SOLAR POWER BASICS

Submitted: Thursday, Aug 08, 2013 at 12:06
ThreadID: 103671 Views:1689 Replies:1 FollowUps:5
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Hello all, I have read a lot of information for solar set ups and have a reasonable understanding. Could someone please give me a very basic list of the items that i should purchase to have a good quality, functioning solar kit. It is for a small caravan and it won't be fitted to the roof, it will be unfolded and placed outside. Cost is not an issue, i have about $1500 to spend - will this be an issue. Cheers.
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Reply By: Member - Frank P (NSW) - Thursday, Aug 08, 2013 at 12:39

Thursday, Aug 08, 2013 at 12:39
What you need depends on your power usage, Heath, and the size of the batteries you'll be charging from solar.

It may be a small van, but do you run laptop, TV, satellite rig, perhaps a car fridge, inverter (and what do you plug into it?), are your lights incandescent or LED, etc, etc?

A bit more info and we can give some more detailed suggestions.

But in answer to your request for very basic info ...

- Monocrystalline panels, total watts to suit your power consumption and battery
- A solar charge controller, preferably not on the panels but mounted in the van near the battery and sized to match the panels.
- As you have a fair budget I would go for an MPPT controller for increased efficiency. There are some well priced ones with up to 30 amp capacity. Smaller would obviously be cheaper, as would PWM technology instead of MPPT (but not as efficient).
-10 meters of decent cable from panels to the controller's solar input to allow you enough freedom to chase the sun/dodge the shade.

As for quality, how long is a piece of string. Just down the page a bit at Thread ID 103667 a poster asks about a 120 watt Jaycar system at $400-ish. One of the replies points to a similar eBay item for less than half the price. Quality comparison? Who knows. But I don't like the built-in controller on the eBay option - it's better to have the controller close to the battery. It may also be less convenient for some, but for you, once you got the controller mounted in the van there would be no difference.

Cheers
FrankP

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Follow Up By: Heath 1 - Thursday, Aug 08, 2013 at 12:49

Thursday, Aug 08, 2013 at 12:49
Thanks for that Frank.

- I was thinking 240w Monocrystalline panels - any brands you can suggest?
- An MPPT Controller
- Upgraded cables to minimise voltage loss
- Not sure which battery to purchase or how many - any suggestions

I was thinking of getting something good quality, we do camp a lot and plan to extensively in the coming years, a number of sites we visit have no power.

We use three way fridges so have gas when needed, but can run 12v when needed.

Small tv every now and then, refitting everything with LED to minimise power draw.

Your thoughts on Anderson Plugs - are they worth doing.

Cheers
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Follow Up By: Ross M - Thursday, Aug 08, 2013 at 13:38

Thursday, Aug 08, 2013 at 13:38
Heath 1
Unless you are able to power the 3way firdge/s off the car while travelling
which may be sort of ok, perhaps maybe, the solar is not going to run a fridge when stopped.

To run both while travelling will mean a large cable/anderson plug supply to caravan from vehicle, DUAL battery system solenoid, as they will be drawing in excess of 25amps from the alternator while driving and still not much, if any, Cvan battery charging happening.

240w panel in full sun might run one fridge but only in ideal conditions and have nothing else left in output capacity to charge a battery.
At night no solar output so gas is a must.

3wya fridges and solar just aren't compatible re energy requirements.

Ross M
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Follow Up By: Member - Frank P (NSW) - Thursday, Aug 08, 2013 at 15:02

Thursday, Aug 08, 2013 at 15:02
I think you'll find Collyn Rivers' article here of great benefit.

Firstly, and pretty much as Ross said in his last line, forget about running your 3-way fridge(s) off 12V while camped. They draw 10 to 15 amps and run nearly continuously, so think 240 to 360 amp-hours per day!!!! No practically sized solar can keep up with that kind of demand. The 12V part of 3-ways is basically only for transit, to be powered by big cabling off your tug's alternator.

Having said that, 240 watts of solar will support an otherwise pretty large and hungry outfit (in electrical terms). I had 240 watts adequately supporting 320 Amp-hours of batteries in a caravan with a compressor fridge. It's the fridge that's the killer, and yours will be gas while camped so the fridge is out of the equation, leaving just lights and a bit of TV and maybe radio/CD and water pumps.

Based on what you've said in your Follow-up, I've estimated your useage at about 18 amp-hours a day:

Lighting 2.0 amp-hours
12V sockets 5.0 (extras like charging phones, cameras, running outside camp light.)
Water pump 1.0
TV/radio 10.0
Total 18.0

That's very modest. Is there anything else?

I used a solar spreadsheet calculator to see what sized battery and panels might be appropriate. It suggested that 120 watts of solar and a 100 amp-hour battery would be more than adequate. In sunny weather in all seasons it suggests you will never run out of power.

How long you will last with no sun depends on how much you are prepared to discharge your batteries. According to all the literature, 50% discharge is the best compromise between practical use and longevity of the battery. In that case a 100 amp-hour battery will give you 3 days. 200 amp-hours will give you 6.

With the above useage and 120 watts of solar, you would be oversolared - slightly in winter, considerably in summer. The benefit of this is you wouldn't need perfect solar days to keep up.

So if I were doing your system I'd go for

- 1 x 100 amp-hour deep cycle battery. More capacity if you want to be self-sufficient for longer in no sun.
- A controller such as this one from Jaycar or on eBay.
- 10m of pretty heavy sheathed twin-core cable, eg the 5825 found here

This system is expandable - if you want to add batteries or panels you can, without changing the solar controller. Batteries in parallel, of course, and the same with the panels.

Anderson connectors are very practical. Rugged, reliable, fool-proof. Only real disadvantage is they're not waterproof. I use them throughout my system and have never had a problem and I think many others would say the same.

Cheers
FrankP

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Follow Up By: Heath 1 - Thursday, Aug 08, 2013 at 16:01

Thursday, Aug 08, 2013 at 16:01
Thanks very much for that, starts to make much more sense now, gas for the fridge did seem like the best option when i first looked so i will continue to operate it like that (last trip with fridge freezer running i got 20 days with gas to spare, so that should be fine)

Looking at the amp hours i will need i think that i will invest in solar for running my other appliances. Pumped.... i think it looks like a much better option than carting a generator around.

Cheers
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Follow Up By: Member - Frank P (NSW) - Thursday, Aug 08, 2013 at 17:09

Thursday, Aug 08, 2013 at 17:09
Heath,

"So if I were doing your system I'd go for "

I left out the most important bit (distracted by babysitting the grandies) :

- 120 watts of solar panels.

I strongly recommend you get them with no controller attached. You can often get a good deal on panels with an attached controller, but first investigate if it's easy to bypass the on-panel controller and use your own.

You can easily upgrade if you need to by adding one or more panels of any wattage in parallel, so it's easy to tailor your solar to your needs. Just plug them together with Andersons. To keep this option available it is most important that your panels all feed into one controller.

I found that with my 240 watts in two pairs of 120 that it was best to have each pair on its own 10m cable, joining up with a double Anderson adapter at the controller. That keeps the current in the panel cable down (fewer losses) and gives maximum flexibility for chasing the sun.

Cheers


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