Leveraging SDGE TOU rates with an EV?

[RichardCullip]

I'm not sure I can adequately describe the method I've come up with to evaluate different EV charging situations. However, I'll try my best at writing a brief summary. I first forecast my electric demand, starting with historic SDGE usage (15/60 min data). This is broken down into TOU periods by billing periods using Excel's VLookup capability. This is then summarized into billing period totals via a Pivot Table. Using a similar technique, I forecast solar production from PVWatts into corresponding billing period totals. From there I can subtract the electric demand TOU results from the TOU solar production for each billing period to get the Net Energy for billing purposes. It got a bit tricky to account for the change in TOU periods for weekends, holidays and the months of March and April but a semi-complex VLookup function takes care of that detail.

From there, I can add in the extra electrical demand for charging an EV, or in my anticipated case, a PHEV. For simplicity sakes, I add all the EV demand to the Super Off-Peak category assuming my charging will be done at night.

Finally I can use SDGE rate tables to calculate what a yearly billing total might be. For my situation, I've looked at TOU-DR, EV-TOU-5, EV-TOU-2, TOU-DR-P, DR-SES and TOU-DR1 rate schedules. I'm a late adapter of solar so I'm on NEM2 and have NBCs to account for (that was fun)

For my base case (no EV charging) all of the rate schedules except for EV-TOU-5 come in within a dollar or two of each other at my yearly true up. No surprise there since I'm currently generating a surplus of solar most months and my monthly bills have been at the SDGE minimum. I can use up to 200kWh/month of EV charging before I have to carefully consider which rate plan I need to be on. Above that amount of EV charging the yearly true up bill starts to have some significant differences btwn rate plans. At 300kWh/month of EV charging the TOU-DR-P rate becomes the best choice as long as I can avoid the stiff penalty for using electricity during the few reduce your use days. It takes an EV demand over 400 kWh per month to make the EV-TOU-5 rate plan attractive for me.

The upshot of my analysis is that I'll be staying on my current TOU-DR rate plan when I add a PHEV early next year as I only anticipate adding about 150kWh to my monthly demand. However, in the future, if I ever get over my EV range anxiety and add an EV to my fleet of vehicles I might reach the electrical demand level where a switch to EV-TOU-5 pays off.

Since I built this spreadsheet for my own personal use, it's not built to evaluate a wide range of solar situations. In other words, if you might want to do a similar analysis you are on your own and at the mercy of your specific level of spreadsheet expertise.

[J.P.M.]

Thank you. I believe I understand what you write and if my understanding is mostly correct, what you've done will probably get similar results to what I use.

Since I'm probably not as spreadsheet literate as you, my guess is your methods are most likely quite a bit more elegant than mine.

I'd add, FWIW and w/apologies if you already know this, if your SDG & E meter is like mine, you have a way to find how many kWh will be charged NBC. Take a tare of the "del" reading from your meter.

Regards,

[Ampster]

I'm not sure I can adequately describe the method I've come up with to evaluate different EV charging situations. However, I'll try my best at writing a brief summary.........

The upshot of my analysis is that I'll be staying on my current TOU-DR rate plan when I add a PHEV early next year as I only anticipate adding about 150kWh to my monthly demand. However, in the future, if I ever get over my EV range anxiety and add an EV to my fleet of vehicles I might reach the electrical demand level where a switch to EV-TOU-5 pays off.
......

Sounds like you got it figured out for the time being. Your description of the spreadsheet tools will help others trying to figure out this complex issue. While there may only be a few comments here, remember there are 1000s of lurkers who will benefit from your work.

You are use of 300kWh a month to charge a PHEV can use up some of those NEM credits. That is a good start on leveraging TOU rates.

In the past I have leased a hybrid and a Plug In Hybrid and I remember the range anxiety I had when my first EVs were limited to 100 miles. My last lease of a PHEV was 4 years ago when longer range EVs and charging networks became more available. As an interim technology between traditional Internal Combustion Engine and electric motor powered vehicles they are extremely complex. I do not generally favor leasing automobiles unless there are extenuating circumstances. In the case of a PHEV the complexity and interim nature of the technology are why I leased a PHEV and did not choose to own. I was influenced by my long term goal to drive EVs and the other factors mentioned above..

[DrChaos]

NEW SDG&E RATE UPDATE 2020-01-01:

As of the new year, the EV-TOU-2 rate has been changed substantially in favor of EV drivers who charge in super-off-peak. Even better for solar + EV customers now.

