24v Off-grid Diagram

[evilvillain]

I'm working on a design for a small off-grid solar system for a garage and put together the diagram below. I was hoping to get some feedback on whether this is valid or not from a high-level perspective. Thanks!

I

 

[Will Prowse]

That is a little tough to read. Can you post a higher definition photo?

 

[evilvillain]

For some reason it is decreasing the quality when posting inline. File is attached. Hopefully that comes across better!

 

[Will Prowse]

Oh right, the forum attachment setting will reduce the size of the image so they are not huge. I will increase it a tad.

And it looks good from a glance. What batteries are you using? Which inverter/mppt system are you paralleling?

How many amps is going into those mppts? Do you have shading issues? What is max input pv voltage?

For that size array you should probably put them in series. Bump up the voltage to 100-150 minimum

 

[evilvillain]

Oh right, the forum attachment setting will reduce the size of the image so they are not huge. I will increase it a tad.

And it looks good from a glance. What batteries are you using? Which inverter/mppt system are you paralleling?

How many amps is going into those mppts? Do you have shading issues? What is max input pv voltage?

For that size array you should probably put them in series. Bump up the voltage to 100-150 minimum

Thanks, Will! I appreciate your help. Most of the design is from watching your videos

In regards to the inverter/mppt system, I plan on using the following : Inverter / Charger
For batteries I'll either go with Sinopoly or something like : Batteries

No shading issues, I have a large area I can place the array in without any shade.

 

[PHoganDive]

From first looks...
Looks like battery bank should be two 12 volts in series for 24 volts, and 3 parallel strings.
Also your AC and DC wiring is not well defined. Does the generator AC go to both inverters?
The inverter on the right has red and black wires labelled AC out.
Each inverter will draw over 100 amps DC at full load, one 80 amp fuse at the battery isn't gonna cut it.

 

[Will Prowse]

Those 24v pip MPP units can only handle 2000w each. In your diagram each one would be pushing 2400w. The amp rating of MPPT is the output, not the input amps.

So considering that constraint, I would put 6 panels in series, so that it will create 132v, and 1800w for each MPPT.

Edit: just realized that those are 40v EACH panel. I thought how you paralleled them, each one was 12v. So scratch that idea. Put 3x panels in series, then 2 parallel strings. Open circuit voltage of 120v, and 1800w.

 

[evilvillain]

From first looks...
Looks like battery bank should be two 12 volts in series for 24 volts, and 3 parallel strings.
Also your AC and DC wiring is not well defined. Does the generator AC go to both inverters?
The inverter on the right has red and black wires labelled AC out.
Each inverter will draw over 100 amps DC at full load, one 80 amp fuse at the battery isn't gonna cut it.

Thanks for the feedback!

It might not be easy to read but the battery banks are 3 sets of 2 x 12 volts in series in a single parallel string.
Good question on the AC in from the generator. I would think that my current needs only require it going to a single inverter but I'll have to review the docs on the parallel kit.
The AC out isn't too clear but it's actually from the parallel kit bridging the two inverters.
Thanks for the heads up on the amp draw. I'll have to double check the amp DC load from the inverters.

 

[evilvillain]

Those 24v pip MPP units can only handle 2000w each. In your diagram each one would be pushing 2400w. The amp rating of MPPT is the output, not the input amps.

So considering that constraint, I would put 6 panels in series, so that it will create 132v, and 1800w for each MPPT.

Nice catch Will! I read that wrong and will adjust accordingly.

 

[Will Prowse]

From first looks...
Looks like battery bank should be two 12 volts in series for 24 volts, and 3 parallel strings.
Also your AC and DC wiring is not well defined. Does the generator AC go to both inverters?
The inverter on the right has red and black wires labelled AC out.
Each inverter will draw over 100 amps DC at full load, one 80 amp fuse at the battery isn't gonna cut it.

Yeah that fuse needs to be much larger. Especially for surge. I would try a 250 amp fuse. Depending on your loads

Also ensure that the wire size is large enough to handle tripping that fuse.

I edited my last comment. Be sure to check the update

 

[evilvillain]

Yeah that fuse needs to be much larger. Especially for surge. I would try a 250 amp fuse. Depending on your loads

Also ensure that the wire size is large enough to handle tripping that fuse.

I edited my last comment. Be sure to check the update

Thank you both. Great feedback and I'm obviously learning a great deal.

I think I need to do a little more research on the parallel kit and if the connection to the batteries is from the parallel kit or the actual individual unit. If it is the individual unit, I would think I need a 80 amp fuse for each inverter to the battery?

 

[PHoganDive]

Good question on the AC in from the generator. I would think that my current needs only require it going to a single inverter but I'll have to review the docs on the parallel kit.

