The Informatics Professor Goes Solar

This summer we installed solar panels on our roof at home. The timing was good since we needed our roof replaced, which enabled us to install solar panels right on top of it. Many people tend to think of Portland, Oregon as a cloudy place, but the summers are mostly sunny and, above the 45th parallel, the days are long. Of course, even when it is cloudy, solar rays still shine down on the Earth (and our solar panels). 

 

 

A natural question is the economics of solar energy for a home and location like ours. They are surprisingly good. Last year, our electricity use averaged about 600 kilowatt-hours (kWh) per month, which averages to about 20 kWh per day. We have always used more electricity in the winter than the summer, perhaps due to the summers being mild and the days of winter being short. We opted to install a system that would aim to zero out our electric bill. We could have added additional capacity to account for an electric car, but we are not looking to buy a new car at this time.

The system includes a reversible meter, so when the panels exceed our electricity use, the excess goes into the Portland General Electric (PGE) grid. While the excess rolls over from month to month, it does not roll over years. So we will likely build up excess production over the summer that will be offset in the winter. We will see for sure when our PGE bills start rolling in.

Our 24 solar panels generate up to 7.68 kW of DC power and 5.76 kW when converted to AC power. The system includes an app that allows us to track the energy generated by the system. It has some nice reporting features that allow us to compare different days. The app does not track how much energy goes into the grid, although we can read that off our reversible meter. The app also allows us to have a public Web page so anyone can look at the data for our system. While the app has more data to show, the public Web page does allow viewing of daily electricity generation:

https://enlighten.enphaseenergy.com/pv/public_systems/LvDv1870535/

As the solar electricity is purportedly cheaper than that delivered by PGE, the system is estimated save about $34,000 over its lifetime. It doesn’t hurt that we will get a 26% federal tax credit this year and additional incentives from the state of Oregon. All in all, we believe it is a sound investment not only in our house, but also in the global energy future.

Our energy usage will also be reduced by the 6.5-inch R35 insulation under the new roof. This will be beneficial both with our electronic air conditioning in the summer and our gas heating in the winter.