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Veteran52

Veteran52

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May 18, 2020
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I have been given 5, 100 watt monocrystaline solar panels in good working order. I want to set up a solar storage systems based on these 5 panels. I've done some research and decided I want to use a MPPT charge Controller and given the poor ventilation of a confined space near a furnace, AGM batteries. What is the smallest amp charge controller I can use? 20a, 30a, 40a? If I use 12 volt batteries what should the total optimal amp hour rating be for my batteries with these panels? What size AC inverter would work best with this capacity? Thanks
 
Divide the max watts by the intended volts to determine amps.

in your case, 400W /13V= 30 amps
 
Be sure to get enough battery for the solar output...
Watts x sun hours equals Watt hours, so your 400W x average 6 sun hours =2400 Wh , divided by 13 volts = 185 Ah...
So get 200 Ah battery storage.
 
Supervstech said:
Be sure to get enough battery for the solar output...Watts x sun hours equals Watt hours, so your 400W x average 6 sun hours =2400 Wh , divided by 13 volts = 185 Ah...
So get 200 Ah battery storage.
Click to expand...
Where did you get the 400 watt figure from? The solar panels? I have 5. Wouldn't that be 500 watts or did you account for some kind of loss or inefficiency?
 
Which would be 38
Likely you will never see 400 watts, but size optimistically and you won’t damage anything.
 
OK. Just to be sure I got this right. I can use a 30 amp MPPT controller with 500 watts of panels without any over charging problems? And I would be optimal with 200 AH battery storage? Would there be any benefit, waste or harm if I used 300ah of battery storage for extra capacity, or would my 5 panels not be able to keep it fully charged if I used it every day?
 
Veteran52 said:
I have been given 5, 100 watt monocrystaline solar panels in good working order. I want to set up a solar storage systems based on these 5 panels.
Click to expand...
5 panels is an odd number of panels that can not be series connected to get a higher voltage input to your MPPT controller.
6 would be better.
100 watt panels are about 23 volts open circuit and about 6 amps.
Look at the back of your panels to get the specs.
You would have to parallel connect 5 panels only inputting 23 volts to SCC.
6 panels could be connected 3series 2parallel or 2series 3parallel.
 
MBR said:
5 panels is an odd number of panels that can not be series connected to get a higher voltage input to your MPPT controller.
6 would be better.100 watt panels are about 23 volts open circuit and about 6 amps.Look at the back of your panels to get the specs.
You would have to parallel connect 5 panels only inputting 23 volts to SCC. 6 panels could be connected 3series 2parallel or 2series 3parallel.
Click to expand...
I only have room for 5 panels. Impossible to add even just 1 more. I guess I'm stuck with what I've got., Or can I just use 4 and do some kind of series/parallel connection to get the higher voltage and amps I need? How would I do that if I can? Open Circuit voltage is 22.5 and amps are 5.29 for my panels. I'm no electrician so I don't quite understand the concept of sending higher voltage to the controller if I am using 12 volt batteries. Can the controller accept higher voltage yet still charges the batteries at 12 volts?
 
Veteran52 said:
I already have 5 panels. Can't use more. Just need batteries, inverter, and charge controller.
Click to expand...
The mpp solar 1kva 12v is a inverter/charge controller, it is 500w max pv array, you could install 4 panels 2S2P, and get 2 100ah batteries and you are done.
 
MBR said:
5 panels is an odd number of panels that can not be series connected to get a higher voltage input to your MPPT controller.
6 would be better.
100 watt panels are about 23 volts open circuit and about 6 amps.
Look at the back of your panels to get the specs.
You would have to parallel connect 5 panels only inputting 23 volts to SCC.
6 panels could be connected 3series 2parallel or 2series 3parallel.
Click to expand...

Why couldn't all 5 panels be series connected and then use a 150 volt solar charge controller? If each panel is 23 Voc, then 23x5=115 volts.

Victron has a calculator on their website where you can enter all the specs of your panels and it will tell you what size solar charge controller to get. Click the 'custom module' button and enter in your specs. https://www.victronenergy.com/mppt-calculator

I ran a mock up doing a 5s1p design using a Renogy 100 watt panel and it says to use a 150/35 controller based on the Renogy panel specs.
 
Last edited:
Will a Renogy Rover 30 Amp MPPT Charge Controller and 2 Renogy AGM batteries, 100ah each, work with my five 100 watt solar panels or do I need a 40 amp controller? I don't understand the whole series/parallel thing with my 12 volt panels. Why wire the panels in series? Why not just parallel?
 
GMB said:
Why couldn't all 5 panels be series connected and then use a 150 volt solar charge controller? If each panel is 23 Voc, then 23x5=115 volts
Click to expand...
You are correct.
Dunno what I was thinking but obviously I did not bother to do the math.
No coffee is my best excuse for saying that 5 100 watt panels could not be series connected.
Sorry for the confusion.
 
