Placing the Inverter close to the solar panels

Brianellul

Hi All

I've been going around asking for quotes and a couple of suppliers suggested that I'll place the Inverter as close to the solar panels as possible! Why is this?
If I use a thick enough cable from the panels to the inverter to carry the DC, what difference will it make if it's DC or AC?

Regards
Brian

stephendv

Re: Placing the Inverter close to the solar panels

I assume this is for a grid-tie installation.

Depending on what inverter and how many panels you have and the distances involved, I would have thought that the higher voltages would be between the panels and the inverter, e.g. 500 VDC for most SMA inverters, so it would make sense to put the longest distance between panels and inverter and the short distance between inverter and grid.

Windsun

Re: Placing the Inverter close to the solar panels

Brianellul wrote: »

Hi All

I've been going around asking for quotes and a couple of suppliers suggested that I'll place the Inverter as close to the solar panels as possible! Why is this?
If I use a thick enough cable from the panels to the inverter to carry the DC, what difference will it make if it's DC or AC?

Regards
Brian

I don't know why they would suggest such a thing. I hope one of them was not us.

mike95490

Re: Placing the Inverter close to the solar panels

Maybe they are thinking of just isolating the DC, so the building inspector does not get confused.

blackswan555

Re: Placing the Inverter close to the solar panels

I'll place the Inverter as close to the solar panels as possible

I would presume they are talking about inverter batteries & charge controller/system as close to panels as poss,
That would be to keep the low voltage DC wire run to a minimum and the wire size down,
You can use "A thick enough" cable but take into consideration 1000w @ 24v is 41 amps, 1000w @ 230v is 4.3 amps nearly 10 times as much, Big cable is not cheep nor fun to install

Have a good one
Tim

BB.

Re: Placing the Inverter close to the solar panels

If you can supply a little more information. Grid Tied or Off Grid, size of system, distances involved, etc.

For a first approximation, whatever has the highest voltage should be the "long run". Grid Tied inverters run around 200-600 volts DC and are very good at long distances.

PWM Off-Grid solar battery charger either run at battery bank voltage (12-48 volts) and are not very good at long distances at all.

MPPT type off-grid solar battery charge controllers can operate around 100 VDC maximum and are a better at long(er) distances between the solar panels and the charge controller (battery leads should always be kept short).

-Bill

Brianellul

Re: Placing the Inverter close to the solar panels

My system will be installed in Malta (Europe), 230v grid voltage.

The system is a grid-tie ~ 2KW (9 x 230W) panels. The panels quoted are the IBC PolySol 230TE, nominal voltage of 29v and a Sunny Boy inverter (don't know the model yet) Therefore 29v x 9 panels = 261v DC. The length from the panels to the inverter will be about 20 meters.

Also I was quoted another system using 12 x ET Solar Panels 180w and a KAKO Inverter (Powador 3002). Nominal voltage of 26v per panel.

I was thinking of using 4mm copper wire to carry the DC down to the inverter. Does DC current need a special type of wire... higher gauge? or DC current = AC current? This is confusing me!

Also, which is the best between MonoCrystalline and PolyCrystalline? I'm asking because both have approx the same conversion rate, both degrade with increase in temp... is it just the cell structure?

mike95490

Re: Placing the Inverter close to the solar panels

Amps are amps, DC-AC, same wire. As long as you keep the resistance losses low, with thick enough wire, you are OK. Insulation is rated by voltage, again AC, DC, no difference.

stephendv

Re: Placing the Inverter close to the solar panels

261V @ 25 degrees C, this will come down when the panels heat up, at 70 degrees you're looking at 213V, so the grid side of the inverter will have a higher voltage. It looks like it's not going to really make a huge difference where the inverter is, so you could choose to install it where it's more convenient.

One thing to watch out for is the low voltage of the array, I could only find the transformerless SB 2100 TL that would accomodate the low MPP of the array in summer. Some European countries have not approved TL inverters yet.

You can play with the configuration using SMA's sunny design tool which is downloadable from their website.

BB.

Re: Placing the Inverter close to the solar panels

One issue to watch with GT inverters... Their output voltage range is set to the legal requirements for utility power. If the run is too long from the pole to your GT inverter, it is possible that the voltage drop from the inverter's/home's current will cause the inverter to read the grid voltage as too high or too low at times during the day and cause it to shutdown for 5 minutes.

So--for "long runs", I would tend towards making that with the Solar Panel cabling instead (no voltage drop issues as long as > minimum input voltage of inverter).

-Bill