Building your own 13KW Solar with 48V Lifepo4 1120AH battery backup

DThames said:

Trackers only make sense if you have very limited space and specific output requirements. If you can add panels to give you the desired output, that is best. Even mounts that allow 1 axis tilt adjustment are often not worth anything extra. The difference in output between adjustable tilt and fixed is about 2%.

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Jonk8id said:

Hi,
I am researching DIY Grid tie solar with battery backup. I live in Connecticut and have called many companies and the sales reps are basically bricks. They push you to start a solar loan program and will give you an undersized system without backup for 60K!!!. My first question is finding reliable panels (400W?) that have a decent PTC/temp rating. What models are affordable and give you the best price per watt? I would like to install panels on my barn roof but the roof needs to be replaced. I have space for some ground mounts. Do cheap/reliable ground trackers exist? or should I just use fixed mounts and purchase additional panels? Ideally I would like backup power for a day, or maybe a day and a half. Looking at building your own battery setup I have read many comments on the size of how many parallel batteries can be used to obatin the desired Amp hours. Can four (4) series 48V batteries ((16) 3.2V Lifopo4 series connected batteries be put in parallel reliably? Do charge controllers/inverters exist that can take separte battery inputs? I would love to go off grid or net zero but the cost is very high!

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Wet1 said:

For the OP being fairly far north (CT), I would disagree that 1 axis tilt adjustment isn't worthwhile. Having the ability to go from say 60 degrees in the winter to say 20 degrees in the summer can make a significant difference given how low in the sky the sun is in northerly locations, especially considering the limited power producing hours in the winter at these locations. This isn't to say more panels can't make up the difference to cover winter needs, but having the ability to tilt them would certainly be of benefit.


First, welcome! Where in CT?

Forget the solar companies, most are a complete ripoff (as you've found). There are tons of panels on the market, most are very good. What you might find is shipping costs can significantly add to the cost of them, so you might want to look for companies in the area which you can pick them up yourself, or even look for used local panels. I know of at least one or two in NY/NJ. I would probably start by shopping by what's available to you, rather than by panel specs and then looking for that panel elsewhere. If shipping cost is not a concern, SunPower, REC/Panasonic, LG (although I think I heard they are exiting the market?), etc are top tier. Many other brands are highly rated as well. IMO, REC might be one of the best values out there for proven and highly rated panels.

Yes, you can run multiple 48V batteries in parallel reliably. The BMS from each bank will control the individual needs. As you'll find, batteries can get expensive compared to the rest of the system so DIY based systems might be a great option for you.

For inverters, you might want to look at the new Sol-Ark 15k. It's a HF inverter, but very flexible in it's usage options for both on and off grid. Not to mention it's an AIO and has a 200A pass-though for easy whole-house backup and easy installation. IMO, their CS/TS is unmatched in the industry as well.

Cheap trackers are nonexistent today IMO. One-axis ground mount tilting can be found for minimal extra money (from at least one company in WI) and I would at least consider going that route being in CT and likely needing all the power you can get in the winter. Otherwise, panels aren't too expensive, so over-paneling isn't a bad idea. Likewise consider multiple directions to cover all day collection (say SSE/SSW), especially if you want to go off grid. Roof mounting is an obvious option, just keep in mind access, especially for clearing snow in your location.

I'm sure others will chime in with more info!

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DThames said:

there is no doubt the statement is true but please provide numbers of a fixed ideal average for the location compared to adjustable tilt. With numbers in hand, one would need to consider the extra costs of a tilt system compared to a fixed system. I don't live that far north but for a house sized system 2 or 3 panels will likely make up the difference between a good average angle and something adjustable.

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Wet1 said:

For the OP being fairly far north (CT), I would disagree that 1 axis tilt adjustment isn't worthwhile. Having the ability to go from say 60 degrees in the winter to say 20 degrees in the summer can make a significant difference given how low in the sky the sun is in northerly locations, especially considering the limited power producing hours in the winter at these locations. This isn't to say more panels can't make up the difference to cover winter needs, but having the ability to tilt them would certainly be of benefit.


First, welcome! Where in CT?

Forget the solar companies, most are a complete ripoff (as you've found). There are tons of panels on the market, most are very good. What you might find is shipping costs can significantly add to the cost of them, so you might want to look for companies in the area which you can pick them up yourself, or even look for used local panels. I know of at least one or two in NY/NJ. I would probably start by shopping by what's available to you, rather than by panel specs and then looking for that panel elsewhere. If shipping cost is not a concern, SunPower, REC/Panasonic, LG (although I think I heard they are exiting the market?), etc are top tier. Many other brands are highly rated as well. IMO, REC might be one of the best values out there for proven and highly rated panels.

Yes, you can run multiple 48V batteries in parallel reliably. The BMS from each bank will control the individual needs. As you'll find, batteries can get expensive compared to the rest of the system so DIY based systems might be a great option for you.

