I think discussing regular use practices of PowerWall systems with solar at home would make sense.
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I've not made any attempt to measure the efficiency loss of the Powerwalls, but it sure seems like it's way higher than the stated 10%.
I think discussing regular use practices of PowerWall systems with solar at home would make sense.
However, I don't know how many folks would be willing to give up control of their battery storage. I suppose a lot would depend on whether the owner could control the amount of reserve to be untouched, max power draw, etc. A much more complex system than what the PW software seems capable now would be required. Say hello to Big Brother.
10. Grid Services. Your System is capable of supporting the reliability of the electrical grid by providing services under programs offered by utilities or third parties. You grant us the right to access and use your System to provide these services. Before we do this, we will explain the terms of your participation in the relevant program and give you the opportunity to opt-out.
Here's a quote from the powerwall purchase agreement:
Yeah. The opt out is a check box in the Powerwall configuration sequence. I noticed it while looking over the tech's shoulder during commissioning.
At least there's an opt-out!
I love most of your post. I have very little of it to add to or comment on. Just this: I think what you just said that I quoted, that a user should be able to set the amount of capacity to be made available for others vs. what is to be made available only for oneself, is essential to a complete settings system, and my bare minimum for sane control of the PowerWall. I would define "capacity" as kW in, kW out, kWh in, kWh out, % SOC range for them, etc. Although nominally they would be max settings (max kW out, max kW in, etc., lowest SOC % they could draw down to, highest SOC % they could charge up to, etc.), additional settings of minimums to others might be required for contractually created edge cases that would require a few fine tuned further settings available. But it's really not super complicated. Anybody who thought of the dynamics of this type of system decades ago realized all of this was required, and I know that includes me, and by today, anybody who looks into this issue with anything but the lowest of IQs. For instance, you, Bigtanuki, brought up basically everything in one simple post, so it can't be that hard for seasoned professionals actually in the field to properly handle it, provided they don't have obstructionist vested interests hindering proper conduct.However, I don't know how many folks would be willing to give up control of their battery storage. I suppose a lot would depend on whether the owner could control the amount of reserve to be untouched, max power draw, etc. A much more complex system than what the PW software seems capable now would be required. Say hello to Big Brother.
Bigtanuki
Here's mine:There was some discussion above about PowerWall 2 efficiency. I have one datapoint about that. Both Yesterday and Today show that I filled my PowerWalls to 100%. Yesterday's "From PowerWall" evening draw was 6.6kWh and Today's "To PowerWall" figure was 7.7kWh. So, the conversion losses to get back to 100% were 1.1/6.6 = 16.6%
I agree on all counts. In addition to my career in the control room I spent the last few years at PG&E being a "business rep" for our SAP implementation. As the business rep I essentially translated customer requests into developer speak. That included writing specs, test plans, change requests and maintaining a semblance of scope control for customers that just "thought of something" they would like to add to their software request. The one phrase I learned to hate the most was "how hard could it be to write that code?". I learned that it may be straightforward to write a piece of code to do something but it's quite another to write a piece of code that (A) looks like the rest of the pre-existing code and (B) not break some innocuous piece of code somewhere else in the package. Testing was a bitch and we were building business software not something that could get you killed. It is impossible to test every piece of new software against every piece of existing software unless you have immense resources and you don't want to get software except perhaps annually.I love most of your post. I have very little of it to add to or comment on. Just this: I think what you just said that I quoted, that a user should be able to set the amount of capacity to be made available for others vs. what is to be made available only for oneself, is essential to a complete settings system, and my bare minimum for sane control of the PowerWall. I would define "capacity" as kW in, kW out, kWh in, kWh out, % SOC range for them, etc. Although nominally they would be max settings (max kW out, max kW in, etc., lowest SOC % they could draw down to, highest SOC % they could charge up to, etc.), additional settings of minimums to others might be required for contractually created edge cases that would require a few fine tuned further settings available. But it's really not super complicated. Anybody who thought of the dynamics of this type of system decades ago realized all of this was required, and I know that includes me, and by today, anybody who looks into this issue with anything but the lowest of IQs. For instance, you, Bigtanuki, brought up basically everything in one simple post, so it can't be that hard for seasoned professionals actually in the field to properly handle it, provided they don't have obstructionist vested interests hindering proper conduct.
As @markb1 said, we already signed an agreement setting the legal permission for the utility to use our system for the grid, and to look at our use patterns. Now, PG&E and Tesla just have to set up the programming and settings. I really don't like how they're dragging their feet on this straightforward step, trying to make it sound and be as complicated as possible, to feed into their dragging their feet even more, in order to make it sound even more complicated, etc. It means that when they do implement, they won't iterate fast enough to debug it, and it will always be a quagmire since it will always be woefully wrong, when instead, it could be really clean and great (like the Australian Tesla battery).
Meanwhile, I'm extremely happy to avoid the utility as much as possible.
Testing was a bitch ... It is impossible to test every piece of new software against every piece of existing software unless you have immense resources and you don't want to get software except perhaps annually
According to @GenSao, "2) Each Powerwall on average uses just over 1 kWH/day to maintain and condition the battery.", so for my approximately 201 days of having our PowerWalls, that's 201kWh for one or 402kWh for two, so:
I think I was being extra conservative and will have to revise my statement.
Recently (over President's Day weekend) I had the Powerwalls set to backup only mode for approximately 72 hours. The Powerwalls charged up the 1st day in the morning (from 84% to 100%) and lost capacity over time. They only recharged the morning of the 4th day. The Tesla app shows that 1.6 kWH was used that morning. So 1.6 kWH / 3 days / 2 batteries = 0.27 kWH / day / Powerwall.
Roughly 2% a day.
Of course the weather can play a part. The temps were:
17th, Hi = 70F, Low = 40F
18th, Hi = 58F, Low = 43F
19th, Hi = 54F, Low = 37F
20th, Hi = 54F