Run 5k BTU Window AC on solar during daylight only

[iamrich]

That makes sense. He said he's got 2 grand that he can invest in it for now, so we'll have to figure what he needs to get this done in budget.

$2k is doable, or at least close. You might be able to source some of this stuff cheaper, especially the racking (I used Iron Ridge on the roof).

If you can drive to Santan, 9 panels will run you $450 and net you 2250w (figure 1800w useable), MPP Solar LV2424 (I like the green one) $695, 12v 100ah LiFePo4 battery (x2) $600, which leaves you about $150 wire and combiner box.

Source​	Device​	Cost​	QTY​	Total (incl Shipping)​
Santan Solar​	250w snail trail panel​	$50​	9​	$450​
Ebay or Amazon​	LiFePO4 24v battery pack (12v 100ah x2)​	$300​	2​	$600​
Watts247​	Hybrid LV2424​	$695​	1​	$750​
Amazon​	TEMCo 100' Red and Black 12AWG wire​	$58​	1​	$58​
Amazon​	Crimpers & Connectors​	$25​	1​	$25​
eBay​	Midnight Solar 15A breaker​	$21​	3​	$64​
eBay​	Midnight Solar MNPV6​	$90​	1​	$90​
GexPro​	Racking​	$265​	1​	$265​
​	​	​	​	Total​
​	​	​	​	$2,298​

You can plug grid into this system so the batteries never die, and on a good sunny day you would get AC all day (10am to sunset) and the batteries would probably go another 4 hours before they are depleted, and then the grid would kick back in to continue to power the AC and if desired recharge the batteries (or you could just wait until morning again when there will be a huge surplus of power).

ROI is 19000 hours at $.12 which I think comes out to about 5 years at 10 hours a day. but you are 100% green and it will run without grid as long as the sun is up.

 

[jwh92020]

$2k is doable, or at least close. You might be able to source some of this stuff cheaper, especially the racking (I used Iron Ridge on the roof).

If you can drive to Santan, 9 panels will run you $450 and net you 2250w (figure 1800w useable), MPP Solar LV2424 (I like the green one) $695, 12v 100ah LiFePo4 battery (x2) $600, which leaves you about $150 wire and combiner box.

Source​	Device​	Cost​	QTY​	Total (incl Shipping)​
Santan Solar​	250w snail trail panel​	$50​	9​	$450​
Ebay or Amazon​	LiFePO4 24v battery pack (12v 100ah x2)​	$300​	2​	$600​
Watts247​	Hybrid LV2424​	$695​	1​	$750​
Amazon​	TEMCo 100' Red and Black 12AWG wire​	$58​	1​	$58​
Amazon​	Crimpers & Connectors​	$25​	1​	$25​
eBay​	Midnight Solar 15A breaker​	$21​	3​	$64​
eBay​	Midnight Solar MNPV6​	$90​	1​	$90​
GexPro​	Racking​	$265​	1​	$265​
​	​	​	​	Total​
​	​	​	​	$2,298​

You can plug grid into this system so the batteries never die, and on a good sunny day you would get AC all day (10am to sunset) and the batteries would probably go another 4 hours before they are depleted, and then the grid would kick back in to continue to power the AC and if desired recharge the batteries (or you could just wait until morning again when there will be a huge surplus of power).

ROI is 19000 hours at $.12 which I think comes out to about 5 years at 10 hours a day. but you are 100% green and it will run without grid as long as the sun is up.

Thank you for the list. I'll forward this to him. He'll drive to San Tan Solar as he's just under 4 hrs away. He's a framing carpenter, so his plan is to build a ground mount rack system. The nearest thing tall enough to block a panel (outside of him standing in front of it) is 3 miles away. There is a whole lot of nothing on his propertyto the south. Thank you for all your help.

 

[iamrich]

Always nice to have open land for panels. The Achilles heel right now is the battery. You can get used panels for $.20 a watt, so it is pretty affordable. The charge controllers are holding flat on price because of the current stupidity in the market. It is the batteries that are the killer. The price of LiFePo4 was coming down nicely and there where a lot of second life type opportunities. Now the price is crazy high, especially on anything plug and play, and the market for second life stuff is decimated. With enough open land you can just keep adding panels, but if you have no place to store the power, you have to either get UL certified equipment with permits to back feed the grid, or just acknowledge that you are not going to use all the available power.

I am building a house next year and plan to put at least 10kw of panels on the roof, and will probably expand the 2kw I have on the existing garage. Hopefully I will end up with about 20kw of panels, but I have no idea where I am going to store that power yet.

 

[jwh92020]

I was thinking about this last night. Since the battery(ies) are storage for those "cloud passing by moments", could he not use lead acid batteries as a starting point until his budget & Lifepo align better? I don't know about the Vegas area (I'm in OKC) and I can get quality 2 year old 230 amp hr 6v GC batteries for $30 - $40/ea. I'm sure with all the golf cart dealers in Vegas, he should be able to find something comparable. If he bought 8 batteries, wired in series/parallel to 24v, he'd have 900 amp hrs- 400 usable for $400 or less. Btw - he's not the guy to build his own battery packs

 

[sunshine_eggo]

I was thinking about this last night. Since the battery(ies) are storage for those "cloud passing by moments", could he not use lead acid batteries as a starting point until his budget & Lifepo align better?

