Please pick apart my system. 200 foot run from panels to system.

[NikkiPotnick]

Hello. Noobie here. I’m being advised to purchase a system and I’m trying to get some more feed back here. Help would be greatly appreciated.

I’m attempting to supplement a tiny home with a solar system, 200 feet from my main home. Panels will be on main home roof due to the most sun exposure.

I’ll be running 50 amps of hydro to the tiny home to service the bulk of the load (mini split, range, water heater.) Solar will service the rest of the tiny home.

Solar system I’m planning on is as follows:

- Volthium 24V, 200AH lithium battery
- Goyopo 24V 4000 watt low freq. inverter
- Lumiax 40amp MPPT control charger
- 4X 120watt SunPower thin film panels
- DC 40amp breaker w/ box
- 300amp inverter fuse

I’m putting those 4X SunPower panels on my house roof which is 200 feet from my tiny home system.

Im told I could run 200 feet of 10AWG from my panels to the solar system and only suffer a 5% voltage drop.

Does this set up seem reasonable?

 

[BentleyJ]

You can verify the voltage drop with this:

Voltage Drop Calculator | Southwire

www.southwire.com

 

[NikkiPotnick]

You can verify the voltage drop with this:

Voltage Drop Calculator | Southwire

www.southwire.com

Thanks. I actually used one of these calculators to get the 10AWG recommendation but I am not sure if I had the right inputs. Total noobie here.

 

[BentleyJ]

The 2 user inputs are voltage and current. The solar panels have specifications for both you just need to make sure you account for the panels being wired in series or parallel. Do you still need help? Let us know.
BTW, If the 5% voltage drop is accurate, I would upgrade to 8AWG if your budget will allow it.

 

[NikkiPotnick]

The 2 user inputs are voltage and current. The solar panels have specifications for both you just need to make sure you account for the panels being wired in series or parallel. Do you still need help? Let us know.
BTW, If the 5% voltage drop is accurate, I would upgrade to 8AWG if your budget will allow it.

I Good to know.

The 2 user inputs are voltage and current. The solar panels have specifications for both you just need to make sure you account for the panels being wired in series or parallel. Do you still need help? Let us know.
BTW, If the 5% voltage drop is accurate, I would upgrade to 8AWG if your budget will allow it.

ok so I’ve been cramming info the past hour trying to understand some things. Lol.

I have to find out the voltage of these panels. I only know they are 120watt thin film.

So I suspect I’ll do a series wiring since it’ll use far less wire runs to the charge controller? Unless I understand that wrong. I think series means all panels are joined together and a single pair of wires goes to the charge controller. Whereas parallel means each panel has a pair to the controller?

Can I splice 4X 25’ 8 gauge wires together? Or should I find 200 feet in one run?

Thanks!

 

[sunshine_eggo]

I Good to know.

ok so I’ve been cramming info the past hour trying to understand some things. Lol.

I have to find out the voltage of these panels. I only know they are 120watt thin film.

They typically have a label on the back. You use Vmp and Isc for voltage drop calculations.

So I suspect I’ll do a series wiring since it’ll use far less wire runs to the charge controller? Unless I understand that wrong. I think series means all panels are joined together and a single pair of wires goes to the charge controller. Whereas parallel means each panel has a pair to the controller?

Yes. Yes. Yes.

Can I splice 4X 25’ 8 gauge wires together? Or should I find 200 feet in one run?

4 * 25' = 100'

Single run wire is preferred. Splices are potential points of failure.

 

[Maitake]

FWIW on a small system like that I'd go with 10awg.
Efficiency difference is 1.3% @8 amps between #8 and #10.
Check the cold weather VOC on the panels. Make sure it is not over the limit for the mppt.
Why a 40amp mppt charger for 8amp cells? Seems excessive.

 

[NikkiPotnick]

They typically have a label on the back. You use Vmp and Isc for voltage drop calculations.



Yes. Yes. Yes.



4 * 25' = 100'

Single run wire is preferred. Splices are potential points of failure.

