Hybrid v AC-Coupled Solar/Battery Inverters ACvDC

Rheumatoid

Bigmacroxy said:

QrizB said:

Bigmacroxy said:

The reason they state is that because the array is 150 metres from the house (ground mount), the AC inverter must be located outside at the array itself and only AC taken into the house, because of DC voltage drop.

This seems a bit odd but it depends on the configuration of your array.

If your array is a single string, the operating voltage of your array could easily be 400VDC or more. That will have a lower loss over a 150-metre cable run than 240VAC will.

Thanks so much for the reply.
There will be two strings of 8 panels, each string with Open Circuit of 420 volts at 11 amps.

I did read from another message board that "you MUST use your highest voltage across your longest run with the thickest wire you can afford".

So I'm still ost as to why this solar company is advocating an inverter underneath the array, bringing back AC which will lose more voltage % compared to the whole. 

Should I insist on DC and a hybrid inverter? I don;t want to get another supplier as the wait now is over 9 months.

Power (W) losses are proportional to current (I) squared x resistance (R). So for transmission of a given power (VI) you need to reduce the resistance (thicker/shorter copper) and/or the current to reduce losses. To transmit a given power you can up the voltage to reduce the current - as happens with national grid. Not sure how significant it would be on a short run like yours tho.

ABrass

G98 is up to 16A per phase, G99 is over 16A per phase 

QrizB

Bigmacroxy said:

QrizB said:

Bigmacroxy said:

The reason they state is that because the array is 150 metres from the house (ground mount), the AC inverter must be located outside at the array itself and only AC taken into the house, because of DC voltage drop.

This seems a bit odd but it depends on the configuration of your array.

If your array is a single string, the operating voltage of your array could easily be 400VDC or more. That will have a lower loss over a 150-metre cable run than 240VAC will.

Thanks so much for the reply.
There will be two strings of 8 panels, each string with Open Circuit of 420 volts at 11 amps.

What will Vmpp be, around 340V and 10.5A, for 3600W per string? 7200W total? 31A at 230VAC or 21A at 340V?

Let's assume that the installer uses 6 sq. mm. cable for the 150m link. At 3 milliohms per metre per conductor, that's a total cable resistance of 900 milliohms (0.9 ohms).

• 31A at 230VAC will drop 28 volts, and will lose 865 watts.
• 21A at 340V will drop 19 volts, and will lose 397 watts.

Neither of those would be acceptable in practice, but at least if you run DC and have the inverter at the house you'll have a working system. With a 28V AC drop your inverter at the array will keep tripping on high voltage.

In practice you'll need to run much thicker cable with an AC system, to ensure that the inverter doesn't trip out, but however thick the cable is it will remain true that the AC system will lose more than twice as much power as the DC one.

Even with 16 sq. mm. cable I think you're looking at a 10.5V drop with an AC circuit, vs. 7V with DC, and you'll still risk tripping on high inverter voltage.

Bigmacroxy said:

Should I insist on DC and a hybrid inverter? I don;t want to get another supplier as the wait now is over 9 months.

I would insist on DC unless the installer can show you their own voltage drop and power loss calculations, and demonstrate that the AC system will work.

(If there's an actual electrical engineer reading this, please correct me.)

NoobSolar

G99 is for anything above the 3.68 limit up to 50MW.