Xminus6
Member
So non-solar PW charge during Off Peak and consume during Partial and Peak? If so it seems like your payoff for Powerwalls is actually better if you don't have PV.
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Surviving the PG&E test?
- Thread starter Boatguy
- Start date
You still are not buying during off peak and exporting to the grid during peak though. You are buying during off peak, and using that power during peak. With solar, you are making your OWN energy (instead of buying from the grid, off peak) and consuming that energy during peak.
What you were asking about (I thought) was buying at off peak and putting it back into the grid at peak. Even if you do that, you just have NEM credits. They dont actually pay you those rates if you still have negative credits at the end of the year. if you are a net producer instead of consumer at the end of the year, they convert what you have left into "wholesale" rates which are 2-3 cents, instead of whatever rate it was when you earned them.
Last year, before my EV, with solar and without a powerwall, I had like $400+ in NEM credits, and got paid around $50 in a check from SCE.
My understanding is, anything over your yearly electrical usage at the true up time is paid for in wholesale prices. Seems to me (although I am not an expert by any means), that "best" is consuming as little from the utility as possible, if one is trying to make the math work for "paying" for solar and battery. The battery helps you avoid NEM some, because the rates are not very advantageous under NEM 2.0 (and likely worse later).
The utilities keep devaluing solar production from a "pay / credit for it" stand point, so better to use as much of your own as possible, rather than "put it in, then take it out". If you just have a battery, you are charing in off peak and using in peak, so you are time shifting your usage.. but with off peak energy instead of energy from your solar. Im not understanding how thats "better", but everyone needs to do their own calculations etc, or decide what they want out of it.
aesculus
Still Trying to Figure This All Out
Can you articulate what you mean by "proactively manage"?
Let's say I only charge my PWs to about 40% daily and use that energy only for peak periods. After my battery reaches it's 40% the extra power spills onto the grid and I get paid by PG&E for it. Then as solar starts to wind down the battery supplements it until it bottoms out, hopefully about the time we hit partial peak.
Now the PSPS question comes up. I don't want to be facing a PSPS with a 40% or less charged battery. What would I have to do to get the battery filled by the grid to 100% prior to the PSPS?
Im not a PW owner yet but have done a decent amount of reading. Someone will correct me if what I am about to say is incorrect.
In order to "only use 40% of your powerwall daily", you would need to set your PW reserve to 60%. You dont set how much you want to use, you set how much you want to reserve in the battery. The balance gets used. So, in your above scenario, you have "reserved 60% of your battery to only use 40%". If you get hit with a grid power outage, you have 60% of your battery that can be used.
If you have a lower reserve, you would have less left if you have a unplanned outage, at least until your solar comes up. If the outage is planned, and you have the "stormwatch" feature turned on, then stormwatch SHOULD trigger, which would charge your battery up to 100% using grid power (at whatever cost grid power costs you at that point). The stormwatch assumption is, you would rather have a full battery in an outage than be concerned about how much that grid power cost you to charge the battery.
If stormwatch activates, you could be charging your PW from the grid during peak time for example.
PW owners can not "trigger" stormwatch to charge from the grid. They can only turn "off" or "on" the feature. Off means that, even if tesla triggers a stormwatch scenario, your PW will not charge from the grid, only charge from your solar. "On" means you are ok with it charging from the grid in a stormwatch scenario.
As for "managing it proactively", you can change your reserve (reserve = the amount of power you want to keep in the battery as a percentage), to prepare for "whatever" you think might be coming. The difference is, when you change your reserve, you are still charging from your solar, vs stormwatch which you can not "trigger", charging from solar / grid to fill your battery ASAP.
PW owners / experts please correct me if I have any of this wrong. Like I said, I dont own one yet, I am in process of buying (2) of them to be installed with my existing solar, so in "info gathering" mode on usage, etc. Feel like I have a decent handle on it, but have not been "living it" personally yet, although looking forward to doing so.
aesculus
Still Trying to Figure This All Out
We are in the same place and you are a few steps ahead of me. Thanks for your feedback and lets see what the experienced users have to fill in.
I think you described it all accurately. About the only correction would be that Tesla calls it "Storm Watch", not "stormwatch".
I think you got it pretty much right, modulo (as @MorrisonHiker pointed out) spelling of "Storm Watch".
The only thing I would add is that my Powerwalls wanted to go to Storm Watch mode 2-3 days before the start of the PSPS. I attribute this to the fluid situation and Tesla's targeting large groups of installations. So I used the app to override the Storm Watch setting (keeping my Powerwalls in their normal mode, which is Cost Saving) until the start of off-peak time the day before the PSPS was to start. Similarly after we got power restored, the Powerwalls still wanted to be in Storm Watch, so again I overrode this in the app to get them back to their normal mode.
Note that there is absolutely no requirement to tweak the controls like this. This just what I did to optimize costs a bit.
Good luck,
Bruce.
I've had my Powerwalls for more than 18 months. I have Storm Watch turned off. I am close enough in to the city that I was not turned off in the PSPS. However, my neighborhood grid is relatively unreliable and I have many random outages.
Proactive Management to me means increasing your Reserve setting when you expect a higher probability of outage. For example, when I expect a significant winter storm, I increase my reserve from ~50% to ~90%. While it's charging up with available solar to meet the new Reserve, it won't discharge at all during Peak like it normally would. In fact, since I have a small solar system, I raise my Reserve so that the remaining percentage available to cycle is approximately equal to the best case daily generation for that time of year. This way, the system cycles between about 60% and 90% in December instead of 25% and 55% like it would if I left the Reserve at 25% year round. This is only necessary because I have a small solar system that cannot generate enough to cover my Peak usage during the shortest days in the 3 months around the Winter Solstice.