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Veteran52 said:
I don't understand the whole series/parallel thing with my 12 volt panels. Why wire the panels in series? Why not just parallel?
Click to expand...
This video does a decent job of explaining the differences. If you have shading issues, then parallel is better since if one panel is receiving shade it doesn't shut down the entire system. If shading isn't an issue, you can series connect and run fewer wires and operate at a higher voltage (less line loss and smaller cabling).

 
Thank You! That is a great video that helps me understand this. Given that I do have a shade problem a few hours per day I clearly have to go with parallel. If I use a large size wire (like a #6) from the panels to the charge controller is it OK to reduce it to a #10 the last few inches to make it fit the smaller terminal lugs on some of the controllers I've seen or does that negate the benefits of the larger wire? Would it be better to just use #10 the whole run?
 
Veteran52 said:
Thank You! That is a great video that helps me understand this. Given that I do have a shade problem a few hours per day I clearly have to go with parallel. If I use a large size wire (like a #6) from the panels to the charge controller is it OK to reduce it to a #10 the last few inches to make it fit the smaller terminal lugs on some of the controllers I've seen or does that negate the benefits of the larger wire? Would it be better to just use #10 the whole run?
Click to expand...
If you parallel all 5 panels, you would need to run the positive and negative wires from each panel to a combiner box and then run one positive and one negative from the combiner box to the solar charge controller. The size of the wires you use depends on how far you are running the wires.

If you could series connect all 5 panels, then you wouldn't need a combiner box and could run the main negative and the main positive directly to the solar charge controller (with proper fusing/circuit breaker)

There is a chart here and probably one in the resource section on this site as well that talks about wire sizing.

Edit - here's the link to the 'Resources' section on wire size and planning: https://diysolarforum.com/resources/categories/planning-and-sizing-tools.5/
 
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Great. More useful information. From what I see I'll have #12 running from the panels to the combiner. (24" from each panel). From there I can change to #6 for the run to the charge controller (10') but it looks like I'll have to reduce to #8 or #10 to connect to the controller lugs. Is it OK to do this? Does it actually help to go with #6 wire for just that 10 feet or should I just run # 8 from the combiner?
 
Veteran52 said:
Given that I do have a shade problem a few hours per day I clearly have to go with parallel. If I use a large size wire (like a #6)
Click to expand...
What time of day do you have shading problems?
The 5 or so peak hours of sun are in the midday. There is not much production in the morning or late afternoon.
Are your panels on an RV?
If so 6 awg is not needed for even 5 panels in parallel because your wire length will be short.
How many feet of wire from panels to SCC?

Renogy controllers are not the best choice and the 30 amp model you asked about is only 100 volts max input so you could not series connect 5 panels.
There are SCC with 145 to 150 volt max input.
 
Shade is mid afternoon from a tree for a few hours. Not an RV. It's my Home. 16 feet total to controller. Since I'm doing parallel the Renogy controller will work.
 
Veteran52 said:
Great. More useful information. From what I see I'll have #12 running from the panels to the combiner. (24" from each panel). From there I can change to #6 for the run to the charge controller (10') but it looks like I'll have to reduce to #8 or #10 to connect to the controller lugs. Is it OK to do this? Does it actually help to go with #6 wire for just that 10 feet or should I just run # 8 from the combiner?
Click to expand...
The Victron 150/35 will accept 6 awg wire. https://www.victronenergy.com/uploa...artSolar-charge-controller-MPPT-150-35-EN.pdf

I personally wouldn't run a 6 awg wire then downsize it to 8 or 10 awg to fit the controller lug. Seems like it would defeat the purpose of the 6 awg wire in the first place. Just my thoughts, I am definitely not an electrical engineer though... Seems like 8 awg would work for such a small system and it's right on the cusp of needing 6 awg wire, but again, not an engineer so I would go with the chart, but it seems the worst that can happen is a little bit of line loss. According to the Windy Nation wire chart I use, 8 awg welding wire will handle 55 amps.

If you're really stuck on a Renogy controller, check their website for the data sheet and it should tell you what size wire it will accept.
 
Veteran52 said:
Shade is mid afternoon from a tree for a few hours. Not an RV. It's my Home. 16 feet total to controller. Since I'm doing parallel the Renogy controller will work.
Click to expand...
I dont remember the Vmp of your panels so guessed at 18 volts.
5 x your panels Isc was 5.5? amps so 28? total.
You can play with the voltage % loss you want changing the fields but looks like 4 or 6 awg wire.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.
www.calculator.net www.calculator.net
 
This is a good video Will did on Solar Charge Controllers. He recommends the EPEVER models and I've seen multiple post here about them being pretty great for their price. I personally have never used one and I prefer to use mostly Victron equipment because of the way it all connects and interacts with each other and their app is so useful for monitoring and making changes.

 
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