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Comparing Electricity price plans -- there's not as much in it as you think

gangzoom

Active Member
May 22, 2014
1,375
1,231
Uk
I'm considering moving from an E7 tariff to Go because we only use off peak energy anyway with the powerwall now installed. The powerwall runs the whole house for the rest of the day.

The Go tarrif would be half what we're currently paying with standing charge identical. Is this the no-brainer it looks like to me?

Our PW cannot last a whole day, certainly not at the weekend. We seem to consumer around 2KW before the E7 cut off starts, add on the base load for additional 3hrs it will means the PW would be empty by about 7pm especially on a weekend. 4hrs will also not fully charge a drained PW - it'll go over by 1hr or so only though.

Car usage only you will know. We tend to do long weekend road trips, often back to back, so need to charge from 10% to 90%, on E7 somethings thats not possible forget just 4hrs of charging!

All in all the cost savings/difference for us on E7 versus Go would be minimal, add in the hassle of switching to a smart meter, I see no incentive to switch.

If you can be sure all your electricity usage is within the 4hr GO period than the numbers will clearly work!
 

Rooster6655

Active Member
May 3, 2019
1,567
571
UK
Is it possible to get a powerwall and get it charged up between 12:30 and 4am? Then use the power for the rest of the day? If so, i'd be tempted to go for a powerwall

12.5kWh real energy delivered per charge. Be generous and say by 'shifting' to off peak you save 10p per kWh AND you use the full 12.5kWh, it will take you 17 years to become cost neutral.

Seems like a nice idea but not practical if the max saving would only be £1.25 per day!
 
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gangzoom

Active Member
May 22, 2014
1,375
1,231
Uk
Seems like a nice idea but not practical if the max saving would only be £1.25 per day!

It shows how cheap electricity is, and how much effort all of us put into trying to save some times literally pennies - load shifting, not charging the car at work etc.

I had go and fill up my wifes car last weekend, £65 gone in a matter of minutes!!! Luckly only have to do that once a month these days.

Lets all hope Government don't start taxing electricity like petrol, though am sure that will come at some stage!
 

Familyfirstj

President/Co-Founder TOC San Joaquin Valley
Supporting Member
Aug 1, 2018
94
85
Stockton
Power Consumption.xlsx

I've put together a comparison of three different electricity price plans: Octopus Agile (I averaged the entire year worth of sample data they give to get each half-hourly price), Octopus Go, and Bulb E7. I live in London, so all the prices I've used are for London. The inputs to the spreadsheet are:

- Your average load (this would be how many kWh you consumed in a month excluding car charging and any "heavy" overnight stuff you do, divided by 30 divided by 24). I chose 0.4kWh because that is what my GlowStick tells me I am consuming most of the time (I have some servers running 24x7 which bumps that up a bit from most normal people would have). This is your lights, washing machine, dishwasher, etc.
- Your car charging. I have set this to 32A x 240V = 7.68kWh
- "Heavy" Load: this is overnight stuff you would do, like night store heaters, heating up under-floor gigantic concrete pads, etc. I've set this to 3kWh (I have no idea what a good figure is, I just made this up).
- The actual electricity rates themselves, in half-hour increments.

You then get to specify (using Xs) which half hour slots of the 24h of the day are consuming the "car charging" and "heavy load" portions. I've chosen 3h for car charging, and 5h for heavy load stuff. In each of the 3 price plans, I've put these loads in the cheap zone (well in Agile I tried to pick what roughly looked like the cheapest block of rates).

Two main conclusions:

- Agile doesn't seem cheap, at all. Maybe averaging across the whole year is the wrong approach, but I don't know how else to analyse it apart from some complex modelling over an entire year.
- There is not a huge difference between Go and E7. In fact I would say there may not be much point in getting too excited about the whole thing, as long as you have a plan that offers you a cheap rate for at least a few hours of the day. Charging the car at daytime rates is triple the cost, so it makes clear sense to charge during the off-peak. But which particular off-peak plan you choose seems to be less interesting.

Let me know what you think, and if you find any mistakes or have any ideas for improvement.

Great post! Thank you
 
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Familyfirstj

President/Co-Founder TOC San Joaquin Valley
Supporting Member
Aug 1, 2018
94
85
Stockton
It shows how cheap electricity is, and how much effort all of us put into trying to save some times literally pennies - load shifting, not charging the car at work etc.

I had go and fill up my wifes car last weekend, £65 gone in a matter of minutes!!! Luckly only have to do that once a month these days.

Lets all hope Government don't start taxing electricity like petrol, though am sure that will come at some stage!

Yes they will find a way to tax electricity
 

Rooster6655

Active Member
May 3, 2019
1,567
571
UK
It shows how cheap electricity is, and how much effort all of us put into trying to save some times literally pennies - load shifting, not charging the car at work etc.

I had go and fill up my wifes car last weekend, £65 gone in a matter of minutes!!! Luckly only have to do that once a month these days.

Lets all hope Government don't start taxing electricity like petrol, though am sure that will come at some stage!

If you can charge at home it's not even worth wasting your time getting the cable out to charge at say Asda for free to save a less than a £1 in free miles for a 30min shop.
 

