Octopus Tesla Energy Plan

[Steerpike]

Until December our GO tariff is 5p/14.12p/25p which works out slightly cheaper than TEP even before taking account of the FiT deemed export.

However, the current GO tariff is 7.5p/35.11p/37.65p and that will be significantly more expensive than TEP even after taking account of the FiT deemed export.

So it seems that TEP will be the best solution for us after December, the loss of the FiT deemed export balanced by the actual TEP export payment, and the gain coming from the much lower standing charge.

Not sure why the TEP standing charge is so low and will watch with interest to see if it increases from 22p to more like the GO rate.

I think that when I first looked at TEP it was 8p and then at some stage jumped to 12p, so price hikes can happen and given that TEP is, I think, one of a kind it is not possible to switch to a competitive equivalent and I suspect that giving up the FiT deemed export cannot simply be reversed.

 

[KennethS]

Until December our GO tariff is 5p/14.12p/25p which works out slightly cheaper than TEP even before taking account of the FiT deemed export.

However, the current GO tariff is 7.5p/35.11p/37.65p and that will be significantly more expensive than TEP even after taking account of the FiT deemed export.

So it seems that TEP will be the best solution for us after December, the loss of the FiT deemed export balanced by the actual TEP export payment, and the gain coming from the much lower standing charge.

Not sure why the TEP standing charge is so low and will watch with interest to see if it increases from 22p to more like the GO rate.

I think that when I first looked at TEP it was 8p and then at some stage jumped to 12p, so price hikes can happen and given that TEP is, I think, one of a kind it is not possible to switch to a competitive equivalent and I suspect that giving up the FiT deemed export cannot simply be reversed.

My understanding of the FiT deemed export is that once you opt out it is gone for good. I did not take that step lightly but for our household usage the TEP was an easy choice.

 

[kuruma]

2021 figures for our current E7 tariff compared to TEP and Octopus Go:

Under TEP, we'd sell at 11.38p, right? As we got into the FIT only in 2018, we currently sell export at 5.57p and generation at 4.1p so TEP gives us significantly more income from approx 2000 kWh annual generation even if we lose our deemed export.

I'd be grateful if anyone can confirm if I've got my calculations right or whether I've missed something here. TIA.

 

[roadcred]

2021 figures for our current E7 tariff compared to TEP and Octopus Go:

View attachment 814071

Under TEP, we'd sell at 11.38p, right? As we got into the FIT only in 2018, we currently sell export at 5.57p and generation at 4.1p so TEP gives us significantly more income from approx 2000 kWh annual generation even if we lose our deemed export.

I'd be grateful if anyone can confirm if I've got my calculations right or whether I've missed something here. TIA.

I think the only thing you missed is the filling and discharging of the powerwall each day. It may be that you already do that with your current tariff but if you dont their is the inefficiency between charging and discharging. Depends on your PW efficiency but the cost would be £37 per annum per kWh. On mine I reckon its about £50 pa.
The biggest problem in comparing tariffs is that Go rates have to date changed at different times and by different percentages to TEP rates.

 

[kuruma]

I think the only thing you missed is the filling and discharging of the powerwall each day. It may be that you already do that with your current tariff but if you dont their is the inefficiency between charging and discharging. Depends on your PW efficiency but the cost would be £37 per annum per kWh. On mine I reckon its about £50 pa.
The biggest problem in comparing tariffs is that Go rates have to date changed at different times and by different percentages to TEP rates

Thanks for the reply. Not sure what you mean about the filling/discharging costs. £37 per year per kWh of what?

 

[kuruma]

I should add that when we don't have enough solar, we charge the PW every night on time-based mode on our E7 rate which is more than double that of the TEP.

 

[Gatsojon]

Thanks for the reply. Not sure what you mean about the filling/discharging costs. £37 per year per kWh of what?

There are losses of around 5 to 10% for each transfer across the inverters, the solar one and the PW.
It won’t change your conclusion, or mine for that matter, that TEP is best for our circumstances for now.

 

[Dave101]

Thanks for the reply. Not sure what you mean about the filling/discharging costs. £37 per year per kWh of what?

I call this the "waste" and I picture it as power which goes into the battery and never comes out again. I calculate it as (generated+import)-(export+used).

For me, it averages out at about 1.6Kw per day. It is slightly higher in colder months than warmer months, I have no idea why.

1.6KW per day * my TEP rate of 11.76 = 18.8 p per day (£69 per annum)

Based on my records over the last 10 years, this is a factor of the Powerwall, rather than the tariff. I assume that if I added a second battery, it would double the waste.

Another way of looking at this is 70W per hour to run all of the electronics inside the Powerwall system. This would be broadly similar to a laptop, which does not feel unreasonable, although it doesn't have a screen.

 

[kuruma]

ah right... that's super helpful. Makes sense and I can follow your working.

As @Gatsojon says, it isn't enough to prevent making TEP the most economical tariff for us at the mo even if we have to give up our deemed export.

 

[Fred2]

The seasonal difference is likely due to battery chemistry being impacted by temperature - if it's cold enough it may need to heat the battery to allow optimal charging ( Powerwall Modes | Tesla Support ).

Where the tariff matters is that if you were in complete control, you choose to only charge the battery from solar, whereas on TEP you will be charging from the grid in winter months, so those efficiency losses are losses of electricity you've paid for rather than solar. If you were already (mostly) charging overnight and discharging during the day then you're probably already incurring those losses

 

[KennethS]

The seasonal difference is likely due to battery chemistry being impacted by temperature - if it's cold enough it may need to heat the battery to allow optimal charging ( Powerwall Modes | Tesla Support ).

Where the tariff matters is that if you were in complete control, you choose to only charge the battery from solar, whereas on TEP you will be charging from the grid in winter months, so those efficiency losses are losses of electricity you've paid for rather than solar. If you were already (mostly) charging overnight and discharging during the day then you're probably already incurring those losses

Not sure how big your PV system is, but I can only dream about any excess solar generation in winter months being available for charging our Powerwall. I do wish our PV system was larger but the roof was a limiting factor.

 

[kuruma]

yeah... I agree. it's the rare person who has solar to burn in winter in the UK. As I mentioned above, from late Sep to late March, we usually need to have the PW on time-based and let it charge from the grid overnight on our E7 night rate. But when that is 21p a kWh on our current tariff, TEP looks much more favourable.

 

[Dave101]

Thanks Fred. We are net exporters, having 2 arrays - the first is 3.84 declared net capacity facing SE, the second is 4.8 declared net capacity facing SW.

From Dec 20th to Mar 19th 2022 we imported 1,196 and exported 1,189 - a net of just 6 Kw - less than £1. During this period we generated 1,156.

From 20th March to date, we have imported 456 and exported 2241. A net of 1785, worth £210. During this period, we generated 2,677.