Our time-of-use electrical meter tracks peak-period consumption separately, because for peak hours we’re billed at about 3x the offpeak rate. Watching this number gives us a good idea of our total energy production, because we need to not only zero out our peak usage, but generate enough extra (at a 3x payback rate) to zero out offpeak usage too.
We’re not there yet.
To be fair, we shouldn’t be there yet; if we were, it would mean we bought an unnecessarily big PV system. We only need to zero our balance over a 1-year period. We’ll build up a deficit through the winter, then make up for it in the summer. In fact, by late August we should have a large outstanding credit, to see us through the Fall’s shorter days.
Prior to the solar install, we burned about 4.5 kWh on a typical weekday afternoon (noon-6pm). (Measuring this was part of our sizing effort.) Therefore, in a 13-weekday period, our pre-solar peak-period usage would have been about 58 kWh. But thanks to the PV array, we’ve burned only 16 kWh. Considering the snotty weather we’ve been having, that’s pretty impressive. I think we’ve only had about three really sunny days since the TOU meter went in, yet the solar array has covered 72% of our peak-period needs. And actually it gets dark by 5:00 PM still, clipping an hour of generation time off the peak period even when it’s sunny.
During one of the many rains we’ve had, I discovered water dripping from the bottom of the DC disconnect switch. Further inspection indicated that, against all reason, the water was coming from inside the weather-tight switchbox. I don’t know what a short-circuit in that box could do to my PV array but I was not interested in waiting to find out.
The installer came out right away to open the switchbox. It was disgusting. I should have taken a picture — the inside of the casing was covered with funk and rust-colored grit and slimy mildew-looking stuff. Apparently two grommets had been left out when this box was wired up. The first grommet would have kept water from following the power cable on the roof through its hole in the eave. The second would have kept water from following the power cable into this switchbox. It was an installation error.
The technician replaced the entire DC switchbox. I was impressed with that.
“What’s that slimy black stuff?” I asked him as he was working.
He surprised me by running a finger through it to feel its consistency. Then he looked a bit alarmed, with an index finger full of goo, and hurriedly wiped it on his pants leg. “It’s … I don’t know. It’s grossness.” he declared. “Um, that’s a technical term.”