Tesla Powerwall, Timeshifting & E7/EV Tariffs

QrizB

AllyDM said:

But something else to consider as well. The reason I said that solar was off the table for this discussion was that I already have a 10+ year old small PV array of 1.2kW and will probably be replacing that this spring with something more like 4.8kW, so there are other factors at play.

If your solar PV has an early FIT payment associated with it, it's probably worth £700 a year to you for the next 12 years. Take that into account in your calculations.

AllyDM said:

The main thing that annoys me with E7 tariffs is the assumption that people use 42% of their energy on the E7 tariff. Which might be true if you use electric storage heaters to heat you home, but can't really be true for most users.

E7 isn't intended for most users, though. It's meant for people with storage heaters.

"Most users" will pay more if they have an E7 tariff, not less.

AllyDM

QrizB said:

AllyDM said:

I am currently with EDF on an E7 tariff and paying 36.74p day rate and 16.52p for the E7 rate. Sadly, most of my energy usage is on the day rate.

If you don't use electricity for heating, E7 is unlikely to make much sense. You'd probably save money on a standard tariff.

How many of those 9800kWh are night-rate?

And, if you'll excuse me saying, 9800kWh a year is a crazy amount of electricity for a property that doesn't use it for heating. It's getting on for four times the average household. Do you know where it all goes?

AllyDM said:

Doing the maths, if I can charge the Powerwall overnight at 16.52p for 13.5KWh, and then use those 13.5KWh during the day, I save (36.74 - 16.52 20.22p on each KWh, or £2.73 per day. If I do this every day of the year, I save £996 a year and the Powerwall basically pays for itself in under 8 years.

I don't think you are doing the right maths there.

Single rate electricity is currently around 27p/kWh (shortly expected to fall). That's the price you'd be paying without the Powerwall.

Plus, you lose perhaps 10% of the electricity you cycle through a Powerwall.

So, your effective cost of E7 through a Powerwall is 16.52 x 1.1 = 18.17p/kWh. That's a saving of 8.83p vs. standard rate electricity, £1.19 per day, £435 a year. You're looking at a 17-year payback period, which could be longer than the life of the Powerwall.

I think you would be better off looking at how much you would save on a standard tariff, and seeing if you can reduce your electricity use to something closer to the norm.

Thanks. As you say, E7 really doesn't make much sense for me right now - but I think if I can move most or all of my consumption to E7 (or other lower cost off-peak rate) via timeshifting, then it would. I haven't done the maths on looking at standard rate, but will do so in the morning.

Thanks for the efficiency factor in the Powerwall - I had not factored in a 10% loss on the in/out cycle. Will add that to the spreadsheet.

As for the electricity use itself, my house is far from the norm. It's about 3,500 sq. ft living space in an old rambling, 5 bed Victorian construction. We have 3 freezers and 2 fridges that are all required (I like to cook). OK - maybe I could cut that down to 2 freezers ;-). A big hot tub, lots of coloured LED lighting throughout, 3 teenage/ 20 something kids who chuck stuff in the washer/dryer without thinking about at all times of the day and pretty much continuously use large screen TVs and gaming consoles as well as high power games PCs. All of our cooking is via electric - induction hob and dual electric oven, and we cook a lot. Also a hot tub, garden and patio lighting. A separate double garage with an office above it. Smart security system and floodlighting, drainage sump pump in the septic tank, etc, etc...

All in all, it's a bit of a power hog. That said, power consumption is down over 10% from last year. But no matter how much we try, we will never have anywhere close to the power usage of an "average" 3 bed semi.

To add to that as per the post above, I will probably be adding more PV later this year, so it's not such a cut and dried comparison. Plus the benefit of protection from the fairly regular power cuts we have out here in the sticks.

Anyway, thanks for the insight - more thinking needs to be done.

AllyDM

Sorry, just to add....over the last year according to EDF, 33% of my usage was night rate. So around 9kWh of about 27kWh per day. If I could move another 13.5 to night rate every day, that would equate to about 83% of usage being on the night rate.

AllyDM

QrizB said:

AllyDM said:

But something else to consider as well. The reason I said that solar was off the table for this discussion was that I already have a 10+ year old small PV array of 1.2kW and will probably be replacing that this spring with something more like 4.8kW, so there are other factors at play.

If your solar PV has an early FIT payment associated with it, it's probably worth £700 a year to you for the next 12 years. Take that into account in your calculations.

AllyDM said:

The main thing that annoys me with E7 tariffs is the assumption that people use 42% of their energy on the E7 tariff. Which might be true if you use electric storage heaters to heat you home, but can't really be true for most users.

E7 isn't intended for most users, though. It's meant for people with storage heaters.

"Most users" will pay more if they have an E7 tariff, not less.

