May Solar Generation and Export Numbers
Here is the overview for May 2025. May once again set a new solar generation record. The previous record was 653 kWh in 2023. This month 695 kWh. That was a massive 110 kWh up on last year. We exported 18 out of 31 days. I count an exporting day as a day when we export more than 10p. We only imported £7.52 from the grid.
This year I am using a different approach to charging the batteries. As the Cosy rate is almost equal to the export rate, there is no point charging the batteries to try and export earlier in the day. When we were on Agile the price difference between import and export was larger and was worthwhile.
We only charged the batteries from the grid on one day. That was triggered by the inverter to do a battery calibration. Unfortunately it doesn’t know about the Cosy cheap rate times and did it at the midnight which is the mid price range.
This year we have had 69 days where we generated more solar than we consumed, and 46 days more solar was generated than we imported from the grid. In May, 26 days the solar generated more than we imported, and of those 31 days more than we consumed.
Below is the cost difference between heat pump and gas for May 2024 and 2025.
Heat Pump v Gas
| Month | Difference | Gas (2024) | Electricity (2024) | Gas (2025) | Electricity (2025) | |
|---|---|---|---|---|---|---|
| May | -41.47 | £39.31 | £34.07 | 10.11 | £21.80 |
According to the Octo-Aid app this was the breakdown of our usage per rate.
Grid Usage by Rate (High, Mid and Low)
You can see the heat pump statistics here.
The worst generation day was the 15th with only 8.80 kWh. The best was the 10th when 30.20 kWh was generated.
The best export day was the 10th with 13.70 kWh.
As solar panels output declines over the years I have added the 2023 generation to the table at the bottom. Of course weather comes into it as well, but I thought it would be interesting to track. I have added this post that shows each year as a graph.
Octopus Energy bill
Octopus Watch Tariff Comparison Report. This does not include exporting
Best Solar Generation
| Date | kWh | |
|---|---|---|
| Generation | 26th May 2023 | 32.90 |
| Front generation | 14th June 2023 | 19.80 |
| Back generation | 7th June 2023 | 14.70 |
| Worst generation | 12th December 2022 | 0.20 |
Solar Generation May 2025
| Date | kWh | |
|---|---|---|
| Best generation | 10th | 30.20 |
| Best front generation | 10th | 18.10 |
| Best back generation | 17th | 14.10 |
| Worst generation | 15th | 8.80 |
| Worst front generation | 15th | 4.70 |
| Worst back generation | 15th | 4.10 |
Best Solar Export and Profit
| Date | kWh | Profit | |
|---|---|---|---|
| Exported kWh | 15th June 2024 | 22.20 | |
| Exported profit | 15th June 2024 | 22.20 | £3.15 (15p kWh) |
| Profit day | 14th April 2024 | 18.20 | £2.67 |
Solar/Battery Export and Profit May 2025
| Date | kWh | Income/Cost | |
|---|---|---|---|
| Best kWh export - Battery & Solar | 10th | 13.70 | |
| Best kWh export - Solar Only | 10th | 13.70 | |
| Best export profit | 10th | 13.70 | £2.06 (15p kWh) |
| Cheapest Day | 10th | £-1.49 |
The graph below shows the generation for both front and back panels
Solar generation for both front and back panels
The graph below shows generation, battery discharge, battery charging, export, import to use and consumption for 2025
Showing generation, battery discharge, battery charging, export, import to use and consumption for 2025
Generation
Overview for May
The graph below shows the generation for each day
Graph showing production for the month
The graphs below show the generation split between the front and back panels
Graph showing production for the front facing panels
Graph showing production for the back facing panels
The graphs below show the yearly generation split across both the back and front panels
Front panel generation for for 2025
Back panel generation for 2025
Octopus Cosy
The costs shown here do include the standing charge. Any comparisons are compared to the unit cost if we were not on Cosy Octopus, which is 0.25575p per kWh. The standing charge was 0.48788p
May Grid Information
| Standard Tariff | 27.33p | ||
| Standing Charge | 47.61p | ||
| Cost from the grid | £ 7.52(Cosy) | £ 9.95(Standard) | |
| Savings including export | £21.04 | ||
| Exported | 124.1 kWh | £18.61 @ 15p kWh | |
| Charging slots used | 4 | ||
| Agile plunge slots used | 0 | ||
| Average unit slot price | 20.67p | ||
| Cheapest slot | 14.14p | ||
| Most expensive slot | 28.83p | ||
| House consumed | 570.90 kWh | ||
| Solar generated 2025/2024 | 695.10 kWh | 581.20 kWh | |
| Battery Charged/Discharged | 279.1 kWh | 269.5 kWh | |
| Percentage generated by solar | 122% | ||
| Self Sustained Days 2025 (More solar than consumed) | 46 | ||
| Self Sustained Days 2025 (More solar than we imported) | 69 | ||
Here is the Octopus Watch report summary
Octopus Watch summary
Featured posts
Solar panel performance declines over the years. I thought it might be interesting to see how mine compares. Of course weather comes into it, but hopefully this will be a useful guide.