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Old 15-04-2013, 04:09   #1
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What Size Solar Panels And Batteries

I'm not very good with the amp hour battery calculations so what i have is i want to run a refrigerator that draws about 6 amps at 120v. I don't have 120v but i"ll buy batteries and set them up for 24vdc. I'll buy a inverter so that's taking care of. I want to run it ,and only it, with solar panels. So if i'm right that would be 750watts at 24v which would be around 30amps DC. Of course it won't run all the time, so my question is where do I begin to size the solar panels and batteries. Of course money is always the problem ,so the least I can get away with the better. I move around alot so where I'm at as far as location would be hard. Help I'm lost. I'm fairly good with electricity but have never delt with sizing solar panels. I have no other way of charging said batteries.
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Old 15-04-2013, 04:39   #2
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Re: What Size Solar Panels And Batteries

From were you want to end up I wouldn't start were you are now. I would ditch the domestic fridge and replace it with a 12 or 24v boat fridge and/or freezer. To change the voltage from 24v to 120v just to run the fridge isn't efficient.

A rough calculation suggests for a 12v system a 1/3rd of the wattage is the daily amp hours produced by solar panels. So 300w of solar will give you 100 AH.

However, you need to calculate all the electrical loads not just the fridge to work out how big a solar array you need because the little things add up. It would be a shame to put together a system that is just too small as you have gathered by asking the questions above.

Worth spending a while going back through the electrical threads about solar, there is a wealth of information in there.

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Old 15-04-2013, 04:42   #3
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Your boat is not big enough for amount of solar panels. Why are you trying to run an AC fridge with a inverter, the current draw is 10 times higher under inverter..?.
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Old 15-04-2013, 04:42   #4
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Re: What Size Solar Panels And Batteries

You need to get some idea of the duty cycle of the compressor to work out the total AHr draw.
A clamp on ammeter will show you the actual draw and easy to observe the duty cycle.
An alternative is one of the household consumption meters.


Often it is cheaper to get a smaller more efficient fridge than the large solar and battery array to run a larger fridge.
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Old 15-04-2013, 05:35   #5
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Quote:
Originally Posted by noelex 77
You need to get some idea of the duty cycle of the compressor to work out the total AHr draw.
A clamp on ammeter will show you the actual draw and easy to observe the duty cycle.
An alternative is one of the household consumption meters.

Often it is cheaper to get a smaller more efficient fridge than the large solar and battery array to run a larger fridge.
Our 2nd fridge was inefficient cheap POS, but works very well. One day, if the main marine efficient fridge / freezer shits itself, I will replace it with a small domestic fridge and an inverter. Even if it only lasts a few years, that is ok. Still worth it.

I think 44cruisincat does the same. It makes sense to us. But, of course, YMMV, because there is less sun where you cruise, the marine fridges really are 7X better than domestic fridges, etc.
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Old 15-04-2013, 06:05   #6
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Re: What Size Solar Panels And Batteries

Quote:
Originally Posted by Jimbo485 View Post
I will replace it with a small domestic fridge and an inverter. Even if it only lasts a few years, that is ok. Still worth it.
.
These days there is some competion to the traditional marine fridge.

Some very efficient domestic models have started to appear with good insulation, even vacuum panels. Because they are domestic not marine the prices are reasonable. It is hard to know the real world efficiency on board a hot boat, but some are close,or possible better, than a typical marine fridge.

Many people balk at the idea of anything running from an inverter, but the modest loss of perhaps 15% can easily potentially be made up with more efficient insulation and compressor design.

The other attractive option are 12v car fridges. Some units are very efficient and can be converted from fridge to freezer.
Two car units would give redundancy and for normal operation one could be used as a fridge and one a freezer.

One big advantage of both of the above options is when they break down they can be thrown away and easily replaced with a new unit. Two smaller units are not prohibitory expensive.
A lot of cruising boats sit in out of the way places waiting for someone to repair their fridge.

A traditional marine fridge is still the best option in many cases, but give some thought if these alternatives may be more suitable.
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Old 15-04-2013, 06:08   #7
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Yep!!!
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