I recently had one Powerwall installed. I do not have solar. I do not have an EV. Currently I am on the PGE 'Tiered rate Plan E-1' plan. Using Tesla app I have noticed that the house is self powered with Powerwall 4% of the time. I would like to take more advantage of Time-of-use and leverage the Powerwall during part of the day. But it is unclear to me how to do that. I am not sure which PGE electric rate plan to switch to. Any recommendation? (Sorry if this topic has been discussed already, I could not find a thread).
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PGE rate plan to go with if I have Powerwall but no solar
- Thread starter dkruz
- Start date
First, we need to establish that a Powerwall does not create energy. In fact it’s only 90% efficient, so you lose 10% of the power you put in to Thermodynamics.
So, what’s it good for? It is a buffer, saving energy for a “rainy day”. If your house used to use 10 kWh, now it uses maybe 11 kWh per day!
The only way to “make money” with a Powerwall without Solar is through “arbitrage” — “buy low, sell high”, or “hoard when cheap, consume your hoard when expensive”. Use the battery to power your house when ToU power is expensive, and charge the battery when power is cheap. Or more extreme, is to dump power back to the grid for a profit.
Utilities HATE that! So, they usually structure their rates to discourage that. You will have to crunch the numbers to see if it makes sense for you. Look out for rules that block charging from the grid, or non-bypassable charges that discourage you from dumping power back to the grid during peak.
So, what’s it good for? It is a buffer, saving energy for a “rainy day”. If your house used to use 10 kWh, now it uses maybe 11 kWh per day!
The only way to “make money” with a Powerwall without Solar is through “arbitrage” — “buy low, sell high”, or “hoard when cheap, consume your hoard when expensive”. Use the battery to power your house when ToU power is expensive, and charge the battery when power is cheap. Or more extreme, is to dump power back to the grid for a profit.
Utilities HATE that! So, they usually structure their rates to discourage that. You will have to crunch the numbers to see if it makes sense for you. Look out for rules that block charging from the grid, or non-bypassable charges that discourage you from dumping power back to the grid during peak.
And what is your ROI for this PW? And how did you calculate and assume it would work?
Without solar there isn't a NEM policy in place, so you can't price arbitrage by exporting. You can effectively use the price avoidance hoarding practice that you describe with a TOU plan using the Powerwall to power the house during Peak and with anything left during the Partial Peak afterwards and then recharging during the lowest cost Off Peak period. I would avoid the first Partial Peak period unless the Powerwall capacity is determined to be greater than the historical house load for the entire Peak and Partial Peak periods.
@dkruz The PG&E EV2 tariff rate has the lowest Off Peak rates and the highest differential to Peak rates. Unless have very low usage your single Powerwall may not be enough. If you are running an AC during the summer the roughly 12 kWh of usable capacity won't be enough during those days. You should download a full year of your usage data from the PG&E site Green Button functionality, import into Excel or Google Sheets and analyze your usage during the different TOU periods.
Recently had 2 Powerwalls installed with no solar. Purely for back up. There's no ROI plan, I didn't care about the money, I just got tired of the power outages and generators were out based on so many factors. Here in Texas our electricity is unregulated so we have a bazillion companies competing for your business. Consequently we can get electric plans that have free nights. The plan at some point is to get one of these plans, charge the batteries at night and power part of the day off the batteries. Even with 2 Powerwalls I don't expect them to last long running AC all out.
I'm also thinking about an EV in my future and charge it for free at night. There's got to be a catch, right?
I'm also thinking about an EV in my future and charge it for free at night. There's got to be a catch, right?
My PW was acquired through a special program with my utility PGE. The strategy for getting the PW was for it to be used as backup in the event of a power outage. So far back power (4 power outage events in 3 months) is the only thing the PW has been used for.
Yes, my PW is a buffer equivalent to a gas powered generator for a rainy day when the grid power goes out.
ucmndd
Well-Known Member
There is unfortunately no easy answer for this and you’re probably going to have to do some digging and modeling.
How much power do you typically use on E-1 over the course of a year? What tier are you usually in?
Depending on your usage switching to a time of use plan with no solar and a single powerwall might end up costing you more.
How much power do you typically use on E-1 over the course of a year? What tier are you usually in?
Depending on your usage switching to a time of use plan with no solar and a single powerwall might end up costing you more.
