cost of charging, in California, Solar City proposal

cost of charging, in California, Solar City proposal

Solar City is installing charger for coming Tesla (80amp !!).
they also sent me a proposal for installing solar system for the house.
I am currently using 12,000 kwh per year.
proposal claim with Tesla, I will be pushed into Tier 3/4 all year (instead of 2 months in summer). rate will be around 30 cents / kwh. This came as a big surprise to me: this means fully charging my 85 Tesla will cost me ~$25 for about 180 miles (using realistic number for way I drive), this is a lot more expensive than running my Prius. about the same as a mid size Camry / Accord.

1. does this sound right ? if not, where did my calculation go wrong ?
2. I asked the rep why can't I use the timed charger feature (rumor to be out this month ?) between 12am to 6am, won't I be charged a lot lower rate. The rep claim (said it is a complicated calculation, which I have no doubt) it still basically comes back to total kwh, so I will still pay ~30 cents / kwh. Is he BS'ing me for trying to sell me a solar panel system ?

thanks all for help....

derek | February 13, 2013

Don't forget that PG&E are launching a separate EV billing rate. To use it, you need to have a separate meter installed, which is a one-time cost, but then your EV charging won't factor into your home use rate tier.

Of course...that's just the kind of useful info the Solar City guy should be telling you.

bellwilliam | February 13, 2013

I knew about separate meter. but Solar City told me something around $4k labor to install ? not quite sure of the number, but it was some ridiculous number.... this was not from the solar panel guy, but the Solar City guy who will install HPWC.

derek | February 13, 2013

Sounds possible. PG&E charge you a $250 fee for the separate meter. Of course, you will need the electrical work done from that meter to a NEMA plug near your Tesla. And you may need a bigger feed in from PG&E (200 Amps instead of 100 Amps). That would bump up the price.

Perhaps a big chunk of the estimate was HPWC related? Was half of that $4k cost the HPWC?

Either way, I can't claim to be an expert on this, so I'll wait to hear what others have to say.

sergiyz | February 13, 2013

Charging your car will push you in tier3 or tier4 for sure.
The tier4 pricing now is $0.34-$0.35 per kwh.
Solar is a no-brainer in CA, look at what they are offering.
Your goal is to stay in tier1 (regulated), so you have to stay under 344kWh a month (their baseline) combined (home use and charging).
The size of the system will depend on how much you need to produce to stay in tier1, how much sun your roof is getting and the kind of panels you install.
Then there are multiple options:
- lease, zero initial cost to you, but you pay a fixed price for electricity that is higher than tier1 rate, I've seen about $0.29 average per kwh
- buy outright: initial investment is high, but you keep the electricity and have to deal with rebates (claim them)
- prepaid lease: you pay for the system, but it's a lease. Electricity is yours, the system is normally cheaper than buying outright, and you don't have to deal with rebate paperwork.
You have a chance to buy it or extend the lease later.
It's taking advantage of depreciation and minimizing taxes that you as individual can't claim, but the business can, and they are passing some savings from that on to you.

GLarwill | February 13, 2013

Get the second meter and you can look to the E9-B rates which are TOD based and you will note the approx 4¢ per kWh costs for midnight to 7am. There is no way to get solar costs down to this level.

For more data, Google for "pg&e tariff" (no quotes) and look for the E9 rates for EVs.

hsadler | February 13, 2013

I was under the impression that here, in California, just putting in a designated outlet (NEMA 14-50 for example) would get you the E-9 rate.

sergiyz | February 13, 2013

there's an E9A and E9B rates.
E9A is for the shared meter (house and charger), E9B requires a separate meter for the EV charger.
Installing the second meter could be a costly proposition, but maybe worth it long term if you're not doing solar.

hsadler | February 13, 2013

@ sergiyz

Yes, but E9B is going away in lieu of just E9

shs | February 13, 2013

Actually the new proposed PG&E EV rates have both an A and B option for single and dual meters, respectively. The difference is that the old (current) rates are tiered, and although the baseline rates are very low at night, the tiered rate structure will likely put most people charging EVs into the higher rates pretty quickly. The new proposed EV baseline rates are higher, but not tiered and so in theory they will work out better for EV charging. My rough calcs suggest that for me it will be break even between the two plans (old E-9A and new EV-A). Of course, the more you plan to drive and charge at home, the better then new EV rates will be.

