Care to Check My Reasoning and Math before I blow Everything up?

[Dreen]

Actually, I think I will be alright, but I definitely need help on fusing concerns!

Okay, here's the run down. We are planning on putting 16 265w panels on a full sun roof. Stats are here:

• Open circuit voltage (VOC): 44.20 V
• Max power voltage (VMP): 35.33 V
• Short circuit current (ISC): 8.20 A
• Max power current: 7.50 A
• Power Tolerance 0/+3%
• Maximum system voltage: 600V (UL)
• Fuse Rating: 15 A

Planning on 3 strings. 2 with 6 panels and one with 4 to 3 charge controllers. The CC's are 60A MakeSkyBlue- I know there are much better cc's, but we're on a budget, and this is what we have.

We only have 4 batts to start, 12vDeep Cycle, wired to 24v. Then we have 2 4000w 24v Giandel inverters that we will run our AC loads from. And we are looking at hooking up an ATS to this as well. We are mainly concerned with running a fridge and a freezer off each line. We thought the ATS would help ensure we have enough to keep those appliances going. Lights and ceiling fans would be good as well! All other large appliances are propane, water heater, clothes dryer, stove. Everything is wired to standard grid AC. We're planning on just putting in an extra distribution box for the solar right next to the grid power distribution panel.

I know we need more batteries, but this is all we can get right now. Maybe next month we can add 4 more. I hope. We were thinking the ATS would be beneficial to us due to the too shallow battery bank. Thoughts?

First, does this framework sound okay?

And then on the fuses, I am a bit confused. The charge controllers say to put a 100 amp fuse between the CC and the battery bank and to use 2 10g wires. Huh? And then there is no suggestion on fuse sizing between the panels and the charge controllers.

I know you don't want to overpanel too much as it endangers all your other components. These say 1440w and we're looking at 1590w on the 6 panel strings. The CC's specs are here:

60A 12V 24V 48V Wifi MPPT Solar Charge Controller for Lead-acid battery V119

60A MPPT Solar Charge Controller with Wifi function for Android The Wifi is between MPPT Controller and Android phones only.Not the internet or cloud connection. V119=V118+Wifi Box 100% MPPT controller Intelligent Maximum PowerPoint Tracking technology Built-in DSP controller with high...

makeskyblue.com

Is that too much in overpaneling realm? We're in SC Missouri.

Thanks very much and I am ready and willing to take warnings, input, and correction. And also any advice on what size fuses I should actually use!

 

[Dzl]

Care to Check My Reasoning and Math before I blow Everything up?

If I'm honest, it sounds a lot more fun to watch everything blow up than to check your math ?

That said you didn't give us a whole lot of math to check. You are likely to get more feedback if you do the math yourself and ask for feedback. Rather than just providing the raw specs of the panels. (speaking for myself, I'm too lazy to do the math for you, but not to lazy to look it over once you've done it, or answer any questions you have). Also, more info is needed regarding the batteries.

If you need help figuring out this math, see this article by Victron, it answered most questions I had about matching PV array to charge controller, overpanelling and how to do the math.

Regarding fusing, keep in mind that "the fuse protects the wire," Size your fuses to be a little greater than 125% of the max load the circuit will carry, but less than the max current limit for the wire. Here is a good video on fusing and circuit protection, and here are a few good resources on fusing, filter guys has put together some great info on fusing in this post

 

[MisterSandals]

We only have 4 batts to start, 12vDeep Cycle, wired to 24v. Then we have 2 4000w 24v Giandel inverters

Without knowing how big your batteries are, this sounds like too much power to draw.

 

[Dreen]

Thanks!

So perhaps I should just hook one string to our batts until we can get more batts?

Will be checking your links, Dzi. Appreciate it very much!

I was referencing the sizing of the panels to the cc's and the inverters.

Off to watch the video and then check the rest of your links! Thanks again!

 

[John Frum]

OP maybe its just me but I find it really hard to parse the details out of prose.
Can you make a diagram?
I use https://www.draw.io/ fwiw.
This may take some iterations but should be educational for all.

 

[boondox]

The CC's are just barely sized for the array. Since you never get the rated amperage (rarely anyway) you should be able to squeak by but you are going to be running them pretty hard on a sunny morning with hungry batteries.

100 amp fusing is too low. 100 * 24 = 2400 watts. You need to have headroom if you don't want your fuses to blow. So a 200 amp fuse to each inverter would be better. I'd use a DC rated breaker instead.

As to the batteries, we need to know how many aH they are and what they are capable of producing in amps. It sounds like 12V marine deep cycle types. If you haven't bought them I would consider golf cart batteries, T-105's or equivalent.

 

[Dreen]

Yes. They are Marine Deep Cycle 100 AH batteries. I've got 3 T 105's, but need to recondition them and would likely put them on the well so that all batts in the other system are the same.

I don't think I have time today to make a diagram. Maybe this evening. I'll give it a whirl. Thank you!

I don't think I covered how I intend to join the panels, which has an effect on the efficacy of the CC. We're going to run two in series and then join those in parallel in the strings to go to the CC. So the amperage should be about 49A at max amperage on the 6 panel strings.

