Which Solar Panel

Jun 15, 2014
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Hi all. Most of my caravanning is off grid. I always carry a spare fully charged battery, for those emergencies. This always works, but would now prefer not to lug heavy batteries around, so am looking at solar panels. I don’t want to run my van off one, just something sufficient to top up. That’s where I need some advice, as the choice is quite bewildering and I don’t want to buy the wrong type/output. Thanks.
 
Nov 16, 2015
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So what size of batteries are you using, and how many days do you go away for off grid, also how low do you let your batteries go down to volts wise. ? This will help to give you an answer.
 
Mar 14, 2005
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Hutches request wont give us the answer.

What is needed is to know how much power in kWH you use. You then need to work out the number of hours of daylight you will have to determine how much charge capacity your panes need to have, but you must also factor in time of year as the length of day can the angle of the sun changes throughout the year,

You need to consider cloud factors, and the possibility you may not be able to point your panels in the optimum direction.

However previously several contributors have reported that using about a 50W panel, has been enough to sustain the 12V system for the duration of a holiday. Some installations have had up to 200W of panels, so my guess is that you will need between 50 and 200W of panel.
 
Nov 16, 2015
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Hutch's , not Hutches, come on Prof. :p
We still don't know from Fithawlk, battery size. 70 amh 90 or 120 amh. It all depends. A motorbike 15 amh would take no time to recharge on huge solar panel. But big 120 amp. On a very small solar panel would maybe never rechrge..
 
Aug 30, 2018
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This is what I have. 150W roof mounted panel feed 2 x 90ah Varta batteries. This copes between around March to the end of October but putting a panel on the roof is inefficient so if you keep the van at home (we don’t ) then I would suggest that a smaller freestanding panel might be just as good. By smaller I mean arround 60w not 5w. For us because we store, a roof mounted panel makes sense. Because, in the winter even if the solar panel hasn’t fully kept the battery fully charged. The battery will charge in storage. Meaning a fully charged battery for the next outing. Also in my opinion, solar panels these days are commodity items, and you will pay a lot more at a caravan dealer than you will if go to the usual suspects online.
 
Mar 14, 2005
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:( Sorry Hutch...

To the subject... The size of a battery does have to be factored in, but it does not determine the capacity of solar panel needed. Obviously the battery needs to be big enough to supply the caravan when there is no charging or spare solar power available.

Basically you need enough solar panel capacity to supply the average power demands of the caravan. It needs a battery with sufficient capacity to supply the caravan during the time the panels cannot supply the instantaneous demand, or when there is not enough light to provide current for appliances or to replenish the battery charge. In essence to carry the load and smooth the supply.

You need to total up your entire days electrical demand, and for convenience its easiest to work in Ah.
Assuming its a modern caravan with high efficiency appliances, and sensible usage:

So for example: assuming caravanning at the March solstice, (equal day and night) careful usage might see:

Modern LED lights may use 100mA per luminair 6hours x 4 lights = 2.4Ah
Water pump 7A for 15Min (0.25H) per day = 1.75Ah
Fridge control circuit (pure guesstimate) 25mA 24hours a day = 0.6Ah
Water heater control 15mA 6hours = 0.1Ah
Space heater control 50mA 12hours =0.6Ah
Heat circulation (fan or Pump) 1A 12hours =12Ah
Cooker hood 1A for 1 hour = 1Ah
Phone charger 0.4A 3hours = 1.2Ah
TV 2A for 3 hours = 6Ah

That gives a total Ah usage of about 25Ah

So a battery (with no charger available) would need a capacity of 25Ah for one days usage.

Conversely if a charger were available and assuming the battery was 100% efficient you would only need a constant charge current of 1.05 A to keep the battery able to meet the needs of the caravan indefinitely.
A larger capacity battery would make no practical difference, except with its better peak current delivery for motor movers.

Unfortunately batteries are nearer 70 to 80% efficient so you’d need a constant charger of nearer 1.5A.