The super-off-peak rate has declined and the off-peak and on-peak rates have increased. With solar generating mostly in the 'off-peak' hours, this is advantageous for rate arbitrage: gaining more $ credits than net kWh would suggest.

There is now a 15c gap from off-peak rates over super-off peak rates in summer, (used to be around 6c) and even better, a 10c gap from off-peak rates to super-off peak in winter months (used to be 1c or so). Summer on-peak are bad, 55c, but I was generally net zero kWh (I don't have air conditioning though) on peak.

I have put in a request to switch (back) to EV-TOU-2 from TOU-DR-P. You can't do it from the main rate plan web page, need to go to the EV special page and put in information about your EV.

My hard money costs will be the same, but I anticipate accumulating generation credits even faster which I could conceivably use for a future air conditioning and winter heating without going positive in my yearly true-up.

If somebody is net consumer yearly, then this rate plan might be even better as the improved generation arbitrage reduces real money outlay.

[Ampster]

Yes, that is the one of the benefits of owning an EV. Otherwise it is harder to leverage TOU rates because there aren't as many other load shifting opportunities in the average home.

[RichardCullip]

NEW SDG&E RATE UPDATE 2020-01-01:

As of the new year, the EV-TOU-2 rate has been changed substantially in favor of EV drivers who charge in super-off-peak. Even better for solar + EV customers now.

The super-off-peak rate has declined and the off-peak and on-peak rates have increased. With solar generating mostly in the 'off-peak' hours, this is advantageous for rate arbitrage: gaining more $ credits than net kWh would suggest.

There is now a 15c gap from off-peak rates over super-off peak rates in summer, (used to be around 6c) and even better, a 10c gap from off-peak rates to super-off peak in winter months (used to be 1c or so). Summer on-peak are bad, 55c, but I was generally net zero kWh (I don't have air conditioning though) on peak.

...

Thanks for the heads up on the new rates, effective 1/1/20

[J.P.M.]

NEW SDG&E RATE UPDATE 2020-01-01:

As of the new year, the EV-TOU-2 rate has been changed substantially in favor of EV drivers who charge in super-off-peak. Even better for solar + EV customers now.

The super-off-peak rate has declined and the off-peak and on-peak rates have increased. With solar generating mostly in the 'off-peak' hours, this is advantageous for rate arbitrage: gaining more $ credits than net kWh would suggest.

There is now a 15c gap from off-peak rates over super-off peak rates in summer, (used to be around 6c) and even better, a 10c gap from off-peak rates to super-off peak in winter months (used to be 1c or so). Summer on-peak are bad, 55c, but I was generally net zero kWh (I don't have air conditioning though) on peak.

I have put in a request to switch (back) to EV-TOU-2 from TOU-DR-P. You can't do it from the main rate plan web page, need to go to the EV special page and put in information about your EV.

My hard money costs will be the same, but I anticipate accumulating generation credits even faster which I could conceivably use for a future air conditioning and winter heating without going positive in my yearly true-up.

If somebody is net consumer yearly, then this rate plan might be even better as the improved generation arbitrage reduces real money outlay.

In terms of your electric bill, the annual money outlay will be [what you use times the TOU rate per kWh when you use it summed for 8,760 hours] minus [what your system generates in kWh times the TOU rate per kWh summed over 8,760 hours].

For most residential users one goal behind alternate energy - besides any environmental goals - is to provide electrical service to a residence for the lowest long term cost. I'm not sure simply looking at the lowest per kWh rates as f(time) and then chasing the biggest change for one goal such as lowest super off peak rate for vehicle charging is the best overall strategy.

I've found care is necessary in rate evaluation more so than you seem to be doing. For the most part, one thing I'm careful to suggest in conversations with neighbors and friends who are also SDG & E cust. is to not not jump onto changing the tariff they're on simply because of the latest rate change. The rates go up, and also go down due to various factors that I'm only vaguely aware of and (to my limited experience) most consumers don't know exist. SDG & E TOU-2 rates did indeed change over the last 12 months.

So have a lot of other rate tariffs and schedules. May experience tells me they will likely change and go back up (some ?) come A/C season. Rate fluctuation is a fact of life. Check historical rates. It happens a lot. Example: I'm on tiered rates, sch. DR. The latest rate change on 12,000 kWh/yr. use on rate sch. DR in my area has an annual bill going DOWN by 3.9 %. My actual usage is closer to 7,400kWh/yr. and that results in my annual bill dropping by 2.1%. The difference is in the way the tier rates changed relative to one another. Making generalizations can lead to unintended outcomes. You gotta run the numbers.

