More Power Scotty!

RogerUnlikely

New Member
Joined
Jun 21, 2022
Messages
12
I am running a DIY 2300w 48v system that includes 12 200 watt panels and 4 100Ah lithium batteries.
During the 12 hours of direct sunlight, the system keeps up and is often over unity for what I am running, but the batteries only last maybe a couple of hours once the panels are shaded.
Opinions on a solution to add more duration…
1. Add another 4 panel array to my combiner box that’s more within evening direct sunlight?
2. Add another (4 battery) battery bank?
3. Both?
4. Other?

Thanks for any comments. I’m new.
 

OffGridInTheCity

Photon Sorcerer
Joined
May 23, 2021
Messages
918
Location
Southern Oregon
I am running a DIY 2300w 48v system that includes 12 200 watt panels and 4 100Ah lithium batteries.
During the 12 hours of direct sunlight, the system keeps up and is often over unity for what I am running, but the batteries only last maybe a couple of hours once the panels are shaded.
Opinions on a solution to add more duration…
1. Add another 4 panel array to my combiner box that’s more within evening direct sunlight?
2. Add another (4 battery) battery bank?
3. Both?
4. Other?

Thanks for any comments. I’m new.
Are you batteries filling up during the daily cycle? - if so, then yes, more battery would be needed to make it thru the night. You might also need more panels but more battery for sure. If you battery is not filling up then you need both more battery and more panels.

Alternately, you could reduce your night-time consumption and extend the battery power.

I'd do an assessment of your consumption. For example, my night-time consumption averages 2000w/hour. In summer that's 8pm to 8am * 2000w = 12 * 2 = 24kwh. So I need a battery that can deliver 24kwh thru the night. From that, I can figure out how much PV I need to charge the batteries to have at least 24kwh extra on a sunny, summer day. (Winter for me is about 25% of the sun I get in spring/summer)

When you say 48v system and 4 x 100ah lithium batteries, I assume you mean 4 in series - so you have 48v @ 100ah. This is about 5.2kwh * 80% (DOD) = 4kwh of useable power. If you're consumption at night is 1,500w/hour then that will last 2.8 hours. To make it 12hrs you'll need 12hrs/2.8hrs = 4.3 more batteries.

Figure out your night-time consumption and then you can do the calculation above for yourself to see what you need battery wise and this will inform what you need PV wise. If you share numbers - I'm sure you can get more exact suggestions on PV.
 

RogerUnlikely

New Member
Joined
Jun 21, 2022
Messages
12
Also, if it matters, this is all going through a 3500w MPPT Hybrid Controller. Everything seems to be working fine. I left everything set to “default” except for the battery type I had to adjust from gel to lithium.
 

Don B. Cilly

Energetic energy padawan
Joined
Aug 24, 2021
Messages
1,117
Location
Mallorca ES
I guess those 4 batteries are in series for 48V. So 100 Ah total. Still, that's 5kWh easy.
A couple of hours? What do you draw off them?
-
 

RogerUnlikely

New Member
Joined
Jun 21, 2022
Messages
12
Are you batteries filling up during the daily cycle? - if so, then yes, more battery would be needed to make it thru the night. You might also need more panels but more battery for sure. If you battery is not filling up then you need both more battery and more panels.

Alternately, you could reduce your night-time consumption and extend the battery power.

I'd do an assessment of your consumption. For example, my night-time consumption averages 2000w/hour. In summer that's 8pm to 8am * 2000w = 12 * 2 = 24kwh. So I need a battery that can deliver 24kwh thru the night. From that, I can figure out how much PV I need to charge the batteries to have at least 24kwh extra on a sunny, summer day. (Winter for me is about 25% of the sun I get in spring/summer)

When you say 48v system and 4 x 100ah lithium batteries, I assume you mean 4 in series - so you have 48v @ 100ah. This is about 5.2kwh * 80% (DOD) = 4kwh of useable power. If you're consumption at night is 1,500w/hour then that will last 2.8 hours. To make it 12hrs you'll need 12hrs/2.8hrs = 4.3 more batteries.

Figure out your night-time consumption and then you can do the calculation above for yourself to see what you need battery wise and this will inform what you need PV wise. If you share numbers - I'm sure you can get more exact suggestions on PV.
You are correct. The batteries are filling up during the day, just trailer off really quickly in the evening once shade hits the panels. Thank you very much for your feedback.
 

time2roll

Photon Sorcerer
Joined
Mar 20, 2021
Messages
3,846
I would build a 48v battery from 16x 280 Ah cells and single BMS. Keep building until normal use runs them down only 50% or less.
Yes may also need more solar if full charge is not recovered most days.
 

Ellcon123

Solar Enthusiast
Joined
Apr 10, 2021
Messages
117
It looks like you have ~1500W load so 5kW of storage will not last long. I think you need to triple your storage capacity. After that your solar may be an issue as you won't charge it daily.
 

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
3,735
Location
USA
A couple of greenhouse fans at 115v and 5.56 amps each. Running wide open in this heat.
115V x 5.56A x 2 fans = 1279W. Run through an inverter that is 1500W from the batteries. If you need to run the fans for 12 hours then that's 12h x 1500W = 18kWh of usable battery capacity needed. If you use 85% of your batteries then that means you need about 21.2kWh of battery capacity. On a 51.2V LiFePO₄ that's about 413Ah.

You currently have 100Ah. Since you probably want a bit of extra capacity for less ideal solar days you want at least an additional 400Ah of 48V battery for a total of 500Ah.

This is basically what @OffGridInTheCity suggested back in post #2.

Of course you will need that much more solar capacity as well. If your solar needs to replace 18kWh of battery capacity from the previous night's fan usage then you will need 18kWh / 5h = 3600W of solar which probably means about 5kW of actual panels. And that's just to recharge the batteries from the nighttime usage. If you also need power to run the fans during the day then you need maybe another 2kW of panels to have enough power to run the fans and recharge the batteries. So that's at least 7kW of panels.

This is getting real expensive just to run two fans.
 

RogerUnlikely

New Member
Joined
Jun 21, 2022
Messages
12
115V x 5.56A x 2 fans = 1279W. Run through an inverter that is 1500W from the batteries. If you need to run the fans for 12 hours then that's 12h x 1500W = 18kWh of usable battery capacity needed. If you use 85% of your batteries then that means you need about 21.2kWh of battery capacity. On a 51.2V LiFePO₄ that's about 413Ah.

You currently have 100Ah. Since you probably want a bit of extra capacity for less ideal solar days you want at least an additional 400Ah of 48V battery for a total of 500Ah.

This is basically what @OffGridInTheCity suggested back in post #2.

Of course you will need that much more solar capacity as well. If your solar needs to replace 18kWh of battery capacity from the previous night's fan usage then you will need 18kWh / 5h = 3600W of solar which probably means about 5kW of actual panels. And that's just to recharge the batteries from the nighttime usage. If you also need power to run the fans during the day then you need maybe another 2kW of panels to have enough power to run the fans and recharge the batteries. So that's at least 7kW of panels.

This is getting real expensive just to run two fans.
You’re not wrong about that last comment for sure. Thanks
 
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