What size solar panel

Pete, it is probably a mute point but I calculate that you would need about 2100w + of solar panels to keep up with that fridge in normal sunlight conditions. Just not an option, but I thought it worth mentioning in case OP was considering 400w of panels.

Agreed. They are a power hungry sucker.

Wondering how you two guys calculate the 2,1OO Watts ?

Maîneÿ . . .

Hi Maîneÿ,

I did say "at a rough calculation" in my post.

My rough calculation to get 400W was:

Fridge draws 18 amps when the 12V is heating - from the dometic site and that is probably best case.

Then the assumptions started:

Fridge duty cycle of 50% = 216 amps per day. This seems resonable given that my chescold could flatten my N70 starting battery to less than 6 volts inside 3 hours. This assumption is also dependant on the 12 V having a themostat - my 50 litre chescold did not on 12V. If this is the case then the figures below are doubled.

So we now need 216 amps from the panels.

Set a peak solar day at say 8 hours, so we need 27 amps per hour - 324 watts.

Allow 75% efficiency from the panels unless you spend all day keeping them right angles to the sun = 432 watts nominal.

Thats where my rough guestimate of 400W came from. And it would be best case.

I have sold my absorbtion fridge and now have a Waeco 50l, 70 AH of gel cells and 160W of panels which all works fine even if I get a few cloudy days or have a shady campsite where I can't get the panles in the sun for the morning or afternoon.

Cheers

Pete

Pete,
Umm, the question was:
"Wondering how you two guys calculate the * 2,1OO * Watts ?

Maîneÿ . . .

Hi Maîneÿ,

My posts do not mention *2,1OO* watts and I qualified my response with the words "at a rough calculation"

You seem to consider yourself an expert on solar. Rather than criticize Boobook and I why not provide some constructive feedback, answer the original question and tell all of us what size solar setup you believe is needed to run a 185 litre Dometic fridge.

I look forward to your solution.

Regards

Pete

I mentioned 2100 watts plus and here are my calculations.

The Fridge uses 18A at 12.8V.
Unlike a compressor type fridge these are 100% duty cycle on 12v mode. So that is 18 Amps times 24 hours or 432 Amp Hours per day!!!!

To generate 432 AH in a day with say 4 hours per day of full sun that is 108Amps per hour you need to charge into the batteries.

108 Amps x 19V =2052 Watts.

How much do you think it would need Mainey? with your calculations too would be good.

Oops

To generate 432 AH in a day with say 4 hours per day of full sun that is 108Amps per hour you need to charge into the batteries.

Should read

To generate 432 AH in a day with say 4 hours per day of full sun that is 108Amphours over the 4 hours you need to charge into the batteries.

Pete, I did not criticise either of you fine gentlemen, my question, yes, it was a question, see the *?* at the end of the sentence, was:
"Wondering how you two guys calculate the 2,1OO Watts ? "

Pete, as Boobook states, a 3 way fridge does not have any 'off' period on 12 Volts, so it is being powered 24/7 by the battery system, sorry but your "rough calculation" of 400 Watts is therefore not relevant at all.

To generate the 432 ah required in a day, with say 7 sun hours, that is 62 Amps per hour over the 7 hours you need to place charge into the batteries.
The Time (7 hours) can be verified on this Australian Bureau of Meteorology map: *Average daily* SUN hours, there is no area in Australia, or even Tassie, that has only 4 Sun hours, as can clearly be seen most of Australia has 8 or 9 sun hours, so 7 hours is realistic.

Using your "19v" my calculations are; 62 Amps x 19 Volts =1,178 Watts, but where in hell do you put all of them panels, and they just run one fridge?

Maîneÿ . . .

Mainey, it may be 7 hours a day over the entire year, but that won't help you much in winter ( unless you have enough batteries to last from summer to winter).

In winter the average daily sunshine looks more like this.

Doh, wrong button.

......Like this Average daily sunshine June

Hell I'm not looking to make points here but the Link I've supplied is for average sun hours *annually* so yes, some months will be higher and some lower, you have used just one month in the middle of winter, however you will see even in that mid winter month more than half of Australia has 7 or in excess of 7 sun hours.
I believe it would be difficult to run a 3 way fridge on solar, even on a generator it would be difficult too, that is why they run them on gas, and also efficiently and by the alternator when actually travelling.

Maîneÿ . . .

Whatever Mainey.

I originally just wanted to point out to the op how impractical it was, but once again the thread turned into a electronics lesson for one individual.

forgot to add that we get about 11 days o a 9kg gas bottle when we run the fridge on gas, plus the hot water system, oven and cooktop. So with 2 full bottles when we get to any location we know we can stay for up to three weeks if we want.

Heather,
* Unisolar * panel is: 64 Watt per Sq Mtr

Sharp ND130T1J is: 130 Watt per Sq Mtr
Sharp is more than *double* the output of the Unisolar panel per Sq mtr.

Both panels are similar physical size but with vastly different power numbers
Sharp is: 149 x 67 = ~1 sq Mtr
Unisolar is: 136 x 74 = ~1 sq Mtr

With 2 x Sharp panels I believe you could stay in one place indefinately
with a 190 Lt Waeco fridge, and you would have also saved money too

Maîneÿ . . .

thanks Mainey,

we had one of the panels fitted as part of the deal at time of van purchase and weren't nearly as knowledgeable about solar and battery setup in those days unfortunately. As soon as we did a two day trip away to test it all we realised that we needed more solar and just had a second one the same as first fitted.

In those days I didnt know about ExplorOz and you - another mistake eh!

I found the website when we were experiencing our problems on our trip to Qld in 2008 and detailed some of our woes in my blog!

Yes it was expensive for us - probably cost us $1600 to change the fridge over to the dometic - but we have been very happy with our current set up. Have travelled in the past 18 months than we have been at home.
Not sure what it would have cost for us to change the solar panels to the sharp ones as we didnt enquire.

Cheers,
Heather