How much Solar Power do you need?

Submitted: Thursday, Mar 31, 2005 at 19:04
ThreadID: 21664 Views:2868 Replies:7 FollowUps:6
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The Undertaker put up a post a few days ago whilst I was away camping. The question of how much solar do you need was asked and there were some very detailed responses.

Some of you may recall my solar test a while back. I will now add my practical experience of the last three days. The first two days involved some driving and some solar. Yesterday I got up at 7am and checked the voltage of my 100 amp AGM battery, 12.30 volts or about 70% charged. The panel went out into the sun at 8am and lost light at 4.30 pm (we were camped in a valley). It was a very sunny day. The panel is a Uni Solar 64 watt. By 7am this morning the battery was showing 12.36 volts. During this 24 hour peroid the battery/solar ran an 80L fridge running hard and a fluoro light for a few hours at night. In essence this tells me that in the circumstances of 8.5 hours of good sunlight and cold nights, it will maintain battery voltage.

Now this may not be the case in other circumstances, but I would suggest start small and add another panel later IF your circumstances dictate. I have never expected my setup to work continuosly for a week in the middle of winter.

However, most of us do some driving at least every other day and solar is a top up. The theoretical figures may be mathematically correct, but in practical situations you may be pleasantly surprised with the results.

Cheers,

Jim.
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Reply By: TheUndertaker - Thursday, Mar 31, 2005 at 19:51

Thursday, Mar 31, 2005 at 19:51
G/day Jimbo, so by your experience in a Victorian autumn ,your 64 watter ran the Waeco + added power to the AGM ,sounds good to me , however i,m wondering 'does Jimbo turn the fridge setting down or heaven forbid off at night' ,,,
AnswerID: 104551

Follow Up By: Member - Jimbo (VIC) - Thursday, Mar 31, 2005 at 20:10

Thursday, Mar 31, 2005 at 20:10
U/T,

I am a firm believer in letting a thermostat do its job ie I never turn the fridge off at night. I run it on 4 lights during the day (set up as all fridge) whilst it is getting solar power and turn it back to 3 lights at night. This ensures 3 to 4 degrees at the warm end and negative 2 to 3 at the cold end (I actaully ended up with some frozen beers as I let too many sit down the bottom rather than rotating them). I don't like to let any of my food (other then salad/vegies in the dairy section) get above 4C in the interests of food hygeine.

I reckon a 64 watt panel is a good starting point. It is an "amourphous" panel which is a lot bigger than a conventional panel, but produces power in overcast and limited light conditions, where a conventional will not. It also produces full power in very hot conditions where conventional panels drop to about 80% efficiency.

By my estimation, based on the research I have done, a 64 watt "amorphous" panel will out perform an 80 watt conventional, and probably match a 100 watt, depending on conditions.

Hope this helps Mate,

Cheers,

Jim.
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Reply By: snailbate - Thursday, Mar 31, 2005 at 20:56

Thursday, Mar 31, 2005 at 20:56
hi Jimbo
you did not mentioned what frige you have
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Follow Up By: Member - Jimbo (VIC) - Thursday, Mar 31, 2005 at 20:58

Thursday, Mar 31, 2005 at 20:58
Waeco CF80
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Reply By: Member- Marc - Thursday, Mar 31, 2005 at 21:21

Thursday, Mar 31, 2005 at 21:21
Jimbo,
I am curious as to where you got your solar panel and the cost?
We are just starting to investigate the use of solar as a back-up to having to drive every second day if stopped somewhere really appealing.

Cheers,
Marc.
AnswerID: 104584

Follow Up By: Member - Jimbo (VIC) - Thursday, Mar 31, 2005 at 22:01

Thursday, Mar 31, 2005 at 22:01
About $700 all up including a good regulator and wiring from Award Caravan Accessories in FTG, Melb.

Cheers,

Jim
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Reply By: snailbate - Thursday, Mar 31, 2005 at 21:22

Thursday, Mar 31, 2005 at 21:22
hi Jimbo
This fridge will take a lot of power if you do not travel every day you may find that the fridge will not operate on one battery if you have a dual battery this fridge will flatten the second battery after two days and you have warm beer
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Follow Up By: Member - Jimbo (VIC) - Thursday, Mar 31, 2005 at 22:04

Thursday, Mar 31, 2005 at 22:04
Mate,

I have a second battery and this fridge will flatten it in just over a day if I don't keep charge up to it, that is why I have gone the solar route.

Cheers,

Jim.
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Reply By: Member - Brian (WA) - Thursday, Mar 31, 2005 at 21:25

Thursday, Mar 31, 2005 at 21:25
Hi Jim. I went away for easter and did my own tests. They did not come out as I
hoped they would. Its thread 21565. We did not have good conditions the
opposite. I did not rely on any driving to top the deep-cycle up just solor. Its
made think a little differantly now. Brian
AnswerID: 104586

Reply By: Grungle - Friday, Apr 01, 2005 at 08:37

Friday, Apr 01, 2005 at 08:37
Hi Jimbo, Do you know what current your panel was producing? I am trying to find out and publish actual current producing figures for given panel sizes.

I also did a comprehensive test over Easter and if interested can be seen as a reply in post 21602

Regards
David
AnswerID: 104632

Follow Up By: Member - Jimbo (VIC) - Friday, Apr 01, 2005 at 09:32

Friday, Apr 01, 2005 at 09:32
David,

I do not have an ammeter fitted so can't say exactly. Al has 2 x 42 watt Uni solars and has a great regulator that gives readouts of volts, amps etc. His setup produces 7 amps in full sun, so I assume mine puts out about 5.3 (being 76% of the size). Uni's being amorphous panels perform at about 10-15% above their rated capacity for the first 8 weeks of use, so I expect that to drop to a worst of 4.5 amps over the next year or two as I eat into the eight weeks. That would be about right for my panel; 4.5 amps x 14 volts = 63 watts.

It is interesting to note that Ken Robinson can only get a max of 6.5 amps out of his Suntech panel. This is not unexpected as Kyocera (similar style to Suntech) print on the back of their panels that they lose efficiency over 25C (about 20% from memory).

It is clear to me that Amorphous panels are more efficient. They also produce power in semi shade and overcast condtions. However, having said that they are much bigger for a given output and cost more. My belief is that a 64 watt amorphous will produce an overall daily output somewhere between an 80 and 100 watt conventional panel, but I don't have any scientific facts to support this, just anecdotal evidence.

Cheers,

Jim.
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Reply By: TheUndertaker - Friday, Apr 01, 2005 at 17:55

Friday, Apr 01, 2005 at 17:55
Thanks for the real usage info Jimbo, going to start the local pricing for 2x same panels that your using with regulator to match [ will keep me solar flush yet bank balance down a wee tad].
AnswerID: 104700

Follow Up By: Member - Jimbo (VIC) - Saturday, Apr 02, 2005 at 08:47

Saturday, Apr 02, 2005 at 08:47
U/T,

For a guide, I paid $545 for the U/S 64, $115 for a 10 amp Morningstar regulator and 10 metres of 8mm cable at $2/metre.

1. Make sure you get the cable as thick as you can get to reduce voltage drop.
2. I would recommend 20 metres of cable as 10 isn't long enough in all circumstances to get the panel in the right spot.
3. Do you really need 2 panels to start with? I suggest start with one and see how you go, you can always add another. Just my thoughts.
4. Avoid cheap regulators. I started with a $30 job that was allowing power to drain back from the battery into the panel.

Let us know how you go.

Good Luck,

Jim.

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