Sdge, Ev Tou5, Solar, Powerwall And Sgip?

[dotbombjoe]

The Return on Investment (ROI) for PWs can be poor if you exclude the value (cost) for an equivalent backup with a diesel generator (installation, maintenance, & fuel). Not many people consider the backup portion of the Powerwall which would help in the ROI calculations. The equivalent backup could be valued anywhere from $2,000 to $5,000.

Completely agree that if backup is important to someone, the Powerwalls can be a great solution. There are pros/cons with more traditional methods so for people who need backup, they will want to compare and contrast the options. I don't think anything can come close to battery backups like the PW in terms of convenience and I think a lot of people underestimate just how important that aspect of backup really is...but the more traditional methods do have benefits that probably make it a better choice for some.

Furthermore, if you get Powerwalls, you can also join a demand response program such as Ohm Connect and make money to help offset the cost of your installation. Note, link includes a referral link.

For reference, I have a similarly sized solar system (5.7 KW). Over the last year our 2X Powerwalls offset 1,800 kWH of home usage during peak and part-peak TOU. Based on PG&E's EV-A TOU and the spread between Peak/Part-Peak and Off-Peak rates, I estimated I save $500/year. I made over $800 last year with the demand response program for a total of $1,300/year saved/earned.

I don't mean to hijack the thread but when I started reading up on Ohm Connect it didn't seem like it would make sense for me. I'm shocked to hear you made over $800 in a year. My understanding (probably very, very wrong) was that the rewards were largely based on beating (reducing) your normal consumption when they trigger a savings event. Since I never use any peak power, assuming that's when the events are typically occurring, I didn't think I'd save anything. Anyway, if you were up for describing your experience with Ohm Connect (probably in a separate thread that you could reference here) I'm sure I and others here would find it helpful to understand how its working for you.

Whatever portion of this sort of savings is enabled by the powerwalls should definitely be incorporated into the equation which isn't something I can do since I'm obviously unfamiliar with them...so that could certainly change the equation significantly.

The ROI will depends greatly if the batteries (with your solar production) will offset a good deal of your peak usage (aka peak shaving). We only see the net peak usage (553 kWh). With Advanced Time-of-Use Control in Cost Savings Mode, you can export all your solar during peak and part-peak while the batteries cover you actual power use for an overall negative net peak use.

Agreed. Unfortunately for those of us with SDGE, their rates plans are not designed to provide fantastic return for powerwall owners.

Our peak time is 4-9pm. Our super-off-peak is midnight - 6am. That means our generation is mostly during the 'off peak' period with a bit of peak. Making it worse, many of the common rate plans do not offer substantial savings between super-off-peak and peak -- $0.25 v $0.30...and worse still, the savings are only true for the summer (5 months). All rates are identical in the winter months. The EV-TOU5 plan offers a $0.09 super-off-peak rate in exchange for a $16 flat monthly fee...so for those of us that can shift usage to super-off-peak times it can make a ton of sense but that's less about the powerwall and more just a truth about the rate plan.

Anyway, the point is that the "arbitrage"/return opportunities for us are limited:

*) charging from super-off-peak/off-peak so we can leverage the powerwalls to feed us through peak
*) selling back whatever peak generation we have back to the grid, capped by the peak usage at that time (because anything beyond your consumption would already be sold back to the grid even without the powerwalls)

So, a quick estimate of the max arbitrage value can be computed by multiplying peak summer consumption (June - Oct) by the rate difference between peak and off-peak (for SDGE EV-TOU2 or TOU5, that difference is $0.24) and add your capped peak generation value.

For my 6.25kW system, summer peak consumption is about 500 kWh and summer peak generation was 624 kWh, but again, that generation number needs to be capped at the 500 kWh...so about $120+$270/year for a total of $390/year...maximum, which is probably not very realistic -- the PWs are not perfectly efficient after all.

So, let's say that's maybe a $350/yr return if I'm fortunate. It isn't horrible, but it isn't a good economic investment either...unless you truly value the backup feature. Again, if a demand response program can supplement another $800/yr -- and that was truly enabled by the powerwalls -- then that would be a massive difference in the equation.

