I now have a full year of electric production and consumption measured. I also have the SCL rate updates for 2017 and 2018 so I have updated my solar ROI estimates. The significant change is that the Net Metering benefit has substantially increased due to:
- SCL electric rates are higher in Shoreline than Seattle.
- The 2017 and 2018 rate increases are 5.6% (estimated at 4%)
- An added RSA surcharge of 1.5%
- The coldest winter in 32 years
- More electricity use than I predicted.
- I was still insulating deep into the heating season.
- I guesstimated the kWh it would require to heat a 1955 house with heat pumps.
- I installed a fast (level 2) charger for our Leaf. We were able to use it more, offsetting gasoline with electricity.
- The increased usage is all at the higher 0.14¢ price tier.
Reasons 1-4 weren’t known during my initial estimates. Reasons 5 and 6 were planned but their scale was unknown. I knew I’d be removing all natural gas appliances (furnace, water heater, fireplace) but I hadn’t yet decided whether to install tankless electric or a heat pump water heater. I hadn’t chosen the heat pumps for house heat yet so I didn’t know their HSPF. I also didn’t know how much more we’d be able to use the Leaf.
The net result is that I now estimate a 100% return on the solar array in the 6th year instead of the 8th year.
Notes
- I did not include the cost of the heat pumps or the heat pump water heater. Those were efficiency upgrades that I’d have done anyway. If I were keeping natural gas, I’d have replaced the old 80% furnace with a 97% modulating furnace and the “well past its expected lifespan” gas water heater with a gas tankless. In both cases the costs are comparable and just like replacing the fridge, the efficiency increases have their own ROI schedule.