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diy solar

Critique my proposed build

rawrr_dinosaurs

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Nov 1, 2020
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First off this build is going into a travel trailer that lives permanently in South Eastern Idaho. My goal is to be able to run the refrigerator all summer so we can leave food etc up there when we are back home for the week. There would also be the occasional use for night time lighting around camp and charging of electronics. This would also be running the trailers 12v system like the heater fan, lights and water pump. I've got a generator for running the AC if needed or the microwave which are both rarely needed.

I haven't had a chance to actually check my refrigerator but it appears based on my research that roughly starting wattage is around 600w and 180w once running

I am looking at buying 4x280ah LiFePO4 cells to make a single 12v system. I assumed this is way more than enough but am curious what the forum thinks.

I would purchase a 750-1000w pure sine wave inverter. Suggestions on brand and size based on my needs are welcome

I need to buy a 4S BMS, and because it has the potential to get very cold something with a reliable low temp cutoff is a must. I was going to order this one from overkill solar but am open to other ideas the forum may have

I already have a Victron 100/20 charge controller so I may also add the temp sensor to that as well as a fail safe

For solar I have 2 x 250W panels in series. I think this should be plenty of power but let me know if I'm wrong.

And lastly have a 120v to 12v power converter I just purchased about 6 months ago to charge my lead acid batteries. I couldn't find any definitive information on if this will work to charge the lithium cells as well. There is a dial on the side to adjust the voltage accordingly, it is also my understanding the BMS would cut off charging if there were to be an over voltage situation. I don't mind buying a lithium specific charger if needed but would rather use the part I already have if at all possible
 
What is the daily kWh use of your fridge?
What is the occasional daily kWh use of all the other items?
What is your available solar?
 
What is the daily kWh use of your fridge?
What is the occasional daily kWh use of all the other items?
What is your available solar?
I haven't run any tests on the refrigerator yet but I've got a Kill A Watt meter up next time I'm there. It will be somewhat different power consumption in 40° vs 90° ambient temp but it'll at least give me a baseline of the running wattage.

We're probably up there once every other weekend so daily usage isn't a huge concern and solar power could be supplemented with a generator if we are particularly power hungry. I assume we will be somewhere around .5kWh-1kWh on the average day when we are there. The main goal for me is to keep the refrigerator running while we are not there though.

Per the above I have 500W of solar panels currently. TBD how much power I can actually extract out of them but I will build an adjustable mount to optimize the panel angle throughout the year.
 
A typical residential fridge takes 1.5-2kWh/day.

A high efficiency compressor type with 10cu-ft of space is about 0.9kWh/day.

"What is your available solar?" referred to available solar energy. Link #5 in my signature for your location, panel orientation and tilt.

Your 100/20 is half the size it needs to be for your full 500W of panel output.
 
This isn't a residential refrigerator, it is a smaller trailer refrigerator around 7 cu-ft, I should be up next week and can crank up the trailer temp and get an idea of my daily draw.

During the months that I'd need it most the low end available solar is around 5.5-6 in spring and fall and a little over 7.3 kWh/m2/day in June.

You're right, at one point I was thinking I would do a 24v system I've got two other charge controllers I can use so we'll run the panels in parallel.
 
I tried leaving a 12V Samlex 1,000W inverter on all the time at our recreational hunt camp. Left it running unattended for 3 weeks. Came back and the thing had a continuous error beep sounding off. Have no idea how long it had stopped working, likely for days. Couldn't get it to work again. Was the only inverter we had at the time, so had no power during that visit. We had a small dorm fridge with some water bottles in it, testing the idea of arriving to an already cold fridge. I can just imagine opening it, if it were full of spoiled food after a few days or weeks.

Some other things to consider: Safety, reliability, redundancy, and probably plan for future growth.

