My Solar Shed Thread

BusLee

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It's been a bit since I posted, my bus build is kind of dragging, but that's another story.

I have a 14' x 24' shed on my property where the bus is located that I intended to use as sleeping quarters while I have the roof off the bus. Well, our place was right in the way of Ida last weekend and took a whollop. Long story short, I need to run a refrigerator, a few 12v LED lights and a 12v composting toilet fan in the shed.

I have each end of the equation; I have (3) 100ah Dakota Lithium batteries and (4) 370w 36v solar panels. I'm torn and looking for opinions, specific product recommendations to fit between the panels and the inverter would be cool too, if something jumps to mind.

Should I do 12v 300ah or 36v 100ah for my set up? I have the ability to set up the panels with a good southern exposure and know the electricity side once it leaves the battery bank, just would like some advice on the panels to the inverter. This is something that I'd usually like to research to death, but I'm kinda in a hurry this time and could use some help brainstorming from much more experienced brains.

Thanks in advance!
 

MisterSandals

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Should I do 12v 300ah or 36v 100ah
36V battery setup is quite odd, you may have trouble finding a good selection of charge controllers and inverters.
If you can get by on 12V for wiring and fusing i strongly recommend that.
If you are needing a bit more than a 2000W inverter, you should strongly consider getting a 4th battery so you could build a 24V (25.6V) system.
 

time2roll

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36v has very limited equipment available. I would stick with 12 volt. Also lithium in series does not balance on its own so it is something more to monitor and maintain. Stick with 2000 watt inverter or less.

I like separate components. As in separate solar controller, separate inverter. Eventually you may look to expanding your battery to have more storage for the 1480w solar.
 

MisterSandals

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370W a 4 = 1480W

With 12.8V battery that is 1480W / 12.8V = 115A max charge rate.

A big victron 150/100 SCC and your panels in 2S2P would be pretty nice.
 

Short_Shot

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370W a 4 = 1480W

With 12.8V battery that is 1480W / 12.8V = 115A max charge rate.

A big victron 150/100 SCC and your panels in 2S2P would be pretty nice.
And in parallel each battery will get 1/3 of that charge current so it won't exceed any ratings.
 

BusLee

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36V battery setup is quite odd, you may have trouble finding a good selection of charge controllers and inverters.
If you can get by on 12V for wiring and fusing i strongly recommend that.
If you are needing a bit more than a 2000W inverter, you should strongly consider getting a 4th battery so you could build a 24V (25.6V) system.

Good to know, I believe we can get by for now with the 12v system. The only thing that's going to be 120v is an apartment fridge and I don't have the funds to drop on a new battery in right now. I do intend to eventually run the bus on a 24v 800ah system, but that's down the road a bit. This is an emergency situation that I need to plug. Budget on this is going to be paramount for the short term, I need something that's going to perform, but I don't think I have Victron money for this exercise either.
 

Mudd

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Good to know, I believe we can get by for now with the 12v system. The only thing that's going to be 120v is an apartment fridge and I don't have the funds to drop on a new battery in right now. I do intend to eventually run the bus on a 24v 800ah system, but that's down the road a bit. This is an emergency situation that I need to plug. Budget on this is going to be paramount for the short term, I need something that's going to perform, but I don't think I have Victron money for this exercise either.
Invest in a victron because it's adjustable voltage. If you decided you wanted to do 36 volts with the three batteries you could. I got one of these 36 volt inverters off Amazon for a project I never finished the project but I am using the same brand inverter in a 24 volt setup seems to work fine.

 

BusLee

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370W a 4 = 1480W

With 12.8V battery that is 1480W / 12.8V = 115A max charge rate.

A big victron 150/100 SCC and your panels in 2S2P would be pretty nice.
I'm a total noob when it comes to solar, this will be my first system, and would just like to confirm my calculations. In a 2S2P configuration I'd be theoretically making 740w/72v/20.5a?
 

MisterSandals

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The key is that your Voc x2 remains below the SCCs max input voltage with about 15% leeway for temp induced voltage increases.
 

BusLee

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The key is that your Voc x2 remains below the SCCs max input voltage with about 15% leeway for temp induced voltage increases.
So I need to look for something that will handle 1480w/72v/20.5a for a 2S2P set up?

Do you guys think I would be better off dropping down and using only (2) of the solar panels to reduce the wattage? Am I over powered for a 300ah set up?
 

MisterSandals

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So I need to look for something that will handle 1480w/72v/20.5a for a 2S2P set up?

Do you guys think I would be better off dropping down and using only (2) of the solar panels to reduce the wattage? Am I over powered for a 300ah set up?
Did you decide on your battery voltage? 36V vs 12V?

