Energy Tariffs

Note: If you are considering moving to Octopus, you can use this referral link and Octopus will give us both £50.

The energy provider you use and the tariffs they provide will be a key factor in maximising your Return On Investment (ROI) on any renewable energy installation that uses solar panels and/or battery storage.

There is no one tariff that will be best all year round. The optimum solution is to use a variable rate tariff with a cheap night rate over winter to charge a battery or EV. You need a good export rate come Spring, when are generating a lot more energy than you can use.

What works best for you will very much depend upon your usage, your usage profile, the specifications of your solar panels and/or battery storage, whether you have an EV, solar water heating, HVAC, etc. The only way to know for sure is to put the right numbers into a spreadsheet and compare the results for all of the tariffs available to you. My goal with this project is to complete this spreadsheet and share it here.

I'm currently with Octopus Energy and plan to stay with them. Their service has been excellent over the years, they are generally very good at clearly communicating things and also responsive to new requests. They also offer a wide range of tariffs and some good rates for exported energy. It did take them quite a long time to set up my Smart Export Guarantee (SEG) payments though.

Although I expect it to be a small part of our Return On Investment (ROI), being paid for electricity we generate and export is part of my plan. The Feed-in Tariff (FiT) programme ended on the 1st April 2019 and was replaced by the Smart Export Guarantee (SEG) scheme. The legislation ensured all energy providers offered to pay for electricity exported to the grid. Octopus is part of this scheme and their SEG tariff is called 'outgoingOctopus'. Octopus offer two Outgoing tariffs: Fixed or Agile. Outgoing Fixed guarantees 15.0p per kWh (7.5p prior to October 2022) for every unit exported. Outgoing Agile matches the half-hourly prices with day-ahead wholesale rates, helping you make the most of the energy you generate.

To become part of the Smart Export Guarantee scheme Octopus need:

• A copy of the Microgeneration Certification Scheme (MCS) certificate - this is provided by Greenscape Energy Ltd
• The DNO (Distribution Network Operator) Notification form and the DNOs response - this is provided by Greenscape Energy Ltd
• To use the industry systems to request a new extra identity for the meter called the Export MPAN
• To add my account and start receiving smart meter data. They have to set up their billing system with the new Export MPAN and preferred tariff

Tariff Switching

Choosing the right energy tariff is a mathematical dilemma and also an interesting challenge! 😊 I'm currently doing some complex monitoring and analysis to determine the optimum time to change my tariff.

Optimum Time

The optimum time to change tariff is not simply a summer v winter thing. I break down my monthly usage into peak usage, off-peak usage, amount exported, etc. You also have to factor in the differing standing charges for each tariff available.

The numbers are currently indicating that the optimum time to move to an agile tariff is at the start of March and the optiumum time to move to a cheap night rate tariff is at the end of October. Being one month early or late is not a huge issue though.

Summer

My needs change over the course of the year. During the sunnier months, I generate much more energy than I can can use, even when charging our CUPRA Born with 100% solar energy. It would be good to get paid as much as possible for exporting this excess.

Winter

During the darker months, will be generating smaller amounts of the energy and our EV uses about 240kWh in an average month:

• Feb = 380kWh
• Jan = 300kWh
• Dec = 265kWh
• Nov = 255kWh

The amounts required to run our home and charge our EV using solar alone is not practical. So we need to be on a cheap night tariff, using a battery to run our home during the day, using the cheap energy we stored over night.

Tariff Options

In October 2024, I moved us over to the Intelligent Octopus Go tariff. My calculations showed that we could save over £500 by moving to this tariff.

Between 05:30 - 23:30 the cost is 26.72p per kWh and between 23:30 - 05:30 the cost is 7p per kWh. The standing charge is 48.79p per day. There is a flat export rate at 15p per kWh.

This tariff also allows you to 'bump charge' in emergencies but, you would then typically pay 26.72p per kWh to charge your EV. In my case it would also use any available solar energy being generated, so it could actually work out cheaper than this but, I would also lose export revenue.

Our Tesla Powerwall has a usable capacity of 13.5kWh, which is not quite enough to last us through a whole day but, because it provides 6 hours of cheap rate charging, the battery only has to really run our home for 18 hours. I have also set the Tesla Powerwall reserve level to 10%, so that we use more of its storage capacity. An important thing to do is to time-shift as much as possible (dishwasher, etc.) to the cheap rate period.

For each kWh that the battery doesn't manage to run our home it costs us 26.72p but, if we had used solar instead then we would have lost the 15p export revenue, so in reality each kWh used from the grid costs us 11.72p.

From the 1^st January 2024 the Octopus Flux tariff rates are:

Octopus Flux is an electricity tariff with three rates for both import and export. It was announced by Octopus Energy in February 2023.

Note: Octopus Flux is a flexible tariff, so prices can change with wholesale price changes and it also varies by region.

You can join Octopus Flux if you have an electric vehicle, so it gives you a better export rates. It is really aimed at people with both solar panels and battery storage, because you need to avoid using energy at the peak rate.

The key things to note with this tariff are:

• In the highest rate window (16:00-19:00) you really need to avoid importing and want to export as much as possible.
• You want to only import at the cheapest rate (02:00-05:00) and this 3-hour window is when you want to charge batteries and your EV.
• With the 5kW charging rate on my Tesla Powerwall it is possible to get to 100% every night.
• A 3 hour windows is more of an issue with an EV though, as you can only get 22.2kWh (7.4kW × 3 hours) into the battery. This requires good planning, especially if you need to get to 100% for a longer journey.
• There are times when you just can't use 100% solar energy to charge your EV, typically when you need 100% charge for a long journey.
• There are at least 3 months of the year where the sun is not up, to enable export at the highest rate.