Our Powerwalls cost $9,700 (rounded up, after 30% fed tax credit, no SGIP). Assuming $0 value for backup, ROI over 10 years is 34%. With a $2,000 value for backup, ROI over 10 years jumps to 69%. This is an oversimplified calculation and does not consider long term fluctuation to the demand response program, TOU rate changes, and fluctuation to actual peak saving.

I think it's important to point out that your cost seems far lower than what most people are posting today to have two PWs installed. The quotes I'm seeing described here are typically $18-24k installed for 2 PWs. Take 30% off the low end of that and you're at $12.5k which pushes out the break-even point a few more years...the high end is more like $16.5k after incentives so again, that would be a dramatic change in the equation.

Anyway, I'm not trying to dissuade anyone from getting PWs. I love these things. But without SGIP and a strong desire/need for backup, I think SDGE consumers will find the financial payback is not a sure thing...and certainly not similar to their investment in solar. That said, it sounds like I really need to investigate Ohm Connect because if that can truly return $800/yr, I need to get with the program!!

The SGIP program made these things an absolute no-brianer...maybe that will receive new funding at some point.

 

[dotbombjoe]

I am glad someone is talking about SDG&E. I would love some advise from NEM 1.0 users. I put in 7kw solar system, but SDG&E bill shows I have 6.25 kW system. I guess there is some inefficiency of the system hence 10% drop after 4 years. My account has -$50 at true up for slightly over generated last year. My bill estimator shows it would cost the same for all the plans (based on last year without EV). But now with the M3, should I switch to TOU5? Not sure if $16 per month would do me any good. We drive/charge about 1000 mile/month.

My daily drive is 36 miles and my car consumes about 22kWh to charge...so if you achieve a similar result that suggests about 611 kWh/mo to charge your car. (611*.09)+16 = $70.99/mo v (611*.25) = $152.75/mo.

BUT...you've also stated you are over-generating currently so the above equations aren't really the full picture. I don't know enough about the differences between NEM 1 v 2 and the details re: what can/can't be offset (ie, that $16 fee for example). Hopefully someone with a better background on that stuff will jump in, but at least you could probably use the numbers above to estimate the true impact of your EV over the course of a year.

If your EV usage mean's you're going to owe money at year end going forward, I'd still think it could make sense to go with EV-TOU5 but yeah, definitely need to run the numbers to be sure...and make sure any other considerations re: changing rate structure might force you to accept.

 

[bkp_duke]

I am glad someone is talking about SDG&E. I would love some advise from NEM 1.0 users. I put in 7kw solar system, but SDG&E bill shows I have 6.25 kW system. I guess there is some inefficiency of the system hence 10% drop after 4 years. My account has -$50 at true up for slightly over generated last year. My bill estimator shows it would cost the same for all the plans (based on last year without EV). But now with the M3, should I switch to TOU5? Not sure if $16 per month would do me any good. We drive/charge about 1000 mile/month.

7kWh is likely your DC production, when converted to AC there are some efficiency losses. I would bet you have never actually seen your theoretical max production. I have a 12.05 kWh system, and I've never seen it produce more 11 kWh even under optimal conditions.

 

[2017ModS]

No, you don't lose the ability to sell power back to the grid.

I switched from EVTOU2 to EVTOU5 after my year was up back in April. The structure of the bill is basically identical -- the primary difference is the $16 monthly fee and the $0.09 rate for super-off peak...but structurally everything else is the same re: seeing the breakdown of power consumption and generation and monthly remaining credit details and whatnot.

EVTOU5 is a killer deal for anyone that can schedule the bulk of their consumption to super-off peak...and from the sound of their calculator, that includes you!

PWs are great for backup, but not particularly economical now that SGIP is done...if you really want/need backup, by all means go for it (again...awesome) but don't do it for financial reasons because it will not pay for itself.

Thanks for your answer! Does the $16 fee include the other random charges (public purpose program, dwr bond charges, etc?)

 

[dotbombjoe]

No. I have separate charges for all that other stuff...I generated 178 kWh more than I consumed, so that $16.87 credit was the total of the NEM charges (those that can be offset).

I sure will miss the EV credit we've been getting the past few years -- that has more than wiped out my bill...between the remaining balance from last year's $500 credit and this years $850 credit, I shouldn't have to pay a dime for about 4 years.