Solar Panels for dummies

Most people seem to use somewhere between 80 and 160 watts of Solar Panels for this type of load.

Colin,

Stop drinking someones Hen Wine and have a read of this informative Blog about Solar Power ;)


Cheers Kev

Hi Colin,

I have an 80 watt on the roof of the ute but the fridge is still not hooked up yet but I am thinking it will be enough to keep the bourbon cold for over a week. All 150 metres of the wire is almost to the battery now and ready to hook up but now I do not have the time to get it hooked before my next adventure on thursday so I can not advise you of the outcome :( Will not be able to complete it until early march now unless I take all the bits with me and do it on the road.

Peter

Colin,

Your question sounds pretty straight forward so there should be a straight forward answer. But there isn't.

The power you need will depend on sunshine, how often you are willing to move the panels so they face directly at the sun, and especially, how cold you run the fridge. And of course, are we talking summer in Alice Springs or winter in Tasmania.

If you've read our blog (refered to above) you'll have some idea of all the factors involved. I'll try to be a bit more specific:

First, what is a 900 CC AGM battery? Do you mean 900 CCA battery? If so, it is a starting battery, not a deep cycle battery, which would be much better for the job. A starting battery will run the fridge and lights, but not for as long as a deep cycle battery and it will die earlier than a deep cycle battery if it is run down too far.

It may be a dual purpose battery which will handle both starting and deep cycle usage, though not as well as the correct batteries for these jobs.

For my rig, I use 145W of solar panels. You are right in saying that you don't get all this out as usable power, but that's how the panels are rated and that's how we talk about sizing. In practice you must simply bear in mind that it isn't all there when you start making calculations. I also charge from the vehicle, but the panels handle the fridge and lights ok when stationary for a week or more.

Your ideal battery would be a 100 Amphour AGM, that is about the same physical size as a big (900CCA) starting battery. This should run your fridge and lights for 2 or 3 days without any charging unless you are running the fridge very cold. (Running it as a freezer you'll maybe get 1 day.)

You need to replace the Amphours you use each day using the solar panels. For that (assuming the fridge is not working very hard) you will need about 140 to 160 watts of solar capacity (that's manufacturer's watts, not usable watts). With that much solar capacity you will charge at up to about 10 amps in strong sunlight, so you MUST have a controller to save the battery from being overcharged.

So, the simple answer to a pretty complicated question is - panels rated at about 140-160 watts should do the job for you if the sun is shining and so long as you're not in the tropics in summer. If the sun doesn't shine, start the car and then use jumper leads to connect the trailer battery to the car battery and run the engine at fast idle for half an hour a couple of times a day. Disconnect the jumper leads when the engine is stopped.

Hope that helps

John

Can't really help with how much you need but be careful with the cheapies and their rating. I bought one rated at 60W but have only ever managed 40W. Use it to trickle charge the dual battery.
I have also noticed there has been a significant price drop over the last 12 months.

I'm no expert here either Colin, but I have found one that works for me.
I have a Trailblaza 70 litre fridge that is very hungry for power from the battery. I purchased a 100 watt bi-fold panel from Derek Bester (ABR) and it works a treat. Keeps the aux battery topped up enough to keep the fridge running.
The panel can be viewed HERE

The usual disclaimer.... I'm just a happy customer, not affiliated with ABR at all, and also for those of you that want to argue that my system doesn't/shouldn't/couldn't work, save your breath, I ain't interested!!

Cheers

Brian