These Reading homeowners approached Spirit Energy in early 2025 with a relatively standard pitched tile roof and an ambitious brief. The household was at the start of a full electrification programme: a Tesla Model 3 already on the drive, gas heating about to be replaced with an air source heat pump, and electricity demand on a steep upward trajectory.
Rather than waiting for grid prices to creep up further while doing nothing, the homeowners chose to install solar and battery storage early in the transition. Twelve months on, the real-world performance numbers are now in.
At the point of quotation, household electricity usage was modelled at 8,000 kWh per year. That figure was always going to understate the picture once gas was removed and the heat pump came online. The question for Spirit Energy was how to design a system that made sense for the household's existing load while also working for the much larger demand profile that was coming within months of commissioning.
There was also a tariff strategy to settle. The household already had an EV, would soon have a heat pump, and needed a battery sized to support both loads alongside daily electricity use. Getting the tariff and storage decisions right mattered just as much as the panel count.
The installed system consists of:
The system was commissioned in spring 2025.
Twelve months on, the household has provided actual generation and usage data, allowing a direct comparison with the original modelling.
Spirit estimated the array would produce 7,040 kWh in its first year. Actual generation came in at 7,172 kWh, less than 2% above forecast. The pattern was uneven: an excellent summer made up for a disappointing winter, but the annual total landed very close to the model.
The best single day produced 49.9 kWh from the 8.28 kWp array. The worst produced just 0.1 kWh during a heavily overcast winter day.
Annual electricity consumption came in at 11,900 kWh, considerably higher than the 8,000 kWh modelled at quotation. The breakdown explains the difference clearly:
The most significant adjustment from the original modelling was on the tariff side. Spirit's quote modelled a move to Octopus Flux, the standard choice for solar plus battery without other large loads. With an EV and a heat pump in the mix, the household opted for Intelligent Octopus Go instead, which provides a six hour off-peak window at very low rates and a flat 15p/kWh export rate.
The numbers strongly support that decision. Across the 12-month period, only 273 kWh of peak-rate grid imports were recorded, with over 97% of imports landing in the cheap off-peak Go window. The peak-rate usage was concentrated on the coldest few days of winter, when heat pump demand briefly exceeded what solar and the off-peak overnight charge could cover.
The original Spirit financial model projected:
These figures were based on the modelled 8,000 kWh annual demand and a move to the Octopus Flux tariff.
The real-world outcome is significantly better than the model projected, for two reasons. The household removed gas entirely, which the original solar PV model did not include. And over 99% of grid imports are now drawn at off-peak rates through Intelligent Octopus Go, which delivers a materially lower effective cost per kWh than the Flux tariff baseline in the model.
The headline number for the first 12 months of operation is straightforward. The household's net energy position (export income minus electricity import costs, with no gas bill at all) was a £92 profit for the year.
For context, the property's previous energy spend was:
A combined 2024 utility spend of £2,491 has effectively flipped to a £92 net profit
The original modelling estimated 1,408 kg of CO2 offset per year, based on a UK grid carbon intensity factor of 0.2 kg CO2 per kWh generated.
The quote presented the lifetime impact as equivalent to:
The household's actual carbon position is more significant than the solar model captures in isolation, because gas heating has been removed entirely. The 2024 gas spend of £676 reflects an annual heating emissions figure that is no longer present at the property.
This case shows what happens when a solar and battery system is designed for a household at the start of an electrification programme rather than for a static load. The 8.28 kWp REC array generated 7,172 kWh in its first year, marginally ahead of the 7,040 kWh Spirit estimated. The household ended the year £92 in profit on energy, against a combined 2024 utility spend of £2,491.
The system has performed in line with product specifications, the household has eliminated gas from its energy bill within months of commissioning, and the design has held up to a household load that has grown by roughly 49% above the figure modelled at quotation.
It's always great to hear when our customers are as satisfied with their install as we are. Big thanks to Nigel for the lovely 5 star Google review, see below:
Following recommendations from friends we had Spirit Energy install 18 solar pv panels, a Powerwall 3 and DC Expansion pack at our home in Reading. The fact they were a recommended local installer, using exclusively in-house technicians, was a key part of our decision. Throughout they have been a very straightforward and proactive company with whom to work. Their advice has always been very sound and fully and clearly explained at every stage. They did all of the background preparatory work, making the whole process seamless and simple for us. Our initial solar plan for 12 panels on roughly south-facing roofs of the garage and house came in under-budget, so we added an extra 5 panels on our west(-ish) facing roof for a final 8.3 kWp system.
The actual work was completed towards the end of March 2025 to a very high standard, with a minimum of disruption and mess, by a team of very friendly, polite and thoroughly professional installers. By fortune of the amazing early April weather spell, the system is producing seriously impressive amounts of energy.
We have no hesitation in highly recommending Spirit Energy to anyone.
Edit: Spirit’s estimated solar generation for our system was 7040 kWh per year. This was within 1%! With the Powerwall 3 and DC expansion pack, the result has been a near £0 nett energy bill for 12 months despite having a heat pump and EV
- Nigel
If you want to see how much you could be saving with solar, please get in touch on 0118 951 4490, or request a quote.