4 PV Panels in Parallel- Fuse calculation

[Feenalicious]

Hello All,

I have 4 100W solar panels connected in parallel. I'm looking for the formula to determine what size DC fuse or circuit breaker I need between the panels and 40A MPPT charge controller.
Hate to start a new thread because I'm sure this is answered elsewhere...

Feenalicious

[Amy@altE]

Use a Combiner box with breaker for each panel, like Midnite Solar PV6. Short circuit current of panel (Isc) x 1.56. Probably around 6.06Isc x 1.56 = 9.45A, round up to 10A breakers.

[SunEagle]

Use a Combiner box with breaker for each panel, like Midnite Solar PV6. Short circuit current of panel (Isc) x 1.56. Probably around 6.06Isc x 1.56 = 9.45A, round up to 10A breakers.

But the single pair of wires from the combiner box to the CC will need to handle 40A and that wire should be protected by a 40A over current device.

[sensij]

Hello All,

I have 4 100W solar panels connected in parallel. I'm looking for the formula to determine what size DC fuse or circuit breaker I need between the panels and 40A MPPT charge controller.
Hate to start a new thread because I'm sure this is answered elsewhere...

Feenalicious

With an MPPT charge controller, why would you have those four panels in parallel (unless they are oriented different directions)? For most true MPPT controllers, you could probably pair the panels and put the two pairs in parallel, or with the better CC's, go all four in series.

[inetdog]

Hello All,

I have 4 100W solar panels connected in parallel. I'm looking for the formula to determine what size DC fuse or circuit breaker I need between the panels and 40A MPPT charge controller.
Hate to start a new thread because I'm sure this is answered elsewhere...

Feenalicious

One of the parameters on the typical panel label is the maximum series fuse size. When you have three or more panels or strings of panels in parallel, each string must have a fuse no larger than that specified (typically between 1-1/2 and 2 times the rated Isc.)

[Feenalicious]

Parallel or Series-Parallel?

But the single pair of wires from the combiner box to the CC will need to handle 40A and that wire should be protected by a 40A over current device.

Thank you, Amy, for your reply. I'm curious if you have an opinion regarding the reply from Sensij which asks why all four parallel instead of series-parallel or four in series. I am wiring the panels as all four in parallel because I have four 12-volt batteries (parallel) and I assumed 24 volts is not right with these batteries. What do you think?

[Feenalicious]

Parallel or Series-Parallel

With an MPPT charge controller, why would you have those four panels in parallel (unless they are oriented different directions)? For most true MPPT controllers, you could probably pair the panels and put the two pairs in parallel, or with the better CC's, go all four in series.

Thank you, Sensij, for your reply. My controller can handle 12 or 24 volt input but I am wiring the panels as all four in parallel because I have 12-volt batteries (parallel) and a Nature Power 2000W pure sine wave inverter. I know I can wire the batteries series-parallel for 24 volts but I thought the inverter needs 12V DC input. Am I incorrect?

[thastinger]

Thank you, Amy, for your reply. I'm curious if you have an opinion regarding the reply from Sensij which asks why all four parallel instead of series-parallel or four in series. I am wiring the panels as all four in parallel because I have four 12-volt batteries (parallel) and I assumed 24 volts is not right with these batteries. What do you think?

What are you trying to do here? Have you already bought the inverter? Lots of unanswered questions.

Provided you have a good CC, wiring all 4 panels in series would eliminate the need for string breakers and reduce cost of the wire since you would raise the voltage and lower the current. I.E. (I'm assuming you have 100W "battery" panels which are 17V 8A) all 4 in series would be 60ish volts and 8 Amps so you could run a smaller ga wire to the CC (length of run will affect required conductor size), in parallel you would have 17V but 32A which requires a more expensive conductor.
For your batteries, batteries configured into 1 series string is your best option for ease of maintenance and battery life as an equal amount of current must flow through all batteries.

edit: you were replying to sensi while I was writing this, disregard unless you plan to buy different CC

[inetdog]

But, if as noted in another thread, you have already purchased a 12V inverter and do not want to exchange it for a 24V model, you are stuck.
With a suitable MPPT controller you could still put all of the panels in series to charge a 12V battery bank.
With a PMW CC you are committed to parallel panels.

