Powerwall Arbitrage DEAD: San Diego's SDGE

[abasile]

Basically, what this means is that the credits I have currently for over-generating (about $1000+ retail) is worth $40 come year end. Many have the idea to draw battery at off peak and sell back at peak hours, sounds good in theory but the utilities rig this game.

The way I would solve this is by reducing or eliminating personal consumption of natural gas, by installing a heat pump system for heating and AC, a heat pump hot water heater, an electric induction range for cooking, and an electric clothes dryer. That will help use up those energy credits. Further, as grid electricity grows cleaner, this will reduce greenhouse gas emissions. Indoor air quality will be helped by using electricity instead of combustion for cooking and baking.

 

[SoundDaTrumpet]

You need to check the interconnect agreement with the utility. I believe PG&E currently prohibits discharging batteries into the grid...

miimura, thanks for pointing this out. I found this that supports what you are saying.

Energy Storage

Typical solar customers are not allowed to discharge to grid. NEM Multiple Tariff (NEMMT) interconnection is a very costly means to discharge to grid. The interconnect fees are exorbitant, so I will stop here.

 

[liuping]

Basically, what this means is that the credits I have currently for over-generating (about $1000+ retail) is worth $40 come year end.

I also generate about $1000 in credits by the true up period. However, with the new SDG&E peak usage time changing December 1st from 12-6pm to 4p-9pm, I expect my credits at the end of next year to drop substantially, maybe even go negative, without a Powerwall to cover the 6-9 period. That combined with whole house backup power is enough for me to pull the trigger at the after SGIP discounted cost.

 

[Kbra]

The utilities, especially CA utilites with a lot of renewables being installed dont want your mid day power. They struggle with the peak demand loads which is when all us powerwall installers (specifically non solar users) will be charging our cars, powerwalls, and using the most energy. In the middle of day when your solar is pumping out they have plenty of their own and thats also some of the lowest demand on the grid. The TOU time periods are not in line with energy demand vs supply. This is slowly being shifted over time to account for it but givent he regulated state and CPUC these have to be slow gradual shifts.

California ISO - Todays Outlook

 

[bkp_duke]

The utilities, especially CA utilites with a lot of renewables being installed dont want your mid day power. They struggle with the peak demand loads which is when all us powerwall installers (specifically non solar users) will be charging our cars, powerwalls, and using the most energy. In the middle of day when your solar is pumping out they have plenty of their own and thats also some of the lowest demand on the grid. The TOU time periods are not in line with energy demand vs supply. This is slowly being shifted over time to account for it but givent he regulated state and CPUC these have to be slow gradual shifts.

California ISO - Todays Outlook

For this reason, and since I work from home, this is why we charge the cars from solar during the day whenever possible.

 

[NanoGrid]

The utilities, especially CA utilites with a lot of renewables being installed dont want your mid day power. They struggle with the peak demand loads which is when all us powerwall installers (specifically non solar users) will be charging our cars, powerwalls, and using the most energy. In the middle of day when your solar is pumping out they have plenty of their own and thats also some of the lowest demand on the grid. The TOU time periods are not in line with energy demand vs supply. This is slowly being shifted over time to account for it but givent he regulated state and CPUC these have to be slow gradual shifts.

California ISO - Todays Outlook

The Duck Curve is a problem for CAISO and the generating side of the deregulated utilities. Power prices go negative day after day from Spring to Fall, when must-buy solar output peaks. California greatly increased SGIP battery incentives but it is an inside game, since the Powerwall etc. owners are aggregated by utilities or corporations. If buying a PW2, suggest you have the chat with Tesla on SGIP participation. The catch (as mentioned above) is for partial payment of your battery cost you are also selling off-peak PV capacity and a lot of battery cycles.

