Basic fusing question (maybe)

[mtts]

I follow Ben Davidson's Suspicious 0bservers (with a zero not an 'O').

I am working on an 1800w array that is a series of panels of two types, adding up to a working voltage of around 180v, and around 10amps {although, I have seen it produce 2200 watts at one time!}. It feeds a Growatt SPF 3000 TL LVM ES hooked to a couple of EG4 batteries (10kw).

The batteries have their own built-in breakers. The metal frame of the solar array is properly grounded. I've seen recommendations of in-line MC4 fuseholders and fuses. I want to know what the best way is to protect the Growatt from some kind of surge from the panels. And, what kind of shut-off to use, with the highest voltage rating.

Thanks!

 

[JBoffgrid2022]

Typically its best, if you're able to, provide a link to a manual for your components FYI. I'm not sure what is called for on your inverter but it is usually a good practice to install a D/C breaker or isolator between the solar array and the MPPT charge controller or inverter if it is an all-in-one unit. You will need to do some calculations on the solar panel voltage and amperage of your string. Once you have your total volts and amps, you will also need to calculate the temperature coefficient to come to the maximum possible voltage your string could put out at the coldest temperature in your area. This will help you to come to the fuse sizing of your fuses (if you choose to install one) and the breaker sizing.

Hope this helps you out!
Also, please look over this post:

Grounding Made simpler - Part 1: AC/houshold grounding

To get the paper, click on the orange button at the top of the screen. The subject of grounding is a complex, multifaceted subject, that is often treated as an after-thought but needs to be considered from the beginning of the design and build...

diysolarforum.com

@FilterGuy has several great reads for beginners. I've referenced many of his documents and found them very helpful for beginners. If you D/M him, he usually is responsive too.

 

[MisterSandals]

I want to know what the best way is to protect the Growatt from some kind of surge from the panels. And, what kind of shut-off to use, with the highest voltage rating.

It sounds like a typical solar combiner box does what you want. I did not check voltage but 180V should be easy to handle and the breakers/fuses should have some kind of rating.

https://www.amazon.com/Combiner-Waterproof-Lightning-Arrester-Current/dp/B0C2CL971W/

 

[mtts]

Potentially, the cheaper version of that is two inline MC4 15 amp fuses? There's not more than 1 string right now.

 

[MisterSandals]

Potentially, the cheaper version of that is two inline MC4 15 amp fuses? There's not more than 1 string right now.

I don't think an inline MC4 fuse is the same as a lightning arrest device, input breaker and a shutoff breaker.

And yes, you don't need more than one input and 1 output. But if there was a better way to make an array with 2 types of mystery panels, you'd be set.

 

[Warpspeed]

There can never be any kind of surge from the panels.
If you get 1,800 watts (or whatever) in full sun that is all there will ever be.

Fuses are to protect wiring from overcurrent, and potential damage through overheating.
As that can never occur from solar panels, fusing the solar panel wiring is a complete waste of time.
As long as the wiring can carry the full combined panel rated short circuit currents, it will be fine.

 

[timselectric]

The only reason for PV fusing is to protect the panels.
And it's only necessary when the available current is over the panels ratings.

 

[Warpspeed]

The only reason for PV fusing is to protect the panels.
And it's only necessary when the available current is over the panels ratings.

And where does all this current come from ?

 

[timselectric]

And where does all this current come from ?

The other strings that are in parallel.

 

[Warpspeed]

The other strings that are in parallel.

So tell me more about this. Where is the extra current flow exactly ?

 

[JLD]

If you follow Ben as I do your worried more about EMP or coronal mass I'm guessing. Do a search on EMP. Best thing to do is have a back up
in a faraday cage.

 

[mtts]

It has occurred to me to move the innards to the conex, and have a separate set of panels non-deployed inside, to replace the fried ones on the roof.

 

[timselectric]

So tell me more about this. Where is the extra current flow exactly ?

PV fusing is only necessary to protect panels from the other parallel strings. In the event that a panel developed a short. In that event, the other parallel sources would send all of their current to that shorted string. This is only a problem if the available current exceeds the panels rating.
Example:
If each string can output 6a. And the panels have a maximum fuse rating of 15a.
If you have 2 strings in parallel. And one string is shorted. The other string will send 6a to it. 6a in under the 15a rating. So no problem and no fuse required.
If 1 string of 2 in parallel gets shorted. The other 2 will send 12a to it. 12a is under the 15a rating. So again no problem and no fuse is required.
Now, if 1 string of 4 in parallel gets shorted. The other 3 will send 18a to it. A fuse is required. Because 18a is over the 15a rating. And could overheat the panel. And possibly start a fire.