FYI, Generators use fuel just to run themselves, they are typically most efficient when running at full load. Running it at full load for 4 hours will be more fuel efficient than running it at half load for 8.

 

[ilia.vikhman]

I'm working on a design for a small off-grid solar system for a garage and put together the diagram below. I was hoping to get some feedback on whether this is valid or not from a high-level perspective. Thanks!

IView attachment 215

@evilvillain which program you used to draw this diagram ?
thanks !

 

[evilvillain]

@evilvillain which program you used to draw this diagram ?
thanks !

@ilia.vikhman - I wish I could say it was something more elaborate or purpose specific but I just used Google Drawings off of Google Drive. While a bit tedious, it worked for what I was trying to accomplish.

 

[evilvillain]

Updated diagrams based on feedback and equipment ordered. Note : I'm using two 24V 200Ah BYD batteries that have Anderson connectors which is why i have an inline busbar to wire them in series.

 

[tictag]

Lovely diagram!

Some considerations:

• Check your power losses. You're going to burning through at least 150W (P(loss) = I²R, therefore P(loss) = 17.2² x 0.64mΩ x 40 feet = 75W x 2 Arrays = 150W) just between the panels and the PV Disconnect. I'm guessing 250 - 300W losses in your PV system?
• I generally don't recommend fusing PV arrays, unless they are large. This one falls into that category. You need to protect from 'backfeeding' panels on short-circuit faults.
• Don't forget your PV bonding and earthing. All exposed metal needs to be bonded then earthed via your AC system ground conductor / utility provided earth.
• A 2 x 2,400 inverter would draw 100A +25% from your 48V battery.
  • 4AWG cable is only rated for 120A (according to here), therefore this cable is under-specified for your intended use.
  • That 120A rated cable is being protected by a 250A fuse, which is under-rated for your intended use.
• The potentially irregular cable run distances from your battery disconnect might cause irregular charging/discharging. See this article for more.

Good luck with your system!

 

[tictag]

p.s. You have labelled your battery bank "Battery Bank 24v 400AH | 1 series" but in an abundance of caution this is a typo, right? The batteries as shown are in series, therefore a 48V system? Or is the typo on the battery, should read "12V 200AH"??

 

[evilvillain]

Lovely diagram!

Some considerations:

• Check your power losses. You're going to burning through at least 150W (P(loss) = I²R, therefore P(loss) = 17.2² x 0.64mΩ x 40 feet = 75W x 2 Arrays = 150W) just between the panels and the PV Disconnect. I'm guessing 250 - 300W losses in your PV system?
• I generally don't recommend fusing PV arrays, unless they are large. This one falls into that category. You need to protect from 'backfeeding' panels on short-circuit faults.
• Don't forget your PV bonding and earthing. All exposed metal needs to be bonded then earthed via your AC system ground conductor / utility provided earth.
• A 2 x 2,400 inverter would draw 100A +25% from your 48V battery.
  • 4AWG cable is only rated for 120A (according to here), therefore this cable is under-specified for your intended use.
  • That 120A rated cable is being protected by a 250A fuse, which is under-rated for your intended use.
• The potentially irregular cable run distances from your battery disconnect might cause irregular charging/discharging. See this article for more.

Good luck with your system!

Thanks for the very detailed and well thought-out feedback!

• Yes that certainly was a typo on the battery bank. It should be in parallel, not series, and I'll need to update the pos/neg wiring on that as well. Thanks for pointing that out but the overall capacity is 24V 400Ah.
• The 250A fuses are built into the each of the BYD battery banks. With the batteries in parallel, do you think these fuses would be sufficient?
• The 'MPP Solar' inverters I'm using are only capable of 60A AC and 80A charging each. Perhaps I'll try see if 1AWG or 1/0 will fit, if needed.
• Grounding / Bonding - I need to add that to the PV panels. I have the wire for it, just forgot to add it to the diagram.
• In regards to power losses, I'm not sure how I could reduce this too much. I may be able to put the PV Disconnect in the middle of the array saving about 1/2 the distance.
• Great articles links! I have some more reading to do now

Thanks again for taking the time to provide value feedback. I truly appreciate it!

 

[tictag]

The 250A fuses are built into the each of the BYD battery banks. With the batteries in parallel, do you think these fuses would be sufficient?

Personally, I would ignore all intra-device fuses - they are there to protect the device. You should be fusing the cables that connect the devices.

Grounding / Bonding - I need to add that to the PV panels. I have the wire for it, just forgot to add it to the diagram.

Most people tend to use WEEB-style bonding these days, rather than one contiguous cable. At least consider them.

In regards to power losses, I'm not sure how I could reduce this too much. I may be able to put the PV Disconnect in the middle of the array saving about 1/2 the distance.

No, you just need to up the PV cable size ... or accept the losses, of course.

And you are welcome. Hope it helps.