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Powerwall 2 - Time Based Control

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I'm trying to understand how the Time Based Control works with Powerwall 2 and if it might be worth it for me to switch to a Time Of Use tariff.

My setup is a 10 year old 10kW solar system (that still works well) and 3 x Powerwall 2 (installed around Christmas) on a fairly power hungry house in Blue Mountains NSW. I also have a Model 3 although recently I have been doing almost all its charging at the NRMA charger at Sydney Olympic Park on my way home. The system is currently set to Self-powered with a Reserve of 5%. I'm on a fixed rate tariff (22.75c/kWh).

If I get a run of sunny days, the solar is enough to charge the Powerwall to 40-70% which usually results in 5-25% left in the Powerwall by the time the solar kicks in again. i.e. with a run of sunny days I take almost no net power from the grid. This will likely change in Winter with shorter days, lower sun height, and AC to heat the house.

If I get a run of cloudy/wet days, the Powerwall barely gets to 10% and so I'm back on the grid by 5-7pm.

I've read the online help that Tesla provide but still can't get my head around how Time Based Control would work in the two scenarios above (run of sunny days, run of cloudy days) or any combination of them.

If I switched to a TOU tariff and used Time Based Control, would I still draw no grid power with a run of sunny days? How does it know? If I had a run of cloudy days, how would I avoid using grid power during the peak (13:00-19:59) @32.33c/kWh? Again, how does it know?

With Time Based Control does the Powerwall still only charge from solar or can it charge from the grid? I'm trying to understand the Excess Solar/Any Solar in the documentation. Does it mean that when there is no excess solar during the off-peak and shoulder times that the house runs from the grid and all the solar is used to charge the powerwall?
 
I’m using my Powerwall 2 set up to have maximum savings (you can also choose a balanced setting, but more in that later). My system is only 5.9kW and I have 1 Powerwall 2.

You don’t tell it your tariffs, instead you tell it when the peak, shoulder and off peak times for your power prices are.

There is a setting for the weekdays and a setting for the weekends, because with TOU then those regimes will be different. Go to the Tesla app, switch to your battery, choose customise, select advanced, choose either balanced or cost saving and then edit schedule to set the times for the relevant tariff periods (just the times, it does not look at absolute costs).

Having done that the software controlling the battery will make an effort to have the thing full just before the peak cost period starts for the weekday - weekend not so much, I think for me because the difference in tariff is not great (it is kind of low shoulder vs shoulder).

The software looks at recent performance of your solar system production to decide when to start charging the battery.

Some days in summer the battery charges a bit early in the morning, then stops and starts again later on to be full at peak time. Some days in summer the battery will charge in the middle of the night when it is very cheap for me and then get topped up by what sun there is available, but still full by peak time.

This will change over a cycle of 2-3 days depending on the solar production - so if you have a cloudy week it charges when it is cheap from the grid and makes do with the solar available (if any) and if it is sunny it leaves the grid alone.

There are a few effects of this. First, you will end up exporting a bit more solar than otherwise - the system is defending the battery against being completely full other than immediately before the peak period starts. Second, this strategy is good if your lowest grid cost is about the same as your feed-in-tariff (mine is), so that whether the solar goes to the grid or to the battery as long as those two are about the same I am cost neutral. My power company has 100% offset electricity as a default. Third, if suddenly the weather is bad one morning then you will be filling the battery at shoulder rates to avoid peak rates and so there is still some cost saving. Finally, you will see that you are importing more power, but because you are exporting more power, and exploiting cheaper tariffs things even out. My costs have fallen by more than 10% even though my gross imports have risen significantly.

If you have a run of sunny days you will still stay off the grid.

As for the splitting of solar between running the house and charging the battery, it still seems that for the most part solar goes to the house first, then excess of that to the battery, then excess of that to the grid. Occasionally when I look at the app, some really weird combinations are happening, but this is not often and not for terribly long.

With things set up as they are, even on miserable days I very rarely use power from the grid in the peak period. For the last couple of bills this has been about 1% of my consumption and I live in a bit of the coast that is a bit cloudier than most other places.

I haven’t explored the difference between balanced and cost saving. I think it might be better if your grid supply was not carbon offset and so you export less, although the savings may not be as good.
 
