Are these panels worth buying?

[Vertex Ranch]

There is a local company that has several hundred of these panels. I'd like to set up a new system (the one I have currently is just a backup system for a Decoupled Aquaponics system to sustain the air supply to the fish tank should the electricity go out).

These panels are VERY high output, check the label I've attached.

So, the question is.. would you Solar Gurus/Pros buy used commercial panels? They WILL let me test them before I buy and if they fail after I install them they'll swap them out.

They're asking $180 per panel. IF the panels prove to be of good quality, this would be a great way for us to build a large system affordably.

My NEXT question is, what controller would you recommend for a medium-sized 4kW system?

Is there any value in setting up TWO 2kW systems, one for primary loads (fridge, fans, lights, fridge, etc.) and another for secondary systems (outdoor lights, modem/router. etc) over ONE 4kW system?

I appreciate all the education and advice you're willing to offer.. I'm learning quickly about solar systems and how to setup them up, but I know I have A LOT to learn when it comes to designing them and selecting components.

Thanks in advance and great work setting up a thriving, informative community.

Jesse

 

[snoobler]

Welcome to the forum.

Purchasing used panels from SanTan solar is a common occurrence on this forum.

If they offer a warranty, and you can confirm Voc and Isc on the panel, absolutely.

$180/panel is on the high side. SanTan sells 240W for $45. They sell brand new Trina 400W panels for $200.

Your SCC needs depend on your battery voltage, e.g.,

4000W/24V = 167A - you'd need enough SCC to provide a total of 167A of battery charging.
4000W/48V = 83A

In both of the above examples, you can shave off the last bit and go with 160A and 80A, respectively.

The only advantage to two systems is redundancy.

You need to determine your available solar via link #5 in my signature.

You need to conduct an energy audit via link #1 in my signature.

With the above two complete, you can confidently design a functional system.

 

[Vertex Ranch]

Welcome to the forum.

Purchasing used panels from SanTan solar is a common occurrence on this forum.

If they offer a warranty, and you can confirm Voc and Isc on the panel, absolutely.

$180/panel is on the high side. SanTan sells 240W for $45. They sell brand new Trina 400W panels for $200.

Your SCC needs depend on your battery voltage, e.g.,

4000W/24V = 167A - you'd need enough SCC to provide a total of 167A of battery charging.
4000W/48V = 83A

In both of the above examples, you can shave off the last bit and go with 160A and 80A, respectively.

The only advantage to two systems is redundancy.

You need to determine your available solar via link #5 in my signature.

You need to conduct an energy audit via link #1 in my signature.

With the above two complete, you can confidently design a functional system.

Thank you for the quick response!

I'd like to run the new system at 48v, though I've heard that it can be more dangerous (eg not as safe to handle as 12v, 24v systems). I'm ok with that, and will just handle the system as I do 120v and 240v circuits we install.

I've done the math on what we use now, in our current home. BUT, we're still designing the new house, which will have a significant passive solar benefit over our current home - essentially an Earthship home built with AirCrete in place of the tires, but still utilizing the south-facing glazing for the 'greenhouse' and a berm against the North facing walls (which will also house our tanks, catchment system and geo-cooling pipes). So, the electrical demand for this new home, which eliminates all of the electric heat and cooking sources of our current home, and only carries over very efficient appliances, will be much much lower. Still working out exactly what it will be though....

A 4kW system would suffice 90%+ of our current home.. so, in our new home, it would be more than sufficient. Given we can place the solar panels at any angle, facing any direction we need to.. we can also optimize it so that winter production is close to summer PV production. Our area provides between ~4 and 5 kWh/m2/day through the year. So, if I use the lower number to design the system... we'll be good all year round. And, we'll have a generator as a backup should anything fail. We're considering a grid-tied system so that we can produce more than we use and feed that back into the Grid.. but, the cost to reach our new home might prove to soak up any financial gains that would provide so the system will most likely be off grid.

 

[snoobler]

What is your actual kWh usage?

 

[Vertex Ranch]

What is your actual kWh usage?

From what we're calculating, we'll be somewhere between 7,000 and 9,000 kWh / day depending on some appliance selections
The calculator suggested a 2.63 kWh system. A 4kWh system would give us surplus, and with a properly sized battery bank we could maintain usage with little to no sun for a couple of days, and recover quickly when the sun comes out.

 

[Vertex Ranch]

The calculators are showing we'd be set with:

4kWh solar panel array
262.5 amp hours at 48 volts (which we'd likely go with four 100ah 12v batteries to achieve the 48v)
So, I need to learn more about Solar Charge Controllers and inverters,.. whether we can run one large SCC or if 2 or 3 smaller ones would be possible/better/more affordable.

 

[snoobler]

Sounds good, except...

4X 100ah 12V in series is only 100ah, so you'd want 12 of those batteries 4S3P. Lead acid would require 100% more storage. LFP would require 25% more storage.

