Newbie Looking for Advise.

[Florida Sun]

Hi everyone,
I am new to this whole solar power community. I am looking to build a small system of 3kw or there abouts. I will be using San Tan 250w panels, I will be ordering 16 of them to do a ground mount system and a additional 4 for reserve. I was thinking of wiring them in 3 strings of 4 per string, open voltage of 150.4w per string. Hear are the specs on them....

Features:​

• 60 cell, polycrystalline
• Weather resistant. Certified for salt mist and ammonia resistance
• Anti-Reflection surface treatment
• IP65 Junction Box w/MC4 Compatible Connectors
• Frame: Anodized aluminum alloy (Black or Silver)

Specifications:​

• Rated Power: 250W
• Open circuit voltage (VOC): 37.6 V
• Max power voltage (VMP): 30.3 V
• Short circuit current (ISC): 8.85 A
• Max power current: 8.27 A
• Power Tolerance 0/+3%
• Maximum system voltage: 600V (UL)
• Fuse Rating: 15 A
• Weight: 41 lbs.
• Dimensions:64.95 × 39.05 × 1.37 in

I would like to have the system grid tied with Battery backup. I would like to go with a 48v system. So my big question is what system components would work with these panels? I am looking at doing DIY battery packs of 18650 battery's. Any thoughts on using 18650 battery packs in 48v configuration?
Thanks and looking forward on hearing your thoughts.
Sean

 

[MisterSandals]

I am looking at doing DIY battery packs of 18650 battery's. Any thoughts on using 18650 battery packs in 48v configuration?

My first thought was that you must REALLY love spot welding!

Seriously, what is the reasoning behind using 18650's rather than LiFePO4 cells? Availability? Cost?

 

[Northernchateau]

As best said by Jonny 5, more input.
It's hard for anyone to suggest anything without more information.
You said battery back up but not how long they need to last or how much power you will be drawing off them.
The better the info the less money you will spend buying the wrong stuff...

 

[Short_Shot]

Yeah not to push anything on you, but the large lithium iron cells most of us use here will probably be easier, possibly cheaper depending on your sources, and will definitely be safer.

Also don't forget to include the temperature coefficient when figuring max open circuit voltage. You should plan for a bit cooler than whatever the record low is just to be on the safe side to be sure you won't over volt your controller because nature is acting up.

 

[Florida Sun]

Hi everyone,
I am new to this whole solar power community. I am looking to build a small system of 3kw or there abouts. I will be using San Tan 250w panels, I will be ordering 16 of them to do a ground mount system and a additional 4 for reserve. I was thinking of wiring them in 3 strings of 4 per string, open voltage of 150.4w per string. Hear are the specs on them....

Features:​

• 60 cell, polycrystalline
• Weather resistant. Certified for salt mist and ammonia resistance
• Anti-Reflection surface treatment
• IP65 Junction Box w/MC4 Compatible Connectors
• Frame: Anodized aluminum alloy (Black or Silver)

Specifications:​

• Rated Power: 250W
• Open circuit voltage (VOC): 37.6 V
• Max power voltage (VMP): 30.3 V
• Short circuit current (ISC): 8.85 A
• Max power current: 8.27 A
• Power Tolerance 0/+3%
• Maximum system voltage: 600V (UL)
• Fuse Rating: 15 A
• Weight: 41 lbs.
• Dimensions:64.95 × 39.05 × 1.37 in

I would like to have the system grid tied with Battery backup. I would like to go with a 48v system. So my big question is what system components would work with these panels? I am looking at doing DIY battery packs of 18650 battery's. Any thoughts on using 18650 battery packs in 48v configuration?
Thanks and looking forward on hearing your thoughts.
Sean

Yeah not to push anything on you, but the large lithium iron cells most of us use here will probably be easier, possibly cheaper depending on your sources, and will definitely be safer.

Also don't forget to include the temperature coefficient when figuring max open circuit voltage. You should plan for a bit cooler than whatever the record low is just to be on the safe side to be sure you won't over volt your controller because nature is acting up.

My first thought was that you must REALLY love spot welding!

Seriously, what is the reasoning behind using 18650's rather than LiFePO4 cells? Availability? Cost?

As best said by Jonny 5, more input.
It's hard for anyone to suggest anything without more information.
You said battery back up but not how long they need to last or how much power you will be drawing off them.
The better the info the less money you will spend buying the wrong stuff...

Thanks for the feedback. I have decided to go with these battery's to save time. What do you think about them? Want to get 4 cases and set up as a 48v system. That would be about 7.6Kwh.

NEW 4/24 Pack Topband 3.2v 25ah Lifepo4 Prismatic

Here are new 3.2v 25ah prismatic lifepo4 cells. These are Topband cells. These cells came out of overstock, never cycled EV modules and every cell is fully tested to meet the most strict standards. Every cell tested between 24-26ah on a higher 1c discharge rate so they are testing perfect. You...

batteryhookup.com

As far as Temp goes where I live, summer is in the low 90s and winter down to 50s if we get unlucky. I am looking to offset some of my power consumption and have a backup for when a Hurricane comes through. Keep frig, lights and fans on if power goes out.

I know I need 2 BMSs for my batteries and a Inverter. Do I need anything else besides the small stuff like fuses and cut off boxes?

 

[MisterSandals]

Thanks for the feedback. I have decided to go with these battery's to save time. What do you think about them? Want to get 4 cases and set up as a 48v system. That would be about 7.6Kwh.

It sounds like you are looking to purchase items for a problem you have not defined.

Have you done an energy audit to see how much power you use everyday? (size your array for this to capture that amount). How much of that energy you will use outside the peak solar hours? (size your battery bank for this). How many days without sun production you wish to store energy for? (add to the size of your battery for this)

 

[Short_Shot]

Yeah you really need to do some more work figuring this out.

How much capacity do you need for storage? I'm guessing a lot more than 25ah.

There are much, much larger cells available for you to use at a more cost effective price. Can you truly get away with 7.5kwh? Do you need to have 48v for some reason despite the relatively small scale that implies?

If you have 3kw of panels it sounds like you'll have surplus energy going to "waste" with that size battery, but that of course depends on your needs and climate.

 

[Hedges]

Those SanTan panels may be the cheapest per watt, but not the best choice for all applications.

The UL labels have been stripped off, so likely fail permit inspection for grid-tie. Bootleg system on your house also not a good idea, gives insurance company a way out. These panels should be used for non grid connected systems, not mounted on the house.

Other panel brands/models put out 50% more power for the same area. That saves labor and mounting hardware.

Be sure to design PV array series/parallel configuration to match a specific charge controller before buying either.
A key parameter is Voc of a series string, adjusted for cold temperature (multiply label Voc by 1.16 if you don't want to go into greater detail.)

Lithium batteries and LiFePO4 have a number of advantages over lead-acid. For a grid-backup system which might cycle 25 or 200 times in a decade, cycle life isn't one of them. I use AGM, which is simpler to use (assuming SCC has good charge algorithm) and avoids a few issues. On the other hand, DIY LiFePO4 is now less than half the price of AGM. And availability - one forum member bought FLA because the AGM he wanted was 6 or 12 months lead time.

Since your application is grid tie, start with your utility bill and total annual usage. If a decent net-metering rate plan is available you can size for that. This is what I have - oversize grid-tie PV inverters, coupled to battery inverters with AGM battery just enough to get through one night. You will probably want a hybrid inverter instead. AC input, AC output, PV input, battery connection.

If there is a motor load you want to run, like well pump or A/C, look up the "LRA" locked rotor amps, or multiply rated current by 5x, to get starting surge. The inverter needs to be able to deliver that.