Are the TOU rate plan and PW operation mode irrelevant for a net producer?

[jgbaum]

I finally got my PTO on a 16kW system with 2 PWs in San Diego and am now trying to determine the best PW operation mode (self-powered vs. time-based) and SDG&E TOU rate plan. Until we get another EV and swap out some more gas appliances for electric, I expect to be a net producer for the next few years. Since we will be paid at the wholesale rate for any excess generation at the end of the year, it almost seems like the rate plan and PW operation mode are irrelevant. What do you all think?

I've dug around the forum a bit and think this is the general sentiment, but wanted to verify. Please point me to any other relevant threads on this. Thanks!

 

[miimura]

If you are sure that you will produce more kWh than you consume over the whole year, then you will not benefit from a TOU rate plan and the accompanying TOU operation of the Powerwalls. You can either leave them in Backup if you are worried about losing power, or just run in Self-Powered mode and vary the Backup Reserve according to your likelihood of losing power. Self-Powered will also minimize your Non-Bypassable Charges if your rate plan has that "feature" like other California utilities.

 

[cwied]

I think there is an edge case where someone who is only a slight kWh overproducer could be penalized by a TOU rate if the production is always at a lower rate than consumption. I believe theoretically you could be a net producer and still owe money at true up. Using self-consumption mode on the batteries would likely eliminate this possibility, though.

 

[holeydonut]

I think it depends on what you think TOU rates will look like and the % of energy you produce/use in each TOU category.

Consider this example with no Powerwalls and a hyper simplistic view where the home isn't contemporaneously using its own generation during peak time:

Home uses 10,000 kWh per year
50% consumption occurs at peak times
50% consumption occurs at off-peak times

Solar generates 10,000 kWh per year
25% generation occurs at peak time start to sunset
75% generation occurs at sunrise to off-peak time end

Assume peak = $0.50 per kWh and off peak is $0.25 (kinda close to PG&E's EV2-A rates today).

Consumption is 5,000 x $0.50 + 5,000 x $0.25 = $3,750 of value
Generation is 2,500 x $0.50 + 7,500 x $0.25 = $3,125 of value

So this home would need a PV that was 120% oversized to just break even on this NEM example.

It would make sense to oversize the PV if the roof could support it. But if the roof is constrained due to space or shading, then some batteries would help smooth this out. Although the homeowner wouldn't see as good ROI for TOU shifting as compared to the solar since they'd be spending like $15k to save $625 per year.

But personally I think the California utilities will continue to widen the peak time and widen the gap between peak and off peak rates. We could see 75% of annual use during peak time, and off-peak solar credits at only $0.05 per kWh in the next few years.

 

[sunwarriors]

I finally got my PTO on a 16kW system with 2 PWs in San Diego and am now trying to determine the best PW operation mode (self-powered vs. time-based) and SDG&E TOU rate plan. Until we get another EV and swap out some more gas appliances for electric, I expect to be a net producer for the next few years. Since we will be paid at the wholesale rate for any excess generation at the end of the year, it almost seems like the rate plan and PW operation mode are irrelevant. What do you all think?

I've dug around the forum a bit and think this is the general sentiment, but wanted to verify. Please point me to any other relevant threads on this. Thanks!

How long did your PTO take from SDG&E after inspection? If you have an EV, did you consider TOU EV-5 instead? Since charging EVs take so much energy, if you charge 2-3 hours a day at 0.09/kWh from 12-6am, that would give you a lot of hours to send energy back to the grid at 0.56/kWh.

I think in my case, I use almost 4x the energy during On-Peak vs. Super Off-Peak and with WFH, use just as much Off-Peak as On-Peak as well.

I think with possible wildfires as a constant concern, generation might be affected as well with what's going on in Northern CA from some posters here.

 

[jboy210]

I finally got my PTO on a 16kW system with 2 PWs in San Diego and am now trying to determine the best PW operation mode (self-powered vs. time-based) and SDG&E TOU rate plan. Until we get another EV and swap out some more gas appliances for electric, I expect to be a net producer for the next few years. Since we will be paid at the wholesale rate for any excess generation at the end of the year, it almost seems like the rate plan and PW operation mode are irrelevant. What do you all think?

I've dug around the forum a bit and think this is the general sentiment, but wanted to verify. Please point me to any other relevant threads on this. Thanks!

Assuming that your goal is to not pay for electricity and you have the excess power, then self-powered may be the best mode for you. This assumes you have enough battery capacity to last through the late-day peak periods. This may changes as you switch more loads to electric and that results in your electricity usage during peak periods increasing.

 

[miimura]

The examples above where TOU could hurt you are definitely possible without Powerwalls, or if the Powerwalls are used for backup only. With Powerwalls, you should be able to avoid using grid power during the Peak hours. For simplicity, I would probably choose TOU-DR-2 because it has a simple 4pm-9pm Peak 7 days a week. The DR-1 plan has a cheaper Super Off-Peak that you could use to charge your EV, but it's probably not worth it if you are a net generator. DR-1 also has that weird double Super Off-Peak mid-day in March and April.

You also didn't say whether you are in the inland San Diego area or the more coastal area. That can have a big impact on how much you use A/C and whether the two Powerwalls will be able to power you through the Peak hours.