I've also found it helpful to separate the $ value of system generation available to offset a bill - not the reimbursement for overgeneration, but the retail value of the generation - from the gross electrical household usage and its cost. That's possible for TOU plans that do not have a tiered rate laid over them, and also if a NEM cust. has a system that does not offset >100% of annual usage.

Example: for my area only, using Miramar MCAS data into PVWatts with the output variability limits described above, a 20 deg. tilt, 180 deg. az. unshaded system will generate the following annual revenue per installed STC kW :
Using DR-SES: ~ $479/yr.
Using TOU-2 : ~ $497/yr.
Using TOU-5 ~ 381/yr. + $16*-12 = $192/yr. annual service charge.

Under NEM and a TOU plan that's not got a tiered rate laid over it, the value of system generation can be treated as independent from the actual cost of what's used (gross usage) and the resulting bill before solar contributions. If a system is designed to produce, say 9,000 kWh/yr., assuming PVWatts is a reasonably good model, both for total output and generation pattern within the published limits of the model, then the annual $ value of that output under any true TOU rate schedule (that is, without a tiered rate laid over it) is independent of household usage - provided annual usage exceeds annual generation.

On your observation that TOU - 2 has changed substantially: It has. So have other rate plans. There may indeed be an advantage to EV owners (and/or those who can or choose to time shift loads for that matter) to take advantage of the lower rate now offered for super off peak use with TOU-2. Or, maybe not.

Care is necessary. Stick with me on this. If, for example, someone reading your post has a PV system and uses rate DR-SES - the residential rate available to PV owners and is about to buy an EV and plan on charging it with ~ 350 kWh /month at home at super off peak times and rates. As it is now, the on peak and off peak rates for both summer and winter are higher for TOU-2 vs. DR-SES by $0.03971/kWh while the super off peak rates for TOU-2, both summer and winter are $0.05546/kWh lower than the super off peak for DR-SES. So, and depending on usage pattern and system size, if a user currently on DR-SES draws .05546/.03971 times as much power (in excess of solar generation) at non super off peak rates - that is, at peak and off peak rates - as at super off peak, all other things being equal - changing to TOU-2 from DR-SES may be an invitation to a foot shooting party for that user.

Under the conditions for rate plans described above, and with no tier rate laid over them and the system provides <100% annual offset, generation "revenue" can be thought of and treated as independent of usage and so billing for usage - that is, for example, and to the extent the PVWatts model can be believed and relied upon, TOU-2, a, say, 5 kW system will generate 5*$497 = 2,485/yr. That "revenue" will, within the limits of the PVWatts model's limitations be available to offset $2,485 of an annual electric bill of any amount.

For my area, TOU-2 will, as you might guess, produce more "revenue" of $2,485/yr. (vs. ~ $479*5 = $2,395/yr. under DR-SES) for a 5 STC kW system in n. county San Diego, but the most likely much greater usage at peak and off peak times vs. what's probably a lot less usage at super off peak time coupled with the $0.03971 greater per kWh charges under TOU-2 for those most likely higher usage times (peak and off peak times) might result in an overall higher bill by switching from DR-SES to TOU-2 even though the super off peak rate is lower for TOU-2.

My guess is it'll take a hell of a lot of EV and super off peak time shifting to make up for the higher TOU-2 peak and off peak rates vs. the lower DR-SES peak and off peak rates.

Point is, you gotta run the numbers. You mat have suggested or implied such. If so, I missed it. Every situation is different and this forum is too limited to get into every machination of rates and usage scenarios.

Take what you want of the above. Scrap the rest.

[DrChaos]

My guess is it'll take a hell of a lot of EV and super off peak time shifting to make up for the higher TOU-2 peak and off peak rates vs. the lower DR-SES peak and off peak rates.

True, if I were a net consumer in all periods then the choice would be less obvious of course and more serious calculation needed.

Personally I am a significant net producer in off-peak and significant net consumer in super-off-peak and about zero in on-peak. So for this situation my main benefit comes by looking for max difference in rate between off-peak vs super-off-peak. When I got my EV my total consumption about doubled (and I'm an average driver, people with more driving or less efficient EV will be consuming more super off peak).

I bet my situation is common for people with EV & solar but not universal. The solar system was sized to provide net total kWh production roughly equal to consumption so the approximate balance between super-off-peak consumption and off-peak generation energy is expected.


