Powerwall Arbitrage DEAD: San Diego's SDGE

[Princeb]

My situation: have EV/PV, NEM 1.0, net generator

Unless I'm mistaken, I spoke with SDGE solar/EV specialist, who told me that any energy put back into the grid via Powerwall will be credited at retail pricing. At year end in March during "true up", any unused credits will be converted to wholesale pricing which is $0.02-0.03 per kwh. While TOU load shifting is allowed, all this does is generates energy credits.

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.

For SDGE, this basically destroys any opportunity for arbitrage using Powerwall or to use it to substantively offset the cost of Powerwall installation.

Battery backup is not worth thousands to me.

 

[Petra]

Similar situation here in SCE land. I've got a 5kW PV system, NEM 1.0, on an EV friendly TOU rate schedule, and am a net consumer. Despite being a net consumer, I usually end up with about $300-$500 in retail credit by the end of the one year billing cycle. All a Powerwall would do for me is provide backup power and increase my annual retail credit (which just gets zeroed out and SCE cuts a tiny check).

If the utilities succeed in dismantling the NEM rules and force all PV production compensation down to wholesale rates, then I think home energy storage will really start making sense.

 

[Az_Rael]

I think Powerwall arbitrage is useful for folks designing their systems or those without solar. I am currently in the design phase of my solar project. If arbitrage was turned on and we knew how it worked, I could include that in my calculations for my solar system, and maybe put up a much smaller system on my roof.

I already sized the system to account for netmetering 2.0, I could probably go even smaller with Powerwall arbitrage in play.

 

[gaswalla]

You still can use this to your advantage to maximize energy consumed (ie: charging another EV at night), but walking off with cash in hand will not work

 

[SoundDaTrumpet]

I only expect see my True-Up cost go to zero at the minimum. In my case, Battery backup might be worth the hundreds (vs. thousands) with rebates/incentives if applied. Yes, it's a lot to spend up-front to makeup for an undersized solar, so battery backup is the only selling point.

 

[davewill]

This is news? Net Metering has always worked this way.

 

[miimura]

This is news? Net Metering has always worked this way.

Agree. If you're already over-generating a battery is not going to convert your surplus energy to cash. Maybe try crypto-currency mining or charging your neighbors to charge their cars...

 

[bkp_duke]

This is news? Net Metering has always worked this way.

Exactly. SDG&E and other power companies never agreed for users to become small power plants to make money. At best, under NEM 1.0, you could use the power grid as a battery to tap back into later to pull your credits out of.

 

[SoundDaTrumpet]

Exactly. SDG&E and other power companies never agreed for users to become small power plants to make money. At best, under NEM 1.0, you could use the power grid as a battery to tap back into later to pull your credits out of.

There are hard-to-believe programs like this (sadly not in my locality though):
Retail Value for Surplus Generation
Rooftop Solar : Silicon Valley Clean Energy

 

[Electroman]

I don't see what is the problem here. Solar and batteries primary function is to make you a consumer for the cheap renewable power you produce, but not necessarily make you a power plant for your community and run a business out of it.

And also when you push power back into the grid, it only makes sense that you pay for using the transmission and grid infrastructure that is being maintained by the utilities. Hence the much lower price than the retail rate.

 

[bkp_duke]

There are hard-to-believe programs like this (sadly not in my locality though):
Retail Value for Surplus Generation
Rooftop Solar : Silicon Valley Clean Energy

Sadly, none of them are in SDG&E territory.

Best I have figured out how to do is to use OhmConnect to reduce usage as much as possible during OhmHours and get paid for it ($130 over the past 2 months). If the software on the PW would improve so you can "force discharge" it to the grid on a whim, that could be maximized further.

 

[bkp_duke]

And also when you push power back into the grid, it only makes sense that you pay for using the transmission and grid infrastructure that is being maintained by the utilities. Hence the much lower price than the retail rate.

The specific problem is the rates.

SDG&E charges clients as much as 50c/kwh during peak hours. So if your PV excess is going next door to your neighbor that doesn't have PV, SDG&E is charging him as much as 50c/kwh, while paying you as little as 3-4c/kwh.

This (insanely stupid) policy is only going to incentivize people to adopt battery storage faster, as they are not going to want to pay the "non-bypassable charges" that the utilities get to tack on for them feeding into, and then pulling back from the grid. I'm one such example. Even if my powerwalls (on order) never pay for themselves, I'll still get them and use them just to give SDG&E the big middle finger. The rates here are simply highway robbery.

 

[comanchepilot]

They've changed the rules on net generation and offseting peak power use [and off peak].

now, I can promise you that if you have solar and a power wall sufficient to power your home you may be the only person with lights and AC after the 'Big One' Provided everything stays in place. . .

 

[miimura]

There are hard-to-believe programs like this (sadly not in my locality though):
Retail Value for Surplus Generation
Rooftop Solar : Silicon Valley Clean Energy

While SVCE does have better reimbursement, it is not what most people consider "Retail" because it is only the generation portion. You still have to pay PG&E the Transmission & Distribution fees. Here is the actual SVCE Generation rate sheet.

SVCE Rates Worksheet

EV-A varies from $0.02560 - $0.19884/kWh Summer and $0.02757 - $0.05566/kWh Winter. They do have "Green Prime" which would add $0.008/kWh to your reimbursement if you are a surplus generator.

 

[comanchepilot]

The specific problem is the rates.