I’m using my Powerwall 2 set up to have maximum savings (you can also choose a balanced setting, but more in that later). My system is only 5.9kW and I have 1 Powerwall 2.
Thanks for your reply!

My power company (Powershop) also is 100% offset.

When you say it makes an effort to ensure the battery is full, do you mean 100% or just what it thinks it will need based on the previous days experiences? I'd rather not export to the grid because I get a pittance (currently 7c/kWh).

Even though I'm still on a fixed rate I set up the app as if I was on ToU and used the times in the proposed tariff.

The first thing that was weird was it immediately started putting ALL the excess solar to the grid even though the SoC was only 5%. I switched between Advanced and Self-Powered a few times and eventually it started charging the battery. I was on the Balanced setting.

All through the shoulder period it appeared as though all the solar (or a close approximation) was going to the battery and the house was using power off the grid. I assume it would do this until the battery is 100% or I hit the peak period (see below).

After reading your comments above (and while still in the shoulder period) I changed to Cost Savings. Immediately it went back to sending all the excess solar to the grid, even though the SoC was around 20%. Switching back to Balanced didn't fix it so I had to do multiple switches before it when back to solar going to battery.

At 1pm (when peak started) it switched to only excess solar going to the battery and nothing coming from the grid. I tried Cost Savings again, and again it sent all the excess solar to the grid.

I don't understand why it keeps exporting to the grid when the battery is far from full.
 
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I'm trying to understand how the Time Based Control works with Powerwall 2 and if it might be worth it for me to switch to a Time Of Use tariff.

With Time Based Control does the Powerwall still only charge from solar or can it charge from the grid? I'm trying to understand the Excess Solar/Any Solar in the documentation. Does it mean that when there is no excess solar during the off-peak and shoulder times that the house runs from the grid and all the solar is used to charge the powerwall?
Wow... where to start with this one.

First, if you have solar and Powerwall (particularly a large array and 3xPW2 😱) then you will absolutely be better off with TOU tariff than fixed. You should be able to almost completely avoid paying for electricity during the peak tariff periods, and get the benefit of cheaper offpeak electricity to charge your car from the grid overnight, or demand-manage other usage, and pay a much lower average c/kWh price for the grid power you do use.

I have only a 5kW system and 1xPW2, and my peak usage is tiny. Only 26 kWh for the entire quarter in my last bill.

As far as TBC goes... it’s an AI algorithm and I remain unconvinced it does sensible things or actually saves you much money. As @Hairyman says, it will do weird things at various times (like export solar in preference to charging the battery, or use the grid in preference to discharging the battery) and I didn’t like the unpredictable ”black box” nature of what it does.

It does result in the grid charging the battery at various times, including filling it prior to the commencement of the peak tariff period. Which often means using shoulder-period grid electricity - which isn’t necessarily smart.

I tried TBC in “cost optimised” mode for a quarter. After loading that three months worth of the 5-minute PW2 data into my spreadsheet, and doing the “what if” alternative scenario of what would my power bill had been if PW2 had have been in “self consumption” mode instead for those 3 months, TBC only saved a few dollars compared to self-consumption.

My conclusion is that TBC is flawed as an optimisation algorithm. Merely telling it when the peak, shoulder and offpeak times are is not enough to do a proper optimisation. It would also need to know the relative price difference of those tariffs during those times, as well as the relative price of the solar FIT (e.g. is it higher or lower than the offpeak tariff?) and to to a proper job, also know what your daily connection fee is. It does an OK job given what it does know, but it could be much better.

I much prefer the predictability of what self-consumption mode does, so I switched it back to that.

I have some ideas on how TBC could be made better with some simple, fixed rules (and be more predictable) as a third alternative to the two current modes offered. I spreadsheeted them and they worked (lower cost) than either TBC or self-consumption, so I am going to send them to Tesla.
 
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First, if you have solar and Powerwall (particularly a large array and 3xPW2 😱) then you will absolutely be better off with TOU tariff than fixed. You should be able to almost completely avoid paying for electricity during the peak tariff periods, and get the benefit of cheaper offpeak electricity to charge your car from the grid overnight, or demand-manage other usage, and pay a much lower average c/kWh price for the grid power you do use.

