Just when I think I got it...

[monicaj]

Thank you both very much!

[Mike90250]

Wow 180V Check the specs of the magnum-energy-pt-100-charge-controller and see if it can handle that, or if you need to use a Midnight Classic 200.

[jflorey2]

I don't know why I thought I needed the CC to handle only 150V pv input... It has to handle at least 179.2v...

Two panels in series will give you 70V. Your 48 volt battery will not need more than ~60 volts for equalize charging (2.5VPC.) Then add overhead for losses and panel temp derating and you should be OK with two in series. Max voltage will be around 90 volts, plus some margin for cold morning startup. Since your charge controller is good for 150 volts it won't be an issue. (Even if you are seeing -25C temps in the morning, that will only add around 10-15 volts to your open circuit voltage.)

However you can also do four in series; the MPPT controller will then drop the voltage for you. As you correctly realized above, in that case you will need a significantly higher voltage rating for the MPPT controller. This probably isn't worth doing unless your panels are very far from your charge controller and the wire is getting too expensive.

In general, one 36 cell panel will give you about 18 volts, and that's enough for one 12V battery. The Suntech panel is a 72 cell panel so it will handle two 12V batteries in series (or 4 6V batteries.) Two in series then will handle 4 12V batteries in series.

[monicaj]

And then get a step down converter that will go from 48v to 12v?

So with 48 volts, then would this charge controller be the size I'm looking for? MPPT 12v/24/v/48v, 60Amp, 150V pv input...
https://www.amazon.com/Hxengy-Solar-...rge+controller

I don't know why I thought I needed the CC to handle only 150V pv input... It has to handle at least 179.2v...

This stuff makes my head spin demon style.

[jflorey2]

You just made me feel good (sane). I was actually thinking the 60 amps would be too high but didn't want to risk looking stupid by asking about in case I was off base. The reason I wasn't sure was because I got confused as to why you'd still use the total amount of watts of the panels in the calculation for CC size if the panels were going to be hooked in series (making the array 280 watt 140v).

So that means the wire going between the charge controller and battery can be smaller, 30amp or larger...

Exactly. There are several benefits to going to higher battery voltages.

[monicaj]

Yes. 48V to 12V won't cost any more than 24V to 12V.

That would work but it's overkill. Since you are at twice the voltage you will only need half the current. So (1000 watts / 50 volts) = 20 amps. You can get the Midnite Kid controller (an excellent MPPT controller, 30 amps) for $280.

You just made me feel good (sane). I was actually thinking the 60 amps would be too high but didn't want to risk looking stupid by asking about in case I was off base. The reason I wasn't sure was because I got confused as to why you'd still use the total amount of watts of the panels in the calculation for CC size if the panels were going to be hooked in series (making the array 280 watt 140v).

So that means the wire going between the charge controller and battery can be smaller, 30amp or larger...

I want to thank you guys so much for helping me learn. Going to take the next couple days and review all the information you've given... and also try to study watts, amps, and volts to know what they really are.

[monicaj]

Mike, thanks! I hadn't even thought of using generator run the washer and well pump. That opens up some paths.

[jflorey2]

And then get a step down converter that will go from 48v to 12v?

Yes. 48V to 12V won't cost any more than 24V to 12V.

So with 48 volts, then would this charge controller be the size I'm looking for?

That would work but it's overkill. Since you are at twice the voltage you will only need half the current. So (1000 watts / 50 volts) = 20 amps. You can get the Midnite Kid controller (an excellent MPPT controller, 30 amps) for $280.

[Mike90250]

You are going to need to add a small generator to the mix of things, both to charge batteries in bad weather, and to handle large loads (washer, well pump....)

Unless you get weekly rain, you need to think of a way to keep clean, stored water, from going stagnant.

If you can install a 500 gal tank, you can fill that weekly and use a RV water pump to move it to the faucets

[monicaj]

I hate to be the bearer of bad news. But the cost just to power those 3 loads will be very high. Based on previous estimates the cost for a solar / battery system to safely generate 1 kWh a day is around $3000. You are looking at more than 4 kWh and that does not include lights, fans, computers or any other electronics.

To help you get a better idea of what you are getting into. There is a number of Sticky Posts in our off grid section that helps you understand how to size a battery system and pv solar panel wattage for your loads. IMO trying to run any type of large load is going to cost a lot up front and then every few years you will need to get another set of batteries.