 

[NanoGrid]

The way I would solve this is by reducing or eliminating personal consumption of natural gas, by installing a heat pump system for heating and AC, a heat pump hot water heater, an electric induction range for cooking, and an electric clothes dryer. That will help use up those energy credits. Further, as grid electricity grows cleaner, this will reduce greenhouse gas emissions. Indoor air quality will be helped by using electricity instead of combustion for cooking and baking.

Buying a heat pump is a great solution if your existing A/C and furnace are worn out, because you'll also get higher efficiency than from your 15- to 20-year-old units. Otherwise, the high first cost won't offset your reduced gas bill. Even then, the lower cost per btu of gas heat may make it a losing plan. You might consider installing a few baseboard heaters to offset some gas heating, then use them just enough for your true-up electric bill to slightly exceed the minimum charge (currently $10/month in PG&E land).

 

[NanoGrid]

... Otherwise, the high first cost won't offset your reduced gas bill...

I meant: Your annualized first cost WON'T BE OFFSET BY your reduced gas bill."

 

[abasile]

Buying a heat pump is a great solution if your existing A/C and furnace are worn out, because you'll also get higher efficiency than from your 15- to 20-year-old units. Otherwise, the high first cost won't offset your reduced gas bill. Even then, the lower cost per btu of gas heat may make it a losing plan. You might consider installing a few baseboard heaters to offset some gas heating, then use them just enough for your true-up electric bill to slightly exceed the minimum charge (currently $10/month in PG&E land).

I agree that the low cost of gas heat makes it tougher to justify a heat pump for winter heating. There are the environmental benefits, but of course there are multiple ways of using money to achieve environmental gains and a heater upgrade might not be a priority, particularly in places like coastal California where winters are mild.

In our case, we are hoping to install a heat pump for zonal air conditioning during the summer, with zonal heating as a side benefit since we already have a high-efficiency central gas heater. We don't currently have AC because we live in a relatively cool mountain climate, but our local climate along with the rest of California has been trending warmer, with more wildfires that impact outdoor air quality, and we'd like to add AC for part of the house. A wall or window AC unit is out of the question because of noise levels, limitations on where it could be placed, and aesthetics. Rather than putting money into central AC, we'd rather install a ductless heat pump and improve our overall HVAC efficiency. Heating comfort is another factor, as a ductless system will be less prone to leakage and consequent loss of moisture during the winter.

 

[astrothad]

We are on SCE. We have a 3kW array which was later bolstered by a separate 4kW array (both leased from SolarCity). The past July, we installed 2 Powerwalls. We mostly run off of solar and batteries from 8 or 9am until midnight or so. Sometimes the battery lasts later into the night until it reaches our reserve setting. Other times - especially if we charge our EV - it runs down to that level earlier. We used to push and receive a few hundred kWh to the grid each month. Since installing the Powerwalls, this amount has dropped below 100 kWh per month each way. In line with NEM policies mentioned above, we now get this bizarre billing cycle:

• If we push even a few kWh more than we receive, there is the minimum monthly surcharge which brings the bill to just over $10;
• If we take in a few more kWh than we push, the monthly bill is less than $2.

This now makes it a game to try to set the reserve at night to use just a bit more than we take. These dollar amounts are tiny, either way, so the benefits are not necessarily financial. With the Powerwalls, it's an interesting diversion to see if we can "beat" the system. Two months ago, we absorbed a few more kWh than we sent back, and our bill was just under $2. Last month, they "won the game" when we used 42 kWh, but sent back just over 60 kWh. Result: a bill of $10.02. This is more satisfying - to us - than getting a $40 true-up for providing over a MWh of power -- offset by $120 worth of bills -- over the course of a year.

Yay for energy independence and, literally, cheap thrills!

