Design of 12kW solar panel system at 100m distance

[cajocars]

I want to design and install a 12kW system at my parents' place; the solar panels would be on the ground as there is a field with plenty of space and also to avoid having to work on a roof (which is also not too big and has a chimney).
I worked out a 12kW system with 15kWh storage to be the quickest to pay for itself. It needs to be an off-grid system with grid connection; the demand is never going to be more than 6kW.

I am looking at a Longi 555W that a seller on Alibaba proposed while I was asking for ground mounting systems

Device	Solar Panel
Type	Monocrystalline
Power	555W
Input Voltage	42.10V
Output Current	13.19A
Size	2256x1133x35mm
Weight	27.2kg
Open Circuit Voltage	49.95V
Short Circuit Current	14.04A

The inverter will need to be close to the house rather than close to the panels (so I don't have to leave the battery outside). I understand the way to minimise power losses on the 100m run is to use a high voltage setup.

If I have 22 of these panels in series I get 1100V and max 13A; is this too high a voltage for an inverter? I could use 4mm2 cables and only have 1% voltage drop.

If I have two arrays of 11 connected in parallel I have them at 550V, 26A max current, but to have the same 1% voltage drop I would need 16mm2 cables.
Or I could have two sets of 11 panels in series connected to two different PV inputs on the inverter (but 4 cables in total)?

What's the best practice?

 

[SeaGal]

The inverter will need to be close to the house rather than close to the panels (so I don't have to leave the battery outside). I understand the way to minimise power losses on the 100m run is to use a high voltage setup.

If I have 22 of these panels in series I get 1100V and max 13A; is this too high a voltage for an inverter?

Probably - but you will need to look at the spec of the inverter you intend to buy and calculate max Voc at lowest temp possible. Around 500V-600V per string seems more common for smaller size inverters.

Hence you could split the panels into 2 strings of 550V each.

I could use 4mm2 cables and only have 1% voltage drop.

Better to go for 6mm2 PV cable as it's not that much more expensive

If I have two arrays of 11 connected in parallel I have them at 550V, 26A max current, but to have the same 1% voltage drop I would need 16mm2 cables.
Or I could have two sets of 11 panels in series connected to two different PV inputs on the inverter (but 4 cables in total)?

What's the best practice?

Personally, I would go for the option in bold (as I mentioned above already, before I read the whole question!) - that will give you more flexibility if there are any shading issues too.

 

[Solar Guppy]

For residential, all voltages must be below 600V ( USA ), so there are no inverters ( charge controller, gridtie or Hybrid ) that would allow for a home install of 1100V. Just for informational purposes commercial is 1500V and there are grid-tie in this voltage range, Solis has a large offering in this type

As SeaGal posted above, 4 wire / two strings would work, but you will be close as most gridtie inverters with 600V maximum ( never exceed ) have 550V as the operational maximum. So you need to be extra careful in your choice on the electronics and make sure you derate for temperature effects on VOC of the solar panels.

 

[cajocars]

For residential, all voltages must be below 600V ( USA ), so there are no inverters ( charge controller, gridtie or Hybrid ) that would allow for a home install of 1100V. Just for informational purposes commercial is 1500V and there are grid-tie in this voltage range, Solis has a large offering in this type

As SeaGal posted above, 4 wire / two strings would work, but you will be close as most gridtie inverters with 600V maximum ( never exceed ) have 550V as the operational maximum. So you need to be extra careful in your choice on the electronics and make sure you derate for temperature effects on VOC of the solar panels.

Not in the USA (Italy), but I can see why 1100V sounds very high (and dangerous, well, even 550V sounds scary)

I haven't researched inverters yet, so I don't know which input voltages are typical.

 

[millsan1]

1100 volts seems a smidge high, by about 2.5 times, lol.

The inverters I looked at wanted around 500, max.

 

[BentleyJ]

Due to the high DC voltage, the suitable product range is greatly reduced. Most of the All in One inverters are limited to 500V or possibly 550V which is right at the STC Open Circuit Voltage and this doesn't account for low temp operation.

The other issue is the PV array is somewhat out of proportion to a typical 6kW inverter. For example, 6 to 8kW AIO inverters would not be able to accept 12kW of solar input. The inverter would have to be up-sized to something like an EG4 18kpv. In a sense you would be paying for inverter capacity you don't need but this would be a good choice since the PV input is rated for 600V.

The alternative is to use separate components such as a Midnight Solar or Schneider Conext charge controller with an inverter that doesn't have MPPT controllers built in or just don't use the MPPT inputs on the inverter if you choose an AIO type.

 

[cajocars]

What exaclty is a charge controller? Does it take the input from the panels and outputs a voltage to charge a 51.2V battery? So the inverter thinks all power is coming from the battery even if part of it is coming from the panels?

 

[BentleyJ]

Yes, There are 2 basic types of Solar Charge Controllers. Older style, not used much anymore but less expensive, PWM (pulse width modulation) these are inefficient. Newer, modern charge controllers are MPPT type (maximum power point tracking)

 

[cajocars]

Looking at the size of cables I need and voltage drop I'm undecided between 6mm2 and 10mm2.

