From my blog, I thought I would crosspost here and start a discussion.
I have had my solar panels now for 6 years, 3 1/2 years of Tesla Roadster driving and charging. I number crunched my data exhaustively and here are my conclusions.
There are many caveats to these conclusions. I expect some feedback on my assumptions. This post was not an easy task, and I assume I have made some errors. I found it quite difficult to create completely accurate data and these conclusions are only good estimates because of the following:
I have had my solar panels now for 6 years, 3 1/2 years of Tesla Roadster driving and charging. I number crunched my data exhaustively and here are my conclusions.
- Charging the car took 10,276 kWh to drive 29,000 miles. This correlates to a 2.82 miles / kWh. The listed rating is 3.3 miles / kWh.
- The system will pay for itself in 5 more years. The first 2 1/2 years without the car only put a few hundred dollars back into the solar because of low usage. I had planned the system while waiting for the Tesla Roadster! So the total number of years with an electric car is about 8 years.
- If I didn’t have solar, my outlay per year for the car at about 7,500 miles per year would be right around $2,000 to charge the car with the standard E-1 rates.
- I am currently on E-6 rates with PG&E. I definitely don’t want the second E-9b meter and the large upfront cost. I also am not very interested in the E-9a time of use periods that are much more restrictive than the E-6 times of use. I think the E-9a rates may make sense for someone whose car charging greatly exceeds their home usage. But I have not done an extensive calculation to compare the two rates.
There are many caveats to these conclusions. I expect some feedback on my assumptions. This post was not an easy task, and I assume I have made some errors. I found it quite difficult to create completely accurate data and these conclusions are only good estimates because of the following:
- The car does not report any useful data such as kWh used for a reasonably long period like a month or a year.
- PG&E data is only the net energy you used. Unfortunately it does not give you a breakdown of energy you generated. Nor do they have any particularly helpful tools on their website.
- My inverter does report the amount it generated on a daily basis, but I don’t have the time or patience to make a record of this.
- I charged the Roadster after 10pm in non-peak hours throughout the period with less than a handful of exceptions.
- I estimated the Roadster charge to be the difference during these periods post-Roadster and pre-Roadster.
- I used someone else’s estimate for monthly variation of solar generation to estimate the amount of power I generated per month.
- I am only using the current PG&E rates to calculate the amount I would have paid without solar, not estimating it more accurately with their frequent rate changes.
- I estimated the amount I generated based upon the solar panel installer’s estimate and the numbers do seem to correlate with what I see when I look at the inverter’s screen readout.
- I had to do some number estimation to put in the monthly baseline calculations.
- I am not considering the time value of money.