 

[EscoguyS75]

I have two choices: more solar or a PW2

Option 1 (proceed with PW2)

Made deposit on PW2 in April with SGIP. Cost pre rebate $21,839, SGIP2 = $9400, ITC=$6551, net cost $5,888.
In SDG&E territory with EVTOU2 rate. Solar produces 10K kWh, annual use is 19.5K kWh.
Two EVs: Model S and Leaf, receive $400 EV credit on bill. As credited 50 cents/kWh for on peak in summer (12-6 pm), value of peak excess production makes for $100 summer utility bill (6 months). In winter, use 6,000 kWh, with net bill of $1,200 (less EV credit) total annual bill about $1,000. 1/2 of winter electric is for heating in north San Diego county.
Approx 1,000 kWh of summer production used during peak time (12-6 pm), if used PW2 to shift morning production to afternoon use, would save additional $300/year. Factoring convenience, would normally shift another 1,000 kWh from morning to afternoon (value at perhaps $200/year. (would allow not to run AC 10am to noon on hot days prior to peak rates). All in looks like 12-19 year payback.

Option 2,
Get more solar panels, cost for 14 more panels about 7K, net of ITC $4,900. Est production of additional panels 3,000 kWh/year. If 30% (970 kWh) at 50 cent per hour rate, lowers bill by $500 plus 70% (2300 kWh) at 20 cents/kWh $450 saving. Total $950/year which would zero out my annual bill (leaves the $10/month minimum charge). Payback about 5 years.

So unless I'm missing something, the financials seem to say just do more solar with NM 1.0 EVTOU2 rate.

What am I missing? As far as I know the EVTOU2 rate is here for the duration. I'm grandfathered in for 17 more years with Net metering 1.0.

I could see the value of having backup at perhaps $100/year as it doesn't happen often. There is the novelty factory too of having a power wall and perhaps that's worth $1000. Might end up doing both but at some point, one wonders can I reach my state of energy bliss.

Input appreciated.

 

[Ed Hart]

Well, thanks everyone, ‘cause I am learning from your experiences. I am SCE. I have 14 kW solar. I ran excess of $1800 last year. Trueup at $77. TOU. Getting hit with charges for sending power back to grid. Have an MS. Adding an MX shortly. Charge only at night. Have applied for two PW2s with plan to take excess juice in day to reduce draw from utility just after sundown to 10:00 PM. Tesla says the software to do this will be coming very shortly. Anyone know details on that software? How smart will it be?

 

[MP3Mike]

Made deposit on PW2 in April with SGIP. Cost pre rebate $21,839, SGIP2 = $9400, ITC=$6551, net cost $5,888.

I don't think you get the ITC credit on the full amount, so I would think that your ITC credit would only be $3,731. Or is it that you only get SGIP funds on the after ITC amount, I'm not sure. (But you have to declare your intent to file for the ITC on your SGIP application so that they can calculate your rebate amount correctly.)

 

[abasile]

So unless I'm missing something, the financials seem to say just do more solar with NM 1.0 EVTOU2 rate.

What am I missing? As far as I know the EVTOU2 rate is here for the duration. I'm grandfathered in for 17 more years with Net metering 1.0.

I could see the value of having backup at perhaps $100/year as it doesn't happen often. There is the novelty factory too of having a power wall and perhaps that's worth $1000. Might end up doing both but at some point, one wonders can I reach my state of energy bliss.

In most cases, I expect that installing enough solar panels to basically "zero out" one's electric bill will be easier to justify than installing Powerwalls. And the environmental benefits of solar panels should be greater, at least to the extent that the grid can absorb solar production.

That said, it seems likely that TOU peak hours will get moved later in the day when there's less solar production. IIRC, in PG&E territory, TOU peak hours are currently 4pm - 9pm. Years in the future, given substantial increases in solar PV production, it's not hard to imagine the late morning and midday hours being treated as "super off peak". In such a scenario, the relative value of energy storage is greater and products like the Powerwall should play an important role in enabling solar self-consumption while supporting grid stability.

For my family, the value of having backup is significant because we live in a mountain area where the grid is not quite as dependable. After incentives, the cost to us of installing two Powerwalls should be lower than the cost of installing a whole home standby generator.