Brant | February 13, 2013

PG&E E9A rate off peak as of 7/1/12
Tier 1: 0.0468
Tier 2: 0.0649
Tier 3: 0.1581
Tier 4: 0.1981
Tier 5: 0.1981

So much lower than the 0.35 rate quoted

shs | February 13, 2013

New proposed non-tiered EV-A off peak rates are 0.97 and .099 for summer and winter.

shs | February 13, 2013

Make that 0.097 and 0.099

gregv64 | February 13, 2013

@shs: If you have solar to keep you under baseline, though, the new rates are worse for you. It all depends.

@Brant: The point is that the extra charge from the EV pushes more of your usage into the higher tiers. Unfortunately you can't just have the high tier charge be for your night usage, it will increase your rates for all time periods (for instance, if 20% of your usage falls into tier 5, then 20% of each time period will be billed at tier 5). So exactly how much your total bill goes up is a complicated matter.

Brant | February 13, 2013

@shs; Thanks for the update..almost had a heart attack

So for 180 miles assuming a real world usage of 3-4 kWh/10 miles (my experience over 2500 miles so far)
at an average .098/kWh will cost you $5.29-7.06

Brant | February 13, 2013

with the proposed new rate that is

shs | February 13, 2013

We do have solar and an all electric house and so my baseline kWh are about 3 times more than if we used propane or natural gas to heat the house. I stay under baseline most of the year, but on the months when it is 15° to 30° at night, we do get over baseline, and if (when) I am charging the car regularly, that would certainly put me over baseline. Plus solar does not work too well covered with snow! Also the higher summer peak and partial peak rates in the new EV-A schedule will also help as that is when we generate our excess electricity, so overall the new EV rates are probably not so bad (or good) for us.

SUN 2 DRV | February 13, 2013

Does PG&E (or anyone else) have a calculator that takes our last year of SmartMeter data and show us what the total cost would be under each of the new rates plans?

With GreenButton giving us access to our consumption in a standard format, it would be great if we could use it to compare rate plans, with the ability to add new loads such as Model S charging.

amptsup | February 13, 2013

Does SCE have similar rate plans as PG&E. Are they better or worst in general?

DaveR75 | February 13, 2013

I'm in Los Angeles with So Cal Edison. We put in a solar system with Solar City and I'm extremely happy. Locked in a 7.5 cent/kwh rate for the next 20 years (up to the system designed output) under their PPA program and this easily keeps us under the Tier 1 rates..if not net negative... all year long. The key is making sure the system is designed for the right output (not too big..not too small) and paying a bit more up front for long term savings. I looked at it as more of an investment (long term/low risk) than an expense.

bellwilliam | February 13, 2013


can you elaborate on this ?

"@Brant: The point is that the extra charge from the EV pushes more of your usage into the higher tiers. Unfortunately you can't just have the high tier charge be for your night usage, it will increase your rates for all time periods (for instance, if 20% of your usage falls into tier 5, then 20% of each time period will be billed at tier 5). So exactly how much your total bill goes up is a complicated matter."

what's the point of midnight charges, if it pushes all your other rates into say Tier 5 ? even if midnight charges is at 10 cents/kwh.

Amped OC | February 13, 2013


Thanks for your input. I’m also with So Cal Edison and just got a proposal from SolarCity last week (I plan on doing the prepaid PPA with the time of use plan). I agree with you that the key is making the system the right size, and that’s my question. How well did the SolarCity proposal estimate the power usage of your Model S?

The SolarCity spreadsheet shows the efficiency of the 60 kWh Tesla Model S as 3.83 Miles/kWh, which would translate to 260Wh/mile. However, Tesla's web site says that you should assume 300Wh/mile ( In addition, I've read a number of posts on the Tesla forums, and it appears that real world performance is more like 340Wh/mile.