The PW does not last long with no power. Yep, when free, who cares, but it does add a bunch of stuff to deal with and will break, for the impact is not zero, or free over time
I have solar but no batteries, so a different starting point, but I have done many a back-of-envelope ROI calculation to evaluate whether it's beneficial to switch TOU plans, add batteries or more solar, or shift/shed/add loads. Since I'm inherently lazy, I've never bothered to do the full detailed spreadsheet with Green Button data - but I've worked out several rules-of-thumb that I think can help give you a rough idea.
The basic arbitrage, as others have mentioned, is essentially load-shifting - moving consumption from a peak price to an off-peak price. Except with Powerwall, you don't change your time of behavior, instead you fill the Powerwall during off-peak, and then self-consume from the Powerwall during peak. Thus for each kwh you do this, you will arbitrage (save) the spread - e.g. if peak is 50 cents, off-peak is 20 cents, you arbitrage (50-20 = 30 cents), vs not doing it.
Steps:
0. Calculate the TOU spread.
Arrange the TOU plans in order of increasing spread - E-1, E-TOU-C, E-ELEC, EV-2A. (E-1 is basically a TOU plan with no spread.) Also to note, as the spread increases, the Off-Peak gets cheaper, in addition to the Peak getting more expensive, that's the incentive of TOU. f a plan has tiers, use the higher Tier 2 (since you have no solar, that's going to be almost assured; if you have solar, use baseline i.e. Tier 1). Fortunately, all the plans have the same Peak Period 4-9 pm, and for most, the only relevant spread is in the 4 summer months June-Sept - so use the summer rates and spread. (In other words, the winter spread is <10% of the retail rate, and thus you'd lose money trying to arbitrage due to Powerwall inefficiency).
In summary, the summer peak spread for those plans are presently $0, $0.08, $0.22, $0.31.
1. Baseline your current annual cost on each plan.
In lieu of downloading your detailed Green Button data, go to the Electric Rate Plan Comparison instead. PG&E wants everyone to move to TOU, so they've already analyzed your past 12 months of usage - furthermore, if you click into the details, they will compare the bills on a month-by-month basis. Generally, the higher-spread plans only become economical as you increase your electric consumption significantly (EV's, or large summer A/C usage). If you do see that a TOU plan is significantly cheaper than what you have now, put down your pencil, and switch NOW - what are you waiting for?
More likely, without an EV, you're in the middle where the TOU plans may be somewhat more expensive than E-1. These are your baselines for each plan, already taking into account your off-peak, part-peak, peak consumption. The difference is what you have to make up vs E-1, via the Powerwall arbitrage, to make a TOU plan worthwhile. Also note that E-ELEC uniquely has a $15/month fixed charge, so there's another $180 you have to make up vs the other plans as well.
2. Calculate how much peak usage you can arbitrage.
Ideally with one Powerwall, you will want to shift 10kwh/day x 120 summer days = 1200 kwh. From E-1 to EV-2A - that could give 1200 x $0.31 = $372 arbitrage. Subtract this from the annual EV-2A estimate from the Electric Rate Plan comparison, if it's now cheaper than E-1, it's worthwhile to change plans. You can do this for all the plans to find out which is best. But the question is, do you have 10kwh of peak usage each and every day - if not, that's where you have to go to the more complex analysis folks are suggesting.
But if you do, then it's as simple as above. Some ways to eyeball summer peak usage:
a. Those with solar (NEM, TOU) have an annual true-up that breaks out Peak, Part-Peak, Off-Peak net consumption by month. If it's well above 300 kwh/month, then you likely have 10 kwh/day.
b. If you go into the Electric Rate Plan Comparison details, it compares each plan again your current plan on a monthly bill basis. If the month summer bills are well higher on TOU than E-1, then more of your usage is during peak.
c. Think about your summer usage - do you run A/C, charge an EV, have a welding hobby - between 4-9 pm every day? Then you may have 10kwh/day.
3. Determine whether you're in the one corner case that warrants more detailed analysis.
If you don't have a clear-cut answer already, there is only one scenario that might warrant a more detailed analysis - EV-2A is the only plan that has other large spreads not accounted for above, that are much greater than 10%. Namely:
a. Summer months, part-peak spread - there is a decent part-peak spread from 3-4pm and 9p-12a.
b. Winter arbitrage - there is a decent spread the other 240 days of the year, in both peak and part-peak (same TOU periods as summer).