Xminus6
Member
I guess I'm being unclear then. What I THOUGHT you could do now with Powerwalls with Solar is to charge from the Grid during Off-Peak, then use that stored energy for the house load during the daytime in order to allow all Solar generation to be sold, rather than some amount of it being consumed by the house load.
If you could do that you could arbitrage between Off-Peak and Partial/Peak to get the maximum savings.
What I'm learning from folks who have PW is that you MUST charge the PW off of solar unless there's an emergency. That means I'd only be able to arbitrage the difference between Partial Peak (whenever my PV system can start generating and storing energy in the PW) and Peak.
If people who don't have PV buy a Powerwall, then they're able to break even on their purchase faster because they're saving more money on their bill by arbitraging a greater difference in rate. If you're forced to charge your PW off of Solar then you can only gain the difference between the rate when the power was generated by PV to when it was consumed by the house.
It doesn't make much sense to me that you're penalized for owning PV by having a much greater payoff period for Powerwall purchases.
You are right, I dont understand what you mean. I mean, I understand what you are saying, but I dont think people are getting approved for interconnect agreements, even without solar, that allow what you are talking about. Maybe they are though /shrug.
Xminus6
Member
Why would anyone buy a Powerwall if they're just storing energy with transmission losses at the same price as they're paying to consume it directly? Seems like a really really expensive solution to having backup energy. I thought the whole point was to load shift to save money and relieve stress on the grid. If they don't have solar and can't arbitrage, they're just storing energy in case of an outage? They would never get money back on their investment.
When you have PV you can take the ITC on the Powerwall, and the requirement for solar charging only last 5 years in theory. So that's going to decrease the Powerwall payoff period for the PV case.
Cheers, Wayne
d21mike
Active Member
I just purchased Solar and 2x Power Walls. Total cost is approximately $50k. Solar = $35k and 2x Power Wall = $15k.
I get a 30% tax credit which comes out to $15k so my out of pocket is $35k. But my restriction for that 30% (on both Solar and PW) is that 1) I must buy Solar as part of the purchase and 2) I can not charge my Power Walls from the Grid (only from solar). This 30% credit is going away at the end of 2021.
So, if you had a choice to do whatever you want but you had to pay FULL PRICE. What would you pick? Remember you are starting off with a $5k refund in your pocket the first year on the PW's alone.
I assume your answer might be "I want BOTH". Well this is the program and for one I am happy with getting the 30% tax credit up front. However, if you wait until 2022 you will (unless extended) pay FULL PRICE and at that point there is a good chance you can do whatever you want since you would not be receiving a tax credit for maximizing the use of SOLAR.
And... With my utility SCE, If I could do whatever I want I am not sure I agree with you that I would still want to charge my PW's from the GRID since I have Solar. If only PW's then of course yes. Remember whatever excess Solar you put to the GRID (at the rate you put it there) you can pull it back at the rate when you pull it which with some rate plans can be less so you get more for less. However, whatever you do not use they will buy it from you once a year at the wholesale price of $.03 which is much less then the least price I pay during super off-peak of $.10. For me, I feel good about the ROI on the Solar and I do not worry about the ROI of the PW. The ability to NEVER have a Power Failure is worth a lot to me and it is hard to put an exact price tag on that. But $10k is what that price tag is for me. I will eventually pay off the Solar with lower energy cost. The PW's do help with that but I can probably generate enough credits (large system) to pay for the Solar on it's own without the PW's. My 2 cents.
- The 30% rate is available for systems placed in service through December 31, 2019. The credit drops to 26% through the end of 2020, then 22% through 2021 before dropping to zero by the end of 2021.
Go Solar California
In order to receive the tax credit, the PWs must be charged from an alternative energy source, not from the grid. This makes sense from an energy / tax policy standpoint and I wouldn't want my tax dollars subsidizing someone's rate arbitrage play.
That said, the tax credit is between you and the IRS. The chance that they are going to come out and audit your house is pretty low. You could have installed PVs ten years ago and the PWs this year and you'd qualify, how do they know? However, you'd have to create your own control software to charge from the grid when there is no NWS storm warning and effect the rate arbitrage.
Thanks for the contributions here as I ordered the PV/PW system yesterday.
Yes, that sounds like a good feature request. We were discussing that on another thread recently:
In other words, if you charge from the grid, NEM / CPUC says you can't export that energy to the grid, so you can't do rate arbitrage with storage alone. But you are allowed use that stored energy to offset your own consumption to maximize your solar export. You are also allowed to do rate arbitrage if you charge the batteries exclusively from solar, i.e. charge from solar during off peak/partial peak then export that energy to the grid during peak. But Powerwall software doesn't support this.
Xminus6
Member
Okay thanks. That’s the missing piece. I’m not trying to have my cake and eat it too, but nobody explained that the alternative source requirement had an expiration date. Without it you’d be better off just denying the tax rebate at all because long-term I’d save more than the $5000 in energy savings.
I may be misunderstanding what you mean. I charge my Powerwalls every day during off peak/partial peak and export during peak. Can you explain what isn't supported?
Exporting to the grid is not supported. In other words, the battery output exceeds your household load, figuratively spinning the meter backwards and earning NEM credits in excess of local solar generation.
For people in PG&E territory on the EV rate plan, the higher value Part-Peak generation is being taken away by the utility forcing people onto the EV2 rate plan that extends the Off-Peak period to 3pm.
So, your wish is granted, you will be able to arbitrage from Off-Peak to Peak just using your solar. Just be careful what you wish for.
Thanks for the clarification. I guess I misread it. I was thinking it said we couldn't charge the Powerwalls during off-peak and shoulder and then export from solar (not the Powerwalls) during peak, while powering the house with the Powerwalls.
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