- Luckily the inverter didn't catch fire and burn the place down
- Samlex is known for quality, but I bought it used at a pawn shop. So no guarantees even with equipment with good reputations
- Have a backup alternative, minimize single-points-of-failure. A recent example, the BMS went bad on the battery. The only BMS. I couldn't just run to Walmart and get another one.
- Whatever power usage you estimate, chances are, it's not enough. Or, it won't be enough next year, ha ha.
 
This isn't a residential refrigerator, it is a smaller trailer refrigerator around 7 cu-ft, I should be up next week and can crank up the trailer temp and get an idea of my daily draw.

During the months that I'd need it most the low end available solar is around 5.5-6 in spring and fall and a little over 7.3 kWh/m2/day in June.

You're right, at one point I was thinking I would do a 24v system I've got two other charge controllers I can use so we'll run the panels in parallel.

To confirm, it's an all-electric fridge; it can't run off propane. The startup and run power requirements strongly suggest that.

It's probably safe to assume about 0.65kWh.

The inverter itself will consume 10-15W 24/7, so that's another 0.36.

You need about 1kWh/day to run the fridge.

Assuming about 250W for the paneling, 5.5 solar h/day puts you over that with a decent margin. With the two panels connected, you'll get peak wattage for longer than you would with a single 250W panel, which should push your daily harvest even higher.

Plenty of battery power for a a couple days of no or partial sun.
 
I tried leaving a 12V Samlex 1,000W inverter on all the time at our recreational hunt camp. Left it running unattended for 3 weeks. Came back and the thing had a continuous error beep sounding off. Have no idea how long it had stopped working, likely for days. Couldn't get it to work again. Was the only inverter we had at the time, so had no power during that visit. We had a small dorm fridge with some water bottles in it, testing the idea of arriving to an already cold fridge. I can just imagine opening it, if it were full of spoiled food after a few days or weeks.

Some other things to consider: Safety, reliability, redundancy, and probably plan for future growth.

- Luckily the inverter didn't catch fire and burn the place down
- Samlex is known for quality, but I bought it used at a pawn shop. So no guarantees even with equipment with good reputations
- Have a backup alternative, minimize single-points-of-failure. A recent example, the BMS went bad on the battery. The only BMS. I couldn't just run to Walmart and get another one.
- Whatever power usage you estimate, chances are, it's not enough. Or, it won't be enough next year, ha ha.
We've accidentally left some food in there and it's pretty nasty 2 weeks later for sure!

I know nothing is full proof but some semblance of reliability would be nice. I've started gathering parts and pieces here and there so I should have plenty of time to tinker and fine tune things until I really need it to be functional in the spring.
 
We've accidentally left some food in there and it's pretty nasty 2 weeks later for sure!

I know nothing is full proof but some semblance of reliability would be nice. I've started gathering parts and pieces here and there so I should have plenty of time to tinker and fine tune things until I really need it to be functional in the spring.
It sounds to me as if you are looking at a solution prior to clearly defining your requirements. I think a few people have already said test, test, test before you look at buying anything.

Is it possible you can park your camper in your drive to monitor its power requirements daily over a month long period?

Have you considered how many days autonomy you might need? Remember that in an unattended system, a few inches of snow might not melt off your panels for a week or more, leaving you without power production for that long. You said primarily summer time usage, but I've lived out west and at altitude. I was snowed in on Memorial Day regularly, Labor Day regularly, and once on the 4th of July.

IMHO, you need to do more analysis of your needs and your weather conditions before putting a design into use.
 
The trailer lives up there permanently now, there is no way I'm towing it back just to run some tests, but I'll do some testing this weekend.

The highest draw rates will be when we are up there and I can easily supplement my solar with a generator. I'm still looking for someone to chime in on if my existing power converter will work to charge lithium. It does appear I can change it to fixed voltage mode and dial it in between 13-16.5v

I'm not particularly worried about snow in the summer, if it's really cold enough to snow then the refrigerator requirements will be lower as well. Long periods of cloudy weather are a concern though.

I'll do some testing this weekend and see where that takes me.
 
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