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Charging Powerwall Overnight

timpharrison

Member
Jul 23, 2019
43
18
London
Hi,

Has anyone calculated how much energy could be drawn and stored overnight (12:30pm to 04:30am) in the Powerwall?

I’m in the UK and on my electricity tariff (Octopus Go), rates are one third of regular during this period.

I can’t fit solar panels so am thinking about the economics of just taking power off the grid when it’s cheaper and using during the day.

Our house consumes a lot of power (70 to 100Kwh per day, including the Tesla).

Tim
 

Gdotp

Member
Aug 1, 2021
20
7
Uk
3.5 *4 = 14 in theory but you can’t force it to do this as it’s down to the so called AI to do it. You can influence is by setting the off peak period and if you are dedicated by setting the minim charge level at 0.30 to 100% and then back down again at 04:30 manually (octopus Go)

The biggest issue with the PW is lack of control of this by the user and it’s reliance on its own, poor, AI. Many such threads discuui g this
 
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EVRider-FL

Active Member
Aug 18, 2015
1,004
570
South Florida
Have you calculated whether your electricity savings would offset the cost of the Powerwall(s)? Seems unlikely. Given your energy usage, I don’t think one Powerwall would be enough.
 
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xWren

Member
Sep 22, 2021
27
19
UK
@timpharrison I'm in Cornwall and on that very same tariff so I can answer your question from actual experience.

Leaving Tesla to control the charging/discharging of the Powerwall is next to useless for us in the UK, their algorithm can't cope with the daily variation in our weather let alone variation in domestic use. In time-based mode it will make very bad decisions, cost you money and leave you angry as Hell!

I run in self-powered mode and adjust the power reserve percentage at 12:29pm and 04:29am to trick the Powerwall into changing from the grid in that off-peak period and not discharge. It does so at 1.7kW (the slow rate, not the possible 3.4kW), hence at most it can store 6.8kWh. This is not ideal but at the moment there is no way to get the faster rate.

Thankfully I have the skills to write a script that I run on a RPi that automates making the API requests to change the settings at the right times. Without something like that you would need to be awake at those times to use the app to change them.
 

Zabe

Member
Jun 11, 2021
87
50
Placerville, CA
I have a 3 powerwall only installation with no solar. I can charge them from 5% to 100% in 4 hours. I use time based control. It took Tesla 10 weeks to get it operating correctly but now it is flawless. You don't have to worry about some poorly designed algo, they charge at the start of off peak and discharge during peak time. I get all my energy at off peak prices. 99% of people here have solar with powerwall and do not know that this works because they are not allowed to grid charge except during storm watch.
 

miimura

Well-Known Member
Aug 21, 2013
6,678
6,511
Los Altos, CA
The OP is specifically asking about Powerwalls WITHOUT solar. The Powerwall system works differently in Time Based Control mode when configured without solar. The API workarounds should not be necessary in this case.

In order to see how well it will work for your specific situation, you need to establish how much usage (total kWh) cannot be shifted to the Off-Peak hours. Things like car charging can be pushed into the Off-Peak, but if you are charging Powerwalls at max rate and charging a car, you may start to approach or exceed you maximum allowable grid draw during that short window.

Let's say you reliably have 40kWh that cannot be shifted into Off-Peak. You would need 3 Powerwalls to nearly supply that with no extra Reserve for power cuts. With 4 Powerwalls, you could supply the 40kWh with 15%-20% reserved for power cuts. I don't know your prices, but you said 3X during daytime compared to the Off-Peak window. Let's call that 10p/kWh and 30p/kWh. You would need to consume 45kWh @ 10p/kWh = 4.50GBP for charging to avoid 40kWh @ 30p/kWh = 12.00GBP. That's a savings of 7.50GBP/day. I don't know how much it costs to install Powerwalls in the UK, but the payback is probably more than the 10 year warranty period.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
11,379
13,224
Riverside Co. CA
99% of people here have solar with powerwall and do not know that this works because they are not allowed to grid charge except during storm watch.

99% of the people in the United States, but this OP is not in the US. Outside the US, there are likely many more people that either have powerwalls only, or have their powerwalls charge from the grid.
 

xWren

Member
Sep 22, 2021
27
19
UK
The OP is specifically asking about Powerwalls WITHOUT solar. The Powerwall system works differently in Time Based Control mode when configured without solar. The API workarounds should not be necessary in this case.
Thanks for pointing that out. My previous post regarding my experience with Time-based mode is with solar generation that can vary by 15kWh from one day to the next. That is what the Tesla algorithm can't cope with (and I doubt the coders considered).
 

Zabe

Member
Jun 11, 2021
87
50
Placerville, CA
99% of the people in the United States, but this OP is not in the US. Outside the US, there are likely many more people that either have powerwalls only, or have their powerwalls charge from the grid.
That is probably true. In this forum 99% of people have solar and powerwall's and tend to give misinformation because they do not know how it works without solar.
 

Gdotp

Member
Aug 1, 2021
20
7
Uk
@timpharrison I'm in Cornwall and on that very same tariff so I can answer your question from actual experience.

Leaving Tesla to control the charging/discharging of the Powerwall is next to useless for us in the UK, their algorithm can't cope with the daily variation in our weather let alone variation in domestic use. In time-based mode it will make very bad decisions, cost you money and leave you angry as Hell!

I run in self-powered mode and adjust the power reserve percentage at 12:29pm and 04:29am to trick the Powerwall into changing from the grid in that off-peak period and not discharge. It does so at 1.7kW (the slow rate, not the possible 3.4kW), hence at most it can store 6.8kWh. This is not ideal but at the moment there is no way to get the faster rate.

Thankfully I have the skills to write a script that I run on a RPi that automates making the API requests to change the settings at the right times. Without something like that you would need to be awake at those times to use the app to change them.
Hi are you sure it can’t charge at 3.4. It looks like mine did the other day and I’ve certainly seen it get to 90% in the past. See below. The usage shown is 3.6kw but I’ve got an overnight load of 200 to 300w.

Could you share your RPi script, I do t have the skills but can probably tinker enough for it to run on my Homebridge RPi.
F5473F93-50D7-4864-9F71-FEB5E229A68D.png
 

xWren

Member
Sep 22, 2021
27
19
UK
Hi are you sure it can’t charge at 3.4. It looks like mine did the other day and I’ve certainly seen it get to 90% in the past. See below. The usage shown is 3.6kw but I’ve got an overnight load of 200 to 300w.
Yes, it can charge at the faster rate when in Time-based control mode and the algorithm decides to do so. I am guessing that is what you are showing. What I described was the rate when in self-powered mode, then it is 1.7kW and in a my 4 hour cheap window can only pull 6.8kWh.

I'll ping you when I get around to putting my scripts (which I modified from the work of others I need to credit) up onto Github. I'm just not that organised.
 

Gdotp

Member
Aug 1, 2021
20
7
Uk
Yes, it can charge at the faster rate when in Time-based control mode and the algorithm decides to do so. I am guessing that is what you are showing. What I described was the rate when in self-powered mode, then it is 1.7kW and in a my 4 hour cheap window can only pull 6.8kWh.

I'll ping you when I get around to putting my scripts (which I modified from the work of others I need to credit) up onto Github. I'm just not that organised.
Thx. Me neither
 

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