 

[FilterGuy]

So tell me more about this. Where is the extra current flow exactly ?

Fusing & Wire Sizing guidelines for solar panels

To get the paper, click on the orange'' button at the top of the screen. This resource is intended to help the user understand when they need to add Over Current Protection Devices (OCPDs - Fuses or Breakers) to the solar panel array and what...

diysolarforum.com

 

[Warpspeed]

Fusing & Wire Sizing guidelines for solar panels

To get the paper, click on the orange'' button at the top of the screen. This resource is intended to help the user understand when they need to add Over Current Protection Devices (OCPDs - Fuses or Breakers) to the solar panel array and what...

diysolarforum.com

I could not get the link to work.

But anyhow, solar panels are inherently current limiting.
There is a short circuit current figure listed on the ratings plate.
Provided the wiring can easily carry that, no further current limiting protection is required.

 

[FilterGuy]

I could not get the link to work.

I just tried it and it works. Be sure to click on the download button at the top of the page. (Not the picture of the download button in the sentence that says to click on the button at the top of the page)

Here is a direct link to the resource page:

Fusing & Wire Sizing guidelines for solar panels

To get the paper, click on the orange'' button at the top of the screen. This resource is intended to help the user understand when they need to add Over Current Protection Devices (OCPDs - Fuses or Breakers) to the solar panel array and what...

diysolarforum.com

Here is a direct link to the resource: (This is what the download button takes you to)

https://diysolarforum.com/resources/fusing-wire-sizing-guidelines-for-solar-panels.144/download

But anyhow, solar panels are inherently current limiting.
There is a short circuit current figure listed on the ratings plate.
Provided the wiring can easily carry that, no further current limiting protection is required.

That is true for up to 2 panels (or strings of panels) in parallel. If there are 3 or more panels (or strings of panels) in parallel, a short inside one of the panels will have the current from the other strings dumping through the panel. Panels can handle the current of two in parallel.... they can not handle the current of 3 or more in parallel)

The good news is that as the MPPT controllers support higher and higher voltages, the need for more than 2 strings in parallel diminishes.
These days, high parallel counts are usually only seen on smaller systems with low voltage MPPTs.

Note: This conversation has strayed off-topic. I believe the OP was asking about surge protection, not fusing. I also believe he said there is only one string.

 

[Warpspeed]

If you are paralleling multiple strings into one controller, a much better solution to protect panels from damaging current back flow, would be to fit a suitable series diode to each string.

A fuse is only for over current protection, almost always to protect wiring from thermal overload in the event of fault current exceeding the wires rated current carrying capacity.

Have to laugh when people are truly shocked that by adding an extra maybe 2% of power loss, caused by fitting a series diode, but are quite happy to put up with with multiples of that loss, in the resistive losses in the wiring to the solar controller.

 

[FilterGuy]

I want to know what the best way is to protect the Growatt from some kind of surge from the panels.

Do a search for "PV Surge Protection" There are a lot of products out there.

Note there are 3 way and 2 way surge protectors.

The two-way protectors will dump energy from either the positive or negative to the ground if the voltage-to-ground of either of the lines spikes.



However, if one line spikes and the other doesn't it can create a large damaging voltage between positive and negative. A three-way surge protector will dump energy between the positive and negative to snub the voltage spike between them.



One of the problems with buying a surge protector is that even after you install it you have no idea if it is working. Consequently, be careful about no-name Chinese units. Midnight Solar has a well-respected line of DC surge protectors but DAMN their expensive.

 

[FilterGuy]

If you are paralleling multiple strings into one controller, a much better solution to protect panels from damaging current back flow, would be to fit a suitable series diode to each string.

That works but it is not to code.....

I don't know why a diode would be better than a fuse. As you point out, there is more energy loss over a diode than a fuse.

 

[Warpspeed]

I don't know why a diode would be better than a fuse. As you point out, there is more energy loss over a diode than a fuse.

What are you trying to protect against ?
1/ Current back flow.
2/ Over current.

Use the appropriate cure for the problem you hope to solve.