diy solar

diy solar

12v Solar Fridges and expanding systems

MaineYankee

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So I am building a small cabin(24'x16') on an island in Maine. We will only be using in Summer so should get plenty of sun even though in North. We plan on powering everything using solar, although not very much overall. Except for the fridge. We are looking at a Sunstar 12v or 24v DC 10 cu fridge. The energy consumption guide says between 490-845 watt hours per day. Average draw of 95 watts. Based on what little I have been able to find out, I was thinking of two 6v 225 amp batteries and three 100 watt panels. First question is whether this makes sense.

Second question is that I want to wire the cabin for a few outlets and a few lights to power some LED lights, charge cell phone or tablets, maybe run a toaster or fan occasionally. Not a great amount but do not really plan on putting all this together till next year in all probability. The fridge we want to put in immediately as we really need but the rest of the cabin will not be finished this season. So my question is can I add capacity next year easily and run the DC fridge and AC outlets/lights off of the same system. I ideally do not want different systems.

In watching Will's videos I thought it might make sense to buy the 24V LiFe PO4 Powerwall, and add the MPP 24v solar system either this year or next to run the AC part of the cabin. It seems like the power wall has the capacity to power the fridge and my AC needs but I was not sure if that was possible. Also did not know how to run the wired cabin off the MPP but figured that was doable. Any thoughts and suggestions welcomed. Overwhelmed with information.
 
Also, is it possible to charge batteries using a honda generator/inverter when needed?
 
So my question is can I add capacity next year easily and run the DC fridge and AC outlets/lights off of the same system.
Yes if you make the system big enough and expandable enough.

If you figure out how much power you will require, you should be able to size your system properly.
Regarding 3x 100w panels... is there a reason you are using tiny panels and not big cheap residential panels? Check craigslist, its pretty common to find big panels for $.50/watt. 300w sounds a bit on the low side, especially for Maine with a low sun angle and likelihood of tree shading.
You will ALWAYS find a use for having more power.

If you get a set of batteries this year, you will not be able to add to the bank without them being nearly identical, including size and age (the strong ones will eat the weaker old ones).
 
Ok, that is very helpful. I have not been able to find any of the larger and cheaper panels on craigslist and was simply thinking that the 100w panels will be easy to expand using the same ones. I can definitely continue to look for larger capacity panels. Seems like setting up my battery bank for the end size makes the most sense seeing I cannot add to them.
 
I have not been able to find any of the larger and cheaper panels on craigslist and was simply thinking that the 100w panels will be easy to expand using the same ones.
How far are you willing to drive? I spotted multiple sellers in Massachusetts. Do you have a pickup truck that can be used for transport?
Personally, I would never buy a 12/24V refrigerator. The price premium is just so high. I think the money is better spent investing in a larger AC system that can power a standard 120VAC frig you can get at Home Depot. Even if you got an AC frig that consumes 3X as much power, I think you'll be better off installing a AC oriented solar system producing 5X as much power. The the extra 600-700$ you'd save on a standard frig, you could install kw of extra panels.
I would go with a 24V system utilizing four 6V batteries, and 8-12 60-72cell grid-tie panels. You could build ground mounts for 4-6 panels like I did, then rotate them left-right throughout the day for even more power. Two arrays like this would let you produce ~12kwh per day in summer.
 

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I have not been able to find any of the larger and cheaper panels on craigslist
Have you seen these guys? Sounds like they have odds and ends too; perhaps a couple 250w panels or the likes.

Regarding batteries: I am wondering what is going to happen to your batteries during the winter. Will they be maintained? Will they be left of the island? It would be fairly hard to keep them good without any intervention for a long winter. Maybe starting with a smaller (hate to say it, "disposable") test bank at first?
 
Yes, I saw the ones from South Portland but I was a bit concerned that they company only manufactured 300 of them. I little concerned about quality. I would definitely drive to Mass or NH to get panels and should be able to fit many in my SUV. The ones in Chelmsford look good.

As for batteries, how to maintain them in Winter is a question of mine. Do I leave the system hooked up so it draws power and keeps batteries charged or unhook and leave. Or take them off island to bring home and maintain in my basement. I did this with one battery I had on the island to power a fan in my toilet and light in bathroom. Put is on a trickle charge and all good.

It is one of the reasons I would like to keep the system relatively small and prefer paying extra for a very efficient fridge. Otherwise I do not have much in the way of power needs. Some lights, recharge a few phones, maybe a toaster occasionally. I have not been able to find much info on off grid systems where they are left for six months at a time.
 
As for batteries, how to maintain them in Winter is a question of mine. Do I leave the system hooked up so it draws power and keeps batteries charged or unhook and leave. Or take them off island to bring home and maintain in my basement. I did this with one battery I had on the island to power a fan in my toilet and light in bathroom. Put is on a trickle charge and all good.
Yes, I think wintertime charging will be an important issue for you. In my own case, I leave my system on year round. It does snow, and the panels do get covered, but my winter angle seems to sluff off all of the snow in a day.

Maine snowfalls will be different. I'll assume your panels will get feet of snow on them and be darkened for days at a time? Fully charged lead-acid batteries can handle extreme cold before they get damaged, but the trick here is how will they stay fully charged if covered with snow? What will the wintertime loads be like with no-one there?

Do you have the option to position a string of panels vertically on a south-facing wall under roof protection? Positioned vertically in winter, they should shed all snow, unless drifts blow high enough to reach them. Though vertical is not an optimal angle even on the solstice, they should keep an already charged battery completely full.

Compared to my own system, I'd guestimate you'll need about 1kwh of power per day with most stuff shut off, and I think 500-600W of vertically oriented panels would produce that much per day, assuming the sun is out. This will give the batteries a lifesaving charge until your main arrays shed their snow.
 
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