For between the batts and the inverters I have 300amp fuses. That's the plan anyway. These:

Amazon.com: TopstrongGear Solid Brass 0/2/4 Gauge 300Amp ANL Fuse Holder with 300Amp Fuses(2 Pack) (300 Amp): Car Electronics

Amazon.com: TopstrongGear Solid Brass 0/2/4 Gauge 300Amp ANL Fuse Holder with 300Amp Fuses(2 Pack) (300 Amp): Car Electronics

www.amazon.com

That should be okay, right?

 

[MisterSandals]

For between the batts and the inverters I have 300amp fuses.

If you have 4000w inverters at 24v, that is 166 amps. I think 200 amp breakers are the right size to do something useful.

We're going to run two in series and then join those in parallel in the stringsSo the amperage should be about 49A at max amperage on the 6 panel strings.

This sounds odd to have the amps high and the volts low. Normally its better to have volts as high as your SCC will reasonably handle to keep the amps low.

 

[Supervstech]

What loads are you placing on the inverters?
Those batteries wont last long under two 4KW inverters...
Like 15 minutes fully loaded...

 

[Dreen]

What loads are you placing on the inverters?
Those batteries wont last long under two 4KW inverters...
Like 15 minutes fully loaded...

Well, that's very disconcerting. Of utmost importance are two freezers that are full of meat and 2 refrigerators. 1 of each on each inverter. Hope that's clear.

 

[Dreen]

If you have 4000w inverters at 24v, that is 166 amps. I think 200 amp breakers are the right size to do something useful.


This sounds odd to have the amps high and the volts low. Normally its better to have volts as high as your SCC will reasonably handle to keep the amps low.

They're 88 volts with 2 wired together. Amps at max 8.2. Should I wire more in series than 2?

 

[Supervstech]

Well, that's very disconcerting. Of utmost importance are two freezers that are full of meat and 2 refrigerators. 1 of each on each inverter. Hope that's clear.

Ok, you will need the Wh load per day of each freezer, and refrigerator, get a kilowatt meter that calculates the.loads.
Your batteries can handle a maximum of 2400Wh discharge per day before damage is done to them... they are capable of 4800Wh, but they wont last a month drawn that low...

 

[Supervstech]

They're 88 volts with 2 wired together. Amps at max 8.2. Should I wire more in series than 2?

The specs on the CC limit you to 2 S... so, for 6 panels, you are looking at 25A
4 panels 17A...

 

[boondox]

They're 88 volts with 2 wired together. Amps at max 8.2. Should I wire more in series than 2?

As long as your CC can handle the input voltage, yes. Remember to use the unloaded voltage of the panels and add a little for safety. I run my panels 3 in series for an input of ~ 100VDC as that is where my CC's sweet spot is.

As noted above, you need to get a handle on how much power your chest freezers and other loads use. Look up kill-a-watt. Then decide how long the batteries need to last. Remember that you don't want to pull a lead acid battery below 50% SOC, preferably more or the batteries won't last long. You need the numbers to plan out a system that will work and continue to work.

 

[Dreen]

It says that it will handle 105v max on the CC's. So I guess that's why I went with the 2 panels in series totaling 88v.

I'm trying to decide on Kill a Watt meter from Damnazon right now. Looks like quality on them went down recently as there a good number of negative reviews on what I've looked at thus far. Have a recommendation?

According to maths available on the interwebs, we should be okay, but reality and numbers reported can differ greatly.

 

[boondox]

Not sure which to get, got mine along time ago.

And yeah, reality is different. For example, my chest freezer is in an open at one end carport. In the winter it runs less than if it was in the house. In the summer it may run more. Also important is how long you want it to run before needing to fire up the generator.

 

[Supervstech]

Well, since you already have everything, you could also order a colomb meter and track the Wh usage of the setup as you go...

battery coulomb counter - Google Search

 

[Dreen]

Well, since you already have everything, you could also order a colomb meter and track the Wh usage of the setup as you go...

battery coulomb counter - Google Search

That's an interesting idea.

We are putting an ATS in there as well. I mean, we definitely would like to go off grid, but I know we need a much larger battery bank to achieve that, and it's just going to take a little time. The ATS is much less than the batteries we need. And I thought that was part of the purpose of the ATS. To reduce your grid consumption and allow you time to build that battery bank, right?

 

[Supervstech]

That's an interesting idea.

We are putting an ATS in there as well. I mean, we definitely would like to go off grid, but I know we need a much larger battery bank to achieve that, and it's just going to take a little time. The ATS is much less than the batteries we need. And I thought that was part of the purpose of the ATS. To reduce your grid consumption and allow you time to build that battery bank, right?

ATS will simply switch you to battery/solar/generator power when triggered... either by power outage, or on a program hat uses some algorithm to switch.

an ats’ purpose is to switch over and isolate the grid from the alternate energy source.

 

[Dreen]

But you can program it to draw from batts then go to grid.

Is this wrong?