Considering a Voltage of 450V and a current of 13A, single run of 100m:
- two pairs of 6mm2 would give me a voltage drop of 1.65%; total cost of 400m of cable would be 640€
- two pairs of 10mm2 would give me 0.98% voltage drop; total cost 1000€

- alternatively a single pair of 10mm2 with double the current (26A) would give me a V drop of 1.96% and be the cheapest option at 500€ (200m)

Do high voltage drops induce any problems apart from the panels producing less power?

 

[SeaGal]

two pairs of 6mm2 would give me a voltage drop of 1.65%; total cost of 400m of cable would be 640€

Sounds very expensive. In UK, 100m is £75+20%VAT, so around €105 for 100m = €420 for 400m

Voltage loss per se is less important on the DC side than AC side, it is power loss that is more important. Obviously thicker cable will result in less power loss, but power loss will be proportional to I^2 R, so 2x the current will result in 4x power loss for same resistance cable.

The other consideration is that you can connect 6mm2 PV cable to MC4 connectors, but I don't think that 10mm2 cable will connect directly (happy to be corrected on that if I'm wrong )

 

[cajocars]

Sounds very expensive. In UK, 100m is £75+20%VAT, so around €105 for 100m = €420 for 400m

Voltage loss per se is less important on the DC side than AC side, it is power loss that is more important. Obviously thicker cable will result in less power loss, but power loss will be proportional to I^2 R, so 2x the current will result in 4x power loss for same resistance cable.

The other consideration is that you can connect 6mm2 PV cable to MC4 connectors, but I don't think that 10mm2 cable will connect directly (happy to be corrected on that if I'm wrong )

Sounds like 6mm2 is the way to go; where can I get them in the UK?

 

[kommando]

All the MC4 connectors I have bought in UK take 6mm2 cable, never had to specify they require to take 6mm2.

 

[cajocars]

All the MC4 connectors I have bought in UK take 6mm2 cable, never had to specify they require to take 6mm2.

He was dubious about the 10mm2

 

[SeaGal]

She He was dubious about the 10mm2

Sounds like 6mm2 is the way to go; where can I get them in the UK?

There are quite a few places - I found tlc-direct to be reliable... https://www.tlc-direct.co.uk/Products/CASOL6.html

 

[cajocars]

Having looked at the Victron MPPT calculator, it looks like it doesn't let me use a SmartSolar MPPT RS 450/200-Tr with more than 7 of those Longi 555W in series. So I would need 3 or 4 strings to reach 11.6 or 15.5kWp. Should I be able to find a combination of panels that allow me to get away with only 2 strings?

 

[zanydroid]

Having looked at the Victron MPPT calculator, it looks like it doesn't let me use a SmartSolar MPPT RS 450/200-Tr with more than 7 of those Longi 555W in series. So I would need 3 or 4 strings to reach 11.6 or 15.5kWp. Should I be able to find a combination of panels that allow me to get away with only 2 strings?

How does parallel look? It looks like these MPPT are designed for 10A panels. So it’s awkward to 2P your 13A panels into them and may exceed the official limits.

Has Victron not updated the product line for 13A? Lame if true.

 

[cajocars]

How does parallel look? It looks like these MPPT are designed for 10A panels. So it’s awkward to 2P your 13A panels into them and may exceed the official limits.

Has Victron not updated the product line for 13A? Lame if true.

With 14A on each panel, it looks like I would need 16mm2 cables to carry 28A at 100m and have acceptable losses (<3%)

By reducing the size of the panels I might be able to squeeze 8 per string instead of 7 (without paralleling)

 

[zanydroid]

How do the LuxPower or Deye AIO compare to Victron for your use case? Feels like a premium is being paid for Victron, which to me provides less value when you can’t grid tie.

The US version of the 6K can take two strings of 13A panels (4kW each string), and is stackable. Deye is supposed to be affordable in Europe.

You can get to 16kW-DC 12 kW-AC with two LuxPower 6Ks (US version) @2*$1500. 230V hardware is generally cheaper (fewer parts higher volume).

 

[cajocars]

How do the LuxPower or Deye AIO compare to Victron for your use case? Feels like a premium is being paid for Victron, which to me provides less value when you can’t grid tie.

The US version of the 6K can take two strings of 13A panels (4kW each string), and is stackable. Deye is supposed to be affordable in Europe.

You can get to 16kW-DC 12 kW-AC with two LuxPower 6Ks (US version) @2*$1500. 230V hardware is generally cheaper (fewer parts higher volume).

Isn’t Deye grid tied?

 

[zanydroid]

Isn’t Deye grid tied?

It’s a hybrid. I don’t know what operating modes it has for using a grid connection, IE whether it will properly control transfer relay to avoid parallel operation if you have no interconnect agreement. Are you allowed to interconnect in parallel with no agreement as long as you zero export?