I've also read that charging is not 100% efficient and that it is best to assume around 81% efficiency. Using these numbers, my SolarCity system should be designed to offset the following usage:

35 miles per day * .34Kw per mile is 11.9 kWh / 81% efficiency = 14.7 kWh per day, or 441kWh per month

However, using the SolarCity EV Energy Calculator spreadsheet, my SolarCity system should be designed to offset the following usage:

35 miles per day / 3.833 Miles/kWh = 9.1 kWh per day, or 274kWh per month

That's a huge discrepancy, and I want to order the right size system. Can DaveR75 or any solar gurus shed some light on this question?

Nelson T. | February 13, 2013

I am in the Bay Area and is a PG&E customer. I have a 8.4kW system installed by SolarCity 2 years ago. I was using about 1.1kWh per month at that time and was paying up to tier3/4 type of rate on some portion of my usage. I told the SolarCity Sales Rep. that I was planning to get an electric car and in the end, he designed a system that covered all my usage which also pretty much used up all my usable roof space. I have a 15 year lease where I paid the whole thing up front. Currently, I am staying with the E1 schedule. Since I have some pumps running continuously for my Koi pond in the backyard, I am not sure if a E9A schedule would be more cost effective. My office provide free charging right now and so I don't always charge at home. But even if I charge at home 100% of the time, I expect that my commute would not push me over tier 1. I have to drive up hill for about 2 blocks and so after 2200 miles, I am averaging about 350 Wh/mile.


gregv64 | February 13, 2013

@belwilliam: the point of the midnight charges is to encourage you to shift daytime power usage to night. If you are just adding nighttime usage without reducing daytime usage you are still penalized. It will still cost you less than if you added the usage in the daytime, however.

Here's a simplified example:

Say that baseline was 90kWh and you currently used 90kWh during the day and nothing at night.

Now you add an additional 10 kWh at night, pushing you 10kWh into tier 2.

You would now have:

daytime: 81 kWh tier 1, 9 kWh tier 2
nightime: 9 kWh tier 1, 1 kWh tier 2

Basically 10% of your usage is now tier 2, and so 10% of each time period is now charged at tier 2.

AaronB | February 13, 2013

@swmedland: The numbers you are coming up with are much more accurate than Solar City's estimates. I drive approx 90 miles/day from Tracy to San Ramon and back (includes up and down the Altamont Pass). My average use over 5k miles is approx 340 wh/m.

Most days I use approx 40kw of power to charge when the car says I need 30.

We have 7.2kw of solar which kept us in tiers 1/2, but with the car we will solidly be in 2/3 during the summer and 4 in the winter.

We are currently still on E-1, as the peak hours on E9A will hurt us in the summer with A/C use at home.

The only options I see to reduce cost are to add more solar (expensive ~$10k) or go to E9B/EV-B with a second meter (also expensive ~$5k).

It is unfortunate that PG&E has made the region such an expensive place to charge an EV.


Brian H | February 13, 2013

The efforts of PG&E and SoCal, etc., to sell less electricity, their sole product, are awe-inspiring. You'd think they wanted to be in some other business.

djm12 | February 13, 2013

The answer varies if PG&E, DWP, or SCE. What is your utility company?

With SCE, my experience is that I can charge after midnight for considerably less than $0.30/kWhr. My composite rate for all utility use is more like half that. I could install a 2nd meter, but I elected not to because I can put my EV on a timer. (BMW Active E)

A lot depends on your charging habits. If you need to charge during the day, you might be more inclined to install a 2nd meter for the better rate that SCE offers for EVs.

In any foreseeable case, if your home is ok for installation of a 4-6kW solar system, why not do it? At worst, you'll just break even. Go and get a bunch of bids from multiple contractors and compare all of your options. SolarCity is not the only game in town.

