When Sam installed a solar and battery system last year, he had the same questions that most homeowners do. Would solar really generate enough energy to make a difference? Would the investment pay off? And was it risky to be one of the first people in the UK to install a Tesla Powerwall 3?
A year later, the results are in and they tell a powerful story of just how transformative home solar can be.
The Setup: A System Built for Savings
Sam’s home was using roughly 8,000 kWh of electricity a year - about average for a family house with an electric car. The goal was simple: reduce that annual bill of around £2,000 while future-proofing his home against rising energy costs.
To do this, Spirit Energy designed and installed a system of 22 west-facing 440 W solar panels feeding into a Tesla Powerwall 3. The Powerwall integrates the battery and inverter into one sleek unit, managing solar generation, storage, and grid interaction automatically.
Because Sam drives an electric car, he also switched to Octopus Intelligent Go, which offers cheap overnight electricity and a solid export rate of around 15p per kWh, allowing the system to charge up off-peak and sell surplus energy back to the grid.
Despite a bit of shading from a chimney and the west-facing roof (not the perfect south-facing setup), the system was optimised using the Powerwall’s three inverter string inputs, configured to limit shading losses without needing extra hardware like microinverters.
The result? A smart, well-balanced system designed not to chase every watt of self-sufficiency, but to maximise financial savings.
Solar Performance: Outperforming the Forecast
When Spirit Energy modelled the system back in 2024, the expected generation was 7,320 kWh per year.
One year on, the panels have delivered 7,430 kWh - around 1% above forecast.
That performance closely mirrors what we’ve seen across hundreds of our installations. UK systems often exceed expectations during bright summers and slightly underperform in darker winters, but the overall yearly output tends to meet or exceed the design model.
Here’s how Sam’s generation broke down:
- Winter: 5% of total generation (forecast 9%)
- Spring: 38% (forecast 33%)
- Summer: 44% (forecast 40%)
- Autumn: 11% (forecast 19%)
A particularly sunny summer pushed performance higher, proving again how solar systems in the UK consistently deliver when the design is right.
The Battery: 9 Power Cuts Stopped and a Year of Seamless Savings
The 13.5 kWh Tesla Powerwall 3 sits quietly in Sam’s utility room, but it’s the unsung hero of the setup.
Over the year, it’s done two key jobs:
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Storing excess solar that the house didn’t use immediately.
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Charging cheaply overnight using off-peak electricity.
It’s also acted as a mini backup power station. Over the past year, it has seamlessly protected the house from nine separate power cuts, each lasting around 15 minutes. Sam didn’t even notice most of them - the Tesla app notifications gave them away.
The system was configured to leave a 20% reserve for backup, so even in a prolonged outage, there’s always enough stored power for essentials.
How the Energy Split Works
Here’s how Sam’s 8,013 kWh of total annual usage broke down:
- 21%: Solar used directly in the home
- 19%: Solar stored and later used from the Powerwall
- 16%: Off-peak electricity stored in the Powerwall and used during peak hours
- 44%: Directly imported from the grid
That means 56% of all the electricity the house used came either from solar or from the Powerwall - effectively halving his reliance on the grid.
Interestingly, Sam’s Powerwall was configured in Time-Based Control (TOU Mode), rather than pure self-consumption. This mode prioritises financial optimisation: charging cheaply at night and exporting solar during the day when export rates are high. It’s a subtle but powerful way to maximise return on investment.
The Numbers: How Much Did Sam Actually Save?
This is where things get exciting.
Without solar and battery storage, Sam’s household would have spent around £2,040 on electricity this year.
In reality, after 12 months of solar generation and smart battery management, his total electricity spend was £891 - a saving of £1,149.
But there’s more.
Because Sam exports surplus solar energy at 15p per kWh, he earned £720 in export payments from Octopus over the same period.
That means his net electricity bill for the year dropped from £2,040 to just £171.
Put simply: his energy savings and export income together covered over 90% of what he would have paid the grid.
Living with Solar: Fit, Forget, and Save
A year on, Sam says the experience has been completely hassle-free.
Once the system was installed and connected to the right tariff, there’s been no ongoing maintenance beyond the occasional app check.
Spirit Energy’s technical support team monitored performance remotely, and apart from a single firmware update issue (fixed within an hour by our electricians), the system has worked flawlessly.
For most homeowners, that “fit and forget” experience is one of the biggest advantages of a professionally designed system. Once it’s running, you can just enjoy lower bills and a reduced carbon footprint.
Sam’s Top Tip: Time Your Appliances to the Sun
If you already have solar, or are planning to install it soon, there’s one small behavioural change that can make a big difference.
By timing energy-hungry appliances - such as washing machines and dishwashers - to run when the sun is shining, you can use more of your own free electricity rather than drawing from the grid.
In the darker months, it’s the opposite. Set these appliances to run overnight during your off-peak window, when grid electricity is cheapest.
As Sam puts it, “Once you get solar, it becomes a bit of a fun challenge - seeing how much you can run on sunshine alone.”
The Bigger Picture: Why This Matters
Sam’s home isn’t just saving money - it’s a small-scale example of what’s possible across thousands of UK households.
Each well-designed system doesn’t just reduce bills; it helps to stabilise the grid, cut peak-time demand, and drive down national carbon emissions. Multiply that by millions of homes, and solar and battery storage become one of the most effective decentralised energy solutions we have.
With electricity prices still volatile, and battery technology advancing faster than ever, the payback period for systems like Sam’s continues to shorten each year.
Ready to See What Solar Could Do for You?
Sam’s story shows how even a west-facing roof and a single Powerwall can dramatically reduce energy costs, improve resilience, and make your home future-ready.
If you’re considering solar and want to know how much you could save, our team can design a free bespoke system proposal tailored to your property and energy use.
We’ve been installing solar and battery systems across the UK since 2010 - and we handle everything in-house, from design to commissioning.
Start your own solar journey today.
Request a quote or give us a call to find out how much you could save.