The key changes to note with this versus Octopus Go are:

• During the day we were paying 40.13p/kWh and now we are paying 33.98p/kWh. In practice this doesn't make a huge difference.
• During the day, we are now getting paid 22.98p/kWh instead of 4.1p/kWh. This makes a huge difference as we export a lot.
• Instead of a cheap 4-hour window (00:30 - 04:30) at 7.5p/kWh, we now have a to pay 20.39p/kWh for a 3-hour window (02:00 to 05:00). In practice, we can use 100% free solar energy to charge our EV from April to October.
• During the peak rate period (16:00 - 19:00), we now pay 47.58p/kWh instead of 40.13p/kWh. Our focus is very much on minimising energy usage and exporting as much as possible during this period because we get paid 36.58p for each kWh exported, instead of 4.1p. This is a huge opportunity to generate income and maximise our Return On Investment (ROI).
• This tariff has a 3 hour cheap rate window (4 hours with Octopus Go). This makes it even harder to fill up an EV over one night due to the 7.4kW charging rate.

Flexible Octopus

I was on the Flexible Octopus October 2021 v2 tariff. The prices follow wholesale costs but were 29.23p/kWh and a standing charge of 37.65p/day.

Outgoing Octopus

Outgoing Octopus comes in two flavours  Fixed or Agile. Outgoing Fixed guarantees 15.0p (7.5p prior to October 2022) per kWh for every unit you export. Outgoing Agile matches your half-hourly prices with day-ahead wholesale rates, helping you make the most of the energy you generate.

Agile Octopus

Agile Octopus is a 100% green electricity tariff with Plunge Pricing. Plunge Pricing pays you to take excess energy off the grid at certain times of the night. It is more suited to people with an electric vehicle, storage heaters, or those who can shift their electricity use outside of peak times. Agile Octopus includes Price Cap Protect, which ensures you'll never pay more than 55p/kWh for your electricity.

Agile's prices are often cheaper when the energy in the grid is greener and more expensive when energy is dirtier, usually between 4pm and 7pm, when the UK's fossil fuel generating stations have been turned on to meet high demand.

You need a second generation (SMETS2) smart meter with half-hourly consumption data enabled. A 45.07p daily subscription (standing charge) covers costs including metering, distribution, and other fixed costs.

Octopus Go is aimed at owners of electric vehicles but it also allows time-shifting of demand using battery storage. It provides cheap electricity at 7.5p/kWh between 00:30 - 04:30 every night. The other rates vary on location but as an example, mine would be: 04:30 - 00:30 : 40.13p/kWh, 00:30 - 04:30 : 7.50p/kWh, standing charge : 37.65p/day.

The Tesla Powerwall can be charged at a rate of 5kW, which means it could be fully charged in the 4-hour window provided by this tariff. It's 13.5kWh capacity would be enough to run our home too. Our CUPRA Born has a 58kWh battery which could be charged up 28kWh each night on this tariff.

My concern with this tariff are that my wife uses a tumble dryer in the winter months and this increases our electricity usage significantly. I'm not sure we could store enough energy in the 4-hour window, to run the home all day.

Tesla Energy Plan

The Tesla Energy Plan is not really an option for me until my Tesla Powerwall is installed but, I've included it on my tariff change spreadsheet to see if it would ever cost in. Tesla Energy Plan is a symmetrical tariff, meaning the import and export rate are the same at 24p to 26p per kWh depending on location. The fixed standing charge is 45.0p per day. Octopus Energy administer the plan and by joining the Tesla Energy Plan, I become part of Tesla's UK Virtual Power Plant. Tesla optimises my Powerwall's performance, connecting it to a growing network of homes across the UK to support the stability and resilience of the grid.

The irony is that when I put my numbers (without Powerwall) into my spreadsheet, this plan worked out to be our cheapest option. Obviously, our usage would change significantly once our Powerwall is installed though. The main down-side with this tariff is that I lose control of my Powerwall 🙁

This also gives me cause for concern (from the Octopus Energy website):
"To support the national grid and therefore allow for the great tariff rates, Tesla Energy Plan requires your Powerwall to export energy to the grid. This exporting to the grid can cause a conflict with 'smart' immersion heater controllers (or any other 'smart' loads that also look to utilise your excess solar generation). For example, some 'smart' devices can monitor a house for solar energy being exported to the grid and then switch on a load to absorb that excess. In the case of the Powerwall exporting to the grid, these smart devices might not be able to distinguish between solar exports or battery exports. There is no troubleshooting available for 'smart' device compatibility, so to avoid such conflicts you must turn off any diversion of excess solar to smart devices when joining Tesla Energy Plan; joining with such devices enabled risks the plan being unable to operate as intended.

Chosen Energy Tariff

12^th April 2023

We moved from Octopus Go to the Octopus Flux tariff. The main reason was to maximimise the return on our significant exports, which will improve our Return On Investment (ROI).

February 2023

Octopus finally set up our SEG payments and we are now getting paid 4.1p for every kW exported. It's not a lot but every little bit helps to improve our Return On Investment (ROI) 🙂

September 2022

I switched to a fixed 12-month Octopus Go tariff for electricity. We now have four hours (00:30 - 04:30) at 7.50p/kWh and the rest of the day is charged at 40.13p/kWh. From 1^st October, the new variable rate will will have a price cap freeze applied to it from 1^st October at 34.0p/kWh. This is less than 40.13p/kWh but, my plan is that most of our electricity is charged at the 7.5p/kWh rate, with our solar panels meeting most of our needs through the day.

We can charge our EV overnight at this 7.5p/kWh rate if need be but the Zappi smart EV charger means we should never need to do this. Once the Tesla Powerwall is installed we can charge it at this 7.5p cheap rate and it will run our house all through the expensive 40.13p part of the day.

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