Thanks!

My problem is that I'm currently only paying 22.75c/kWh. The tariff that I'm looking at would be 32.33c/kWH 13:00-19:59 and 23.12c/kWH for 07:00-21:59 (less the peak), so the bulk of the day would be higher than the fixed rate I'm on now. From 22:00-23:59 and 04:00-06:59 is only 13.78c/kWh and 00:00-03:59 is even less at 6.94c/kWh but would I be able to get enough charge into the battery at that time?

I wonder what would happen if I set peak to be 07:00-21:59 and off-peak to 00:00-03:59.
 
Thanks for your reply!

My power company (Powershop) also is 100% offset.

When you say it makes an effort to ensure the battery is full, do you mean 100% or just what it thinks it will need based on the previous days experiences? I'd rather not export to the grid because I get a pittance (currently 7c/kWh).

Even though I'm still on a fixed rate I set up the app as if I was on ToU and used the times in the proposed tariff.

The first thing that was weird was it immediately started putting ALL the excess solar to the grid even though the SoC was only 5%. I switched between Advanced and Self-Powered a few times and eventually it started charging the battery. I was on the Balanced setting.

All through the shoulder period it appeared as though all the solar (or a close approximation) was going to the battery and the house was using power off the grid. I assume it would do this until the battery is 100% or I hit the peak period (see below).

After reading your comments above (and while still in the shoulder period) I changed to Cost Savings. Immediately it went back to sending all the excess solar to the grid, even though the SoC was around 20%. Switching back to Balanced didn't fix it so I had to do multiple switches before it when back to solar going to battery.

At 1pm (when peak started) it switched to only excess solar going to the battery and nothing coming from the grid. I tried Cost Savings again, and again it sent all the excess solar to the grid.

I don't understand why it keeps exporting to the grid when the battery is far from full.
I’m with Powershop as well, and in their electric car TOU arrangement.

What you are seeing is typical with the battery waiting to charge later in the day and timing it’s run to be full just before the start of peak pricing.

It takes a day or two to settle into a pattern of behaviour because the software has to work out what to do. Changing frequently from one to the other will make things a bit confused.
 
Thanks!

My problem is that I'm currently only paying 22.75c/kWh. The tariff that I'm looking at would be 32.33c/kWH 13:00-19:59 and 23.12c/kWH for 07:00-21:59 (less the peak), so the bulk of the day would be higher than the fixed rate I'm on now. From 22:00-23:59 and 04:00-06:59 is only 13.78c/kWh and 00:00-03:59 is even less at 6.94c/kWh but would I be able to get enough charge into the battery at that time?

I wonder what would happen if I set peak to be 07:00-21:59 and off-peak to 00:00-03:59.
I exploit the very cheap 0000-0400 tariff by setting the car to charge then, and setting timers for dishwashing, washing machines etc to then.

From the behaviour I have seen then the battery will charge itself in that very cheap period and only charge from the grid when there is an unexpected failure of solar production (ie today is cloudy when the last few days have been sunny).

I agree that being able to nominate costs as well as times would help improve the performance of the system
 
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When
Thanks for your reply!

My power company (Powershop) also is 100% offset.

When you say it makes an effort to ensure the battery is full, do you mean 100% or just what it thinks it will need based on the previous days experiences? I'd rather not export to the grid because I get a pittance (currently 7c/kWh).

Even though I'm still on a fixed rate I set up the app as if I was on ToU and used the times in the proposed tariff.

The first thing that was weird was it immediately started putting ALL the excess solar to the grid even though the SoC was only 5%. I switched between Advanced and Self-Powered a few times and eventually it started charging the battery. I was on the Balanced setting.

All through the shoulder period it appeared as though all the solar (or a close approximation) was going to the battery and the house was using power off the grid. I assume it would do this until the battery is 100% or I hit the peak period (see below).

After reading your comments above (and while still in the shoulder period) I changed to Cost Savings. Immediately it went back to sending all the excess solar to the grid, even though the SoC was around 20%. Switching back to Balanced didn't fix it so I had to do multiple switches before it when back to solar going to battery.

