Long term feasibility of max exporting to the grid

[invalid]

I got the call from an ISA today that its time to start our home assessment on our PW reservation.

Lately, I've been skeptical as to whether or not it makes sense to move get the Powerwalls. If anything, I could probably put some additional west facing panels on our house, spend less than the PWs, and eliminate all our summer peak power utilization. Additionally, next spring we will be replacing our 25 yr old AC condensors and expect to see a usage decrease with more efficient ones.

The "My PG&E Toolkit" iOS app has a mode where it shows your utilization with 1-2 PWs, and basically has it where they charge at night and fully discharge during peak hours. It makes it look like it'd save a ton of money, potentially have the power company paying us, even with our two EVs charging at night.

However, is that actually practical? Isn't it something the utility companies would likely catch on to and eventually try and squash? I mean its the power company, they aren't your friend. Seems like it could lead to limits, tiers, or moving from NEM to separate import/export rates.

Mainly looking at it in terms of how much savings potential there is to compare peak savings, limiting peak usage, or if expanding solar would make more sense.

 

[Ampster]

However, is that actually practical? Isn't it something the utility companies would likely catch on to and eventually try and squash? I mean its the power company, they aren't your friend. Seems like it could lead to limits, tiers, or moving from NEM to separate import/export rates

What is practical is reducing your total KWhr consumption from the grid to the point that you are only paying the minimums. To me that is the sweet spot of grid tied battery systems. For that you only need a building permit and don't have to get permission from the utility. I am assuming you send nothing to the grid and self consume all that your panels produce.

 

[miimura]

If you have solar, you can't charge at night and discharge during Peak. That would also make you ineligible for the Federal Tax Credit. The right way to calculate your savings is to add up how many kWh you consume during Peak hours and multiply that by the difference between Peak and Part-Peak prices. So, PG&E EV rate with an average of 20kWh/day Summer usage is ($0.48-$0.264)*20 = $4.32/day. For 180 days of the Summer rate period that would be $777. Winter rate differentials are less and your A/C usage is less, so it's maybe $1,000/year savings due to the Powerwalls. You would need two Powerwalls to shift 20kWh/day.

Usage patterns are not this simple, but it gives you an idea and you can adjust it for your situation.

 

[invalid]

If you have solar, you can't charge at night and discharge during Peak. That would also make you ineligible for the Federal Tax Credit.

I'm aware of that limitation on the federal credit. Just to be clear, you can do that. You just can't do that and claim the credit. Correct?

The right way to calculate your savings is to add up how many kWh you consume during Peak hours and multiply that by the difference between Peak and Part-Peak prices. So, PG&E EV rate with an average of 20kWh/day Summer usage is ($0.48-$0.264)*20 = $4.32/day. For 180 days of the Summer rate period that would be $777. Winter rate differentials are less and your A/C usage is less, so it's maybe $1,000/year savings due to the Powerwalls. You would need two Powerwalls to shift 20kWh/day.

Usage patterns are not this simple, but it gives you an idea and you can adjust it for your situation.

Yeah, I've been starting to calculate it similar. Mainly looking at my overproduction in part peak and peak usage. My panels mostly face east, so a larger part of my production is in part peak.

 

[miimura]

I'm aware of that limitation on the federal credit. Just to be clear, you can do that. You just can't do that and claim the credit. Correct?

The Tesla software in the USA actually prevents it except in special circumstances like Storm Watch. Others in the UK and Australia can routinely charge from the grid during Off-Peak periods. People have stated that they want to forego the tax credit and charge from the grid, but Tesla is not accommodating to allow it. Your grid interconnection agreement for the batteries would also have to state that you plan to charge from the grid in addition to charging from your solar.

Yeah, I've been starting to calculate it similar. Mainly looking at my overproduction in part peak and peak usage. My panels mostly face east, so a larger part of my production is in part peak.

Mine also produce almost all their energy during Part-Peak. I have hills to my West, so my afternoon generation is truncated.