Amped OC | February 14, 2013

@AaronB: Thanks for sharing your usage numbers. I did more research and found out why Solar City’s power usage estimate seemed low. It gets complicated, but it has to do with net metering and me being on a Time of Use plan. They don’t design the system to offset 100% of kWh usage. They design the system to offset (ideally) 100% of the electric bill. In a TOU plan using solar, you are selling power back to the grid at higher daytime (peak) rates and using power from the grid at lower nighttime (off-peak) rates. Therefore, a TOU customer with solar may still be using, for example, a net 300kWh per month from the grid, but their SoCal Edison bill would still be pretty close to $0 (assuming the customer produces 600kWh at $0.30/kWh and uses 900kWh total at a cost of $0.20/kWh). The credit would be $180 and the bill would be $180, so the two would offset each other. This is admittedly an oversimplification, but I think it illustrates the point.

DaveR75 | February 14, 2013


Unfortunately I'm not sure our system is sized right. We recently moved into a new house. Solar City originally wanted a year of billing history, but I ended up sizing the system myself based on a couple months of use and knowledge from having a solar system on our previous house for 7 years. It's a total guess, but there are some levers you can tweak as you go..install LED lighting, better insulation, hound the kids into turning off lights, etc. Right now I'm hoping to charge primarily at work so didn't factor much of the EV charging load into the equation. Will just have to see where we land after the 1st year.

I do know that the rate SCE will pay you back for over generation is not worth the cost of over building the's a wholesale rate @ something like 5-7 cents/kwh.

Also, having a hard time evaluating whether it's better to be on the Domestic or TOU rate plan. SCE does not make it easy to evaluate your options.

Brian H | February 14, 2013

They're trying to get the max revenue out of the least power possible. You want the reverse.

Amped OC | February 15, 2013


You may want to call SCE at 1-800-4EV-INFO and have them send you a personalized home and EV fueling cost comparison. It’s not all that detailed, but it may help. They look at your last 12 months of usage and estimate how much you’re going to charge your Model S (based on number of miles driven per day), and show you the cost of Residential (Schedule D) vs. the two TOU plans. It takes them about a week to mail you the one page summary.

For me, the Electric Vehicle Plan (TOU-EV-1) initially looked the cheapest, but the estimated $2k-$4k cost of installing the second meter made it not worth it. That’s why I’m opting for the Home & Electric Vehicle Plan (TOU-D-TEV), which doesn’t require a second meter.

lov2krz | February 15, 2013

Get multiple bids for the solar PV system. I believe SolarCity is very high priced for the jobs they have bid for friends of mine.
I'm a believer in owning and not leasing.

I have a 3300 square foot home with dual A/C and am running a surplus back to PG&E every year with a 7.7kWh (36 Panel system). My MS should be free to operate.

I don't know your particular electrical usage other than what you state in your opening comments. I do know you don't have to produce all of your power needs instantaneously. I believe your goal should be to overproduce slightly so you only pay the electrical distribution and electrical fee's/taxes (~$13/mo) every month with you gas bill. When on solar PV you are on Time of Use (TOU) metering where the summer peak can get up to, as I remember, $0.43/kWh tier 4 and as low as $.21/kWh tier 1. Off peak is as low as $.06/kWh and I think up to $.011/kWh. My wife and I are retired and live in our home full time during the day and we still overproduce power. If your house is empty most of the week during the day then all that power goes back into the grid and you get to consume at partial and off peak rates.

Charge at night when you're sleeping and I'd think you might not get out of tier 1 unless its dead of winter (I have two months a year where we exceed tier 3 but that is wiped out by the rest of the years production). But as long as you overproduce during the day it doesn't matter because you settle your bill once per year. If you overproduce you'll get a small check if not you'll pay a minimal amount as long as your PV system is sized correctly.

If you live in the Bay Area and want to discuss (get referrals or just chat) send me a private message from the Tesla Motor Club site, my user name is lov2krz

Brian H | February 15, 2013

but be polite when you PM him. He likes to cuss people out, you know. Quite shocking!
Some people do just "love to curse".


lov2krz | February 16, 2013

bellwilliam, it's love to cruise not curse. I'm dyslectic so I get it.

I love to cruise (krz) on my motorcycles, autos, bicylces and on ships.

I also love solar PV, not sure how that relates to cruising other than with I cruise right through my electric bill. You get the point.