At 1pm (when peak started) it switched to only excess solar going to the battery and nothing coming from the grid. I tried Cost Savings again, and again it sent all the excess solar to the grid.

I don't understand why it keeps exporting to the grid when the battery is far from full.
When I said my battery is full for the peak period, I mean 100%. The management fir more than one battery may be different, it may be looking to make sure you have enough plus some sort of buffer to help protect the battery - but this is just speculation.
 
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I’m with Powershop as well, and in their electric car TOU arrangement.

What you are seeing is typical with the battery waiting to charge later in the day and timing it’s run to be full just before the start of peak pricing.

It takes a day or two to settle into a pattern of behaviour because the software has to work out what to do. Changing frequently from one to the other will make things a bit confused.
Thanks again!

I'll have another play with it next week. I don't see much point in testing it over the weekend when the ToU conditions are different.
 
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When

When I said my battery is full for the peak period, I mean 100%. The management fir more than one battery may be different, it may be looking to make sure you have enough plus some sort of buffer to help protect the battery - but this is just speculation.
It does seem a bit silly getting it to 100% just before peak because
a) peak is likely to be in the middle of the day when solar production is highest (so nowhere for the excess solar to go but the grid)
b) 100% may be far more than is required. I think I could easily get through the peak period with only 50%.

I wonder where making the peak start time earlier than it really is would help (me) get around that problem. For example, if I set the start of peak to be before sun up, it might drain the battery enough for some room for top-up later.
 
It does seem a bit silly getting it to 100% just before peak because
a) peak is likely to be in the middle of the day when solar production is highest (so nowhere for the excess solar to go but the grid)
b) 100% may be far more than is required. I think I could easily get through the peak period with only 50%.

I wonder where making the peak start time earlier than it really is would help (me) get around that problem. For example, if I set the start of peak to be before sun up, it might drain the battery enough for some room for top-up later.
I think the idea is that if it suddenly gets cloudy at the start of peak you will have a full battery regardless. Also the battery will spend less time at 100% which is not necessarily good for it.
 
My problem is that I'm currently only paying 22.75c/kWh. The tariff that I'm looking at would be 32.33c/kWH 13:00-19:59 and 23.12c/kWH for 07:00-21:59 (less the peak), so the bulk of the day would be higher than the fixed rate I'm on now. From 22:00-23:59 and 04:00-06:59 is only 13.78c/kWh and 00:00-03:59 is even less at 6.94c/kWh but would I be able to get enough charge into the battery at that time?
Everyone's consumption pattern is different, but for me over the past 12 months, 16.6% of all power consumption at my house was during the peak period, 42.2% during shoulder, and 41.2% offpeak. However, 80.3% of all peak usage was renewable (solar/battery) not grid. For shoulder it was 74.1% renewable, but offpeak was only 20.9% renewable. (I am a 100% GreenPower customer, so my grid use is also renewable, but you know what I mean)

On my current plan, I pay 44.75 c/Kwh for peak, 19.59 for shoulder, and 11.59 for offpeak. So I calculate my "blended" (consumption weighted) grid tariff to be 15.78 c/kWh. Before I went on to TOU, my fixed grid rate was 22 c/kWh. So TOU saves me 28% per grid kWh.

With a larger solar array than what I have, and 3xPW2, I suspect your saving would be even bigger.
 
I think the idea is that if it suddenly gets cloudy at the start of peak you will have a full battery regardless.
Yes, I think that's the idea of TBC, but it's not necessarily always the smartest strategy. You might be able to get through the peak period with the battery less than 100%, so you've used grid power (or sacrificed solar export) to fill the battery when you didn't need to. So that could cost you money rather than save it.
 
Yes, I think that's the idea of TBC, but it's not necessarily always the smartest strategy. You might be able to get through the peak period with the battery less than 100%, so you've used grid power (or sacrificed solar export) to fill the battery when you didn't need to. So that could cost you money rather than save it.
Correct. I can say that running the current strategy is saving me about 10% of my total bill compared to prior and the battery is spending less time at 100.
 
Wow... where to start with this one.

First, if you have solar and Powerwall (particularly a large array and 3xPW2 😱) then you will absolutely be better off with TOU tariff than fixed. You should be able to almost completely avoid paying for electricity during the peak tariff periods, and get the benefit of cheaper offpeak electricity to charge your car from the grid overnight, or demand-manage other usage, and pay a much lower average c/kWh price for the grid power you do use.

