Solar Panel and Battery

Rob in MT

New member
I am getting a camper from ATC and am debating having them do the solar and aux battery. I know it would be less expensive to do it myself, but having them do it, means less chance of me screwing it up.

I will be running an Engel and LED lights. The panel is 80 watts and the battery is 75 ah.

I know the amount of sunlight is the missing factor here, but generally, would these be adequate? Thanks for your help.
 

dwh

Tail-End Charlie
Solar rules of thumb...

PV modules (solar panels) will on average put out 80% of their nameplate rating.

(They put out less when hot and more when cold. Since they are dark and pointed at the sun, they are usually hot.)

Flat mounted PV modules will on average get a decent harvest for about 4 hours per day.

(IF you park in full direct sunlight. Anything less than full direct (NO SHADE AT ALL) sunlight on the PV module and your harvest will be basically nothing. Even just a touch of shade on one corner can cut the module output by 1/3 or 1/2 off the top.)

So you can figure on average 80w x .8 x 4 = 256 watt*hours per day harvest.

Then, the charge controller (between the PV and the battery) will not be 100% efficient so you'll lose a few watts there, and the battery will only be about 80% efficient. Let's ignore the loss from the charge controller and just figure the battery. So 256wh x .8 = 204.8.

So you can figure on average that you'll end up with about 200 watt*hours per day actually getting into your battery and being available for use.

Not including recharging from the vehicle engine or a generator, your "solar only" power budget is 200wh/day.

Now you need to figure out how many watts your loads draw, and for how many hours per day and you can compare that to your power budget.

Say your fridge draws 30w when the compressor is running, and it runs at a 30% duty cycle (20 minutes out of every hour). That would be 30w x 8 hours of run time for a total of 240wh per day. That would exceed your "solar only" power budget.


An 80w panel isn't very big. If you rigged it with an extension cord and manually deployed it (leaned it on a nearby rock) facing the sun and moved it a couple of times a day, you could park in the shade and also get double or triple the harvest.
 

LandCruiserPhil

Expedition Leader
I wanted to do all the calculations but I had the 55W Siemens panel, Costco battery, and Waeco CF-50 fridge with a blanky. Here is my real world findings - I can run my fridge full of 30° beer in the summer in Mexico without starting my vehicle for days. Your mileage my vary
 

Jeff Wanamog

Off Road Camper Guy
Never enough

Take it from me. You will never have enough. I know, I know, what a stupid comment. What I mean is there is noway of seeing into your future as you get used to your new way of camping.
At least have the camper wired. I am pretty sure they come that way anyways. That way when you have the money to do the best panel and charge controller, you can do it right.
If you do calcs for just the fridge and lights, you will bring chargers for phones and other items, you might bring a radio and on and on.
What I am saying is that there is nothing wrong with doing it later and it is very easy. There are a lot of people here, and DWH is one of them, that knows a lot about solar. I can always take pictures of my install and send them to you.
Hope this helps.
Jeff
 

grizzlyj

Tea pot tester
We have I think (came with camper!) two 100W panels and 2x 255Ah AGMs. Northern Scotland in winter the panels may as well have not been there! The French Med coast in summer the panels alone kept the batteries full despite halogen lights, Eberspacher for hot water, water pump for two showers a day and compressor front opening fridge, 37deg C max :)

Links to a UK campervan site for more opinions! Do US campervans go for solar much? UK campers like solar so when they visit France where you can legally park up anywhere they can be independant.

http://www.motorhomefacts.com/ftopic-83576.html&postdays=0&postorder=asc&highlight=diy&start=20

And a thread regarding if making a tilting bracket to follow the sun is worthwhile, from where the attached table comes from

http://www.motorhomefacts.com/ftopic-89919.html&postdays=0&postorder=asc&highlight=solar&start=40

Edit Having read the above post, yes, even twice what we have would be cool. You know Series III Landys had a Safari roof? Our whole camper roof covered with a seperate layer of solar, with an inch gap to keep the inside cooler might be enough ;)
 

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dwh

Tail-End Charlie
I wanted to do all the calculations but I had the 55W Siemens panel, Costco battery, and Waeco CF-50 fridge with a blanky. Here is my real world findings - I can run my fridge full of 30° beer in the summer in Mexico without starting my vehicle for days. Your mileage my vary

Yea, but the question is, how long could you do it without the solar panel?

Probably about the same.

For a small solar setup, the best that usually happens is that the PV just stretches out the time until the battery is dead. If your battery could run the fridge for say 5 days, with the solar now maybe it can go 6...

Look at my example above - taking out 240wh/day and putting back 200wh with the PV. The battery is going down by 40wh/day. That's called "deficit charging" - when you recharge, but not all the way.

Of course, I have no idea what your fridge draws or what duty cycle it runs at. It's entirely possible that your 55w panel in good sun harvests more than the fridge draws.
 
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LandCruiserPhil

Expedition Leader
Yea, but the question is, how long could you do it without the solar panel?

Probably about the same.

For a small solar setup, the best that usually happens is that the PV just stretches out the time until the battery is dead. If your battery could run the fridge for say 5 days, with the solar now maybe it can go 6...

Not my experience at all prior to installation of the panel. Battery would be good for about a 1-1½ days max with summer time temps, from the limited testing I have done. Depending on the time of day battery was metered I would still see 12v after a couple days with my solar set up.

Keep in mind Im in an area with some of the longest days and highest solar insolation (2500btu/ft) in the world. My panel is mounted flat on the roof with an 1½" of air space.
 

dwh

Tail-End Charlie

Thanks for that. I'm always interested. Skimmed for now, will read later when I have time to digest it and follow the links.

$10/watt? I dunno what the exchange rate is but even last year we could get normal mono or poly modules here for 2-3/watt. I saw one place selling a pair of 100w panels along with a Morningstar 15a MPPT for ~$500 USD.

So, to me anyway, $10/watt is WAY more than I'd ever want to pay for PV modules - even those extremely cool bulletproof stick-ons.

Now...if I could get them for 4.50/watt that's in the ballpark.
 

whatcharterboat

Supporting Sponsor, Overland Certified OC0018
$10/watt? I dunno what the exchange rate is but even last year we could get normal mono or poly modules here for 2-3/watt. I saw one place selling a pair of 100w panels along with a Morningstar 15a MPPT for ~$500 USD.

So, to me anyway, $10/watt is WAY more than I'd ever want to pay for PV modules - even those extremely cool bulletproof stick-ons.

Now...if I could get them for 4.50/watt that's in the ballpar

Man, we are so ripped off in Australia with taxes and duties etc. With the strong AuD at the moment ($1Aud = $1.02 USD), all the new new Chinese panels coming into the country and the increased competition from the Solar Grid Connect industry, prices here have come down a little over the past 12 months but certainly not as much as they should. Not even close. Someone's making a killing.

It's probably more like $8.50 to $9.00 per watt average for poly/mono solar here now. BTW Stick-on Amorphous are around the same price too.

a pair of 100w panels along with a Morningstar 15a MPPT for ~$500 USD.
>> we would pay $400 AuD ($408 USD) just for a Morningstar 15a MPPT by itself. That's the one they'd probably be offering with 2 x 100watt panels. Here's one online from a reputable company down the road from me. If you walked in and bought it over the counter, it would probably be more. >>> http://www.watts2c.com.au/index.php...-15amp-12/24volt-/detailed-product-flyer.html

We know how much the retail shops pay for stuff too cause we on sell solar ourselves and there's no profit in there for the retailers either. It just sucks.
 
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