1480W / 42V charging = 35A max charging
1480W / 14V charging = 115A max charging amps

You can throttle your charging amps with most SCCs. Having more array is almost never a problem. In fact it will start producing earlier, produce more when cloudy and produce later. You could also put 2 in series facing east-ish and 2 in series facing west-ish and charge all day long at lower amps (this works really well... solar tracking with more panels!).

Lets step back a bit and look at the big picture. How much power do you want and need? How much will need to come from your batteries (outside solar charging hours, which can be maximized with a split array)?

I do not see a case someone would make to use just 2 panels instead of 4 unless there were space and weight considerations.
 

BusLee

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Did you decide on your battery voltage? 36V vs 12V?

1480W / 42V charging = 35A max charging
1480W / 14V charging = 115A max charging amps

You can throttle your charging amps with most SCCs. Having more array is almost never a problem. In fact it will start producing earlier, produce more when cloudy and produce later. You could also put 2 in series facing east-ish and 2 in series facing west-ish and charge all day long at lower amps (this works really well... solar tracking with more panels!).

Lets step back a bit and look at the big picture. How much power do you want and need? How much will need to come from your batteries (outside solar charging hours, which can be maximized with a split array)?

I do not see a case someone would make to use just 2 panels instead of 4 unless there were space and weight considerations.
I like the eastish westish idea, I think I can pull that off where it's going to be located.

I plugged everything into the energy calculation spreadsheet and this is what it came up with. Most of this load will be in the evening and night with the exception of the refrigerator and composting toilet fan.

1631576909961.png

1631576851998.png
 

BusLee

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OK, I went back to Will's book and realized I was calculating everything wrong. My numbers will be more like 1480w/72v/123.3a...I think that's right.

So for a 12 volt system I'm going to need an SCC that can handle at least 120a as long as it has over-paneling protection, correct? That cost in conjunction with the cost of the larger wiring is making me reconsider the 36v option. I mean, that puts me at 41.1a charge rate, if my math is correct. I believe that also means my wiring can be approximately 1/3 the size as well. Since budget is a big consideration, I'm thinking I may need to look around and build the odd ball 36v system. Am I at least looking at the numbers correctly now?
 

MisterSandals

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So for a 12 volt system I'm going to need an SCC that can handle at least 120a
Yes and no. Your panels can produce enough power to your SCC to allow it to charge to (1480W/14V=106A) but its not like it "has to handle 106A". You could use a 30A SCC with your big array but its capability is only 30A charging. How many amps can your batteries handle? If you split you array east/west, how many panels will be powering the SCC ((1480W/14V) / 2 = 53A). So if you split your array east/west, you could get by with a 60A SCC and not leave any power unused.
 

BusLee

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Ok, so we've sort of switched gears. The immediate crisis has been solved a different way and we're back to building the system we're going to use for the bus, into the shed until we get the bus finished. The immediate differences being we're using (4) solar panels instead of (6) that are planned for the bus and (2) 100ah Dakotas in 24v configuration to start, so....

This is the general idea for the bus, 24v system, (6) of the 370w 36v panels and eventually want to have 800ah of lithium battery storage. We still want to move forward fairly quickly, so the 4th battery and the rest of the components will be collected as soon as possible and as budget allows. I believe I can migrate the system to the bus in a (4) battery configuration, then expand the battery bank from there, in pairs. If money/availability allows, I may keep the Dakotas in the shed and do the bus with (4) of the 200ah SOK batteries, but only time and budget are going to tell that story.

Thanks for all the help so far, you guys are an amazing source of information and great at teaching a noob the basic principles of solar. I'm going to slow down a bit, get really serious about the research and keep you guys posted on my thought process over the course of the next few weeks. Since I'm building it into my shed, I guess this is the right place to keep the thread, moderator, please let me know otherwise.
 

BusLee

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This will be 8x 12V 100Ah batteries to make 24V 800Ah.

4x of these (12V?) 200Ah batteries will make 400Ah at 24V. (not your stated goal of 800Ah)
Wait, I don't understand. What's the difference in (4) 12v 100ah batteries in parallel and (2) 12v 200ah batteries in parallel then put in series with the equivalent to make a 24v storage bank? If anything I would think they'd both be 400ah at 24v. Why wouldn't the output of each match if the overall storage is the same? I admit I've never assembled a battery bank of more than a single battery used in this fashion, but I have used lots of RC lithium cells, in different configurations and I don't remember it working that way. What am I missing?
 

MisterSandals

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If anything I would think they'd both be 400ah at 24v.
No both are 200Ah at 24V. Amp hours is voltage dependent. If you really want to work in proper units use watt hours.

4x 12.8V x 100Ah = 5120Wh
2x 12.8V x 200Ah = 5120Ah

5120Ah / 25.6V = 200Ah

When you serialize like cells/batteries you sum the voltage, the amp hours stay the same. When you parallelize like cells/batteries the amp hours are summed and the volts remain the same.

Dissimilar cells/batteries is a little more complicated.
 
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