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Validating Powerwall Math

h2ofun

Active Member
Aug 11, 2020
3,700
891
auburn, ca
Thanks everyone. I have to confess I was not reading my bill properly, and the generation charges are the actual SVCE charges, not what credit I am getting. I am not close to being a net exporter. I do get a generation credit during the month, but even off peak I only exceed the what I use a few months in the summer, and I never get close to offsetting peak hour use. The bill is not that easy to understand, but I will dig into it more.

So you are clearly right about the offset of load shifting being a lot smaller than what I was assuming, so the PW's clearly don't pencil out on the load shifting side.

Part of the reason electricity usage is high is I have a couple racks of servers in the basement that I use for a home lab. On average it's about 1800 watts, but it is continuous load - disks spinning, network switches, etc... Still, that's not explaining why in the middle of the night with the lights out I still am burning 5-6 kilowatts every hour. Pool pumps and car chargers shouldn't be running then, so something more investigation is called for.

In any case, the powerwalls clearly don't make sense, but I appreciate all the help I got here! Thanks everyone!
thats a huge load in the night. Yep, will be interesting what you find
 
We're about 10 miles from Menlo Park and our 2200 sqft house is heated with a very efficient Mitsubishi heat pump. COP at 47F is 4.2. I have Emporia Vue current transformers on some of our electrical circuits. This heating season we have used 598kWh (Nov), 1112kWh (Dec), 1110kWh (Jan), 886kWh(Feb), and 838kWh (Mar) for the heat pump alone. For December through March, the average is about 30kWh per day and most of the energy consumption is at night. Presumably your house is noticeably larger than ours, and possibly your heat pump(s) are less efficient. So I suspect if 5-6kW power consumption includes the servers, then it probably is a reasonable draw.

On the other hand, our solar capacity is 1/3 the size of yours, and we are a net generator. We don't have EVs, and I imagine that your AC usage is quite a bit higher than ours, but still 25kW of solar seems like enough to bring you close to even.
 
My system has a math problem. I have a Powerwall with the controller that is telling me that my 16.5kW solar system is putting out 24kW of power.
My Enphase inverter is reporting within a tenth of a kW what my electric meter is saying I'm drawing from the grid, so I would think that the Enphase controller is much closer when it's telling me that I'm only producing around 13kW of power
 

miimura

Well-Known Member
Aug 21, 2013
7,314
7,294
Los Altos, CA
My system has a math problem. I have a Powerwall with the controller that is telling me that my 16.5kW solar system is putting out 24kW of power.
My Enphase inverter is reporting within a tenth of a kW what my electric meter is saying I'm drawing from the grid, so I would think that the Enphase controller is much closer when it's telling me that I'm only producing around 13kW of power
If the power flow diagram in the Tesla app is showing incorrect solar power compared to the meter and the Enphase monitoring, then the Tesla CTs are configured wrong. This is a common problem. Open a case with Tesla Energy Support and give them the data for what you're seeing.
 

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