I have only a 5kW system and 1xPW2, and my peak usage is tiny. Only 26 kWh for the entire quarter in my last bill.

As far as TBC goes... it’s an AI algorithm and I remain unconvinced it does sensible things or actually saves you much money. As @Hairyman says, it will do weird things at various times (like export solar in preference to charging the battery, or use the grid in preference to discharging the battery) and I didn’t like the unpredictable ”black box” nature of what it does.

It does result in the grid charging the battery at various times, including filling it prior to the commencement of the peak tariff period. Which often means using shoulder-period grid electricity - which isn’t necessarily smart.

I tried TBC in “cost optimised” mode for a quarter. After loading that three months worth of the 5-minute PW2 data into my spreadsheet, and doing the “what if” alternative scenario of what would my power bill had been if PW2 had have been in “self consumption” mode instead for those 3 months, TBC only saved a few dollars compared to self-consumption.

My conclusion is that TBC is flawed as an optimisation algorithm. Merely telling it when the peak, shoulder and offpeak times are is not enough to do a proper optimisation. It would also need to know the relative price difference of those tariffs during those times, as well as the relative price of the solar FIT (e.g. is it higher or lower than the offpeak tariff?) and to to a proper job, also know what your daily connection fee is. It does an OK job given what it does know, but it could be much better.

I much prefer the predictability of what self-consumption mode does, so I switched it back to that.

I have some ideas on how TBC could be made better with some simple, fixed rules (and be more predictable) as a third alternative to the two current modes offered. I spreadsheeted them and they worked (lower cost) than either TBC or self-consumption, so I am going to send them to Tesla.
I dont agree with your first sentence and “obviously be better off”. its just not that simple, which I’m sure you know. I have 30kw solar, 3 pw2, 2 tesla, and an energy efficient house. I now have a year of data with this full setup, and I have the added benefit of being able to charge cars during the day With excess solar. I’ve always been on a single but expensive flat rate of around 32c and exports are dropping to 12.4c. i have a good solid model for determing the best power company for my circumstance, and the point is whats right for me is not so much the next person. Recently I adapted my model to use the pw2 data to see if time of use is better. I ran the scenario with several companies, and my conclusion was that not only would I be significantly worse off, but life wouldnt be as simple on the power front.
 
A tip for multiple pw2 on 3 phase. I record all data at least monthly, and noticed a significant disparity between the retailer meter and the tesla meter. I was buying 60-120kwh per month that tesla wasnt seeing. So after everyone ducked and weaved, it was eventually narrowed down to tesla, and once I got past the useless US call centre and got to local people instead, tesla were able to find an issue with the way the nurio meter works in this setup....or more to the point doesnt work, and calls for grid power without showing it or even requiring it. They switched the nurio and solar meter and now all good. If you have pw2 on 3 phase. Do your monthly readings and act on significant differences. My understanding is that the nurio wasnt faulty, its a quirk with this type of setup. And a further tip also learnt this week. If you have a very high draw appliance that doesnt spool up. The battery cannot turn off charging fast enough to accomodate it so calls the grid for help. Hence you may see a small grid use even though you’ve been on solar with plenty of battery all day. This is only a quirk when charging. It doesnt happen when the battery is full. Must give credit to the adelaide tesla battery guys for persevering and sorting it out. Very good capable people. They made the US ‘engineers’ look foolish.
 
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I dont agree with your first sentence and “obviously be better off”. its just not that simple, which I’m sure you know... Recently I adapted my model to use the pw2 data to see if time of use is better. I ran the scenario with several companies, and my conclusion was that not only would I be significantly worse off, but life wouldnt be as simple on the power front.
OK, but did you factor that with TOU, you will be incentivised to demand manage and shifting it to time periods with lower grid cost? With flat rate, there is zero incentive to demand manage, and if you don’t change your temporal pattern of consumption, TOU might not be better.

My point is, with solar and a battery, there are strong incentives to demand manage on TOU. It’s not hard to shift certain demand like car charging, dishwasher, washing machine, dryer etc to offpeak times or times when there is excess solar. That can make a big difference to your bill.