The price difference between 1 big, 2 small or 3 smaller is negligible. Having essentially started a test 24V system, I already have a "backup" 24V 2kW inverter, 5kW of batteries and a 60A SCC, so I only have a single primary SCC - a big $1000 Victron 250/100 for my 3kW (current) and eventual (6kW) array. I do have dual inverters, but they'll be working in parallel 120/240VAC split phase, so that's not really redundancy.

Its really a matter of preference. Most have only one. My neighbor has spent the last 25 years on the same single inverter and charge controller. He's on his 3rd set of lead-acid batteries.

 

[Hedges]

The calculators are showing we'd be set with:

4kWh solar panel array
262.5 amp hours at 48 volts (which we'd likely go with four 100ah 12v batteries to achieve the 48v)
So, I need to learn more about Solar Charge Controllers and inverters,.. whether we can run one large SCC or if 2 or 3 smaller ones would be possible/better/more affordable.

4 kW of PV! That might cost $800; think you can afford it?
263 Ah at 48V, on the other hand ... I paid $5000 for 8x 6V 405 Ah AGM. I hate spending money on expendables.

By placing your panels at a couple different time-of-day orientations, you can flatten production for less cycling of the battery.
Maybe your 9 kWh/day would be 3 kWh/night? In which case a battery like mine would only cycle 15% DoD, except for cloudy days.
Given difference in cost of panels vs. batteries, I'm inclined to over-panel so even partially cloudy days produce enough.

Its really a matter of preference. Most have only one. My neighbor has spent the last 25 years on the same single inverter and charge controller. He's on his 3rd set of lead-acid batteries.

So in his case, lead-acid has been a good fit. How many Wh? How many times daily consumption?

 

[snoobler]

So in his case, lead-acid has been a good fit. How many Wh? How many times daily consumption?

Yep.

24kWh total. Typical daily, 6-7; 9-11 when grandkids visit.

Heat is either wood burning stove or propane. Climate and his insulation mean no A/C for 25 years.

 

[Vertex Ranch]

What would be the most affordable way to build a 400ah battery bank (type and config)? Would you recommend Lead Acid, LeF, LiPo ???
I'm ok with buying several forklift batteries,. LOL. Where they came from or what they're used for doesn't matter to me, only that they work for us and they don't cost as much as the house :D

 

[Hedges]

Yep.

24kWh total. Typical daily, 6-7; 9-11 when grandkids visit.

Similar power consumption as OP.
2x the battery size suggested by calculator OP used, 1.25x the size I have.

So good data point for him.

 

[Hedges]

What would be the most affordable way to build a 400ah battery bank (type and config)? Would you recommend Lead Acid, LeF, LiPo ???
I'm ok with buying several forklift batteries,. LOL. Where they came from or what they're used for doesn't matter to me, only that they work for us and they don't cost as much as the house :D

You won't need several forklift batteries. Just one would be very large, more than enough for your needs (give or take size of forklift.)

I've read, "You will kill your first set of batteries", which can be true with lead-acid and (at least DIY) lithium.
Maybe a BMS would protect lithium from all damage other than leaving it disconnected until self-discharged too low.
Lead-acid gets killed by failing to recharge fully (not enough sun) or bad charging parameters, or over-discharging.

Quality FLA gives the longest life of LA, possibly 15 to 20 years for some. There are forklift batteries, also Rolls and other top brands.
I used AGM which costs twice as much and doesn't last as long, but doesn't require care and feeding. OK for my use of occasional power failure.

Here's what I used:

Sun Xtender Solar Batteries - Photovoltaic Battery

The Sun Xtender Battery line consists of specialty lead-acid solar, photovoltaic batteries, and renewable energy storage batteries manufactured by Concorde Battery Corporation.

sunxtender.com

I set up a previous small system with 4x 12V 104 Ah ($1300). Now using 8x 6V 405Ah ($5000), with individual batteries of a weight I can just handle moving on a dolly and lifting into place. Some forklift batteries let you lift out individual 2V cells to move.

Commercially assembled LiFePO4 will cost several times as much as LA, and cycle life is proportionally higher. About the same $$/kWh of lifetime use, give or take brand/chemistry/etc.
DIY LiFePO4 can be same price or cheaper than premium AGM per kWh of capacity, therefore several times cheaper over lifetime. If it lasts as predicted.

Note that to get the value out of LiFePO4, battery needs to be small enough that it typically cycles 70% to 90% on a daily basis. If you size the battery so large as to get by for 3 days without sun, cycle life of lead-acid would have been 7 to 20 years and LiFePO4 doesn't offer an advantage.

For my grid-backup of a conventional house, I sized AGM battery to last a single night. If used daily off-grid, then I'd need to run a generator any day the sun didn't shine.