For inverters, you might want to look at the new Sol-Ark 15k. It's a HF inverter, but very flexible in it's usage options for both on and off grid. Not to mention it's an AIO and has a 200A pass-though for easy whole-house backup and easy installation. IMO, their CS/TS is unmatched in the industry as well.

Cheap trackers are nonexistent today IMO. One-axis ground mount tilting can be found for minimal extra money (from at least one company in WI) and I would at least consider going that route being in CT and likely needing all the power you can get in the winter. Otherwise, panels aren't too expensive, so over-paneling isn't a bad idea. Likewise consider multiple directions to cover all day collection (say SSE/SSW), especially if you want to go off grid. Roof mounting is an obvious option, just keep in mind access, especially for clearing snow in your location.

I'm sure others will chime in with more info!

Click to expand...

Jonk8id said:

I am located in Danbury CT

I am located in Danbury. I would like to roof mount on my barn but it is old and needs some work and maintenance would be an issue. It could easily fit a 15K+ system. I have space for ground mounts but the need to be close to the house/barn for utility connections. Trees may block the sun exposure depending on time of year. What is typical solar panel sun exposure on a fixed mount per day?

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PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

Wet1 said:

For a 13k system located in CT at say 25, 40, and 65 degree so you can see the difference (especially in the limited solar winter months.

Month	Solar Radiation ( kWh / m2 / day )	AC Energy ( kWh )
January	3.36	1,108
February	4.17	1,230
March	4.93	1,519
April	5.58	1,653
May	5.73	1,711
June	6.00	1,686
July	6.00	1,715
August	5.83	1,669
September	5.50	1,541
October	4.14	1,263
November	3.31	1,022
December	2.65	877
Annual	4.77	16,994

Location and Station Identification
Requested Location	hartford ct
Weather Data Source	Lat, Lng: 41.77, -72.66 0.7 mi
Latitude	41.77° N
Longitude	72.66° W
DC System Size	13 kW
Module Type	Standard
Array Type	Fixed (open rack)
Array Tilt	25°
Array Azimuth	180°
System Losses	14.08%
Inverter Efficiency	96%
DC to AC Size Ratio	1.2
Capacity Factor	14.9%

Month	Solar Radiation ( kWh / m2 / day )	AC Energy ( kWh )
January	3.88	1,274
February	4.63	1,355
March	5.14	1,575
April	5.49	1,623
May	5.40	1,612
June	5.55	1,563
July	5.61	1,604
August	5.64	1,613
September	5.63	1,571
October	4.49	1,363
November	3.79	1,159
December	3.10	1,021
Annual	4.86	17,333

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Download Results: Monthly | Hourly
* Caution: The PVWatts energy estimate is based on an hourly performance simulation using a typical-year weather file that represents a multi-year historical period for Hartford, CT for a Fixed (open rack) photovoltaic system. The kWh range is based on analysis of a nearby data site described here.

All of these results are based on assumptions described in Help that may not accurately represent technical or economic characteristics of the project you are modeling.

Location and Station Identification
PV System Specifications
Requested Location	hartford ct
Weather Data Source	Lat, Lng: 41.77, -72.66 0.7 mi
Latitude	41.77° N
Longitude	72.66° W
DC System Size	13 kW
Module Type	Standard
Array Type	Fixed (open rack)
Array Tilt	40°
Array Azimuth	180°
System Losses	14.08%
Inverter Efficiency	96%
DC to AC Size Ratio	1.2

Month	Solar Radiation ( kWh / m2 / day )	AC Energy ( kWh )
January	4.24	1,381
February	4.78	1,393
March	4.86	1,490
April	4.70	1,398
May	4.28	1,288
June	4.23	1,203
July	4.36	1,259
August	4.68	1,347
September	5.16	1,443
October	4.50	1,366
November	4.07	1,238
December	3.43	1,122
Annual	4.44	15,928

User Comments

Find A Local Installer

Download Results: Monthly | Hourly
* Caution: The PVWatts energy estimate is based on an hourly performance simulation using a typical-year weather file that represents a multi-year historical period for Hartford, CT for a Fixed (open rack) photovoltaic system. The kWh range is based on analysis of a nearby data site described here.

All of these results are based on assumptions described in Help that may not accurately represent technical or economic characteristics of the project you are modeling.

Location and Station Identification
PV System Specifications
Requested Location	hartford ct
Weather Data Source	Lat, Lng: 41.77, -72.66 0.7 mi
Latitude	41.77° N
Longitude	72.66° W
DC System Size	13 kW
Module Type	Standard
Array Type	Fixed (open rack)
Array Tilt	65°
Array Azimuth	180°
System Losses	14.08%
Inverter Efficiency	96%
DC to AC Size Ratio	1.2

It's not a huge difference as you noted, but with limited solar access in the winter, it does make a difference when you need every little bit you ca get. I think the add-on cost for the GM system I was referring to convert to 1 axis was $800. About the cost of a couple of panels (which also require more racking, wiring, inverter, etc). It's at least worth considering IMO.

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