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The power company charges more for power during peak hours than at night. In theory, a wall-mounted battery like the Powerwall or several competitors could help mitigate this by drawing power when it is cheap and then emitting it - either back to the grid or to the home - as necessary when power is more expensive.

It is my understanding that batteries also increase the resilience and reliability of the power grid.

Are there any resources that will help me estimate the useful life and estimated return on a battery, based on state and power utility? I don't have solar panels which doesn't help.

  • Cost of battery cf cost of electricity replaced...taken over a time period... – Solar Mike Apr 8 at 4:43
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I've looked into the ROI of batteries and solar and I haven't found something as nice as an online calculator, but a search for "Powerwall Return on Investment" does pull up several blogs and studies about the topic such as this paper on the Stanford website.

We will now calculate the yearly cost of electricity for a family consuming 20 kWh Off-Peak, 0 kWh Peak, and 10 kWh Partial Peak for the entire year for each state average, A.

Cost Per Day = (20 kWh × (1 -.202) + 0 kWh × (1 + 0.819) + 10 kWh × (1 + 0.202)) × = 27.98 kWh × A

Cost Per Year = 365 days/year × Cost Per Day This means that in California, the cost Per year using our PowerWall 2 strategy would be $0.188 kWh × 27.98 kWh day × 365 days year = $1919.98 year.

That's the type of calculations that you need to do. From what I've read you're looking at anywhere from 8-12 years to recoup the investment on this or a solar install.

My personal opinion is that this is a cool thing to do as a hobby and it may eventually pay for itself, but there are so many better ways to "invest" money. Look at typical 10 year returns on any other $7k investment. Another thing to keep in mind as you read is that most of these "studies" ignore battery degradation to simplify the calculations and they assume electric prices will be constant for 10 years (ha!). And then what about the install costs? And what if anything needs to be replaced or diagnosed?

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