PV Solar sizing with and without EV

[fooljoe]

I'm under SCE, so I can confirm at least that it's not a "North vs. South" thing, although I can't speak from experience for how SDGE works. That document you linked to isn't very informative, as it doesn't say anything about net metering together with TOU. What you really need is to look at someone's actual bill who's on such a plan in your utility territory.

Hopefully someone in here can help you with that, but to widen the net I'd suggest you check out this thread in the Leaf forum and seek out more information there, since there are so many more Leaf owners than Rav owners. My cursory review of that thread indicates that things are basically the same in SDGE territory as they are for me, but of course you should do your own research. This thread in the Tesla forum should also help.

You could also just try calling your utility, but it could be difficult to find someone knowledgable about this who can give you a clear answer.

 

[Ferdball]

Thanks for the link, but it goes into detail about the best rate plan. At a glance, I didn't see a discussion about PV sizing. But I'll register and check around.

The SDGE doc quoted does confirm that they get the net difference in power produced versus used before they apply any rate to it. That would mean that I would have to go with the Stellar Solar method.

 

[fooljoe]

The SDGE doc quoted does confirm that they get the net difference in power produced versus used before they apply any rate to it. That would mean that I would have to go with the Stellar Solar method.

That's incorrect - it only applies to getting a credit if you generate more kWh than you consume overall.

Go to page 4 of the Tesla forum thread I linked to. There people have posted their actual SDGE bills. You can clearly see a negative $ balance despite a net consumption of energy. You can also see (not quite as clearly, but it can be figured out) that rates are applied to different TOU periods BEFORE dollar values are combined.

 

[miimura]

Compared to PG&E, SDG&E bills are really f'd up. SDGE calculates delivery charges separate from energy charges and generation credits. The Tesla forum thread linked above shows the PG&E TOU Net Metering true-up statement and the SDGE EV-TOU-2 bills and it is MUCH easier to figure out what's going on on the PG&E one. In principle, they work the same way, but PG&E bills total bundled rates in a much more straight forward way.

 

[fooljoe]

To make things easier, I'll post the relevant part of an actual SDGE bill here and see if I can make sense of it:

Skip down to the 2/29/12 bill date, because apparently this person wasn't on TOU and/or didn't have solar yet for earlier periods. The "NEM Charges" for the month are 87.05, which apply to the off-peak and super-off-peak consumption of 591 kWh (275 + 316), so those are billed at an average rate of 14.73c/kWh.

The "Applied Credits" for the month of 30.79 apply to the 186 kWh produced during on-peak, for an average rate of 16.55c/kWh. So you can clearly see that on-peak production is being billed at a different rate than off-peak and super-off-peak consumption (off-peak and super-off-peak are in turn billed at their own rates, but I combined them for simplicity.) It's not much different, because the winter rates aren't as favorable as summer, but it's clearly different.

When it switches over to summer rates the difference is more pronounced - let's look at the 7/30/12 bill for example: It's a little tricky to see how much of a credit was applied for on-peak production. You have to take the "Remaining Credits" of 257.31, but the SUBTRACT the remaining credits from the previous month (153.01) since it's a cumulative figure. Then you have to add in the applied credits that are capped at the amount of the NEM charges. So you have

257.31-153.01+30.78=135.08

That applies to 544 kWh of net production in July, so it's credited at 24.83c/kWh. Compare that to the 13.2c/kWh that was charged for combined off-peak and super-off-peak usage in July.

 

[Ferdball]

Thanks guys, actual bills really help. According to the thread, even SDGE employees are contradictory. This RandyS guy is backing what is shown in the bills though. Quote per RandyS, employee of SDGE's EV department:

If you are on the EV-TOU2 rate with a PV system, you are credited for your generation produced during the TOU period that it is generated. And if you have a large load like an EV or a pool pump, hopefully those can be timed to run during the super off-peak time (midnight to 5am). If that usage occurs then, you will be billed at the appropriate super off peak rate for that consumption.

http://www.teslamotorsclub.com/show...-E-rates/page4?p=349829&viewfull=1#post349829

So, you guys are right, and Stellar Solar is wrong. To be fair, the US Green Solar guys was right.

