couldn't mount it in the optimal direction easily without raising it up and building a platform for it. So I went with the second most optimal direction. This means it misses the first part of the sun during the day but gets the sun for longer in the afternoon.

I didn't measure the amperage coming from the solar panel but did do a quick check if the voltage which was giving 18-19V but that is fairly meaningless without knowing how many able it is pushing. The charger controller seemed happy once it was all set up though and showed it was charging the battery. There is probably a setting somewhere to show the amperage but I didn't have time to mess with it.
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