Off grid, means no mains power, and the OP is looking for solar power which would only be available in meaningful quantities for roughly 60% of the daylight hours. Therefore at the solstice that would be 7.2Hours

So during that period the panels would need to produce an average charging current of 3.5A

Panels are rated in Watts and that at 12V would be 42W.

Allowing for other problems such as clouds, and other restrictions to the light available, perhaps a 100 or 150W panel would give peace of mind. A charge controller would be a very useful thing as it should maximise the efficiency of the panels, and prevent overcharging of the battery.

With such capacity, some of the daytime load would be carried directly by the panels, and that means the battery would only have to supply the night time load. You could conceivably get away with a 10Ah battery!

So battery capacity does not dictate the size of panels.

By careful choices of what appliances you use and for how long you use them for can make quite a difference to the total power usage. Often the big current hungry devices (e.g. Movers and Pumps) are only run for relatively short periods and in fact consume relatively small amounts of power over a day, The big power users are the items that are used for long times, for example lights and tVs and chargers, that use bigger chunks of battery capacity over a day.
 
Jun 15, 2014
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Ok, some more info based on some of the questions you raise:

X 2 120’s. One in use.

Average 8 days carefull usage in good conditions. Down to around 6 otherwise.

Non LED Lights spareingly.
Water Pump as required.
Mover on arrival/departure.

No other electrical use.

Hope that helps a bit?
 
Dec 7, 2010
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I have a 150w folding panel and 110amp battery, have been away for 15 nights, so far, battery keeps charged up including TV usage and the caravan 12v systems. Have a 150w inverter to charge up my shaver and laptop, USB adaptor which plugs into the 12v socket to charge phones, watches, etc. Most of our caravanning is off grid using the C&CC 3/5 day meets and THS's, just use more gas which is cheap using a Safefill refillable cylinder. Also used it in winter off grid.

42963345305_94870fe57a_c.jpg
 
Nov 16, 2015
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Tukums said:
I have a 150w folding panel and 110amp battery, have been away for 15 nights, so far, battery keeps charged up including TV usage and the caravan 12v systems. Have a 150w inverter to charge up my shaver and laptop, USB adaptor which plugs into the 12v socket to charge phones, watches, etc. Most of our caravanning is off grid using the C&CC 3/5 day meets and THS's, just use more gas which is cheap using a Safefill refillable cylinder. Also used it in winter off grid.

42963345305_94870fe57a_c.jpg

That looks more like a 13 kg calor bottle to me. Not a safefill one. !!!
 
Aug 30, 2018
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EH52ARH said:
Tukums said:
I have a 150w folding panel and 110amp battery, have been away for 15 nights, so far, battery keeps charged up including TV usage and the caravan 12v systems. Have a 150w inverter to charge up my shaver and laptop, USB adaptor which plugs into the 12v socket to charge phones, watches, etc. Most of our caravanning is off grid using the C&CC 3/5 day meets and THS's, just use more gas which is cheap using a Safefill refillable cylinder. Also used it in winter off grid.

42963345305_94870fe57a_c.jpg

That looks more like a 13 kg calor bottle to me. Not a safefill one. !!!

Carefull reading of Tukums’ post, tells me he doesn’t say he is using a Safefill bottle, merely it is cheaper gas which is. Looks more like a 11kg bottle to me btw.

More seriously my set up is similar most things are charged of 12v/usb chargers. My Fitbit is charging as I type. I also have a 150w inverter which is used occasionally for a laptop. As I said in an earlier post I have a 150w SP, mine is roof-mounted. I have no doubt that Tukums Panel will have a greater output than mine when it is deployed. So if you can plug in at home to charge your battery then a freestanding panel is probably the way to go, but it does come down to personal choice.
Re Mono and Poly crystalline panels I don’t think it makes any significant difference .

PS, It is worth imho looking on you tube to see the effects that even a small amounts of shading can have on the output panel.
 
Dec 7, 2010
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Back onto Safefill now that Morrisons allow filling, had to use the bit left in a 11kg Flowgas. My local garage who allowed the filing of Safefill closed down so had to go just over a year using expensive gas, now back to cheap gas.
 

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