Our Solar PV system was sized to produce 6,131 kWh annually. I am happy to say actual production exceeds the design targets. The average for our 5 years of ownership is 6,510 kWh per year, as shown in the chart to the left. In 2018 we had our best PV production year generating 6,728 kWh as of post-sunset, Dec 31, 2018. I attribute the 2018 increase to SunPower’s micro-inverter upgrade they installed in Spring 2018.
Lifetime production to date is 32,574 kWh. That is, in five years of ownership, we avoided purchasing 32.6 mWh of utility supplied electricity from PG&E, instead using clean, renewable power from our rooftop. Additionally, our SunPower owner’s web page reports that our solar plant avoided some 25 tons of CO2 emissions or 24,000 pounds of coal being burned.
To the right is a composite chart comparing our utility company (PG&E) sourced electricity before and after we installed Solar PV in December 2013. The reduction in PG&E sourced power in the first year of ownership, 2014, is impressive compared to our consumption in the previous year. The top half of the chart shows 2013 utility-sourced power by month without benefit of PV. The bottom shows 2014 purchased power after the PV investment. The blue bars show purchased power and the green bars in June and September 2014 reflect excess PV power we sold back to the utility company. All values are in kWh (kilo-Watt hours).
Our purchased utility power decreased to 507 kWh in January 2014, our first full month after the PV installation, at a cost of $43 ($.085/kWh). Compare this to January, 2013, when we purchased 1,159 kWh for $186 ($.16/kWh -- a difference of 652 kWh and $143 in one month.
Since we installed our solar, our yearly utility expenses have steadily increased, mostly because of PG&E price increases and add-on fees aimed at solar-installing customers. Our power consumption also increased due in part to purchasing a plug-in hybrid electric vehicle (PHEV) in late 2014.
The table to the left shows our history of kWh consumption and expenses since 2009, with the addition of Solar PV in 2014. The last column applies estimated annual savings against the initial cost of the solar installation and projects that the purchase break-even point will occur in May of 2021 after 7.5 years of ownership. This is consistent with what the SunPower salesman told us before our purchase, even with the unplanned power requirements of our PEHV.
Speaking of our PEHV, a few comments about the marriage of that vehicle and solar. The MyFord web site reports that of our C-Max's total 24,609 miles driven, 21,370 miles were on battery that we charged mostly at home. If we assume a mileage of 30 miles to a gallon of gasoline, and a price per gallon of $3.00, then the annual savings on gasoline over the 5-year period is $427/year. You could say we are driving this car for free, or at least offsetting most of our electric utility expenses. I should add that the purchase price of this car was the same as the non-PHEV model when Federal tax credits are included. Conclusion: our PHEV and Solar PV investments are working well for us.