The "novelty factor", or pleasure of being an early adopter and experiencing the future now, is worth something. Further, if you can afford to spend money on both solar and batteries, and thereby help support Tesla's mission, then why not? Our time in this world is short and you can't take the money with you when you're gone.

 

[bkp_duke]

I don't complete agree with this point:

And the environmental benefits of solar panels should be greater, at least to the extent that the grid can absorb solar production.

Without a battery system to draw from during the nightime and cloudy hours, you are utilizing fossil fuels for the energy you get during those hours. Sure, you are pushing extra back in the grid with more solar panels, but in some states like California there is an excess for that solar energy that at times can be hard to get rid of.

If you want really minimize your carbon footprint, the powerwalls would help reach that minimum, after of course you get past their initial production carbon footprint.

 

[abasile]

Without a battery system to draw from during the nightime and cloudy hours, you are utilizing fossil fuels for the energy you get during those hours. Sure, you are pushing extra back in the grid with more solar panels, but in some states like California there is an excess for that solar energy that at times can be hard to get rid of.

If you want really minimize your carbon footprint, the powerwalls would help reach that minimum, after of course you get past their initial production carbon footprint.

I agree that, to minimize the direct carbon impact of your energy use, you would need to self-consume your PV generation which would of course require batteries. This is a good way to have the lowest possible dependence on fossil fuel-based electricity generation. The downsides are the additional cost, the impact of manufacturing those batteries, and the round trip charging/discharging losses inherent in using batteries.

The whole premise of solar NEM (net energy metering) is that exporting clean energy to your local grid during the daytime provides at least enough value to society (including environmental benefits) to offset the dirtier energy that you're using when the sun isn't shining. This was certainly true when no one else had solar PV systems, but I agree that we're now seeing days (primarily in Spring) when the grid can't absorb all of the solar and there has to be curtailment at the utility-scale solar plants. (Hence my above qualification, "at least to the extent that the grid can absorb solar production.")

One key question is, how long will it be before we see enough curtailment to substantially reduce the environmental value of residential PV systems not coupled with battery storage? Today, seen in aggregate, this factor probably isn't all that big a deal. At least with the current TOU schedules in place, however, the day is coming when storage will be essential.

As we know, the State of California is attempting to address this by providing big incentives (SGIP) to install storage systems. A more market-based approach would involve a larger carbon tax applicable to fossil fuel-based generation, coupled with dynamic TOU schedules to value grid energy more accurately. Unfortunately, such proposals will provoke howls of protest and likely get shot down.

 

[EscoguyS75]

New info on SDG&E
EVTOU-2 rate shift for me in April 2019. Peak will then be 4 pm to 9 pm vs noon to 6 pm.
Expect $900/year impact if my usage doesn't shift. My wife will be able to charge her car in the day now so that can mitigate about 1/3 of the increase. Still running numbers on PW2.

 

[Foodnut]

With the new On-peak shift from SDG&E, I too am considering PW2. It used to be the on-peak summer days would net enough credits to offset the True up period... I gotta crunch some numbers too to see if it makes sense.

 

[liuping]

New info on SDG&E
EVTOU-2 rate shift for me in April 2019. Peak will then be 4 pm to 9 pm vs noon to 6 pm.
Expect $900/year impact if my usage doesn't shift. My wife will be able to charge her car in the day now so that can mitigate about 1/3 of the increase. Still running numbers on PW2.

Daytime charging on EVTOU-2 would using the off peak rate of $0.249 / kWh. It's still best to charge the car midnight-5am for the super off peak rates $0.196 / kWh.

 

[Frankman60]

I am in SDG&E territory and am also considering a PW to mitigate change in peak period hours on EV-TOU2. I am presently grandfathered in NEM 1.0. Installing Powerwalls doesn’t trigger a change that would bump me into NEM 2.0 would it?