Sadly, the old solar PV system has no FIT at all. It's just a hobby project that I did some years ago. I was importing PV panels and did a City & Guilds course on PV installation at the time. So it was really just a test project and I quit importing panels and gave up plans to set up a PV installation business due to other factors, including the market crashing.

And yes, most users (i.e. ME) are indeed paying more on E7. Which is why I would like to actually try and benefit from it if possible.

QrizB

AllyDM said:

Sorry, just to add....over the last year according to EDF, 33% of my usage was night rate. So around 9kWh of about 27kWh per day.

That's an average price per kWh of exactly 30p/kWh, so you could save roughly 10% on your energy bill (3p per kWh, about £300 a year) by just switching away from E7 to a flat rate tariff.

Scot_39

AllyDM said:

Sorry, just to add....over the last year according to EDF, 33% of my usage was night rate. So around 9kWh of about 27kWh per day. If I could move another 13.5 to night rate every day, that would equate to about 83% of usage being on the night rate.

83% annually on E7 would look more like 36.74*.17 + 16.52*.83 = 20p per kWh.

Your existing 33% with effort - is a little more expensive than SR - looking at EDF's current E7 card assuming your on DD in South East at those E7 rates - SR currently 29.38p  - not so far from the c30p estimate above for 33%.

Your 33% figure is not excessively low (a few months ago a user posted using c21% night rate on E7) - so it's not absolute killer to stay on E7 whilst make plans - ironically it's actually probably better for you to be on EDF's new expensive night rate then when it was when sub 10p last year - because that should give you a correspondingly cheaper day rate on 2/3rd of usage.

But in another post you are also considering installing a new 4.8 kWp solar array - which would reduce the number of days you are likely to need to draw 27 kWh from grid anyway - and so reduce the E7 percentage.  And currently many solar export rates seem to be lower than E7 off peak rates - so there may be no point charging from E7 if excess solar output available most months of year - so that would lower the 83% from grid.

The other possibility is looking at say a tariff like agile - not as predicatable price wise perhaps - but some here say have made great savings over last year - using the batteries to run as much as you can of house across the normal peak periods. At times peope have had negative overnight pricing for battery or Ev charging etc. 

Do these battery systems have links to smart tech / to allow low price slot optimisation - or take an external signal in some way to do so ?

And re the 13.5 kWh - although one battery might give you the kWh to close the gap - it might not give the kW - to avoid peak rate use completely (e.g. 1 10.5kW shower - needs more than 2 powerwalls continuous 5kW rating - not sure how long their peak can be used for ).  (If you have an IHD - try looking at your peak power draw around its peak times say 4-7 pm - or AM as family cooks breakfast / showering etc etc)

AllyDM

Scot_39 said:

AllyDM said:

Sorry, just to add....over the last year according to EDF, 33% of my usage was night rate. So around 9kWh of about 27kWh per day. If I could move another 13.5 to night rate every day, that would equate to about 83% of usage being on the night rate.

83% annually on E7 would look more like 36.74*.17 + 16.52*.83 = 20p per kWh.

Your existing 33% with effort - is a little more expensive than SR - looking at EDF's current E7 card assuming your on DD in South East at those E7 rates - SR currently 29.38p  - not so far from the c30p estimate above for 33%.

Your 33% figure is not excessively low (a few months ago a user posted using c21% night rate on E7) - so it's not absolute killer to stay on E7 whilst make plans - ironically it's actually probably better for you to be on EDF's new expensive night rate then when it was when sub 10p last year - because that should give you a correspondingly cheaper day rate on 2/3rd of usage.

But in another post you are also considering installing a new 4.8 kWp solar array - which would reduce the number of days you are likely to need to draw 27 kWh from grid anyway - and so reduce the E7 percentage.  And currently many solar export rates seem to be lower than E7 off peak rates - so there may be no point charging from E7 if excess solar output available most months of year - so that would lower the 83% from grid.

The other possibility is looking at say a tariff like agile - not as predicatable price wise perhaps - but some here say have made great savings over last year - using the batteries to run as much as you can of house across the normal peak periods. At times peope have had negative overnight pricing for battery or Ev charging etc. 

Do these battery systems have links to smart tech / to allow low price slot optimisation - or take an external signal in some way to do so ?

And re the 13.5 kWh - although one battery might give you the kWh to close the gap - it might not give the kW - to avoid peak rate use completely (e.g. 1 10.5kW shower - needs more than 2 powerwalls continuous 5kW rating - not sure how long their peak can be used for ).  (If you have an IHD - try looking at your peak power draw around its peak times say 4-7 pm - or AM as family cooks breakfast / showering etc etc)

Thanks. Couple of things.... I just checked tariffs with EDF this morning and the offer I got to move to a non-E7 standard variable tariff was 27.4p. Running the numbers, that would save me about £422 a year. So that's actually interesting.