SDG&E charges clients as much as 50c/kwh during peak hours. So if your PV excess is going next door to your neighbor that doesn't have PV, SDG&E is charging him as much as 50c/kwh, while paying you as little as 3-4c/kwh.

This (insanely stupid) policy is only going to incentivize people to adopt battery storage faster, as they are not going to want to pay the "non-bypassable charges" that the utilities get to tack on for them feeding into, and then pulling back from the grid. I'm one such example. Even if my powerwalls (on order) never pay for themselves, I'll still get them and use them just to give SDG&E the big middle finger. The rates here are simply highway robbery.

Bingo - with Net Metering 1.0, the power company had to buy back from you at the price they sold it.

In my case we use about 31kwh a day, with 15-16 of that going into the car.

I priced a 6kwh solar system, which at 90% efficiency facing 200 degrees on a 30 degree sloped roof would generate about 5.2kwh from April to August - and 4.5kwh in the winter = from 11a - 4pm.

During the day the load graph showed we never used more than 1kwh during the day [AC off] so that gives us about 21kwh urplus in summer at 0.34 kwh. Or a credit of $7.14 a day. That about $$210 a month. On the shoulder we would use no power in summer from about 7a to 11 and then again from 4p - 7 - so thats a reduction of 7kwh from the 31, or about 24, minus the 5 at peak time is 19kwh at a lower rate of about .20kwh or $3.80 a day.

Thus, given Net Metering 1, you can offset the COST of electricity if not using grid power, and thats the goal for me - FREE power - not offsetting the production of all power.

The credit I build up of about $90 a month [down to $40 a month in winter ] or a total of ~$600 a year offsets my higher electrcal use in August and September when I need AC. So my net bill [projected] would be about zero with only a 6kwh system. This would have allowed a full recovery of system cost in 56 months.

However, I did not install the system because we have an approximate 4 year horizon in this house. And - Net Metering changed to what @bkp_duke notes. You can no longer save the cost offset and apply it as cash to future power use.

This completely changes the equation. And recommends installing two power walls to feed the house. But You can NEVER recover the $22000 price tag, and figure another $3000 for install. $25k is 100 months - I'd need to stay the house another 8 years to pay it off. . . . for a total of 156 months or 13 years.

Now, as I mentioned having power after the Big One would be great, but - what about food, water, and our heat is by gas - as is the hot water. Assuming no damage to the house and systems, which is not realistic. So the plan remains walking, if necessary, the 6 miles to the local airport and get out of dodge until LA is liveable again.

 

[SoundDaTrumpet]

Best I have figured out how to do is to use OhmConnect to reduce usage as much as possible during OhmHours and get paid for it ($130 over the past 2 months). If the software on the PW would improve so you can "force discharge" it to the grid on a whim, that could be maximized further.

I would curious what are people's expectations when the PW software improve and enables "forced discharge." Does one expect 5kW per Powerwall? It is likely much lower than what some homeowners expect unfortunately. It depending how your system was installed and what you have. For example, if you are high power user, meaning your 200A panel needs a 200A main breakers, and you have a 7680VA solar inverter (40A), your option may only be self-consumption. It seems like it is best to install a Powerwall after the software is upgrade to allow "discharge to grid" therefore the installers don't preclude high discharge rates. This doesn't affect me fully since I have 20A back-feed capacity to spare though downsizing the main breaker could get me more current provided house loads don't trip the breaker.

 

[bkp_duke]

I would curious what are people's expectations when the PW software improve and enables "forced discharge." Does one expect 5kW per Powerwall? It is likely much lower than what some homeowners expect unfortunately. It depending how your system was installed and what you have. For example, if you are high power user, meaning your 200A panel needs a 200A main breakers, and you have a 7680VA solar inverter (40A), your option may only be self-consumption. It seems like it is best to install a Powerwall after the software is upgrade to allow "discharge to grid" therefore the installers don't preclude high discharge rates. This doesn't affect me fully since I have 20A back-feed capacity to spare though downsizing the main breaker could get me more current provided house loads don't trip the breaker.

Not an issue here. New construction with 400A (2 x 200A) main panel. There is a 12kw PV system on the roof, and even if I wanted I should be able to feed 100% of the PV in and discharge up to 4 powerwalls as max discharge rate (which according to specs is about 5kw per hour per PW).

Again, I'm exploring this only for financial reasons (i.e. maximize the **** out of OhmHour opportunities) to reduce payback time on the PWs.

 

[miimura]

You need to check the interconnect agreement with the utility. I believe PG&E currently prohibits discharging batteries into the grid. So, the best arbitrage you can do during the Peak period is to satisfy your internal loads with the battery and let the solar feed into the grid. Also, if you take the SGIP incentive or the ITC tax credit you have to charge the batteries from solar, so the best you can do is charge up the batteries in the morning, hopefully before the Peak period starts, then ride it through the Peak period on batteries.

 

[deonb]

I have a somewhat unrelated related question:

With a bunch of people doing Solar to grid and Battery to grid whenever, why am I still required to install a generator transfer switch?

Does the 'grid' have a way to magically stop personal solar and battery back-feed into the grid during maintenance?

 

[miimura]

I have a somewhat unrelated related question:

With a bunch of people doing Solar to grid and Battery to grid whenever, why am I still required to install a generator transfer switch?

Does the 'grid' have a way to magically stop personal solar and battery back-feed into the grid during maintenance?

No, it's not magic, it's completely by design. Grid tied solar automatically shuts down within a specified maximum time. All self-generation equipment must either shut down when the grid goes down or start up after the grid is disconnected by a transfer switch.