Any Benefit for TOU Power Shifting in My Situation?

[BIC1]

Have a four-year old 12k PV (actual peak 10k) system and one PW for emergency backup only. I leave them it 100%. Finally, after a four-year wait, I'm promised two more PWs installed in October.

On October 1, Missouri is implementing TOU plans with only one specified for (monthly tru-up) net-metering customers. Base rate is about 14 cents per kWh. For Jun - Sep, add on a penny penalty for 4 - 8 pm and credit a penny bonus for midnight to 6 am. For Oct - May, 4 - 8 pm peak penalty drops to 1/4 of a penny; still get the full penny credit for midnight to 6 am. Any monthly overproduction is bought back for a whopping 2 cents per kWh.

I can easily set my PHEV to charge overnight and set dishwasher delay for same. My wife does a lot of baking but can keep that and laundry outside 4 - 8 pm.

While I could program 3 PW to provide all power 4 - 8 pm, is it worth the wear & tear of cycling the PWs up & down? My annual electric bill totals about $600. I would be close to zero if we had annual net-metering instead of monthly. I'm guessing I might save some nominal amount like $10 a year using PWs to shift power. My total grid usage has been 2950 kWh in 2020; 2132 kWh in 2021, 1168 kWh in 2022, & 2424 kWh for the first 9 months of 2023. If 1/4 of my usage is peak, that's an extra $5-10 per year if my math is correct.

That wouldn't be worth the battery wear on $30,000 worth of PWs. If I'm going to save a few thousand dollars per year, that might be a different matter. Again, the primary reason for the PWs is emergency backup.

Am I viewing this correctly? Any thoughts on this? Thanks.

 

[wwu123]

I believe you lose about 10% of the Powerwall energy due to inefficiencies in the charge-discharge cycle, so I would look at it as every 1 kwh you load shift using the Powerwall, you're losing 1.4 cents (at the base rate), which is larger than the max 1 cent from time-shifting. So wouldn't be worth it to use the Powerwall to load-shift alone.

However, if you have large loads like the PHEV charging that you can use behavioral shifting as you describe, then might be worth to get the 1 cent discount to move those past midnight. That's assuming the base rate is the same 14 cents on the non-TOU plan as well.

 

[BIC1]

That's assuming the base rate is the same 14 cents on the non-TOU plan as well.

There are various plans and rates, but this plan is mandatory for net-metering.

 

[Jeremy3292]

For Jun - Sep, add on a penny penalty for 4 - 8 pm and credit a penny bonus for midnight to 6 am. For Oct - May, 4 - 8 pm peak penalty drops to 1/4 of a penny; still get the full penny credit for midnight to 6 am. Any monthly overproduction is bought back for a whopping 2 cents per kWh.

I can easily set my PHEV to charge overnight and set dishwasher delay for same. My wife does a lot of baking but can keep that and laundry outside 4 - 8 pm.

While I could program 3 PW to provide all power 4 - 8 pm, is it worth the wear & tear of cycling the PWs up & down?

Again, the primary reason for the PWs is emergency backup.

Doesn't seem worth it for only $0.01 per kWh savings. Most on-peak vs off-peak rates have a much bigger spread than what you have. I would just manually shift loads like you said (EV charging, laundry, dishwasher, etc.) to the off-peak or super off-peak hours.

In my area the on-peak rate is $0.065 per kWh difference from 6-9pm, so I plan on manually load shifting like you and only running large necessities like HVAC and fridge during those periods from the Powerwalls. You can also set your HVAC thermostat to heat/cool higher/lower than normal ~1 hour before the on-peak period so you don't sacrifice too much comfort during the on-peak periods.

I'm not really worried about the cycling as leaving them fully charged at 100% all the time and never really using them is arguably worse for degradation than some minor cycling. However, if you're doing heavy cycling from 100% to 10% every single day, then I would agree that is not good for longevity.

The batteries have a 10 year warranty for minimum 70% remaining life though. I'm sure in 10 years batteries will be so much cheaper you can probably just get new ones then also worst case scenario.