 

[Bigtanuki]

I got the call from an ISA today that its time to start our home assessment on our PW reservation.

Lately, I've been skeptical as to whether or not it makes sense to move get the Powerwalls. If anything, I could probably put some additional west facing panels on our house, spend less than the PWs, and eliminate all our summer peak power utilization. Additionally, next spring we will be replacing our 25 yr old AC condensors and expect to see a usage decrease with more efficient ones.

The "My PG&E Toolkit" iOS app has a mode where it shows your utilization with 1-2 PWs, and basically has it where they charge at night and fully discharge during peak hours. It makes it look like it'd save a ton of money, potentially have the power company paying us, even with our two EVs charging at night.

However, is that actually practical? Isn't it something the utility companies would likely catch on to and eventually try and squash? I mean its the power company, they aren't your friend. Seems like it could lead to limits, tiers, or moving from NEM to separate import/export rates.

Mainly looking at it in terms of how much savings potential there is to compare peak savings, limiting peak usage, or if expanding solar would make more sense.

I have a 4.1kWp solar array facing S and W as well as 2 PW2 units and a 2017 Model S90D. Our setup has allowed us to access the PG&E EV-A rates and charge the cars solely from off peak power at ~.12c/kWh and using the output of the solar panels to run the house for the partial peak and peak hours. I've had moderate success with the Time Based Control (TBC) software settings but recent updates have caused me to go back to Self Powered settings due to behaviors like routing solar to the grid before the batteries are fully charged. I suspect that the behavior in the TBC mode is per design and that perhaps I'm just not using to its fullest potential because of my settings for reserve, etc. However, since Tesla has failed (miserably) to offer the user base and meaningful information about how the TBC settings are supposed to work most of what we know is by conjecture or empirical testing by users such as miimura.
As noted in other posts charging at night and discharging during peak hours to "arbitrage" isn't supported by PG&E. They aren't really interested in having thousands of small generators feeding into the system during peak solar hours. It's hard enough managing the large solar generator inputs into the grid.
The real beauty of the PW systems is that they allow you to decide when to use of your solar generation, reduce your bills by accessing better rate structures and finally, have an assurance that you won't be without power during a blackout since your solar PV system will continue to work during a grid outage essentially making you energy independent.
That last item for me was the real kicker. We used to have several brownouts and a handful of blackouts every winter. Local distribution line improvements have reduced those by 90% but they are still an issue. In addition, now that PG&E is embracing shutting off power to areas potentially impacted by windstorms during high fire danger periods (link) having a long term source of backup power could be a seriously good thing.
Most everyone here on these boards has different ideas of why the PW system is good for them. The numbers really don't seem to work out for a payback for many folks but I think that is because it is very hard to assign a dollar value to something as intangible as "energy security". You'll have to make up your own mind about that. Personally, having the one house in the neighborhood still lit during a power outage last winter was one of those "priceless" moments that made buying the powerwalls worth it.
Best of luck in your quest for information about the powerwalls.

Bigtanuki

 

[cwied]

I'll just add that in the long term one way that Powerwalls will probably pay back is when Tesla aggregates them to perform grid stabilization. The agreement signed at purchase time has an opt-in for this and mentions revenue sharing. There's been no announcement of actual plans to do this in California, though. In the short term you can get some of this benefit by using a demand-response aggregator like OhmConnect.

 

[montreid]

Arbitrage won't pay for the PW2. The sweet spot is this:
By 2021, most everyone will be on TOU with pk rates in the non-solar hours. Batteries will be a MUST to zero peak hours.

Right sized PV array for household + battery to allow time shifting to meet zero hours in peak. Anything netmetering beyond zero back into the grid is NOT financially gainful at this time.

PW2 certainly CAN allow for opportunity in the future to allow grid support, but we're a long ways off on that -- it will come as we get more experience on stabilization through transition to TOU for all and reduction like OhmConnect -- Ironically since we've TOU to zero pk, out baseline is zero and no longer meet goals with OhmConnect alerts as they run at night mostly now. ---

With winter month rates in efffect now, we may play around with the manipulation of demand shifting (bolus demand 7p-9p to get baseline up and not time shift support, then on alert days support with PW2) to get the $20 per alert max. -- just for kicks and giggles

 

[Ampster]

In the short term you can get some of this benefit by using a demand-response aggregator like OhmConnect.

