May Solar Generation and Export Numbers
Even with major changes happening around the house—most notably the arrival of our first EV, the VW ID.3—our solar statistics show a clear improvement over last month! Our success is directly tied to adapting our energy strategy to our new Octopus tariff (Intelligent Octopus Go - IOG). This new plan gives us access to incredibly cheap electricity overnight, from 11:30 pm to 5:30 am, at only £0.08 per kWh. We also get extra 8p slots when the car is plugged in. These aren’t used for battery charging yet, but will be in the winter.
This month, we were almost entirely self-sufficient! We generated enough power from the sun to cover a phenomenal 99.63% of our house consumption. This high level of efficiency was achieved through careful planning: charging the batteries during the cheapest overnight slots and implementing a new 'force discharge' strategy between 4 pm and 7 pm when grid demands are highest. The Octopus export rate is £0.12p per kWh.
Below we are breaking out our energy usage much further—tracking dedicated use for the car charger, the heat pump, and even the immersion heater for the Legionella cycle. This level of detail has helped us manage every watt smarter than ever before! The fact that we managed this complex setup while having no gas standing charge (since the cut-off on the 6th) really shows how robust our solar investment is becoming.
Solar Generation
Looking at the numbers, we generated a fantastic 682.20 kWh this month. While this is slightly down from last year’s generation of 695.10 kWh, it remains exceptional and covered an impressive 99.63% of our house consumption! We had a total of 14 days where our solar output exceeded the home's usage, proving that our system is highly reliable even through variable weather patterns.
Battery Performance
Our battery management was key to this month’s success. With the new charging strategy—charging at the cheapest rates and forcing discharge when from 4pm to 7pm. We used 189 total charging slots. The battery would normal be charged to 100% by 3am. We remained on the grid until 5.30am when the expensive rate would kick in. This meant we used 170 suspended battery slots. This figure shows how efficiently the system maintained its charge level by foregoing unnecessary top-ups from the grid, saving us money and maintaining high operational health. This also led to the solar exporting much earlier in the day.
We charged the battery a total of 374.50 kWh this month and discharged 370.70 kWh. The ability to manage these cycles through new tariff structures is giving us unprecedented control over our energy usage.
Grid Usage
We imported 518.40 kWh from the grid. This was an increase from the preview month when we were still on the Cosy tariff where the import cost was £0.14 per kWh. The import cost on the IOG tariff was minimal! Our overall electricity bill on the Intelligent Octopus Go tariff was only £51.94, a remarkable saving compared to what the Standard Tariff house consumption would have cost (£168.92).
Our average unit cost for the year has dropped to an incredible 13.92p, which is significantly lower than the current price cap of 26.48p. Our Standing Charge remains at £52.19p. The grid slot costs were varied this month, with the cheapest being only £8.00p and the most expensive hitting £33.32p. We had a brilliant day on the 24/05/2026, when our electricity cost us only -£0.55!
Cost Savings Summary
The numbers this month are truly outstanding and prove that smart energy management pays off immensely. We achieved massive savings compared to imported kWh (our tariff vs price cap) of £127.59. More importantly, we our savings compared to house consumption kWh of £168.62.
Furthermore, our exported excess power amounted to 344.30 kWh, giving us Exported Savings this month of £51.65.
Overall, the successful integration of our EV and the adoption of a highly optimised charging routine have made this arguably our most efficient solar performance yet. Our solar system is proving that it can handle complex modern energy demands while delivering incredible financial returns! Stay tuned for our June’s generation report!
According to the Octo-Aid app, this was the breakdown of our usage per rate.
Grid Usage by Rate
Electricity Usage By Kind
As solar panels output declines over the years I have added the previous years 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
Octo-Aid Tariff Comparison
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 |
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 Generation
| Metric | Date | kWh |
|---|---|---|
| Best Generation | 27 May 2026 | 30.90 |
| Best front generation | 30 May 2026 | 18.40 |
| Best back generation | 27 May 2026 | 13.40 |
| Worst generation | 4 May 2026 | 9.70 |
| Worst front generation | 4 May 2026 | 5.20 |
| Worst back generation | 4 May 2026 | 4.50 |
Export and Profit (Rate 12p kWh)
| Metric | Date | kWh | Profit |
|---|---|---|---|
| Best Battery and Solar Export Profit | 24 May 2026 | 20.70 | |
| Best kWh export day (Solar) | 8 May 2026 | 10.80 | |
| Best export profit | 24 May 2026 | 20.70 | £2.48 |
| Cheapest Day | 24 May 2026 | -£0.55 |
The graph below shows the generation for both front and back panels
Total Solar Generation
The graph below shows generation, battery discharge, battery charging, export, import to use and consumption for 2026
Showing generation, battery discharge, battery charging, export, import to use and consumption for 2026
Energy Breakdown
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
Total Front Solar Generation
Total Back panel generation
Intelligent Octopus Go
The costs shown here do include the standing charge. Any comparisons are compared to the unit cost if we were not on IOG. There are two comparisons. One is the cost of what we imported from the grid for battery charging. The other is, the cost of the energy used by the house, house consumption.
Overview for the month Grid Information
| Standard Tariff | 24.67p | |
| Standing Charge | 52.19p | |
| Cost from the grid | £51.94 (IOG) | £127.89 (Standard) |
| Savings including export | £127.59 | |
| Exported (@12p kWh) | 344.30 kWh | £51.65 |
| Charging slots used | 189 | |
| Battery Suspended Slots | 170 | |
| Average unit slot price | 10.02p | |
| Cheapest slot | 8.00p | |
| Most expensive slot | 33.32p | |
| House consumed | 684.70 kWh | |
| This month the car charger used (kWh) | 104.10 kWh | |
| The month the heat pump used (kWh) | 74.20 kWh | |
| The month the immersion used (kWh) | 9.20 kWh | |
| Solar generated 2026/2025 | 682.20 kWh | 695.10 kWh |
| Battery Charged/Discharged | 374.50 kWh | 370.70 kWh |
| Percentage generated by solar | 99.63% | |
| Self Sustained Days (More solar than consumed) | 14 | |
| Self Sustained Days (More solar than we imported) | 24 | |
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.