EV-2A is the only plan that benefits from doing a detailed hour-by-hour spreadsheet analysis, if Steps 0-2 make is close but not clearly better.
The basic arbitrage, as others have mentioned, is essentially load-shifting - moving consumption from a peak price to an off-peak price. Except with Powerwall, you don't change your time of behavior, instead you fill the Powerwall during off-peak, and then self-consume from the Powerwall during peak. Thus for each kwh you do this, you will arbitrage (save) the spread - e.g. if peak is 50 cents, off-peak is 20 cents, you arbitrage (50-20 = 30 cents), vs not doing it.
Steps:
0. Calculate the TOU spread.
Arrange the TOU plans in order of increasing spread - E-1, E-TOU-C, E-ELEC, EV-2A. (E-1 is basically a TOU plan with no spread.) Also to note, as the spread increases, the Off-Peak gets cheaper, in addition to the Peak getting more expensive, that's the incentive of TOU. f a plan has tiers, use the higher Tier 2 (since you have no solar, that's going to be almost assured; if you have solar, use baseline i.e. Tier 1). Fortunately, all the plans have the same Peak Period 4-9 pm, and for most, the only relevant spread is in the 4 summer months June-Sept - so use the summer rates and spread. (In other words, the winter spread is <10% of the retail rate, and thus you'd lose money trying to arbitrage due to Powerwall inefficiency).
In summary, the summer peak spread for those plans are presently $0, $0.08, $0.22, $0.31.
1. Baseline your current annual cost on each plan.
In lieu of downloading your detailed Green Button data, go to the Electric Rate Plan Comparison instead. PG&E wants everyone to move to TOU, so they've already analyzed your past 12 months of usage - furthermore, if you click into the details, they will compare the bills on a month-by-month basis. Generally, the higher-spread plans only become economical as you increase your electric consumption significantly (EV's, or large summer A/C usage). If you do see that a TOU plan is significantly cheaper than what you have now, put down your pencil, and switch NOW - what are you waiting for?
More likely, without an EV, you're in the middle where the TOU plans may be somewhat more expensive than E-1. These are your baselines for each plan, already taking into account your off-peak, part-peak, peak consumption. The difference is what you have to make up vs E-1, via the Powerwall arbitrage, to make a TOU plan worthwhile. Also note that E-ELEC uniquely has a $15/month fixed charge, so there's another $180 you have to make up vs the other plans as well.
2. Calculate how much peak usage you can arbitrage.
Ideally with one Powerwall, you will want to shift 10kwh/day x 120 summer days = 1200 kwh. From E-1 to EV-2A - that could give 1200 x $0.31 = $372 arbitrage. Subtract this from the annual EV-2A estimate from the Electric Rate Plan comparison, if it's now cheaper than E-1, it's worthwhile to change plans. You can do this for all the plans to find out which is best. But the question is, do you have 10kwh of peak usage each and every day - if not, that's where you have to go to the more complex analysis folks are suggesting.
But if you do, then it's as simple as above. Some ways to eyeball summer peak usage:
a. Those with solar (NEM, TOU) have an annual true-up that breaks out Peak, Part-Peak, Off-Peak net consumption by month. If it's well above 300 kwh/month, then you likely have 10 kwh/day.
b. If you go into the Electric Rate Plan Comparison details, it compares each plan again your current plan on a monthly bill basis. If the month summer bills are well higher on TOU than E-1, then more of your usage is during peak.
c. Think about your summer usage - do you run A/C, charge an EV, have a welding hobby - between 4-9 pm every day? Then you may have 10kwh/day.
3. Determine whether you're in the one corner case that warrants more detailed analysis.
If you don't have a clear-cut answer already, there is only one scenario that might warrant a more detailed analysis - EV-2A is the only plan that has other large spreads not accounted for above, that are much greater than 10%. Namely:
a. Summer months, part-peak spread - there is a decent part-peak spread from 3-4pm and 9p-12a.
b. Winter arbitrage - there is a decent spread the other 240 days of the year, in both peak and part-peak (same TOU periods as summer).
EV-2A is the only plan that benefits from doing a detailed hour-by-hour spreadsheet analysis, if Steps 0-2 make is close but not clearly better.
