moving, and adding off grid 24v system- need advice.

[kpreuss77]

im moving in under a month, and want to buy a starter solar panel kit. looking at (2) Rich Solar 800w systems(redundancy). off-grid. North of Detroit, Michigan.

However, my roof faces east and west and I cannot do a ground based array. is it better to face east, west, or split the difference?

My brother and i just started balancing my 8 cell LiFePo4 3.2v for my 24v earlier today.

My goal was to build (2) 24v 6.7kw battery systems being charged by (2) Rich Solar 800w arrays and mppt controllers. keeping a fridge and freezer working plus a few other things for at least a few days without sun or power. I did buy a 24v inverter already and brother got me a 24v BMS months ago.

I read that Will Prowse now recommends 12v or 48v. should I stop building 24v and finish building out to a 48v system?

thats the 2 questions.

direction to face panels?
24v or 48v system?

 

[Rednecktek]

You'll be best off splitting the difference most likely. Now, trees and giant chainsaw carvings shading the panels may well change that, but for the most part you'll start getting power earlier from the east panels, big watts from direct overhead mid-day, and power later from the west panels.

If you read through the thread you'll see a lot of good reasons for going with a 24v system. Now, having said that, have you done your power audit yet? A 24v system kinda tops out about 3Kw so if you're trying to power a jacuzzi under the multi-zone air conditioner with you L33T gaming PC pwning n00bs online and feeding an ice machine, well... yeah... not so much.

If your power audit comes in around 2Kw or so then a 3Kw system still gives you head room to work with. Besides, you've already got the inverter so you might as well use it, right? You can always expand your system later if need be, but there's nothing wrong with rocking a 24v system as long as it can provide for your needs without breaking the battery banks and exploding.

 

[kpreuss77]

original intention is solar powered battery back up for a fridge and chest freezer. they consume a total of 2kw/day. 3 days = 6kw goal plus 10% loss. I was building a second system as redundancy or extra power for lights or a movie for the kids.

I have another future plan for some undeveloped property. Family is looking for 10-20 acres with water on it. Adding a geodesic home getaway fully powered by solar/wind(off-grid). That one would be 48v system.

 

[JWLV]

That's a huge battery for only 800 watts of solar panels.

As for mounting panels east or west, I would estimate when you are more likely to use more electricity. For me personally living in a hot climate with lots of sun, my heaviest usage is typically from late morning/noon through the evening/night. In my situation, I would mount my panels facing west. That is because I would want my batteries to be near fully charged before the sun goes down. If I had the panels facing east, with heavy usage during the day, my batteries would not be fully charged at the end of the day. I hope that makes sense.

 

[kpreuss77]

direction theory helps alot. thank you.

the kits and batteries are for backup purposes not a primary source of power. I cannot see going without power for more than 5 days. i also have an emergency generator, 2400w.

after we get settled into the new place, we will start looking for property. Maybe more southern in Ohio. That will be a balanced off grid system .

is there an issue with not having enough solar cells to charge backup batteries? could it degrade the batteries? 2kw per day max useage.

 

[rmaddy]

FYI - you need to use proper units. Your batteries will not be 6.7kw. They will be 6.7kWh. Your cells are 3.2V 260Ah. 8 x 3.2V x 260Ah = 6.7kWh.

Same issue with your power consumption of the fridge and freezer. Let's say they take 80W to run. If you run them for an hour that's 83Wh. If you run them for 24 hours then that is 2000Wh/day or 2kWh/day. In three days you would consume 6kWh.

In both cases the h (hours) is an important part of the units. Leaving off the hours has a different and misleading meaning.

As for 24V vs 48V you need to look at the currents involved. For solar you want to avoid going over about 50A charge current or the charge controllers really start getting expensive. 50A at 24V means no more than 1200W of solar. But 50A at 48V is 2400W of solar possible. Of course you can add additional charge controllers if you need more solar at a given voltage. It also depends on the size of the inverter you need. At 24V you probably want a max of about 3000W. At that you are pushing 150A through the wires. If you need 4000W or more you probably want 48V. Of course 48V can be used at 3000W or even 2000W. Then you can use much smaller wires due to the lower amperage.

Many people will state that for a residential system you should only consider 48V. It gives you a lot more options.

 

[HRTKD]

In a recent thread, there were quite a few forum members that disagreed with Will's removal of the 24 volt system. For your situation, 24 volt is OK. If you were planning to actively power a larger system then 48 volt would be better.

What is the lowest temperature your garage will see? If going below 32° F is possible then you'll need to figure out a way to keep your batteries warm.

 

[kpreuss77]

lucky me. Batteries not going into the garage. Batteries will be behind a panel in the house in our mud area. I have about (h x w x d) (5'x6'x1') to play with and is only about 8 feet from the fridge and 6-8 feet from where the freezer will be in the garage. need to add wiring for both. we Get the keys to our new house in less than 2 weeks.

Again this is my first learning system as a backup to fridges and freezers. I am planning on a duplicate system just to power other electronics.

1st system.
6.7kwh Battery powered by (2) 800w Rich Solar 24v 40a kits facing west. Thats (8) total panels and (2) 40a mppt controllers. Giandel 1200w pure sine( I just double checked because i thought i got the 2000w-wrong) dedicated to the fridge and freezer. 2000wh per day as tested by my kill-o-watt meter nock-off. I will need another inverter when i build the other half since this one is soo small in wattage.

2nd system.
same Rich Solar kit
buy premade batteries this time
buy larger inverter

3rd system- different location.
Summer of 2023 we plan on having a family plot with some geodesic homes and green houses all powered by 48v solar. but we are looking to drive more south into Ohio for that hopefully better sun and weather.