# Using an ammeter to monitor a grid tie PV solar inverter?

#### RandySea

Joined Sep 9, 2011
7
We are putting in a 5kw, grid tie photovoltaic system with a Silicon Energy Aurora DC to AC inverter. We will generate a max of 5kw of 240v AC, running to our house electric panel. The run is 260'. That's a long way to walk in winter and deep snow to check on the inverter.

We've been told that digital monitoring equipment compatible with this inverter costs $550 to$2,000, plus the additional conduit and ethernet cable that would go in the power trench between the inverter and our house. We'd have a readout device that would give us all kind of nifty figures and statistics, alarms and emails, etc. At the high end price, we'd be able to monitor over the internet.

All we really want is to be able to tell from the house that the system is working approximately as it should.

#### Bernard

Joined Aug 7, 2008
5,719
My inverter processes each half seperatly, generally 119V & 121V, so there is some unbalance allowing some neutral current. Just to monitor general operation monitoring one leg is probably OK.
Is there any reason that the inverter cannot be placed adjacent to grid panel?

#### RandySea

Joined Sep 9, 2011
7
My inverter processes each half seperatly, generally 119V & 121V, so there is some unbalance allowing some neutral current. Just to monitor general operation monitoring one leg is probably OK.
Is there any reason that the inverter cannot be placed adjacent to grid panel?
The solar panels are 260' from the main power panel in the house, where we make the grid connection. Running 240v AC we can use #4 aluminum wire for a >2% line loss. I hate to think what size wire we'd need to run DC over that distance.

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#### RandySea

Joined Sep 9, 2011
7
The solar panels are 260' from the main power panel in the house, where we make the grid connection. Running 240v AC we can use #4 aluminum wire for a >2% line loss. I hate to think what size wire we'd need to run DC over that distance.
I meant <2% line loss.

#### Bernard

Joined Aug 7, 2008
5,719
It seems to me that the only difference in line loss between AC & DC would be inverter efficiency; or is your panel low V, say under 300V?
AT 48V there would be an unacceptable difference.

#### RandySea

Joined Sep 9, 2011
7
Ok, so here I show my ignorance. There will be 24 panels each with a nominal output of 24v DC. The inverter has two parallel inputs, with one output of 240v AC. I don't know for sure how they are connected.

The inverter specs say Dual Maximum Power Point Tracking, so each array feeds it separately, I guess. The specs also say Operating MPPT Voltage Range: 90  580VDC (360VDC nominal). This suggests 12x24=288v DC output from each array.

At 288v DC, it does seem like the inverter could be at the house. The # of wires would have to be doubled to feed the arrays separately into the inverter's two inputs.

As I said, I don't understand all the logic behind this. What I do know is that the inverter is sold as a unit (waterproof panel) with the two DC inputs (switch boxes with thermal protection), inverter, output switch box, and meter base.

I don't have much choice in inverters since they must be manufactured in Washington State. Which brings me back to the original question of whether I can use an ammeter on the incoming 240v AC as my rough test of solar performance.

#### Bernard

Joined Aug 7, 2008
5,719
To your last question- I see no reason that the 240V AC line cannot be monitored with ammeter.
I believe that my inverter, Sunny Boy 5000US is similar to yours, & that mine, much to my surprise, hard wires the two hot DC lines in parallel from two 12 panel arrays 0perating @ about 348V & 8A. If the same then the panels could be paralled at the source requiring single + &- 16A to 20A lines, about the same as the AC I.
PS: system rated 5.5 kW DC, but only 4 occasions saw 5 kW AC, but really enjoy the \$8.oo, inc. taxes, / mo electric bill. Enjoy.

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#### RandySea

Joined Sep 9, 2011
7
It seems to me that the only difference in line loss between AC & DC would be inverter efficiency; or is your panel low V, say under 300V?
AT 48V there would be an unacceptable difference.
I've got an answer. In theory we could have 576v DC by putting 24 panels in series. That would really reduce the current. However, the inverter panel is designed for two inputs, max 3kw each. So we'd have to run two DC circuits at 288v each. Plus we'd need an additional pair of DC breaker/cutoffs, although I'm not sure why.

#### Bernard

Joined Aug 7, 2008
5,719
Can you check inverter mfg. literature to see if inputs can be paralled?