Today is the solstice, the shortest day of the year when the sun is lowest in the sky. Therefore, our solar system has its worst possible performance, so its time to evaluate the system again. Yesterday we also got our first regular PECO bill accounting for solar generation.

But first, there were a few additional problems getting to this point. PECO continued to charge us “estimated” energy use through November. The week before Thanksgiving, I tried to call PECO, but they just kept transferring me over and over to people that couldn’t do anything to help me. Finally, I filed an informal complaint with Pennsylvania’s PUC and reached out to my elected officials. Sen. Kane’s office was the fastest to respond. Nancy from his office called me a few hours later, and by the end of the day she’d resolved the problem. By the following Monday we’d gotten a corrected bill in the mail from PECO. By the time the PUC did anything, Sen. Kane’s office had already sorted the problem, so well done to Nancy and Sen. Kane’s office. Elected officials can solve a lot of problems like this for you and we are fortunate to have two elected officials with very dedicated staff.

The Tesla system continued to not work and the solar contractor couldn’t send someone out until the middle of November, over a month later. They still couldn’t resolve the issue then, but they gave us a number for Tesla. We called Tesla and they sorted it out in short order and the system has worked without issue since then. However, our electrician came out to do some unrelated work for us in early November and pointed out the solar contractors had not done all the work up to code – if inspected, the system would fail because the insulation was not pulled through into the box. While the contractor couldn’t resolve the issue with the Tesla system, we were able to make them fix that problem.

We are currently at the lowest point of the year for solar energy, and there’s been a number of cloudy days. That said, in our most recent bill we were charged for 5 kWh, so about 30 cents of electricity for the month. PECO also bills about $12 in fees, taxes and an interconnection fee just to be hooked up to the grid. The rest of our energy use was covered by our solar generation plus a reserve credit we’d built up over the previous months. Our expectation is that December and August should be the worst months (August because of air conditioning), so this is pretty good.

The Tesla system provides a wealth of information about energy usage in our house as well as energy production. Because the daylight hours are currently so short, the battery does not cover the entire night. I have it set to discharge to 50%, leaving a reserve in the case of an outage and usually it discharges to that point by midnight. This is primarily due to us doing our most energy intensive activity – cooking – during night time hours currently. If I allowed it to discharge to 10%, it would make it through most, but not all of the night. I’ll have to revisit this again in a sunnier part of the year, but likely it would require 2 Tesla batteries to fully power our small house overnight during the winter. Also of note, the battery cannot fully power the kitchen during cooking, you can see small bumps in the grid use where the power supplied from the battery is insufficient to power the stove, oven and microwave at the same time. Two batteries would also resolve this issue.

Although it says we only supplied 2/3 of our own power, you can also see we generated 31.6 kWh and used only 17.8 kWh yesterday. The Tesla system ignores whatever is produced and sent to the grid, but PECO will account for it and give us a credit to zero out our usage on cloudier days. Even here at the shortest day, the solar panels can produce far more electricity than we use or the battery can store. So far we have not produced enough electricity to produce a SREC – a solar renewable energy credit. The first notice we got was about a month after we turned the system on, so it was early yet. We’ll have to revisit this again in the spring.