 

[Matt-FL]

If I bought a $30k car, would I leave it in the garage only for the event I might need it in an emergency? Maybe a car isn't a good analogy, as in 10-15 years the car will still be usable. I imagine in 15-20 years our Powerwalls will be giant paper weights, regardless of whether you used them or not.

Even idle, these batteries will degrade. My thoughts are to use them while you have them and they are of value (pre-warranty expire). You can set your backup %, but let them get used.

 

[BGbreeder]

If I bought a $30k car, would I leave it in the garage only for the event I might need it in an emergency? Maybe a car isn't a good analogy, as in 10-15 years the car will still be usable. I imagine in 15-20 years our Powerwalls will be giant paper weights, regardless of whether you used them or not.

Even idle, these batteries will degrade. My thoughts are to use them while you have them and they are of value (pre-warranty expire). You can set your backup %, but let them get used.

So that makes a pricey generator a better investment as its resale value in ten years is good?

I'm with you; use it, or lose it. The Powerwalls are degrading as we surf the web.

 

[Jeremy3292]

I'm with you; use it, or lose it. The Powerwalls are degrading as we surf the web.

I agree. Powerwalls aren't something you can resell like a car if you keep it in great shape. The only time they will be sold is as part of selling your entire house and I doubt anyone will be like "nah it's a deal breaker your Powerwalls have been cycled too much"

 

[MtBean_COCR]

Have a four-year old 12k PV (actual peak 10k) system and one PW for emergency backup only. I leave them it 100%. Finally, after a four-year wait, I'm promised two more PWs installed in October.

On October 1, Missouri is implementing TOU plans with only one specified for (monthly tru-up) net-metering customers. Base rate is about 14 cents per kWh. For Jun - Sep, add on a penny penalty for 4 - 8 pm and credit a penny bonus for midnight to 6 am. For Oct - May, 4 - 8 pm peak penalty drops to 1/4 of a penny; still get the full penny credit for midnight to 6 am. Any monthly overproduction is bought back for a whopping 2 cents per kWh.

I can easily set my PHEV to charge overnight and set dishwasher delay for same. My wife does a lot of baking but can keep that and laundry outside 4 - 8 pm.

While I could program 3 PW to provide all power 4 - 8 pm, is it worth the wear & tear of cycling the PWs up & down? My annual electric bill totals about $600. I would be close to zero if we had annual net-metering instead of monthly. I'm guessing I might save some nominal amount like $10 a year using PWs to shift power. My total grid usage has been 2950 kWh in 2020; 2132 kWh in 2021, 1168 kWh in 2022, & 2424 kWh for the first 9 months of 2023. If 1/4 of my usage is peak, that's an extra $5-10 per year if my math is correct.

That wouldn't be worth the battery wear on $30,000 worth of PWs. If I'm going to save a few thousand dollars per year, that might be a different matter. Again, the primary reason for the PWs is emergency backup.

Am I viewing this correctly? Any thoughts on this? Thanks.

Hi, I have a similar situation. My utility is a rural electric (not Investor Owned Utility IOU) so rates are pretty bad too. One thing you appear to be missing is the time shift of the batteries which allow for charging of your PHEV from stored PV (free) energy. Most of these PHEVs to my knowledge are less than 40 kWh, so with 3 Powerwalls at 13.5 kWh you should just be able to charge your car for free, assuming you run it down completely every day. If you need to charge less, all the better. In the summer I leave 60% available for arbitrage and 40% for backup, in winter it is the opposite because that is when the power is more likely to go out and the roof panels more likely to get covered by snow for days at a time.

 

[RKCRLR]

With regards to wear and tear I ran the numbers once (I don't remember the exact results) but a powerwall is warrantied for 70% energy retention for 10 years and unlimited cycles for self-consumption/backup mode, and 37.8 MWh aggregate throughput for other uses. 37.8 MWh which equates to about 7.8 years (as I remember) of 100%-0% cycles so that gives you an idea its cycle life. So if you cycled it daily to 50% that means it would last about 15 years. You get to a point that it is likely to die of old age rather than cycles.

 

[BIC1]

If I recall correctly, think the installer suggested that with it only cycling between 98-100% daily, it should last 20 years.