Fredneck

Member
Nov 8, 2019
478
293
Pennsylvania
It shows how cheap electricity is, and how much effort all of us put into trying to save some times literally pennies - load shifting, not charging the car at work etc.

I had go and fill up my wifes car last weekend, £65 gone in a matter of minutes!!! Luckly only have to do that once a month these days.

Lets all hope Government don't start taxing electricity like petrol, though am sure that will come at some stage!

Smarter to just tax the car. Some will charge from dedicated solar panels which no one can track that it is charging a car. If they tax car charging solar will become very popular.
 

gangzoom

Active Member
May 22, 2014
1,375
1,231
Uk
Without a 'smart' meter taxing car charging will nearly impossible, am in no rush to get one.

For road taxation, if government carry on with the previous history new taxation rarely effects older cars - Don't some classic cars not even need a MOT??

The current crop of EVs may well be seen as the best longterm ownership propositions.
 

mmca22gr

Member
Aug 13, 2019
115
42
Ireland
I've been waiting for the "pay for itself" vultures to gather... None of us are going to pay for our cars either but it didn't stop us buying them. .

But I compare my car usage to other options like using an ICE car or walking or cycling. There is also the 'green' element of driving electric.
Is my electric car cheaper than my previous diesel - no, but the difference is marginal and I value to other benefits such as not polluting my street as I drive away every morning. I would so the same with a powerwall - will it save me money? No - am I happy to pay the difference to avail of some of the green advantages or can I find those elements elsewhere?

A powerwall is £8k
I give it 10yrs of life as that is the warranty.
£800 per year (not counting any finance costs) is a lot of energy per year even on standard tariff. I can buy green energy from a provider also and satisfy myself.
 

im85288

Member
Aug 31, 2019
86
72
Newcastle
A powerwall is £8k
I give it 10yrs of life as that is the warranty.
£800 per year (not counting any finance costs) is a lot of energy per year even on standard tariff. I can buy green energy from a provider also and satisfy myself.

I think we can all agree the prices for a battery are not where they should be if savings are to be factored in. Where it becomes a bit more of a saver is when combined with Solar PV. Personally that was why I got my Powerwall as the thought of exporting energy back to the grid for free (missed the FIT) is something I did not want to deal with. Having had the system for just over a month (and obviously with this being the worst time of year for PV) it's currently putting in around 4kwh per day of energy that would otherwise of went back to the Grid so I'm happy with all that
 

hmy7k

Member
Nov 7, 2019
95
62
Shropshire
The subject of the powerwall is an interesting one. I considered getting one earlier in the year but in the end I opted to add another 4kW of solar to my array. I felt that there is only a small environmental benefit in the powerwall at the moment as all it does it switch energy consumption from one time of day to another. I know that peak rate electricity has a higher carbon content so there is a benefit but its quite hard to quantify.

In the future when we have a smart grid which can adapt to customer demand and supply these types of technology are going to be important in smoothing out supply and demand.

Kudos to those who have done it but i think I am going to wait till the grid gets a bit smarter.
 

Glan gluaisne

Supporting Member
Supporting Member
Sep 11, 2019
2,782
2,912
UK
I've been tracking home battery prices, their capabilities and the life versus price versus possible cost savings through life. None yet break even for us within their most probable usable lifetime, and our house is all-electric, so we have the option to use more battery stored electricity than most. If I factor in the price of a standby generator (we get regular power cuts here) then the sums just about stack up for one or two of the home battery options, but I cannot get the sums to work for the Tesla Powerwall, primarily because it doesn't allow total user control of charge and discharge.

To get a system to work well for us, I have to be able to have complete control of both the excess solar panel generation that gets stored in the battery when available, and the energy taken from the grid overnight when the battery needs topping up to meet the following day's needs. Not hard to do, if the battery charge/discharge control system allows it, and there are a couple that do this well. Luckily one of the systems that does allow total control of charge and discharge also has a separate "off grid" output, that can be used, with a suitable changeover relay, during power cuts.

It's still a bit too expensive to pay for itself, without making an allowance for the purchase of a standby generator, though, so either battery prices need to come down, or electricity prices need to increase, to make it worth doing.
 
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Lx2m3

Member
Jul 4, 2019
258
76
Rugby
I've been tracking home battery prices, their capabilities and the life versus price versus possible cost savings through life. None yet break even for us within their most probable usable lifetime, and our house is all-electric, so we have the option to use more battery stored electricity than most. If I factor in the price of a standby generator (we get regular power cuts here) then the sums just about stack up for one or two of the home battery options, but I cannot get the sums to work for the Tesla Powerwall, primarily because it doesn't allow total user control of charge and discharge.

To get a system to work well for us, I have to be able to have complete control of both the excess solar panel generation that gets stored in the battery when available, and the energy taken from the grid overnight when the battery needs topping up to meet the following day's needs. Not hard to do, if the battery charge/discharge control system allows it, and there are a couple that do this well. Luckily one of the systems that does allow total control of charge and discharge also has a separate "off grid" output, that can be used, with a suitable changeover relay, during power cuts.