Think of it this way - a retailer will set a fixed rate tariff based on the entire aggregate of demand it sees across all time periods of the day, and its corresponding wholesale costs, then work out what single fixed tariff would return the required financial margin. TOU is set the same way, but separately for each defined time period.

As soon as you are able to shift your grid demand to a different, lower cost temporal pattern in TOU compared to the aggregate, you win. It’s as simple as that.
 
For typical family or even solo consumption.
Spike 7-8am, then say 4-10pm, I just don't see TOU being optimal at the current rates in the market.

Yes you can shift hot water heaters and washing machines.
But you can't shift ovens, microwaves, TVs, computers and generally a/c.

If you've got solar + a big enough battery to cover the peak, and use a lot of energy off-peak (eg. Overnight charging an EV) then maybe there is a benefit

ToU only works if your consumption patterns are abnormal
 
OK, but did you factor that with TOU, you will be incentivised to demand manage and shifting it to time periods with lower grid cost? With flat rate, there is zero incentive to demand manage, and if you don’t change your temporal pattern of consumption, TOU might not be better.

My point is, with solar and a battery, there are strong incentives to demand manage on TOU. It’s not hard to shift certain demand like car charging, dishwasher, washing machine, dryer etc to offpeak times or times when there is excess solar. That can make a big difference to your bill.

Think of it this way - a retailer will set a fixed rate tariff based on the entire aggregate of demand it sees across all time periods of the day, and its corresponding wholesale costs, then work out what single fixed tariff would return the required financial margin. TOU is set the same way, but separately for each defined time period.

As soon as you are able to shift your grid demand to a different, lower cost temporal pattern in TOU compared to the aggregate, you win. It’s as simple as that.
Thanks for the lesson......I already only charge cars with excess solar during the day, and my hydronic floor/pool heating is also only from excess solar. These are my big ticket items, as well as charging 3 powerwalls. Our power hungry items during peak are typically cooking appliances, so not about to make dinner 4pm.
My data definately shows buying power at TOU rates during the peak (only when battery is flat) is what makes it worse for me compared to the flat rate. Yes the battery could be topped up during the day cheaply, however its generally a wild guess if it would need it or not, so theres nothing cheap about buying cheap power that you dont need. Like I said, every house is different and there is no simple applies to all answer. I’m also open minded enought to regularly test the market with my data, especially when FIT’s reduce as thats where my best gain is.
 
I played a bit more last night and this morning - well set some things and let it run its course.

Yesterday evening I switched back to Time Based Control (Cost Savings). I set peak 07:00-22:00 and Off-peak 23:30-04:00. (I really wanted to set Off-peak to 00:00-04:00 but it appears the app doesn't let me do that).

The battery was down to 20% at 18:20 and 10% at 22:25. It never got to 5%. At 23:30 the battery started charging from the grid at around 10kW. Battery got to 50% at 01:15 and when I woke just after 04:00 was at 98%.

I then switched back to Self-powered.

As it is a sunny day today I topped up my Model 3 and took the battery down to around 53% (at around 05:20). The battery got down 50% at 06:25 and then went below. The battery was back up to 50% at 08:10 thanks to the solar and 60% at 10:05. It is now sitting at 68% even though my wife is using the dryer.

So what does this all mean to me?

During Autumn and Spring, when I get a run of sunny days, Self-powered will probably work better for me as I can have no net grid consumption I think when there's a run of cloudy/wet days, TBC with ToU might work a little better. For Winter when there's not much solar production and AC is heating the house TBC with ToU will almost certainly be better. For Summer I'm not so sure as I get good solar production - but then the AC for cooling draws a lot so TBC/ToU is probably going to be better.

I still think I don't need 100% in the battery to make it through the peak period but I haven't had the Powerwall long enough to know what will happen in Winter. I figure, though, the less I use, the less it needs to top up at night so it may all balance out.

What I need to figure out is how to have the Off-peak start at 0:00 instead of 23:30. The thirty minutes of charging it can do from 23:30 will be at 13.78c/kWh rather than the 6.94c/kWh from midnight. If it's going to fill the battery so I export to the grid I'll be losing.
 
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