[Raul]

Thank you, Sensij, for your reply. My controller can handle 12 or 24 volt input but I am wiring the panels as all four in parallel because I have 12-volt batteries (parallel) and a Nature Power 2000W pure sine wave inverter. I know I can wire the batteries series-parallel for 24 volts but I thought the inverter needs 12V DC input. Am I incorrect?

You are confusing CC input here
If you are certain that your controller is a true 40a mppt it must have at least 70v pv input . Those you mention above are battery voltage to the controller . The controller can take a higher input from pv and convert it to the appropriate battery voltage.

[sensij]

Thank you, Sensij, for your reply. My controller can handle 12 or 24 volt input but I am wiring the panels as all four in parallel because I have 12-volt batteries (parallel) and a Nature Power 2000W pure sine wave inverter. I know I can wire the batteries series-parallel for 24 volts but I thought the inverter needs 12V DC input. Am I incorrect?

It depends on the specs of your charge controller. A good MPPT controller might be able to take 80 V x 6 A input (480 W), and turn it into 12 V x 40 A output (480 W) (less 5-10% conversion losses). However, there are some knock-off charge controllers out there that are labeled MPPT, but are in fact purely PWM. With PWM, your amps in = amps out, so you are better off keeping the array voltage closer to the battery voltage and the amps as high as possible. Since even 12 V panels typically operate at about 17 V (subject to temperature, hard shade, and other considerations), PWM losses can be high, 20% or worse. (There are also true MPPT controllers out there that just have a very small voltage range... helping efficiency somewhat relative to PWM, but not offering the advantages of series wiring for the panels)

The input voltage rating of your charge controller could be a good clue as to how it actually operates, if you are unsure. If your controller really says dc input must be 12 or 24 V, then parallel is probably your only choice, and there is a chance that it isn't actually MPPT at all.

[thastinger]

OP, you should really reconsider your system design here. Your inverter is way to big and, assuming your batteries are 12V 100AH, and you discharged them at a C10 rate, a 500W load is all you could run. If you tried to run a much larger load, the inverter will likely shut down due to voltage sag from the battery bank (unless these are AGM batteries). If they are 100AH batteries, you'll have a 400A connection, you won't be able to terminate that to a 12V battery post without increasing the risk of fire/spark. A 600W inverter is plenty. Whatever you decide, please understand that your 2000W inverter would be pulling 153A through the cables and understand the risks associated with that.

[Feenalicious]

Ah, I see. So I can have 24 volt output from pv-

You are confusing CC input here
If you are certain that your controller is a true 40a mppt it must have at least 70v pv input . Those you mention above are battery voltage to the controller . The controller can take a higher input from pv and convert it to the appropriate battery voltage.

That was one of my questions, thank you. So the controller can indeed take 24V solar output and convert it to 12V to go the battery bank.

[Feenalicious]

Thanks for the heads-up

OP, you should really reconsider your system design here. Your inverter is way to big and, assuming your batteries are 12V 100AH, and you discharged them at a C10 rate, a 500W load is all you could run. If you tried to run a much larger load, the inverter will likely shut down due to voltage sag from the battery bank (unless these are AGM batteries). If they are 100AH batteries, you'll have a 400A connection, you won't be able to terminate that to a 12V battery post without increasing the risk of fire/spark. A 600W inverter is plenty. Whatever you decide, please understand that your 2000W inverter would be pulling 153A through the cables and understand the risks associated with that.

I was originally planning a larger system when there were two people living here and bought the inverter then. Didn't realize these repercussions from keeping the 2000V inverter. I actually have a 650W inverter I can use.

[Feenalicious]

With an MPPT charge controller, why would you have those four panels in parallel (unless they are oriented different directions)? For most true MPPT controllers, you could probably pair the panels and put the two pairs in parallel, or with the better CC's, go all four in series.

I see, I'm not utilizing a key benefit of the MPPT controller, the higher voltage I can get by putting the panels in series, right?