After a rough start, I now love our rooftop PV system

It’s been over 3 months since our rooftop system has been hooked up to net metering. I remember the day, October 31st, 2017 when our utility (PECO), replaced our old meter with one that could read the flow of electrons in both directions.

The installers got the panels onto our roof in early August. But to get the generation from our panels interconnected with the grid took some time. This was critical, because we wanted net metering – credit for excess generation that was fed back to the grid.

Why the 3 month delay? The power line to and from our house could have high voltage, said our utility. Meaning sending homegrown electrons out to the grid could be unsafe. The recommendation? Join a pilot program to use an inverter that would limit the voltage we’d push onto the line.
We jumped on this suggestion. But, the initial settings caused the inverter to turn off when voltage hit 253 Volts for just one second, taking 5 minutes to come back on. This happened so often (663 times in a 2-week period, for a total of 55 hours of lost generation) that I began dreading sunny days due to system shutdown. In fact, our system appeared to work better on cloudy days.
To share my frustration visually, take a look at the 2 charts below showing solar production throughout the day. The one on the left is our system; the one on the right is a neighbor’s, on the same day. Our system kept shutting down, right at mid-day, wiping out the beautiful green hump of solar generation that the neighbors saw.

It took a few phone calls with both PECO and our installer, and a re-reading of the PUC regulations, to discover that a setting change (power down the system only after a full minute of high voltage, instead of one second) could resolve this. That made all the difference. Now I’m in love with sunny days and my chart looks more like my neighbor’s.

Our system has been running nicely since mid-November, about 3 winter months. From that date through the end of February,  we generated 1,604 kWh of solar electricity. Our household used 512 kWh of that before it went to the grid, and we imported 1,068 kWh from PECO, mostly at night, for a net export to PECO of 24 kWh. Agreed, this is a tiny amount, but this was over the winter! Given that generation is expected to be much higher in other seasons, this should allow us to gradually replace gas appliances to electric, and eventually charge an electric car.

How big is our system? A total of 29 panels, 12 on the roof facing southeast, and 17 on the rear southwest roof, at a few different angles on an 1880’s Victorian with steep roofs. We selected 335 Watt panels, for a total system size of 9,715 Watts (9.7 kW). Curious what this looks like? Take a look at the time lapse photography of the installation.