I used OhmConnect for a few years when I had an Outback Radian doing load shifting. I never got much payback for Ohmhour load dropping because Ohmhours usually came during early evening when my critical loads were already off the grid. (@montreid, said the same thing in previous post)

I havn't used it in six months. Is there a new program?

 

[cwied]

I used OhmConnect for a few years when I had an Outback Radian doing load shifting. I never got much payback for Ohmhour load dropping because Ohmhours usually came during early evening when my critical loads were already off the grid. (@montreid, said the same thing in previous post)

I havn't used it in six months. Is there a new program?

There isn't, but I adjust my TOU schedule so that two evening hours aren't covered by the Powerwall. Since my part-peak starts at 7pm, I picked 7-9pm. Given the frequency of OhmHours during the summer, this makes my marginal cost for power negative during those two hours. Since these are the hours that we do laundry (electric dryer), I have significant baseline usage. Now that I have a Tesla, I could also charge during those two hours, but I usually end up charging at work instead.

I have mixed feelings about the perverse incentive to consume more during a part-peak period, but looking at how much the spot price for energy fluctuates at that time I figure that the actual cost of the energy I use on non-event days is probably much lower than reflected in the static TOU rate, even if it isn't actually negative. I'm really hoping that a real-time program comes from Tesla that more accurately reflects the benefit of discharging the Powerwalls at high-load times.

 

[Shygar]

I'll just add that in the long term one way that Powerwalls will probably pay back is when Tesla aggregates them to perform grid stabilization. The agreement signed at purchase time has an opt-in for this and mentions revenue sharing. There's been no announcement of actual plans to do this in California, though. In the short term you can get some of this benefit by using a demand-response aggregator like OhmConnect.

I actually suspect they are already doing some sort of grid stabilization, that's why we're seeing weird charging all of a sudden. Normally before 1.25 or so I would just charge until full, but now I'll see these weird drops where instead of charging it's sending power back to the grid. Seems to me that would make a lot of sense if they were already stabilizing the grid with some program with PG&E.

 

[Ampster]

I adjust my TOU schedule so that two evening hours aren't covered by the Powerwall. Since my part-peak starts at 7pm, I picked 7-9pm

I am on PG&E EV-A and my peak goes until 9pm.

 

[cwied]

I actually suspect they are already doing some sort of grid stabilization, that's why we're seeing weird charging all of a sudden. Normally before 1.25 or so I would just charge until full, but now I'll see these weird drops where instead of charging it's sending power back to the grid. Seems to me that would make a lot of sense if they were already stabilizing the grid with some program with PG&E.

I would like that to be true, but I don't think the timing of the unexplained charging/discharging matches any kind of grid loading pattern. I suspect this is just the algorithm being too smart for its own good. My powerwalls start discharging half an hour before peak starts at 1pm, which makes no sense from a grid standpoint since that should be a time when solar is abundant.

 

[Jigglypuff]

If I didn't want/need backup power, I wouldn't have gotten Powerwalls. They don't make sense financially.

 

[invalid]

PG&E must be running s marketing campaign for Tesla right now, since our power is currently out.

 

[coleAK]

Check your local regulations for how much you are allowed to produce. I built and installed my own hybrid solar system 2 years ago. Per my local regulations in Anchorage AK you can only produce up to 5% more power than you consume. I have 27 295w panels connected to a hybrid inverter with 12 12v 234AH batteries with a 2ndary breaker panel I can operate from “off grid”. I’m about a net zero in my peak production 4 months but if I made much more the MLP could make me remove solar panels. At some point (when they come down in price) I’ll add a wind turbine for winter but will probably have to lock it out durring sunny periods peak summer unless the regulations change.