Solar panel power

Submitted: Wednesday, Nov 07, 2001 at 01:00
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We are planning to purchase a 40 litre Engel fridge and have a dual battery system installed. It is likely we'll want to regularly camp in one spot for perhaps 4 days. What sort of deep cycle battery (what ampage) and solar panel (wattage) combination is likely to work well together and get us 4 or 5 days fridge use. I have seen that Dick Smith is selling a 46 watt solar panel for around $470 - would this do the job?? Thanks Gary
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Reply By: keith Walshe - Wednesday, Nov 07, 2001 at 01:00

Wednesday, Nov 07, 2001 at 01:00
As an electrical consulting engineer who has installed and run a solar installation in NE of NSW I would like to offer a few thoughts.
1. the power output quoted for a solar panel can mean many things; very often the 46watts quoted by Garry means in full sun light (see next item) and when feeding a matched load (see no3).
2. the solar flux ranges from 1bove 1.2kW/m^2 in northern areas to a fraction of that on cloudy days. you must make sure that the panel has enough surface area to give you the minimum amperage required by the fridge under dull conditions.
3. if the load impedance does not match the internal impedance of the panel, maximum power trasnfer will not be achieved and this is before reductions due to partial cloud (inc smoke haze) cover effects.
4. depending on the type of compressor motor used in the fridge you may find that the panel is unable to supply sufficient starting current for the motor even in sunny conditions. if the voltage gets a bit low then you might get a condition where the compressor stalls.

My advise is to put the question to Engles and get them to nomnate the make and size of the panels required for the weather / locations you want to go to.
AnswerID: 1344

Reply By: Mark Wilson - Wednesday, Nov 07, 2001 at 01:00

Wednesday, Nov 07, 2001 at 01:00
Gary,
I have a older previous model engel 39litre fridge. We operate ours from a dual battery system that from memory is a deep cycle one built expressly for the purpose of handling lower than normal discharges. We have coupled this to a 87watt solarex array (solar panel) via an 8 watt regulator. This seems to do the job pretty well and it has only let us down on one occassion when the temperature was so hot for 3 days that the fridge couldn't keep up. Had we been a bit cleverer and insulated the fridge against the high ambient temp we would have probably been OK. Still we were learning the ropes then and are now a bit wiser.
As added insurance against cloudy days we have purchased a small 12 volt generator called "Flash" from memory. This gives us the added benefit of charging batteries at 16amps per hour. A bit noisy though given its a 2 stroke.
The cost of the generator was about $500.00 and the solarex about $900.00 six years ago. It sounds like a lot of money but what price cold beverages at the end of the day, eh! We have also recently purchased one of those insulating covers and they seem to make our engel work much more efficiently.
Hope this helps Mark Wilson
AnswerID: 1346

Reply By: Porl - Wednesday, Nov 07, 2001 at 01:00

Wednesday, Nov 07, 2001 at 01:00
Gary, I went down the solar panel route and ended up with a generator. However, I use the generator, as with your second respondent, to charge my deep cycle battery. Using the generator also means while I am charging the battery off the twelve volt charging set up i can also run the fridge off the generator as a 240v power source.

An engineer called Les Christie has done the obvious and mated a bosch alternator to a 50cc Honda 4 stroke engine - it is advertised on page 258 of the December 2001 (i know it is currently november) 4WD Monthly magazine. Doesn't state a price but it can put up to 55 amps per hour into a battery, i would estimate roughly that you could probably charge your battery for 30 minutes in the morning and afternoon maybe.

You can check out how many amps are left in your battery by purchasing a $30 digital multimeter and download yourself the voltage rates from the internet which indicate what's left. Just type "deep cycle batteries" into a Yahoo search or something and you get lots of wonderful info on batteries. From memory when a battery is at 12.65-12.70 volts it is fully charged, at I think 11.40 volts it is fully discharged. At 12.00 volts it is 50% discharged, at 12.23 it is 60% full, at 12.30 it is 70% full, at 12.40 it is 80% full, at 12.50 it is 90% full and as i have said at about 12.65 it is 100% full. You can then determine how long to charge a battery by working out that if you have a 65 amp hour battery and it is 80% full then you need to put back into it 20% of 65 which is 13 amps. My generator put in 8 amps per hour so I'd run it for one hour and 37 minutes (calculator might be handy). I think you just run les christie's machine until the battery is pulling only one amp and then you can switch it off but i am only guessing.

As the first bloke said, solar panels are very expensive, don't work at optimum watts unless in full sun, and you need to keep moving them all the time. I hate to say because it is not environmentally friendly, but the best way to charge a battery is by a petrol motor. Good luck. And as for a battery get the biggest you can afford and lift - ask advice from a battery specialist, i would suggest not less than a 65 amp hour battery which should mean you only need to charge it once a day except in extreme temperatures, but of course you can always check your battery yourself as i have said.

Les Christies number is advertised as 02 9620 1208, his invention, if you can call it that, was reviewed a few months ago and it is great to see it is now out there. I have a Honda EUi 10 generator which is very quiet, but looks twice the size of les chrisitie's recharger.
AnswerID: 1352

Reply By: Patrick - Thursday, Nov 08, 2001 at 01:00

Thursday, Nov 08, 2001 at 01:00
Have you had a look at the new Weaco 52 litre fridge recently released to the market? I bought one at the Brisbane 4WD show for $879 from Motorama 4X4 and it has performed beyound my expectations. I priced an Engel fridge from ARB and that was 100's of dollars dearer for what I thought a lessor product (space and finish)
AnswerID: 1359

Reply By: Jason - Wednesday, Nov 14, 2001 at 01:00

Wednesday, Nov 14, 2001 at 01:00
Gary, we are currently travelling around oz and have been for 5 months now. We have a 39 litre turbo fan Engle a deep cycle aux battery and a 64 watt uni solar, solar panel. We have done Alice, East and west Mc Donnel Ranges Gibb river Rd Mitchell plateau and a lot of other HOT places. My thoughts are as follows. At Mitchell plateau it was 50 deg in the vehicle and the fridge was running 24 hours non stop the solar panel could not keep up and we were able to camp for about 2 days but not much longer. People who had no solar or generator could only stay overnight and the battery was flat! However when we came further down the coast and the temperature dropped we can now stay about 5 days depending on how much cloud cover there is. I would say that about 120 to 140 watts of solar would give you all the power that you need and you could stay put for as long as you wanted. As for a generator we looked at that option however in most National parks in WA and NT you are not allowed to run them and they can be quite annoyoing to other campers. The other thing was that I have a deisel car and I would have to carry a jerry of unleaded around. As for costs two panels would work out to $1100 to $1400 depending on which ones you buy and after that its free! One other trick we learnt with the fridge was to cut the mesh out of the transit bag that covers the motor we were told this in Kunnanara and after I did this I could run the fridge a 1/2 setting lower because it worked that much more efficiently. Best luck and good travelling.
AnswerID: 1430

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