Got an unsolicited 315W panel offer

[12VoltInstalls]

Got contacted from someone near me offering some spare NIB panels.

I don’t wasn’t looking but I am now.

Thoughts on these for a 12V battery system? I would need a 150V SCC and maybe bump to 24V batteries but they seem decent and the price would be low for 1800W of panels. I was going to do something next year after I start building a house but I feel like it would be less expensive to buy now.

 

[Rednecktek]

Here's a GREAT idea! Buy the panels since they're at such a good price, mail them to me, worry about your project later on in the future. ?

Well, I thought it was a great idea!

More importantly, how much are they asking and do they ship pallets?

 

[12VoltInstalls]

I don’t know how many they have

I’m just wondering about the specs- bigger than anything I’ve ever considered to date, and the VOC seems to indicate a “weak” 36V panel. Though the AN40 mppt won’t care with one for sure, I’d need a 150V to 2S them as I’d probably ’poof’ the 100V AN40 on the first bright sunny day over the winter

 

[Rednecktek]

Don't you wish that MPPT manufacturers would do their math to evenly divide by panel voltages? It looks like a 2S would push your AN40 right to the raggedy edge and over, not worth the risk.

Yup, definitely gonna have to send them to me and my 145VoC systems.

 

[Hedges]

1800W is a small amount for a house.
Best to have more of the same type, need to hit good voltage/current range for a string with same spec panels.
Array design should be done for a specific SCC/inverter (I do mix PV strings of different brand but similar string Vmp)
Prices generally have been going down, but not always.
What price were you quoted?

Rather than 100V or 150V limit, I like 600V. Gets expensive for DC SCC, but I use GT PV inverters, AC coupled. Slightly more $$/watt new retail, but for off-grid systems not requiring latest features, old models can work. (Or grandfathered like my grid tie system.) I've paid $0.10/W for string inverters.

 

[12VoltInstalls]

1800W is a small amount for a house.
Best to have more of the same type, need to hit good voltage/current range for a string with same spec panels.

Yup got that. I thought it 6 panels but actually it’s 10 panels for $1200, so 3250W nominal.

Even at 1800W…Even when my two kids hadn’t grown up yet and we had powerco, I’ve historically used very little electricity.

Prices generally have been going down, but not always.
What price were you quoted?

$120/ea for 10 panels. Twelve makes more sense, ten is an annoying number.
But that price feels pretty good.

Rather than 100V or 150V limit, I like 600V. Gets expensive for DC SCC, but I use GT PV inverters, AC coupled. Slightly more $$/watt new retail, but for off-grid systems not requiring latest features, old models can work. (Or grandfathered like my grid tie system.) I've paid $0.10/W for string inverters.

Maybe prices are going down, but will that maintain? Or go up next year?

Plus, I can drive to get them, no $600 to $800 for west-coast-shipping a pallet of used panels to Vermont

 

[Hedges]

It is Voc, Vmp which matters.
With 45.67Voc, 10x in series is good for 600V max controller, 457V plenty of headroom.
But other paralleled strings need to be similar. The PV strings I run are about 504Voc per data sheet.
I have 24x 12V, 12x 24V, 8x 36V panels.

We think PV keeps amazing us with declining prices, but demand, market upsets, and politics can change things.
You can shop for bargains on other components too, especially if they don't have to do UL-1741-SA for grid connection.
I like old heavy SMA battery and PV inverters, of course. But minimum system may be larger than you want if a light user.
Batteries will be the biggest consideration.
$1200 isn't that big of a deal, and would be enough for a modest system. Even if you end up only using 8 or 9 panels to match series/parallel needs of some SCC, not a big deal.

 

[740GLE]

With that high of string voltages, how do you deal with partial shading?

 

[Hedges]

With all the PV watts and many strings, I don't care!

Originally, my system had multiple SWR-2500, each with one string of 24 AstroPower 120W or 9s2p Sharp 165W.
If panels in series get shaded, current goes through bypass diode.
I tested shorting one Sharp panel, and power output only declined about 1/18th, not 2/18ths or 1/2.

Now I have multiple strings paralleled into one MPPT of 5000US or 8000US.
Shading several panels of one string would make it stop producing.
With 12s2p Sharp, I discovered low current on one string, determined 5 panels had varying degrees of degradation. Similar to what shading might do.

How well MPPT finds highest available power peak for a given partially shaded array depends on its algorithm.
A poor algorithm can find a high voltage, low current peak which is much lower power than if bypass diodes were activated by drawing voltage lower.
Some situations of partial shading will make an array with single MPPT produce less than it could with separate MPPT per string.

 

[chrisski]

I was going to do something next year after I start building a house but I feel like it would be less expensive to buy now.

Unless you can use these now, I recommend passing.

I got a great deal on my first solar panel, brand new, unopened for 1/3 the price. What made this terrible, was now I had to get more panels just like the first one when I added on to my system. This involved four more purchases totaling an additional seven panels just like that one. None of the other 7 panels were anywhere near that great first price, and I spent days shopping for them.

I think these you mention will be set up 3S2P with one 150 VDC SCC. If that is as far as your project will go, then purchasing now is fine, but when does a project ever sit for a year without bring changed. This may force you 12 months from now to build your system to these panels.

Especially the bigger panels though like you’re getting, finding a match wattage, voltage and amperage wise to grow beyond 3S2P to 3S4P may be difficult to find matching panels. You can always add another SCC keeping this original, but that can lead to a hodgepodge system that only you can understand.

As much trouble as I said getting more panels were for me, mine was easier because they were 100 watts. So many of those are manufactured, finding like outputs is easy. What made it harder for me was them being portable panes.

 

[12VoltInstalls]

I’m chewing on it.
What I’d do is probably buy a controller that would handle 3S3P or 2S5P or 2S4P and run it parallel with another controller if I determined more W was desired.

I do know a guy here in Vermont that installs gridtie stuff. I should ask him what he could get me ‘spare’ bigboogie panels for.

Reality is I don’t have to do anything which is making this fun.

 

[12VoltInstalls]

10 panels for $1200, so 3250W nominal.

So I’m thinking about this again/still. I need to find out if there’s more or what else he has. 10 panels is a bad number to have; 12 or 15? Much better. Or 21…?

I know I’ll be needing something more robust down the road. One thing that pointed out needs: It’s been cloudy, fog, raining, or dark clouds and raining since Friday mid morning. So like four days + of basically no charge and I’m down to 12.1/12.0 on the controller readout.

If I was running a minisplit or more electric items like circulator pumps (heat), this dark period is like much of November and December here- when you can go for weeks without seeing the sun. More panels during the dark days of the dark months won’t help me, I know; but it WILL eak out more than a lesser system would, and recovery will be faster once the fall fog burns off (few clouds forecast today, but the clear at sunup is now obscured by fog)

I’m hesitant to buy them because a) I’d just be storing them until next year, b) I’m waiting for a closing when 80%+ of my savings will be transferred, and c) I’m going to spend 6-7 grand to rent someplace (I would have rigged stuff up to use the camper overwinter if I’d gotten on that property back in May like I should have)

Plus my income slows greatly over winter and I don’t want to run out of money before May