May 2025 updates
May Electric:
I managed to maintain a 6% Peak/Off-Peak ratio, which is huge improvement on last month’s 12%.
There were 3 days that were overcast, and on the rest I managed to have only minimal peak usage.
The Peak usage on the sunny days is largely balancing the load between solar and battery as it takes a little while to switch from charging to discharging when the sun goes behind a cloud or comes back out again.
I was playing around this month with exporting the battery towards the end of the day, some methods worked better than others – more on that later.
Electricity costs for the month of May: £106.08 for 2025, £184.51 for 2024 and £394.20 for 2023 – yet more great on-going savings.
Electricity demand for the month of May: 1764kWh for 2025, 1791kWh for 2024 and 975kWh for 2023.
The additional savings for this year are almost entirely down to the Solar and Battery as I was on the same tariff last May as I am now, I used about the same amount of electricity, yet it cost me about 42% less.
The off-peak/peak/SC values for May were £0.075/0.2794/0.4785 for 2024 vs £0.07/£0.2896/0.47605 for 2025, so not a huge difference and the same as last month.
This can also be seen in the month on month usage vs cost graphs:
May Solar:
Actual production for May far exceeded the forecast for every day, often by way more than double.
The various arrays produced the following levels of energy: Garage 341.87 kWh, Office 267.90kWh, East 247.52kWh, West 289.10kWh for a total of 1152.39kWh which is again my best month to date, beating last month by 104.56kWh.
A very good month for solar production, I also managed to export 437.28kWh for a total saving of £65.59.
The import costs of £106.08 less the export savings of £65.59 means my net cost for May was £40.49 for 1764kWh of demand making my average rate £0.0232/kWh.
May Gas:
Gas costs for the month of May: £31.89 for 2025, £25.07 for 2024 and £192.58 for 2023.
Gas usage for the month of May: 480kWh for 2025, 365kWh for 2024 and 1575kWh for 2023.
£6.00 more than last year, 31% more gas consumed and on the Octopus Gas Tracker tariff vs the Octopus Standard Gas Tariff, so similar to last month.
Gas prices have started to fall again this month, I would have paid a lot more had I still been on the Octopus Standard Tariff, which was £0.0603 per kWh for May £44.07 ((480 * 0.0603) + 15.13) or an additional £12.18 for the month.
The heating was off for the entire month, so gas was only used for heating the hot water.
Again all visible in the usage vs cost graphs.
As mentioned earlier I have been playing around with exporting back to the grid at the end of the day as most days I still have charge in the battery.
The reasoning here is that if I force discharge the remainder of the battery I will be paid £0.15/kWh, but it will only cost me £0.07 to replace it when I start charging, so a net gain of £0.08/kWh.
Initially I was discharging just before the off-peak rate kicked in at around 22:30, however the house then ran off peak electricity for this hour at £0.29/kWh, effectively costing me £0.14/kWh, not what I had in mind!
I then switched to force discharging at the start of the off-peak period at 23:30, so any house usage would be at the off-peak rate and this worked much better.
On sunny days I am able to discharge around 5kWh for an additional £0.75 saving each day.
I have also added a couple of automations that stop my Zappi from charging the car if I am exporting to the grid by putting it in ‘stopped’ mode as again it is more cost effective to export and then charge at the off-peak rate than to charge from the solar.