 

[Ferdball]

Another caveat, the winter rates suck. So you should size your system so that the summer credits offset the winter rates.

 

[pchilds]

Those rates are BS. Glad I am not in San Diego anymore. Isn't the top tier on residential around $.22?

 

[smkettner]

Amazing that super off peak is double the national average.
And people wonder why solar is so popular in CA.
Just a little more and we will be cutting the cord completely.

 

[Ferdball]

Those rates are BS. Glad I am not in San Diego anymore. Isn't the top tier on residential around $.22?

Tier4 = $.40
Tier3 = $.38

 

[fooljoe]

Another caveat, the winter rates suck. So you should size your system so that the summer credits offset the winter rates.

Yeah, the overall average for that bill I posted earlier is only a little better than a 3:2 ratio for on-peak to other rates, and that was missing a couple winter months. Of course that bill was from 2012, so things could've changed a little, and different people will have different results depending on their tiers, how much you use off peak vs super off peak, etc., but that's a really weak TOU schedule overall. Here in SCE territory I think my overall average is more like 3:1.

EDIT: I pulled out a few of my SCE bills (2 summer and 2 winter) and found the overall ratio to be about 4.2:1 in summer and 2.35:1 in winter, or about 3.5:1 overall. San Diego sucks! You should move to Orange County.

 

[miimura]

PG&E E-9A (Off/Part/On Peak)
Summer: $0.051/$0.115/$0.331 Tier 1 = 6.5:1
Winter: $0.060/$0.115/NA Tier 1 = 1.9:1
Winter: $0.110/$0.260/NA Tier 3 = 2.4:1

PG&E EV (Off/Part/On Peak)
Summer: $0.097/$0.210/$0.393 = 4.0:1
Winter: $0.100/$0.160/$0.265 = 2.65:1

I only listed Tier 1 for summer E-9 because most people with solar will push their net usage down to that level, causing all calcs to use those prices. Depending on your situation, December and January can push into Tier 3 and 4 even with solar. Schedule EV has no tiers.

 

[Ferdball]

I've tentatively decided on a 5.67 kW system at a cost of $25,685. This includes a panel upgrade to 200A, and a 14-50 plug, all equipment has a 25 year warranty.

The amount of power that you will "pull from the wall" to operate your RAV4 EV is about 1 kWh per 2 to 2.5 miles.
So, 12,000 miles divided by 2.25 miles equals 5,333kWh per year divided by 12 months is 444kWh per month, assuming all the charging is done at home.
444kWh plus 639kWh = 1,083kWh per month.

How's this for Miles per Dollar math?
=-=-=-
The Pilot get about 16.5 MPG. If a gallon of gas were $4, that would equal about: 4 Miles per Dollar

The Benz can get about 2.25 miles per kWh. So, at 1000 miles per month, it uses about 444kWh. If we charge between midnight and 5am, it costs $.16 per kWh. So that equals about $71 per month, or about: 14 Miles per Dollar

 

[Ferdball]

Okay, here's my Solar sizing analysis. Assumptions are that I'm going with EV-TOU2 rates with SDG&E. I use about 730kWh in the Summer, and about 550 kWh in the Winter.

https://docs.google.com/spreadsheets/d/1LSkzwa3ya-6w2NpgHgJTSgg5vsFpqvrbnnLl9c31AxE/edit?usp=sharing

Edit: Okay, I had 400kWh for the car in the Production rows. So, needless to say, I need to recalculate.

 

[smkettner]

4kW system should serve you well and provide an excellent return on investment. (pay back is the primary issue to invest, yes?)
Much larger stands a good chance of diminished returns.
You will want to shift your consumption away from the on-peak and onto the lowest off-peak rates for best results.

