Powerwall Reserve - How Low Do You Go?

[jacobp]

Since we don't have TOU pricing and have full net metering, I'm planning on leaving ours essentially full. Not only does it give the most protection if there is an outage, but it avoids the efficiency loss and potential reduced lifespan that can come with using the battery.

If and when (and I do think it will happen in the next several years) our utility offers us TOU pricing, I could see changing how we use the battery.

Looks like we live in the same general area. I have TOU pricing from PEPCO. I believe that happened when I was part of a pilot program they had years ago where they installed a separate meter for my EVs. The EVs rate is about 1/3 of the rate I pay for electricity for the house. As part of the deal, I think, they put me on a TOU pricing structure.

So given that I have TOU pricing, what would suggest my reserve be for the powerwall?

 

[jacobp]

Based on your location, I'm assuming you are also in PEPCO territory. That is why, for me, leaving it maxed out is the way to go. I'm not as concerned about Tesla's "Self-powered" score since my goal is not to be off-grid, so keeping the powerwalls full is the best choice financially, and it conveniently means I'm always as prepared as can be in the case of an extended outage.

The other side of this that hasn't been discussed might be what is best in terms of environmental impact, which perhaps gets even more complicated. On that front, the ideal would presumably be to operate your home on battery during peak load times and export solar to the grid (and/or not import grid power.) But, since PEPCO doesn't provide an incentive in the form of TOU pricing, it would be something you would have to choose to do on your own (and, as a note, PEPCO's pilot TOU program sets peak in the afternoon in the summer but the morning in winter.) And the impact does depend a lot on what mix of fuels the utility uses during those times, taking into account also the ~10% energy lost by storing it in the powerwall.

Where do you find the times of day for PEPCO for on-peak and off-peak.

 

[wjgjr]

Looks like we live in the same general area. I have TOU pricing from PEPCO. I believe that happened when I was part of a pilot program they had years ago where they installed a separate meter for my EVs. The EVs rate is about 1/3 of the rate I pay for electricity for the house. As part of the deal, I think, they put me on a TOU pricing structure.

So given that I have TOU pricing, what would suggest my reserve be for the powerwall?

Where do you find the times of day for PEPCO for on-peak and off-peak.

PEPCO's rate information can be found here, and the "Current Tariff" link does mention peak periods (usually): Current Tariffs (Maryland) | Pepco - An Exelon Company

I don't know for sure which rate plan you have, but I'm guessing either PIV or R-PIV for the EV (there is an older rate plan called "EV", but that has not been available for some time to new customers.) I don't have an EV, so I don't know all of the details of the rates, but I did look at it when I was installing solar for future planning and noted that the PIV and R-PIV rate plans explicitly said they are not compatible with the NEM rider. I am not sure if you are just adding a PW or solar+PW, but if adding solar, note that the rate plan you have now potentially is not compatible if you were planning to take advantage of the good net metering terms that PEPCO offers.

 

[bob_p]

We're under a Free Nights plan (free electricity from 9PM to 9AM) and have set our reserve to 30%, to provide us a reasonable amount of power if we're hit with a power outage.

If we lowered the reserve %, we would have more power to lower the prime time usage (9AM-9PM), but the trade-off would be less power if we have a power outage when the PowerWalls are at the set reserve %.

For a specific home, estimate how much power the house typically consumes and then multiply that by the number of hours you want to operate during an outage - and then convert that into the % of your PowerWall capacity.