Absolutely.

I don't know about the Vegas area (I'm in OKC) and I can get quality 2 year old 230 amp hr 6v GC batteries for $30 - $40/ea. I'm sure with all the golf cart dealers in Vegas, he should be able to find something comparable. If he bought 8 batteries, wired in series/parallel to 24v, he'd have 900 amp hrs- 400 usable for $400 or less. Btw - he's not the guy to build his own battery packs

4S2P battery bank comprised of 6V 200A batteries would only have ~400Ah total. IIRC those are about 200Ah each, and each series string of 4 only gets to count the 200Ah once. You only add Ah when in parallel. Two parallel banks means you have 400Ah total - 200Ah usable. To get 900ah from 8X 6V in 4S2P config for 24V, you'd need to use 450Ah 6V batteries.

Sometimes those GC batteries have a tiny fraction of their rated capacity, and they may have wildly varying capacity. The biggest concern is that all 8 batteries would need to have very similar capacity - hard to get with "second life" batteries that may have been abused in prior service. I bought 12 12V Trojans. 4 were amazing, 4 were 75-90%, 4 were pure garbage - all about the same age. Difference was how they were treated in the golf cart. First group was faithfully charged after every use and floated between uses. The second group was mostly well maintained, but they sat on several occasions, and one was replaced (90%). The last group was owned by an idiot that only charged when the batteries got weak. All % numbers reflect their condition AFTER aggressive equalization to maximize their recovery.

IMHO, 4X Everstart MAXX 29DC "Deep Cycle" Marine batteries @ $400 total with ~100Ah usable and you have a 3 year warranty. As a "buffer" they should be able to run the AC for about 5 hours and still remain above 50%.

 

[jwh92020]

Absolutely.



4S2P battery bank comprised of 6V 200A batteries would only have ~400Ah total. IIRC those are about 200Ah each, and each series string of 4 only gets to count the 200Ah once. You only add Ah when in parallel. Two parallel banks means you have 400Ah total - 200Ah usable. To get 900ah from 8X 6V in 4S2P config for 24V, you'd need to use 450Ah 6V batteries.

Sometimes those GC batteries have a tiny fraction of their rated capacity, and they may have wildly varying capacity. The biggest concern is that all 8 batteries would need to have very similar capacity - hard to get with "second life" batteries that may have been abused in prior service. I bought 12 12V Trojans. 4 were amazing, 4 were 75-90%, 4 were pure garbage - all about the same age. Difference was how they were treated in the golf cart. First group was faithfully charged after every use and floated between uses. The second group was mostly well maintained, but they sat on several occasions, and one was replaced (90%). The last group was owned by an idiot that only charged when the batteries got weak. All % numbers reflect their condition AFTER aggressive equalization to maximize their recovery.

IMHO, 4X Everstart MAXX 29DC "Deep Cycle" Marine batteries @ $400 total with ~100Ah usable and you have a 3 year warranty. As a "buffer" they should be able to run the AC for about 5 hours and still remain above 50%.

Sounds like a good way to go. He's getting excited about this. I hope to be able to go out & help him do the insta.

 

[sunshine_eggo]

Sounds like a good way to go. He's getting excited about this. I hope to be able to go out & help him do the insta.

Walmart MAXX battery supplies have been very inconsistent. Costco sells Interstate 6V GC2 for about the same price. will cost a little more and only have a 1 year warranty, but I would personally still rather spend $400 on a new known than $400 on used unknown, UNLESS I was willing to fully test each individual battery for capacity/health, and that would involve many hours of touch time and some equipment expenses. I probably spend 40 hours testing those 12 Trojans.

 

[iamrich]

I was thinking about this last night. Since the battery(ies) are storage for those "cloud passing by moments", could he not use lead acid batteries as a starting point until his budget & Lifepo align better? I don't know about the Vegas area (I'm in OKC) and I can get quality 2 year old 230 amp hr 6v GC batteries for $30 - $40/ea. I'm sure with all the golf cart dealers in Vegas, he should be able to find something comparable. If he bought 8 batteries, wired in series/parallel to 24v, he'd have 900 amp hrs- 400 usable for $400 or less. Btw - he's not the guy to build his own battery packs

Actually if you are going to use grid assist, the 24v battery is really only needed to turn the AIO on. It could be as little 50ah I think. Just enough power to keep the system running if there is a cloud moment or if the grid is slow to switch over. Additional amp hours will just get you longer runtime in a power outage and let you store more energy before you have to cut over to grid, but the size in this case is not critical (you just have to have something). You could probably get away with a couple of car batteries if you had to.