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December 12, 2020 / Jim Fenton

Photovoltaic system updates

This past spring, I noticed that our 20 year-old wooden shake roof needed serious work. The roof condition, combined with all of the recent wildfire activity in California, prompted us to replace the entire roof with asphalt shingles. This, of course, necessitated the removal and replacement of the solar panels we had installed in 2006.

In anticipation of doing this, we consulted with our local contractor, Solar Lightworkers, to see what might be done to update the system as well as to add a bit of extra capacity since we now have an electric car. Photovoltaic technology has advanced quite a bit in the past 14 years, so we wanted to take as much advantage of that as possible while reusing components from our existing system. As described earlier, our system had consisted of 24 200-watt Sanyo panels, with half of the panels facing south and half facing west. Because these two arrays peaked at different times of day, we had two inverters to optimize the output of each array.

Design

SolarEdge inverter
SolarEdge inverter

Mark from Solar Lightworkers strongly recommended a SolarEdge inverter that uses optimizers to minimize the impact of shading of some of the panels on the overall system output. This also compensates for the fact that different panels have maximum output at different times of day. As a result, a single inverter is sufficient for our new system. We also added four 360-watt LG panels to increase our capacity. This SolarEdge inverter is also capable of battery backup, but we haven’t opted into that yet.

Since our original installation, building codes had changed a bit requiring that the panels be installed at least 3 feet below the peak of the roof. This made us rethink the layout of the existing panels. When we did the original installation, we were concerned about the aesthetics of the panels on the front of the house. But since that time, so many other houses in our area have installed solar panels that we weren’t as concerned about appearance of panels on the front (south) side of the house. We still have some panels facing west, because they seem to be nearly as efficient economically as those facing west due to time-of-use electricity pricing.

South-facing solar panels, showing 10 legacy panels in a line with 4 new (larger) panels
South-facing solar panels

Data Collection

I have enjoyed collecting data from our photovoltaic system, and have done so more or less continuously since the original system was installed, using a serial interface from one of my computers to the inverters. I wanted to continue that. The SolarEdge inverter comes with a variety of interfaces through which it can send data to SolarEdge’s cloud service, which I can view on their website. Wanting more detailed information, I found that they provide an API through which I can get data very comparable to what I got from the old inverters, and continue to analyze the data locally (as well as using their facilities, which are very good).

One of the unexpected benefits of the SolarEdge optimizers is the ability to see the performance of each panel individually. It turns out that one of the old panels had a power output almost exactly half of the others. I’m not sure how long that had been going on; perhaps since 2006. I found that the panels have a 20-year output warranty, so I contacted Panasonic, which had acquired the Sanyo product line, and filled out some paperwork and sent pictures. They sent me three very similar panels (replacing two panels with cosmetic defects as well as the one with low output) soon after. I was very happy with the service from Panasonic. Solar Lightworkers installed the new panels, and output is where it should be.

Performance

On a typical summer day with little shading, the system generated 23.7 kWh in on 8/30/2019 and 34.8 kWh (+47%) on 8/27/2020. The additional panels would account for 30% of that increase and the defective panel an additional 2%. In the late fall, the old system generated 14.6 kWh on 11/25/2019, and the new system 22.9 kWh (+57%) on 11/26/2020. There are of course other variables, such as soot on the panels from the California wildfires this year.

It will take quite a while for the increased output to pay for the upgrades, of course, but much of that cost would have been incurred just as a result of the need to replace the roof. We are quite pleased with the performance of the new system.

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