On November 21st I finished my first year of solar power with good news: I still had a surplus of power sold to Seattle City Light! Despite using just over 2500 kWh for the year I sold an extra 718 kWh. This just goes to show that solar power really does work in Seattle!
Here's a look at my daily numbers, both raw and a 7 day moving average. When the red "Grid" line is below zero that's a day that I sold power to the utility. I think the daily chart would make for an interesting art print with the gridlines and legend removed. I'm surprised to see the seemingly periodic behavior of solar production oscillating every few days. Click the pictures to open a larger version.
Below are the cumulative numbers for the year. Based on this it looks like I started building a surplus right at the start of June (grid value crosses from positive to negative on June 1st). The plot on the right shows a couple of different interpretations of the data. The blue curve representss the percentage of my use provided by solar on a year-to-date basis, while the red curve represents the solar production as a percentage of my total use for the full year. On the blue curve I started building a surplus on June 1st, while on the red curve I had generated 100% of my annual power needs on August 18th.
Something that's crossed my mind is what to do with my excess of "free" power. Now, it's all actually sold to City Light through net-metering so I'm getting it back as a bill credit, but it's an interesting thought experiment. I've toyed with the idea of getting an electric car in the next few years so I'm curious how far I could drive one using only my power surplus. I looked up the battery capacity and range for each of the cars to figure out how far they can get on each kilowatt-hour, then multiplied that by my surplus.
My recent post on driving showed that in the last couple of years I've been driving my car about 2,500 miles/year. Through sheer coincidence all of these cars are very close to that amount, meaning I could drive them without having to buy any extra power! My most common trip is a drive from Seattle to Bellingham to visit my parents, which is just over 90 miles. Unfortunately only one car is able to make that drive: the Tesla D. My hope is that in the next couple of years the range of the cars will come up enough to let me make that trip.