Oops. Yes 8X 25’. Ok I’ll try to find 200 feet online. Could you recommend a decent website to buy various gauges of solar wire?

FWIW on a small system like that I'd go with 10awg.
Efficiency difference is 1.3% @8 amps between #8 and #10.
Check the cold weather VOC on the panels. Make sure it is not over the limit for the mppt.
Why a 40amp mppt charger for 8amp cells? Seems excessive.

the back says “operating temperature” at -40C and +85C and the VOC says 21.24V.

Pmax is 120watt
Ipmax is 6.67a
Vpmax is 18
Isc is 7.33a

I was going to actually return my 40a charger and get a 60a or 80a incase I wanted to add 4 or 8 more panels in the future.

How do I find the limit on the mppt that you mentioned?

 

[sunshine_eggo]

Your system is limited to:

40A * 28.8V = 1152W, so you could have 10 of those panels. You can overpanel them as well.

4015 can have a 6S array and be under the 150Voc limit
4010 can have a 4S array and be under the 100Voc limit

4S would give you a 4.07% drop w/10awg:

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

For more panels, recommend you get a XX15 controller that can go to 150Voc, so you can put 6 panels in series.

Array size for higher current MPPT:
60A * 28.8V = 1728W
80A * 28.8V = 2304W

A 6S3P array would yield:

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

3.22% drop with 6awg.

You could also run a set of 10awg/string (3 sets of 10awg wires):

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

2.71%.

It's typically about balancing gauge, copper cost and voltage drop.

No. Don't use Aluminum wire.

 

[NikkiPotnick]

Your system is limited to:

40A * 28.8V = 1152W, so you could have 10 of those panels. You can overpanel them as well.

4015 can have a 6S array and be under the 150Voc limit
4010 can have a 4S array and be under the 100Voc limit

4S would give you a 4.07% drop w/10awg:

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

For more panels, recommend you get a XX15 controller that can go to 150Voc, so you can put 6 panels in series.

Array size for higher current MPPT:
60A * 28.8V = 1728W
80A * 28.8V = 2304W

A 6S3P array would yield:

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

3.22% drop with 6awg.

You could also run a set of 10awg/string (3 sets of 10awg wires):

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

2.71%.

It's typically about balancing gauge, copper cost and voltage drop.

No. Don't use Aluminum wire.

Thanks for all this info.

I already purchased those 4 panels and the 40a MPPT so ideally I can run with this set up. But if I'm backing myself into a corner I can swap things out with the guy selling me this stuff.

Would the 4.07% drop be acceptable to you if the bulk of energy was from 50amps of hydro?

And if I may ask, in your opinion, what am I losing by going with these thin film compared to a home solar panel? I was offered 330 watt Longi home solar panels which I was told were 20.4% efficiency, whereas the thin film were 120watt and 24.7% efficiency. I was told thin film would meet my needs, being a mobile tiny home. But the math on wattage vs efficiency isn't working for me.

Thanks again for your help

 

[sunshine_eggo]

4.07% is 4.07%. It's basically a 4% loss in power. It's a balance between cost and efficiency. If I would have to spend 2X on wiring to get 2%, I'd probably be fine with 4%.

If the panels are flexible, hell no. They just don't last, even with an ETFE coating on them, and your mounting options get complex. You don't want to mount them to a fixed surface in most cases.

Efficiency simply equates to surface area. a 20% efficient panel will require a larger area than a 24% efficient panel. It comes down to $/Watt and sq-ft/Watt.

 

[Maitake]

That 2% extra loss of power for the smaller AWG is only when panels are operating at IMP, which is almost never or actually never depending on your location. Real world diff is closer to 1%. P=I^R

 

[sunshine_eggo]

That 2% extra loss of power for the smaller AWG is only when panels are operating at IMP, which is almost never or actually never depending on your location. Real world diff is closer to 1%. P=I^R

Not typically true. Panels typically work at notably lower than Vmp due to elevated cell temperature. Typical is 8-9%. You can confirm for yourself by checking NOCT ratings vs. STC. My 37.7Vmp panels regularly produce MPP at the NOCT rating of 34.6V.