It's still a bit too expensive to pay for itself, without making an allowance for the purchase of a standby generator, though, so either battery prices need to come down, or electricity prices need to increase, to make it worth doing.
Have you seen the YouTube Fully Charged regarding Powerwall 2 and Tesla Backup Gateway 2?, interesting, but they don’t talk money.
 

rotor2k

Member
Sep 16, 2019
524
293
London
Have you seen the YouTube Fully Charged regarding Powerwall 2 and Tesla Backup Gateway 2?, interesting, but they don’t talk money.
Yeah I saw it, and was disappointed there was no mention of money. I think Robert got it free through referrals, but he spent an enormous amount of money getting 3-phase installed.
 

rotor2k

Member
Sep 16, 2019
524
293
London
The subject of the powerwall is an interesting one. I considered getting one earlier in the year but in the end I opted to add another 4kW of solar to my array. I felt that there is only a small environmental benefit in the powerwall at the moment as all it does it switch energy consumption from one time of day to another. I know that peak rate electricity has a higher carbon content so there is a benefit but its quite hard to quantify.

In the future when we have a smart grid which can adapt to customer demand and supply these types of technology are going to be important in smoothing out supply and demand.

Kudos to those who have done it but i think I am going to wait till the grid gets a bit smarter.
You don't need the grid to get any smarter than it already is. By shifting your load you are contributing positively to less "bad" electricity being needed during the peak hours. That's all good. However, building and shipping your home battery has an environmental cost (as well as monetary), so I'm not sure it balances out, let alone is a net positive.
 

Glan gluaisne

Supporting Member
Supporting Member
Sep 11, 2019
2,782
2,912
UK
Yes, I've seen the Fully Charged videos, but there doesn't seem to yet be a change to the Tesla Powerwall control system to allow the user full control of charge and discharge. For us this is essential, as I do not want some algorithm trying to guess what we are going to do tomorrow and only store enough charge to allow for that. As we're both retired, our day to day pattern of use is pretty random, and depends on what we chose to do, so the Tesla algorithm would undoubtedly get things wrong a lot of the time.

I understand entirely why Tesla have opted to control the Powerwall this way, it's to do with maximising battery life in a very high cycle life application; a home battery gets cycled far more often than a car battery ever will, maybe twice a day if you have solar panels and a cheap overnight rate. Cycling twice a day on a model 3 LR is roughly equivalent to driving around 200,000 miles a year.

The system I've been seriously considering for a while now uses a battery chemistry that is more suited to a high cycle life application, but which is nowhere near the energy density of Tesla cells. Energy density doesn't really matter for a home battery, though, neither does peak charge/discharge capability, as a home battery never needs to charge at more than about 0.2C, or discharge at more than maybe 1C. That's a lot lower than something like a Model 3 LR, that has a peak charge rate of around 2C and a peak discharge rate of around 4.5C.
 
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rotor2k

Member
Sep 16, 2019
524
293
London
I have a good couple of feet of space below my ground floor floorboards -- I could fit a *lot* of batteries down there. As you say, we need a different chemistry that focuses on price, high cycle count and overall longevity without worrying about compactness (is that a word?).
 

gangzoom

Active Member
May 22, 2014
1,375
1,231
Uk
Have you seen the YouTube Fully Charged regarding Powerwall 2 and Tesla Backup Gateway 2?, interesting, but they don’t talk money.

Gateway 2 is an additional £1000 or so extra I believe, but if your buying you can only get Gateway 2 now. Installation is also abit more complicated.

We are currently awaiting planning permission on a reasonably large roof extension on the bungalow, the final build costs will be £150k+ I recon all done.

Am going to do the sums on adding addition 4KW or solar, but an additional PW may add to the cost too much, easily £15k I recon - another 10% of on top of already a large sum isn't going to get SWMBO approval, especially if it means cutting costs else where :(

We also have 3 Phase power coming into the house but currently only using 1 phase, even with 2 EVs I don't see the need for additional complexity of 3 phase setup but DNO may require it if we want to add another PW.

At the end of the day just like the cars, there is no real need for anyone to waste so much money on this stuff, but if you can afford it why not? I can think of worse ways to spend the money.....like fancy floor titles.
 
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gangzoom

Active Member
May 22, 2014
1,375
1,231
Uk
I understand entirely why Tesla have opted to control the Powerwall this way, it's to do with maximising battery life in a very high cycle life application; a home battery gets cycled far more often than a car battery ever will, maybe twice a day if you have solar panels and a cheap overnight rate. Cycling twice a day on a model 3 LR is roughly equivalent to driving around 200,000 miles a year.

I've really noticed this. Most of our other battery powered devices spend most their time sitting idle or tiny power drains, the PW is literally doing something ALL the time.

The warranty though is 25 years, so I assume Tesla believe lots of smallish action all the time is better for cell life than having 1second of 5C+ discharges you get with any of 'P' cars.

The only other battery that gets worked so hard is the tiny NiHm pack in my wife Lexus hybrid. But even than, most of the time the car is sat idle doing nothing.
 

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