During the winter months the National Grid run Demand Flexibility Service sessions where by consumers are paid to reduce energy consumption at certain times in return for rewards.
The Demand Flexibility Service sessions are likely to occur when electricity supply margins are likely to be tight. By reducing demand on the national grid expensive and polluting fossil fuel generation sources may not be required to be used.
In the case of Octopus Energy they send out a Saving Session notification, usually 24 hours before, which you can opt into if you want to join the saving session. Last winter the DFS sessions only rewarded decreased consumption compared to your average consumption over the same period of time. This winter there has been a change where by SEG exporters are now able to be paid for every kWh exported during the DFS sessions. This means normally home battery owners who wouldn't be able to reduce consumption during the DFS sessions because their normal imported electricity consumption during these periods would likely be zero (they are normally running their homes off their home batteries during this time) can now help by exporting electricity back to the national grid.
During a saving session that you're exporting into you would also reduce home consumption too as any electricity discharged from the home battery would be consumed by your home. Any excess would be exported to the grid by which you would be rewarded for.
This year the saving sessions takes an average of the previous 10 days during the saving session period. This feels like a better way than last year where it was possible to 'game' the session by increasing electricity use in the 3 hour period before the saving session. I heard of people increasing their electricity by charging the car & home battery and running high use appliances like ovens, washing machines and even hot tubs to increase their electricity use prior to the start of the saving session to get a higher reward.It didn't feel right that it was possible to waste electricity before the saving session to gain a higher reward.
Winter 2023 Saving Sessions
In November and early December 2023 there were four saving savings that we took part in. They ranged from a 1 hour session on 16th November and 5th December to 1.5 hour sessions on 29th November and 1st December. During these periods our home battery was set to discharge at a rate of 3kW. The actual export rate was 3kW less home consumption.
We worked out force discharging our home battery at around 3kW meant it would use circa 30% of the battery capacity for a 1 hour session, and 45% for a 1.5 hour session,
If our home battery capacity was high we would have plenty of battery capacity for both normal daily use and exporting in a saving session. You can see the export during the saving session and the corresponding battery capacity drop over that period.
During the last 1 hour session I did make the mistake of charging the EV in the afternoon before the evening saving session. I forgot to adjust the home battery schedule to stop the home battery discharging whilst the EV was charging. This meant the home battery provided 3.3kW of power to the EV whilst 4.1kW of imported electricity came from the national grid. This drain resulted in the home battery discharging from 98% down to 30%. I had to then recharge the home battery to back up to 60% so we had enough storage battery capacity to export it during the saving session. This would have cost 31p per kWh imported as it was done at the daytime unit rate, but as the saving session was paying £2.25 per kWh it made sense to do this.
The interesting point for us was at 23:00 we found out what the maximum discharge point of our home battery was 20%. After 20% our home battery will stop meeting the home load and import electricity from the national grid. There is still a slight drain which would mean if it wasn't recharged it would force recharge once down to 10%.
The reason for the discharge stopping at 20% is to protection the health of our home battery. It will drop the useable capacity of our 10.2kWh home battery down to 8.1kWh but that's plenty to cover our normal daily consumption. I'd rather have a healthy buffer than discharge to the home battery too far which would result in decrease life expectancy over time.
The Results
Over the saving sessions we actually exported around 2.6kWh per hour after our self use consumption of the home battery discharge.
The Saving Sessions are a great way for home battery owners to help the national grid during times of high demand, whilst also earning some extra payments during the winter period when solar generation is much lower than the summer months. Overall during the 4 sessions by exporting we earned £42.99 in Octopoints.
As a comparison our SEG payment in November for exporting 150.24kWh was £22.54. The two Saving Sessions in November provided 16,920 Octopoints, which is equivalent of £21.15 for exporting just 6.46kWh. The Saving Sessions really help improve export revenue during the low generationwinter months.
Summary
The Saving Session this year feel like they are much better run than last year. This year points are earned by either reducing consumption if don't have a home battery, or by exporting during the saving session if you have a home battery.
Whilst this may initially feel that home battery owners are taking advantage of Saving Sessions by exporting many kWh of electricity back to the national grid to gain high reward payments, they are actually helping the national grid during these peak demand periods by providing stored greener energy back to the national grid. That should help decrease the need to start up high carbon intensive power generation plants, which is the point of the Saving Sessions.
The Saving Sessions also help solar and home battery owners gain some extra export payments during the winter months when solar generation is at its lowest.
For home battery owners every day is effectively a saving session, as they effectively don't import electricity from the national grid during peak periods each day as power is provided by their home battery. Imagine if a high number of UK homes had home batteries and were able to be self sufficient during the evening peak periods. It would reduce peak demand and stop the need to operate high carbon intensity power generation. Imagine further if the power stored isn the majority of parked cars could be used during peak periods and replaced later using renewable power sources when demand was lower. The technological advancement of battery storage take up across theUK could help us meet our future energy needs and by using green energy at the same time.