Grid-tied solar

[aczlan]

It should also be possible to make the inverters believe grid power is present by using a pair of automotive-type 120v, 60 hz inverters powered by a 12v battery. The DC cables on the battery could be diode protected, at least the battery wouldn't get fried if things aren't working well.

You would have to have a pair of inverters that could parallel or it would not work well.

Aaron Z

[Redneck in training]

The best think is to use inverter that can automatically switch between grid tie or stand alone. It will fail (shut down) only if the demand exceeds available power. Google hybrid solar inverter. In example Off-Grid Inverters.*SMA Australia Pty Ltd

[dave1949]

You would have to have a pair of inverters that could parallel or it would not work well.

Aaron Z

Yeah, two independently running 60 Hz, 120v inverters are going to cause problems with 220v circuits.

I was thinking a generator is not really necessary. It can't take that much power for the voltage sensing lines on a couple strings of microinverters. If one of the AC devices being powered by the solar pv is a 12v battery trickle charger, it might be possible to home brew something that works without a generator running.

Or, buy one of those hybrid inverters that Ladia linked and don't burn down the house.

[dave1949]

The March, 2013 results.

Below the model again this month. Like last month, it was down by about 2 sunny days. This month I saw the highest daily output (30.0 AC kWh) since installation. The better days were producing 25-28 AC kWh. The first week of the month was very weak, 49 kWh in seven days.

My net usage was 489 kWh of which the system produced 462 kWh. To date, I have taken 268 AC kWh more from the grid than supplied to the grid. For a perfect result for my grid-tied arrangements here in Maine, that number would be zero by the end of this July.

The PVWatts model AC kWh predicted/actual:
2012
Aug. 383/460.7
Sep. 394/480.9
Oct. 369/378.6
Nov. 283/400.3
Dec. 331/297.2
2013
Jan. 388/440
Feb. 412/375
Mar. 509/462
Apr. 374/TBD
May 353/TBD
Jun. 308/TBD
Jul. 341/TBD

[TheGoose]

Great info Dave. At these rates how long do you think the system will payback?

[dave1949]

Great info Dave. At these rates how long do you think the system will payback?

I think the original payback estimate of 17-18 years back in post #3 is holding up. Cumulatively, I am 225 AC kWh's ahead of the model prediction, so I am not too worried about meeting that. When the system is new, and there is no history, the question that really matters is will the system produce what the model says it will, since that is the basis for the payback period. With some history now, I am gaining confidence that the model is in the ballpark.

As near as I can tell from our mostly useless percentage gauges on the propane tanks (I have two 120 gal tanks), I probably under-estimated the amount of propane that was being used for domestic hot water. If so, that would reduce the payback period some.

[Redneck in training]

The March, 2013 results.

Below the model again this month. Like last month, it was down by about 2 sunny days. This month I saw the highest daily output (30.0 AC kWh) since installation. The better days were producing 25-28 AC kWh. The first week of the month was very weak, 49 kWh in seven days.

My net usage was 489 kWh of which the system produced 462 kWh. To date, I have taken 268 AC kWh more from the grid than supplied to the grid. For a perfect result for my grid-tied arrangements here in Maine, that number would be zero by the end of this July.

The PVWatts model AC kWh predicted/actual:
2012
Aug. 383/460.7
Sep. 394/480.9
Oct. 369/378.6
Nov. 283/400.3
Dec. 331/297.2
2013
Jan. 388/440
Feb. 412/375
Mar. 509/462
Apr. 374/TBD
May 353/TBD
Jun. 308/TBD
Jul. 341/TBD

My system also didn't reach predicted production.
predicted/actual
3420/3160 kWh

[Redneck in training]

Here is a different perspective of viewing PV system performance.

https://enlighten.enphaseenergy.com/...ems/h2eX136588 That is my system.

https://enlighten.enphaseenergy.com/public_systems Other public access systems. Click on "e" on the map.
When system view is displayed. Click on "Get a fresh perspective on solar monitoring. Click here to preview" on top of the screen.

[dave1949]

April is off to a good start. 193 AC kWh for the month as of this morning. That is 51% of the model prediction in 12 days. I will count today in, April 12th, since it is going to be a loser with the storm passing through.

[Redneck in training]

I just read few days back that US solar market increased 76% last year.