Over the course of a year we use about $2600. And typically we're using electricity on off-peak about 60% of the time.
In order to figure this out for yourself, you are going to need to do what @wwu123 mentioned in the post right above yours. There is no "its this" cut and dried answer, especially when comparing tiered rates (and their general lack of non bypassable charges) and time of use rates.
I have solar and powerwalls, and am still on a legacy tiered rate. Every single time I look into "should I switch to a time of use plan willingly" the answer is a RESOUNDING "no", because any modeling I do (or the utility does when their tool used to work for me) shows that such a swap would cost me an EXTRA $1000 to $1200 a year.
There is no guarantee you would save money by switching from your tiered rate to a Time of use plan, so you will need to model it as pointed out by @wwu123 .
wwi123 said:
Ideally with one Powerwall, you will want to shift 10kwh/day x 120 summer days = 1200 kwh. From E-1 to EV-2A - that could give 1200 x $0.31 = $372 arbitrage. Subtract this from the annual EV-2A estimate from the Electric Rate Plan comparison,
6kwh/day x 120 summer days = 720 kwh x $0.31 = $223 arbitrage
$2370 (from Electric Rate Plan Comparison for (EV2—A) - $223 = $2147
my E-1 rate is $2600.
wwi123 said:
do you have 10kwh of peak usage each and every day - if not, that's where you have to go to the more complex analysis folks are suggesting.
No, my peak usage (4-9pm) is about 6 kwh (summer) and about 4 kwh (winter).
wwi123 said:
more detailed analysis - EV-2A is the only plan that has other large spreads not accounted for above, that are much greater than 10%. Namely:
a. Summer months, part-peak spread - there is a decent part-peak spread from 3-4pm and 9p-12a.
b. Winter arbitrage - there is a decent spread the other 240 days of the year, in both peak and part-peak (same TOU periods as summer).
EV-2A is the only plan that benefits from doing a detailed hour-by-hour spreadsheet analysis, if Steps 0-2 make is close but not clearly better.
With my cursory spreadsheet analysis EV2-A seems better but I’m still working on more complex analysis. I had a conversation with a PGE rate plan/solar specialist. What I was told is that I could switch to EV2-A or E-ELEC and then try TOU with PW for 6 months or a year. If I see that I’m saving money then I could stay with that rate plan. Otherwise switch to another TOU plan or back to E-1. Two rate plan changes per year are allowed.
It seems like somewhat of a no-brainer then - even if you don't do any Powerwall arbitrage, EV-2A is already estimated to be about 10% cheaper for you. Shifting summer peak just adds another 10%, and that only uses 6kwh of the full 13kwh capacity - you could eke out further savings from shifting summer part-peak, or winter peak, if you don't need to keep the reserve for possible grid outages.
So broadly speaking, you'll save around 10-30% switching to EV-2A, depending on how much load-shifting you want to do with Powerwall. If you do try it out, don't be in a rush to switch back after 6 months if you're not seeing results - because the savings on EV-2A might be more realized in the four summer months, not the next six "winter" months - refer again to the Electric Rate Plan Comparison for the monthly breakdown comparison to see which months realize more savings on EV-2A, and conversely some individual months might be more expensive vs E-1.
Working backwards from this WHY EV-2A is better for you vs E-1. You have moderate-high consumption with no solar to offset it - so you have a lot of Tier-2 usage on E-1. Your 6kwh/day summer peak is relatively modest, suggesting you don't have a lot of summer air conditioning in peak, and probably off-peak - that is the killer for TOU plans. So you have enough year-round consumption off-peak, which benefits from the lower $0.28 off-peak TOU rate, vs $0.45 for E-1 Tier-2.
The reason why TOU rates don't necessarily benefit say @jjrandorin or me over E-1 (I happen to be on E-TOU-C, but it's been a wash with E-1 for as long as I can remember), is that solar panels, even though most is only credited at Off-Peak rates now, push down the remaining net consumption from PG&E mostly into the Tier-1 baseline levels, so now the $0.28 EV-2A off-peak is only modestly better than $0.36 E-1 Tier-1. So with solar, you have to still have a LOT of net off-peak consumption, say multiple EV's, before the TOU rates can benefit.
Thanks wwu123 and others. This has been an education for me and hopefully others too. I know what to do now. I will report back in the future on my use of load-shifting using the Powerwall and with differences on my PGE bill.