BTW for DR-SES (and old EV-TOU2 which was nearly the same) there is only about 1c between super-off-peak and off-peak in winter rate period, 7 months a year, but new EV-TOU2 has a gap in this period as well, which is new.

And somebody who has an EV and is a net consumer might also benefit from EV-TOU-5 which has lower kWh charges in return for +$16/month base fee.

[PugPower]

With no EV, I'm on TOU-DR since going solar in Oct. 2019. TOU-DR-P might be slightly better, but I can not reduce usage between 2-6PM on Reduce Your Use Days and don't want to worry about it. The winter rates are the same. Under my current plan of TOU-DR I'm only getting a minimum bill of $10 per a month from SDGE.

[Ampster]

............
I bet my situation is common for people with EV & solar but not universal. .....

I believe you are correct that most people are not aware of their usage patterns. That may be especially true for those that have fought to stay on tiered rates. EV owners by necessity have control over the timing of much of their consumption and don't have to do pages of analysis to find the optimum rate plan. I have to admit I did some extensive spreadsheet analysis until the concept of leverage became clear.

[J.P.M.]

I believe you are correct. Most people are not aware of their usage patterns. That is especially true for those that have fought to stay on tiered rates. EV owners by necessity have control over the timing of much of their consumption and don't have to do pages of analysis to find the optimum rate plan. I have to admit I did some extensive spreadsheet analysis until the concept of leverage became clear.

Can you explain how you see/define the concept of "leverage" as you use the term ?

[Ampster]

Can you explain how you see/define the concept of "leverage" as you use the term ?

It is a term that has been used on another forum frequented by EV drivers, I started using it here because it made sense with regard to solar and TOU rates. I did not invent it but my background in finance found it an appealing way to express the concept. When used as a noun it means the ratio of debt to equity. However in this context is is a verb, the meaning of which is, "to use (something) to maximum advantage." That quote is from a simple Internet search. In one sense it reminds me of the physics of a lever.

I hope that clarifies it. I can give more examples but the one I gave at the beginning of this thread still seems the simplest."buy low and sell high".

[J.P.M.]

It is a term that has been used on another forum frequented by EV drivers, I started using it here because it made sense with regard to solar and TOU rates. I did not invent it but my background in finance found it an appealing way to express the concept. When used as a noun it means the ratio of debt to equity. However in this context is is a verb, the meaning of which is, "to use (something) to maximum advantage." That quote is from a simple Internet search. In one sense it reminds me of the physics of a lever.

I hope that clarifies it. I can give more examples but the one I gave at the beginning of this thread still seems the simplest."buy low and sell high".

Thank you. I respect what you write in this post, but the way I learned process economics, it seems or feels to me that's sort of like throwing out the baby with the bath water.
Or at least not starting with the bigger picture:

The objective of an economic analysis for an alternate energy system can be viewed as the determination of the least cost method of meeting the energy need, considering both solar and non solar alternatives. For solar energy systems of any type, the goal is to determine the size of the solar energy system that gives the lowest cost combination of solar and the least cost electrical power option(s).

Once a system is in place and assumed fixed in size (at least for the near future), it would seem to me the discussion would shift to comparing various tariff plans to determine the one that results in the lowest total bill.

On the baby and bath water situation, what I think I'm reading from you and also from DrChaos looks like more but perhaps not total concern about finding the greatest differential cost/kWh from one tier to the next within a single tariff schedule rather than a comparison of total annual bills from a comparison of net annual bills from one tariff to the next or the lowest annual bill among all available tariffs.

[Ampster]

As I have said before it all depends on where you are standing. Your big picture and my big picture are different and that leads us to have different objectives.
Process economics concerns itself with the production of goods and services. My objectives are more about the efficient consumption of goods and services and the allocation of resources to facilitate that. Picking the optimum rate is a subset of those objectives. Looking at rate differentials is just part of that process.

Some time ago I realized my consumption of energy was not limited to only the energy used to run my home. During the past decade my transportation choices have evolved from a succession of hybrids and a plug in hybrid to the two EVs I currently own. I put approximately 25,000 miles on those cars annually.

[Ampster]

.....
The objective of an economic analysis for an alternate energy system can be viewed as the determination of the least cost method of meeting the energy need, considering both solar and non solar alternatives. ......

The title of this post is about leveraging TOU rates with an EV. Real world experience with EVs and TOU rates is probably more relevant to this discussion. If you want to discuss the broader issue of optimum alternative energy system design starting a new thread thread would give that topic a broader audience.