The thought experiment:
Is it possible to save money eventually by charging the power wall during off peak hours and power your house with the power walls during on peak or higher rate times of day. How long will it take to recoup the costs before you start saving money?
Current 2018 Duke Energy Wake County, North Carolina Rates
| Type of Rate | On Peak | Shoulder | Off Peak |
|---|---|---|---|
| Normal/Flat | 23.955¢ per on-peak kWh | 12.444¢ per shoulder kWh | 7.511¢ per off-peak kWh |
| Time Of Use (TOU) | 10.868¢ per kWh | 10.868¢ per kWh | 10.868¢ per kWh |
Lets Do the Math!
According Tesla’s website for powerwall, the cost of the power wall for 30 kWh per day (average) requires two power walls @ $14,500 (not counting installation)
My worst month or highest energy usage was in August which was around 2200 kWh.
| Scenario | Monthly Bill@ 2200 kWh | Monthly Savings@ 2200 kWh | Break Even Time |
|---|---|---|---|
| Normal | $239.10 | $0 | Impossible |
| PowerWall off Peak rate | $165.24 | $73.86 | 197 Months or 16.5 years |
So “Best case” scenario every month is your worst or most power used month of 2200 kWh, it would take about 16.5 years to start making money or breaking even. This is for North Carolina and maybe other states have a better Time of Use program. If you are in North Carolina, you might want to think of another strategy.
