Best Set-up for my Tesla Solar & PW System for NEM 2.0

[cciesingh]

I am based in California and on PGE NEM2.0, I have a 17KW Solar System form Tesla with 3 x Power Walls.

My rate plan is TOU EV2A home charging. Charge at home once a week at most. My power wall is currently set to be used for 55% for Time Based Control,

How should I set my Powerful configuration to optimize my set-up? Any tips & guidance would be greatly appreciated.

 

[lodar]

I have a similar 16.5kW system, 3 Powerwalls, in California.

I think your approach will depend on your home’s power consumption and what goal are you optimizing for.

Some people want maximum independence, some want maximum profit, some want maximum power outage protection.

 

[buckets0fun]

VPP
Any other suggestions, we don’t have enough info.

Do you reach 55% before your peak times are over? What amount of energy(kWh) do you use in a day? Do you charge the car from behind the TEG/PWs or from your main panel/grid? Can your production meet your demand, if you went to self powered? Summer? Winter?

 

[lodar]

My house takes 50-80 kWh per day, but the Powerwalls generally can carry me through the Peak hours.

I upgraded from about 9kW to 16kW solar before the NEM 3.0 cutoff, so I am still getting used to the new capacity.

In terms of efficiency (minimize loss and costs):

0) Use less power - duh!

1) Directly Consuming Solar - No battery conversion loss ($), no Non-Bypassable Charges (NBCs) ($). Penny saved, penny earned.

2) Solar to Grid at Peak - At least getting max money from power to grid.

^^^ —- Makes Money —- ^^^
vvv —- Neutral-ish —- vvv

3) Consume battery - Slightly negative of neutral because of battery conversion loss (10%)

4) Solar to Grid Off Peak - Doesn’t quite offset grid consumption kWh for kWh, thanks to NBCs.

vvv —- Costs Money —- vvv

5) Consume Off-Peak from grid - NBCs is a natural tax that simulates conversion loss using the grid as a battery.

5) Consume Peak from grid - Worst, paying max rate with NBCs.

Personally, I cycle through 4 patterns in order of preference:

1) All Day Self-Powered - No NBCs, zero power from grid, overflow automatically goes back to grid.

When it backfires I end up running out of battery during peak in the evening which blows all the hard work. The battery runs at a net loss, so I can’t do it unless there is a big surplus from the previous day to burn.

2) Default Time-Based (most common) - Sells back solar during peak, runs on autopilot. Downside is NBCs and when batteries fill early, it sells back off-peak, rather than spent offsetting house loads.

3) Micromanage, Off-Peak Time-Based, Peak Self-Powered. Maximum selfish mode when I know there will be a big power load like a holiday with the AC running, ovens, cooking, and fridge door opening a lot. Backfires when I forget to reset to Time-Based.

4) Super Micromanage: Same as 2 or 3, but switch early to Self-Powered when batteries are full. Backfires when I miss a transition.

 

[swedge]

How should I set my Powerful configuration to optimize my set-up? Any tips & guidance would be greatly appreciated.

I have a similar set up, but smaller. 5kW solar, a Model Y, one PowerWall. I've done a lot of work on optimizing, and realized that there are three very different scenarios based on the balance between your total annual solar generation and your total annual consumption.

If you produce more than your use, things can be pretty simple. If you use a lot more than you produce, you work a bit more to minimize your true-up. If you are in between, which I am, it gets more complicated trying to get the true-up as close to zero as possible.

So, to answer your question is that the strategy depends on your situation. Are you a net generator, for example. Air conditioning? Can you car charge at night? Does your PW let you "Export Everything".

In any case, it is the True-Up calculation which determines your costs. There are a number of threads on TMC discussing various aspects, and several people who are quite knowable. There is a good example and discussion of PG&E True-Up on TMC here: NEM-PS Annual True-Up Calculation [PG&E example]

That all being said, I'd guess that your Time Based settings, with 55% backup reserve is a good start. To do a good job of deciding how to behave, your PW needs to know about NEM2 Non-Bypassable Charges of around 3¢ per kWh which is charged on all imports but not credited on exports. So I edit the utility rates to make the sell price 3 cents lower than the buy price. Some folks suggest 6 cents instead to account for the 10% or so PW efficiency loss.

One other suggestion is that you keep an eye on your system. If for any reason your solar quits producing, you can get a very nasty surprise come true-up time. One guy had his home heat pump fail so the compressor ran continuously, running his bill up, up, up, till he noticed.