However, I also looked at what they are offering for E7 tariffs right now and I could switch today to a 12 month fixed deal with a 33.81 Day rate and an 11.22 Night rate. That would save £346 a year. However, with a 13.5KWh battery, that should save a whopping £1,459 a year (not including a 10% loss on the battery cycle). That would bring battery payback down to 5.2 years - or call it 6 years with the 10% cycle loss.

But....then it's a gamble. Take the 11p rate now and potentially lose out if it drops lower than that in the summer.

Now, on to the battery system. I am probably going to get one anyway as the ability to keep power when the grid goes down is very beneficial for me anyway, and moving more of the usage onto the cheapest E7 tariff I can get is attractive in itself. So if I am going to get a battery for solar storage and power outage protection, it makes sense to stay on an E7 (or other off-peak type) tariff. Something else I hadn't thought about is that we sometimes get brown outs here, where the grid doesn't go down, but the voltage does drop. I don't know if a battery would act to keep the voltage up or not, but it's certainly food for thought.

I have Tesla quotes already, and I waiting on quotes from Octopus for their GivEnergy all-in-one 13.5KWh battery system (plus solar). The Tesla batteries are very smart, but I don't know if they can allow price slot optimisation or not. I do know that the GivEnergy system DOES allow price slot optimisation and is certified by Octopus for use with their Agile tariff. It's bulkier than the Powerwall, but potentially slightly cheaper. Not much though.

However.....I do have some concerns with the Agile tariff. It seems that it gives you cheap energy early in the morning to charge your battery - but it also basically wants to discharge the battery between 4-7pm back into the grid, which is typically when I would want to use it. I'll have to dig more into this though as it may be a good tariff in conjunction with solar and battery.

Your question about peak load is very valid - we don't have an electric shower here as we have an oil boiler with an unvented cylinder to get great water pressure. But my largest consumer load is probably the induction hob. That has a maximum draw of 7.4KW with all the rings at 100%. Realistically though, that never, ever happens and I am more likely to be running one at about 60% and one at about 30% as a typical use case. But certainly, given the other energy consumers in the house we could easily be pulling  more that the Tesla battery 5KW maximum discharge. I guess that is unavoidable though and whichever way you look at it, 13.5 "cheap" KWh is a benefit anyway. I'd still need to use some from the grid at peak times to supplement the battery power, but less.

QrizB

AllyDM said:

However.....I do have some concerns with the Agile tariff. It seems that it gives you cheap energy early in the morning to charge your battery - but it also basically wants to discharge the battery between 4-7pm back into the grid, which is typically when I would want to use it.

When on the Agile tariff, Octopus has no control over when you charge or discharge your battery.
That's entirely up to you.

Petriix

There's not much point in talking about freezers etc... The vast majority of your usage is the "large hot tub". I'd guess it's mostly used in the evening so solar panels aren't going to help with that. I guess you're paying around £3,000 per year for electricity in total.

You could consider getting a second hand EV and moving to Intelligent Octopus Go (with a compatible charging point) but you'd only save ~ 15p per kWh you manage to load-shift into the off-peak window. Maybe 10kWh per day on average so a little over £500 per year with a powerwall or similar. That doesn't seem like a great saving for the cost, especially when you consider the potential returns of simply keeping that money in the bank.

There's not much I could advise other than using the hot tub less, or simply enjoying the luxury and accepting the cost. 

AllyDM

Petriix said:

There's not much point in talking about freezers etc... The vast majority of your usage is the "large hot tub". I'd guess it's mostly used in the evening so solar panels aren't going to help with that. I guess you're paying around £3,000 per year for electricity in total.

You could consider getting a second hand EV and moving to Intelligent Octopus Go (with a compatible charging point) but you'd only save ~ 15p per kWh you manage to load-shift into the off-peak window. Maybe 10kWh per day on average so a little over £500 per year with a powerwall or similar. That doesn't seem like a great saving for the cost, especially when you consider the potential returns of simply keeping that money in the bank.

There's not much I could advise other than using the hot tub less, or simply enjoying the luxury and accepting the cost. 

:-) Well, I think I have dealt with the hot tub to some degree. I had an air source heat pump fitted to it last year, so that should help considerably with the energy cost there.....so it's now a case of definitely enjoying the luxury!

Getting an EV is indeed on my mind. Via my work, we have a salary sacrifice scheme available via Arval Ingnition, so I may see if it makes sense to get a cheap EV as a runaround. It actually might make some sense as my current runaround is a Mercedes SL, which is quite fond of petrol.

I am probably also going to add a 4.8Kw solar array in the near future as PV pricing has come down significantly, so that coupled with the Powerwall would hopefully have a major benefit. Of course, it does come down to payback period and ROIC....