Optimization of solar in winter/grey days

[FilterGuy]

Having said all of that. I do not know of a device that will automaticly switch panels in and out of the array..... It would typically not be needed on an MPPT controller.

 

[Randij]

So it is separate from the Midnite? Is it between the panels and and the midnight? Or is it between the battery and the Midnight?

If it is between the panels and the midnight..... it should never pop.
If it is betwwn the midnite and the battery it should be larger. It should be at least a 94A x 1.25 = 117. Round that up to a 120A.

You should never run a fuse or a breaker right at it's trip value.

Found a schematic :

 

[Randij]

Having said all of that. I do not know of a device that will automaticly switch panels in and out of the array..... It would typically not be needed on an MPPT controller.

Because the MPPT controller clamps voltage. , yes?

 

[FilterGuy]

Found a schematic :

Is it #16 or number #17 on the diagram that is popping? What are the trip ratings on each?

Because the MPPT controller clamps voltage. , yes?

No. Because MPPT controllers typically limit the current. The controller can not limit the voltage and If you let the voltage get too high it will damage the MPPT controller.

 

[Randij]

Because the MPPT controller clamps voltage. , yes?

 

[Randij]

Sorry, yes your right of course. But if the array is 24V and this fuse is tripping, although rarely. Would it just be heat?
And could I add 2P (400W ea) and increase the fuse to 130A . Would the MidNite at 96A tolerate that safety or is it too much?

 

[Randij]

Sorry, yes your right of course. But if the array is 24V and this fuse is tripping, although rarely. Would it just be heat?
And could I add 2P (400W ea) and increase the fuse to 130A . Would the MidNite at 96A tolerate that safety or is it too much?

I’m talking about #16 fuse

 

[Randij]

I’m talking about #16 fuse

Again, thank you

 

[FilterGuy]

Sorry, yes your right of course. But if the array is 24V and this fuse is tripping, although rarely. Would it just be heat?
And could I add 2P (400W ea) and increase the fuse to 130A . Would the MidNite at 96A tolerate that safety or is it too much?

I’m talking about #16 fuse

OK..... thank you for the information. If that is a 100A breaker between the combiner box and the midnite, something seems really wrong. Could you tell me the Voc and Isc of the panels? (Or the make/model of the panels) Also, what size breakers are in the combiner box?

My guess is that your series Voc is running at around 75V (maybe higher). That means the PV current would be 6x385/75 = 31A and your Array Isc would be around 35A. A 100A breaker should never pop!!. In fact, a properly designed system does not even need a breaker were #16 is. (but it does need a disconnect)

You may want to review this:

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

Meanwhile..... if it was #17 that was poping and it is a 100A breaker, it would make perfect sense. it needs to be something closer to a 120A breaker.

 

[Randij]

The schematic I showed you is the one recommended in the MidNite documentaction. I’ll try and check the panels tomorrow for the Voc and Isc of the panel. Again it has only happened twice over 4 years in the summer and so I’m thinking it also could be heat and a laze fuse. Has not happened last year or this year. But because I want to add more panels, I’m trying to understand so I don’t reck the MidNite . I may be chasing a ghost. I’ve moved since and at the moment a tree is limiting my solar.
fuse #16 is 100A and Ill try to check #17 tomorrow as well.
Thanks again for your help and patients I really appreciate it.
I am seeing 30-40 Amp presently, but usually only 20+ Amps because of the tree. Lol
until tomorrow, thanks

 

[FilterGuy]

But because I want to add more panels, I’m trying to understand so I don’t reck the MidNite .

I hear ya! That midnite classic is not a cheap item.

 

[FilterGuy]

One nice feature of the Midnite Classic is their HyperVOC,



The Classic 150 will turn off if the PV input goes above 150V but no damage occurs till the top of HyperVOC (174V for a 24V battery).

This allows you to use a the HyperVOC voltage for the worst case conditions but 150V for normal conditions. That way you could design a system that works well for -10F, but does not get damaged in that once-a-decade -25F.

Your configuration will probably never produce voltages that high, but it is good to know you have the extra safety margin.

I am 95% sure you can over-panel the Midnight Classic as long as you keep the voltage below 150..... but I have not found conformation of that yet.
If I am correct, you should be able to put that extra string in and leave it all year round. (but I have no idea why that breaker was popping)

 

[NHRenewables]

I’m interested to hear how big your wires are back from your combiner box?!? Any design room to bump up the voltage Instead of throwing away photons?

 

[FilterGuy]

I just sent Midnite a message asking about over-paneling. Once I get an answer and we have the Voc and Vsc of the panels we can look at what can work. We can also look at how to minimize the impact of the shading.

 

[Randij]

th

I just sent Midnite a message asking about over-paneling. Once I get an answer and we have the Voc and Vsc of the panels we can look at what can work. We can also look at how to minimize the impact of the shading.

Thank you , you are so kind! I did a lot of reading on the MidNite last night and I found the bit about 174Voc
i learned that the #16 & #17 breakers are really for disconnecting the PV #16 and batteries #17 and not so much about the current from the PV although, if it were too low, it would trip. I

I’m interested to hear how big your wires are back from your combiner box?!? Any design room to bump up the voltage Instead of throwing away photons?

 

[Randij]

The from the Pv to the combiner box are #6 AWG

 

[Randij]

My 4 panels are CanadianSolar CS3U-380MS
Pmax: 380 not 385W, Vmp: 40.0V, Imp: 9.5A, Voc: 47.8, Isc:10.1A

The from the Pv to the combiner box are #6 AWG

Also I go down to -40C in winter averaging -22C so how does that affect the 174Voc @ -10C?

 

[Randij]

The from the Pv to the combiner box are #6 AWG

The other 2 panels are 385W, Isc: 10.1A, Voc: 48.21, Imp: 9.61, Vmp : 40.05

 

[Randij]

It think I’m understanding better. (Abt time! Lol) The Hyper Voc is the max amt of PV I can drive to.
ie if I add two more panels at 385W, I’m adding 770W combined with (4@380+2@385) 2290W of PV must not exceed 174Voc
ie Add 2 panels, I’ll go to 3060W. If divides by 24V, that’s a 127.5Voc which is < 174Voc max
so it looks like I can do it?

 

[Randij]

I don’t have to worry about breaking my PV array into 2 parts to stay safe.
How is the -40C factor in ? Ie 174Voc at -10C