 

[Ferdball]

Company B (US Green) just came back with a 4.8kW system that produces 669kWh monthly at a cost of only $20. That makes my SDG&E payment to about $45 monthly. I think I've found my winner.

 

[dstjohn99]

Ferdball, here is a previous post from a different thread. I'm with SDGE and I've had net metering since 2001 and I modified miimura's spreadsheet for SDGE rate schedules. I'll post some bills soon. PM me if you would like to talk or get more info.

Be careful which SDGE rate you sign up for. Also remember that when you switch rates you are locked in for 12 months.

I completed my spreadsheet analysis based on 1) the past year's electric usage data in 15 minute intervals and 2) electric usage since owning my Rav4 EV (2 months). Aside from the 3 weeks or so of rate shift for daylight savings time (SDGE DST does not match current DST, so they must make an adjustment), and not adjusting for holidays the spreadsheet calcs are spot on.

The rates I compared were SDGE DR-SES, EV TOU and EV TOU2. The EV rates are much lower than the DR-SES for peak and about 3 cents lower semi-peak / super off peak. The EV rates are probably the best if you do not have solar AND can benefit from TOU metering. HOWEVER, if you do have solar you need to look very carefully at your excess generation times, overall usage, etc.

For my suituation I found that the DR-SES saves me $80 to $100 over the two months I've had the EV:

Since I have significant excess production during the Peak hours, I get the maximum credit ($.49/kWh - Summer instead of $.29) with the DR-SES. That way I can use the credits to offset the cost of much more power during off-peak times like charging my car - even though I'm paying $.03/kW more than the EV rates during the off-peak times. Also my off-peak time is 10pm - 6am instead of midnight to 5am. The on peak rate is 20 cents higher but it's also 11am - 6pm (best solar production) instead of 12pm - 8pm / 12pm - 6pm.

For the entire year's data (2 months with car) I show a 2582kW surplus generation. With DR-SES I have a ($1277) credit ($113 payout if not used). With EV TOU it is ($760) and EV TOU2 is ($812). So I can buy $465 to $517 more electricity than the other rates.

I did not compare the standard tier rate(s), but I can add it if someone is interested.

I hope this helps. By the way, the spreadsheet logic formulas were challenging. I never would have succeeded without miimura's spreadsheet as an example - Thank you.

 

[Ferdball]

TOU2 summer peak is $.49, not $.29. Where is this spreadsheet?

 

[dstjohn99]

TOU2 summer peak is $.49, not $.29. Where is this spreadsheet?

I was about to argue with you, but after checking the rate sheets (again) you are correct. It appears ALL the EV rates I used are now different. I use the rate sheets, not the illustrative graph.

Complete Tariff rates are here http://www.sdge.com/rates-regulatio...ariffs/electric-tariff-book-residential-rates

Rate sheets here http://www.sdge.com/total-residential-electric-rates

Calendars are here http://www.sdge.com/residential/daylight-saving-time-update

Spreadsheet is in my Google Drive, but I don't know how to make it public like photos. You'll have to PM me with your email address and I will send it to you. It would be nice to get a second set of eyes on this to verify the rates used and the calendar dates & times. As far as I can tell the EV rate TOU applies 7 days, where the SES rate is weekdays with weekends being semi / off peak only.

This definitely changed the comparison with the surplus credits as follows (remember these credits are used to trade for electricity at the applicable rate, but the remaining surplus at year end is paid at approx. .037 / kW).

DR SES -$772.67
EV TOU -$787.76
EV TOU2 -$815.17

So for my usage history, it looks like EV TOU 2 gives me the best overall return on investment.

 

[dstjohn99]

SDGE Bill summary from 2013 - 2014 and 2014 with EV. EV was purchased 8/12/14, so the bills starting 9/8/14 reflect EV charging during off-peak times.