Adding solar panel
Thinking about adding another solar panel to our unicorn Barcelona and a second battery to do more off grid caravanning we already have done up to 3 weeks off grid but by end of each day power is down . Looking for any help or has anyone done what we are thinking,any ideas would be appreciated
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Assuming space isn’t an issue, no reason not to do it - battery and/or panel, you’ll notice the difference. On this topic we usually have the lithium discussion here, worth checking out, but the economics don’t work for me. Make sure you understand the series -v- parallel connection issues before fitting extras yourself. Plenty of good advice on the web.
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Given the parsimonious payloads on caravans, consider the weight of panels. Whilst some decry them, semi-flex panels are much lighter and I've had no problems with good quality ones when fitted to a bonded roof. It may be worth replacing the existing one with a larger or lighter panel. I changed the single framed one for three semi-flex on my motorhome for no additional weight.
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I see that there are some 120w 18amp foldable solar panel blankets for under £70 on ebay. Are they any good for keeping ones leisure battery charged when the van is parked up at home?
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Better than some, I grant you. My old Abbey had 240Kg and we needed it all.
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Back of a fag packet calculation:
120w x 4 (average sunshine hours) x 0.75 (factor in inefficiencies) = 360 watts per day.
Convert to Ah = 360w / 12v = 30Ah. So, the panel should be able to charge at the average rate of 1.25A. Trickle chargers typically produce 1 to 2 amps, so should be ok.
That’s my understanding of the solar maths, but could be well of the mark and others will see it differently? Obviously lots of variables, not least sunshine hours, so very ‘ball park’.
Wouldn’t buy any solar stuff of eBay tho’.
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You can borrow a few kWh from the tow car each evening if the car is running daily. We used to do this by running the TV from the car via a separate lead. The car never seemed to mind.
That way, the caravan battery lasted a lot longer. This was before solar panels were around.
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Thanks, SB. Any advice on the best size, type and where to purchase? I don't want to fix one permanently to the van.
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Depends on your circumstances but if you’ve got a secure location a folding solar kit like this Photonic Universe might do you? If it’s not secure, maybe a semi rigid kit that you can prop up inside your window like this Photonic Universe will do? Solar panels behind glass/perspex will lose some efficiency, so go for more than you need. Photonic Universe sell quality stuff and will give you as much help as you need.
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👍 Thanks.
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This is not at all my area of expertise but as I have a different thread running about solar panels, I thought I’d try to apply this calculation to a different rated panel.
In the example given, I note you’ve divided the output of 30Ah (which is generated based on 4 hours of sunshine per day) by 24 (hours in day). Why isn’t that a lesser figure, possibly the same 4 hours, as the panel is only generating when sun is shining? It isn’t, for example, producing anything at all in hours of darkness, so does that mean the actual output per productive hour is greater than 1.25 amps.
Not that it may help, because the battery will presumably only draw what is needed to charge, so even if more than the trickle rate of, say, 1-2 amps, the surplus will be lost.
Now, I’ve confused myself as well as you. Anyone care to comment on my logic, flawed or otherwise?
Ian
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Yes, it’s what’s generally referred to as ‘peak sun hours’ when the output is higher, but obviously that’s variable and unknown so any calculation has to be based on a daily average. However, there is data for the average number of sun hours in various UK locations and times of year. The job of the solar controller (recommended for any panel above 5w) is to regulate the charging rate to avoid over charging. It also prevents the battery from discharging via the solar panel.
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If these are the 8 panel types on eBay then I would be very suspicious. You would certainly need to add a controller to those. An supply straight from the panel could fry your battery.
Most of the folding panels are simply 2 framed panels hinged together with a cheap controller stuck to the back. A lot of people will tell you that this is not an optimum setup but it will work well enough.
If all you want to do is keep the battery topped up between trips. I would be tempted to buy a cheap even 2nd hand panel and a basic £15 controller it will work. We have panels on the roof as a permanent installation for convenience. It keeps the battery charged between trips often off grid even in the depths of winter and we store the van with no prospect of plugging in.
Final point you quote specs of 120W x 18amps. You are mistaken it is 18V which is the voltage the panel feeds into the controller before the contoller converts it to charging voltage. This is relevant because panels can come in a 24v version which have a 36V output you wouldn’t want to buy one of those by mistake.
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