What size Solar Panels.

Yes I know this has probably been done to death, but I can't find older posts, and the topic area just got me confused.
Shops are giving me options that involve their largest, most expensive units.

All I use is one Waeco CF40 fridge. Supposedly max of 5amp per hour, when it is in full cooldown mode, otherwise only at 0.87 amp per hour. Every now and then, a small dvd player might get used. (rainy days)

I have a dual battery in car, but often I take the fridge out, and leave it in camper where it is cooler attached to a battery(about to get new battery as battery pack I had been using was reclaimed by owner)

To keep the battery at a decent state of charge while having fridge attached, what size solar panel/panels would I need?

I'm also aware that I will need regulators etc

Thanks in advance
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Reply By: SDG - Sunday, Apr 24, 2011 at 02:03

Sunday, Apr 24, 2011 at 02:03
While i'm here.
Does any one have any ideas on why my raps power unit in the car, has constant power regardless of the switch setting? Suddenly decided to do this function last week.
AnswerID: 452149

Reply By: Member - Boobook - Sunday, Apr 24, 2011 at 06:20

Sunday, Apr 24, 2011 at 06:20
You need to supply more information to really stipulate the size of the panels.

-Where will you use it,
-Summer or winter or both
-How many days will you be going without driving

However as a rule of thumb you will need a minimum of 120W if you get a MPPT reg and 160W if you get a normal PWM reg.

You ahould have at least 80AH battery for it to work continously with the above.
AnswerID: 452151

Reply By: Member - John and Val - Sunday, Apr 24, 2011 at 07:42

Sunday, Apr 24, 2011 at 07:42

As Boobook says, we need more information to be of much help. Particularly, size of batteries and how you are charging the battery in the trailer.

I think the figures you've been given for the fridge are close, but a suspect too. We have a Waeco of that size and it draws about 3.7 amps when running, and runs about 1/3 of the time once temperatures have stabilised. Ours uses an average of roughly 25 amphours each day. For other demands like charging torches and cameras, radio, camp lighting etc we use roughly another 12 amphours per day. Your requirement sound a bit less than ours.

Suggest have a look at our blog Electricity for Camping for a lot more detail, but in very brief summary - I'd suggest at least a 100 Ah AGM battery for the camper, charged from the vehicle via a heavy (6mm sq minimum) twin cable from the vehicle. If you are likely to spend more than a day without running the engine, a solar panel will be very useful. I agree with Boobook's panel sizing, maybe a bit bigger if you want to be totally independent for extended periods. Check out the blog; I think it addresses a lot of stuff that may help you.


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AnswerID: 452153

Reply By: Member Al (Sunshine Coast) - Sunday, Apr 24, 2011 at 11:00

Sunday, Apr 24, 2011 at 11:00
SDG, I totally agree with BooBook and John on this.

The problem is that you can go on endlessly with calculations and specific advice but ultimately you are at the mercy of the weather and available sunshine which affects all of the considerations.

It seems to me to be appropriate to simply follow what other successful users have done and that seems to be for a fridge of your size (and operated as a fridge, not a freezer) that a 120w solar panel with an MPPT regulator and a 100ah AGM battery will do it for you MOST of the time. For those odd times when "The Sun Don't Shine" you can always run the car at a fast idle for half an hour or so each day, which won't fully charge the battery but should keep you operational.

The issue with many salespersons is that they wish to appear highly knowledgeable and/or keen to sell you the ultimate and most expensive products. Of course, these ultimate products are more certain to do the job, at a price, so you are unlikely to go back and complain of inadequacy.


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AnswerID: 452165

Follow Up By: tg123 - Sunday, Apr 24, 2011 at 11:45

Sunday, Apr 24, 2011 at 11:45
I have 2 x 65W panels on my camper running through a 100ah AGM battery. As long as the sun shines reasonably consistently I am able to run my 60L Engel plus an assortment of other low draw 12V stuff for a long time. Longest to date was 8 days in 1 spot with voltage still around 12.6V in the morning prior to the sun hitting the panels.
I also have 2 x 50W folding portable panels running through a 55ah AGM in the car - keeps my 50L Waeco running very happily for extended periods - again 8 days is the longest I've done this.
Hope this helps
FollowupID: 724851

Reply By: S Paul - VIC - Sunday, Apr 24, 2011 at 11:24

Sunday, Apr 24, 2011 at 11:24
Another consideration - which depends on how long you will be away from 240V and not driving is to have 2 X 100 aH AGMs in the trailer - with your fridge this will probably allow 4 days ...
If you stay for longer than that then you will need Solar ...


AnswerID: 452166

Reply By: SDG - Sunday, Apr 24, 2011 at 12:40

Sunday, Apr 24, 2011 at 12:40
Thankyou for the reply's.

To update the info I was asked for,
Camp mainly in the mountains and coastal areas, with some inland.
Summer and Winter.
Fridge can be in camper up to two weeks. I might go for a drive, but the fridge stays behind.

So it looks like a battery of at least 80Ah, Been looking at the 120Ah.
When driving the battery will be charged via the car, but when parked the car and camper will be separated.
And around 120 watt solar panels seem to be the norm.
Days with no sun may need to boosted via car

Anything else?
AnswerID: 452174

Reply By: Member Bushy 04(VIC) - Sunday, Apr 24, 2011 at 15:28

Sunday, Apr 24, 2011 at 15:28
SDG I have set up a 65w panel on the cannopy of my ute running with a 80ah battery which is also charged through the vech system.
My idear was to be able to run my 21ltr Engle if I park for a day or two.
When traverling around the West we would stop around 1300hrs for the day so the vech might not get run again for several days which usualy meant that the battery alerm would be on by the following day, the new system seems to work fine, as it has only been up for a couple of weeks.
Hope this helps.

AnswerID: 452185

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