At this exact moment, my array is performing at STC Imp and NOCT Vmp making wiring resistance worse than when calculated with STC Vmp/Isc.

 

[NikkiPotnick]

Your system is limited to:

40A * 28.8V = 1152W, so you could have 10 of those panels. You can overpanel them as well.

4015 can have a 6S array and be under the 150Voc limit
4010 can have a 4S array and be under the 100Voc limit

4S would give you a 4.07% drop w/10awg:

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

For more panels, recommend you get a XX15 controller that can go to 150Voc, so you can put 6 panels in series.

Array size for higher current MPPT:
60A * 28.8V = 1728W
80A * 28.8V = 2304W

A 6S3P array would yield:

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

3.22% drop with 6awg.

You could also run a set of 10awg/string (3 sets of 10awg wires):

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

2.71%.

It's typically about balancing gauge, copper cost and voltage drop.

No. Don't use Aluminum wire.

THanks again. Can I ask for clarification for a few things?

1) Can you break down your first equation: 40A X 28.8V = 1152W. Where are you getting these numbers from? I assume 40A is the charge controller size? What is the 28.8V? The back of my panel says VOC 21.24V.

2) Can you break down what these following numbers and letters mean?

4015 can have a 6S array and be under the 150Voc limit
4010 can have a 4S array and be under the 100Voc limit

3) What does over panel mean?


I plugged in what I think the parameters are and it says a drop of 12.55%

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

 

[Leeds]

Is this setup meant to deliver 110vac around the clock?

If so, home the battery bank and inverter on/near the panels on the main house. Then you're basically running any old extension cord from there to your tiny house with minimal losses. And no expensive wire.

 

[sunshine_eggo]

THanks again. Can I ask for clarification for a few things?

1) Can you break down your first equation: 40A X 28.8V = 1152W. Where are you getting these numbers from? I assume 40A is the charge controller size? What is the 28.8V? The back of my panel says VOC 21.24V.

Peak charge voltage of a 24V system is around 28.8V.

2) Can you break down what these following numbers and letters mean?

4015 can have a 6S array and be under the 150Voc limit
4010 can have a 4S array and be under the 100Voc limit

4010/4015 are model numbers of the brand of MPPT you have selected.

6S means 6 panels in series.
4S means 4 panels in series.

3) What does over panel mean?

Putting a larger array on the MPPT than it can handle. This is very common in poor solar conditions.

I plugged in what I think the parameters are and it says a drop of 12.55%

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

You use the Vmp, not Voc of the array, i.e., if you have 4S or 6S, you would multiple the panel Vmp by 4 or 6, respectively.

A 6S array would have 6 * 18Vmp = 108V. Use your Isc, not Imp, as you're looking for the worst case.

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

 

[NikkiPotnick]

Is this setup meant to deliver 110vac around the clock?

If so, home the battery bank and inverter on/near the panels on the main house. Then you're basically running any old extension cord from there to your tiny house with minimal losses. And no expensive wire.

What do you mean by 110vac? I might be better off just doing this.

I’m amidst yard construction where I’ll trench in a number of other services to/from tiny home (sewage, 50amp hydro, water, etc.) So I figured I’d throw a solar cable into the same trench. But it seems like a bit of a pain and kinda pricey

 

[NikkiPotnick]

Peak charge voltage of a 24V system is around 28.8V.



4010/4015 are model numbers of the brand of MPPT you have selected.

6S means 6 panels in series.
4S means 4 panels in series.



Putting a larger array on the MPPT than it can handle. This is very common in poor solar conditions.



You use the Vmp, not Voc of the array, i.e., if you have 4S or 6S, you would multiple the panel Vmp by 4 or 6, respectively.

A 6S array would have 6 * 18Vmp = 108V. Use your Isc, not Imp, as you're looking for the worst case.

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

So helpful. Thank you tons.