Don't feel bad about being the bearer. I already figured that my wants were much bigger than my means.

The well pump... I've been picturing using a 12v pump with a small system like I did before, but when I did it before, it was with an artisan well and the water was right up there at the surface, the pump didn't have to suck it up from a depth. I had no idea an AC pump would be so much watts. I have to rethink the whole water system. It wouldn't be good to spend a bunch of money for the well to get dug and not have enough solar power to run the pump to bring the water up. Sigh. Maybe use the money I was going to spend to dig a well to make a rain catchment system instead. And have $$ left over

At first I was only focused on trying to crunch the washer and freezer into the system. Thought maybe by unplugging the freezer when I ran the washer, and unplugging it at night, that I could make it work. But I didn't get my hopes up.

Is ok. I'll still be able to do more than I did before.

[monicaj]

Not ideal but workable. A single string would be ideal, but you can't beat the cost on T105 flooded cells (i.e. GC2's, golf cart batteries.) Two strings isn't too bad. One warning - make sure that these batteries start together and stay together.

Question - why not 48 volts? That would let you do one string.

And then get a step down converter that will go from 48v to 12v?

So with 48 volts, then would this charge controller be the size I'm looking for? MPPT 12v/24/v/48v, 60Amp, 150V pv input...
https://www.amazon.com/Hxengy-Solar-...rge+controller

[jflorey2]

So then it would be a total of 8 batteries. 2 sets of 4 batteries hooked in series for 24v, 235 Ah... Then hook the 2 sets to each other in parallel to get 470Ah. Good?

Not ideal but workable. A single string would be ideal, but you can't beat the cost on T105 flooded cells (i.e. GC2's, golf cart batteries.) Two strings isn't too bad. One warning - make sure that these batteries start together and stay together.

Question - why not 48 volts? That would let you do one string.

[monicaj]

Thanks jflorey.

... https://www.batteriesplus.com/produc...ZG4aAnPF8P8HAQ ...

Golf cart batteries, 235Ah, 6v...

So then it would be a total of 8 batteries. 2 sets of 4 batteries hooked in series for 24v, 235 Ah... Then hook the 2 sets to each other in parallel to get 470Ah. Good?

[SunEagle]

I have the sloppy plan of just matching up the battery system to the panel wattage and then seeing what I can and can't do. I haven't the funds to add more panels.

The 3 big things I'd like to run are: washing machine, freezer, and water pump.

I don't have any of those things yet so I don't know the watts, etc.

But just to see if I have a handle on calculating kWh... (not counting surges)

If:

freezer is 200 watts, then 200 x 12 hours usage = 2,400 watt hours
washer is 500 watts, 500 x 1/2 hour usage = 150 watt hours
well pump is 750 watts, 750 x 2 hours = 1,500 watt hours

2,400 + 150 + 1,500 = 4,050 total watt hours. 4,050 / 1,000 = 4.05 kWh

Am I on the right track?

I have to get off here for now, but I was going to try to muddle through calculating how much power my solar system would produce and see if it would meet the needs of all 3 appliances... I think I would have stumbled.

I hate to be the bearer of bad news. But the cost just to power those 3 loads will be very high. Based on previous estimates the cost for a solar / battery system to safely generate 1 kWh a day is around $3000. You are looking at more than 4 kWh and that does not include lights, fans, computers or any other electronics.

To help you get a better idea of what you are getting into. There is a number of Sticky Posts in our off grid section that helps you understand how to size a battery system and pv solar panel wattage for your loads. IMO trying to run any type of large load is going to cost a lot up front and then every few years you will need to get another set of batteries.

[jflorey2]

ok. So, batteries. I guess lead-acid battery is most commonly used, but how about AGM? I read that they take a really long time to charge and so aren't efficient for a solar setup?

AGM's are lead acid; you just can't add water to them.

Flooded batteries are cheaper, last longer and are pretty easy to maintain. And it's harder to kill them by abusing them.

...12v 255ah... I would need to get 4, hook 2 sets in series, then hook them together in parallel for a 510ah, 24v battery system? Should I not go up to 510ah, but go a little lower instead?

Do as many series batteries, and as few parallel batteries, as possible. 6V in your case would probably be the best bet.