Review: Is residential battery and solar the future for UK homes?
by Linus NjoguView the associated event for this review
How long does it take a £12,000 home solar-and-battery system to pay for itself, and is it worth it at all? David Howey, a battery expert, used his own home as a test case to find out. This, he stressed, was “very much a personal presentation rather than a research one,” even joking that “it may all just be absolute nonsense.” His answer, based on three years of data from his own home, was a data-rich maybe.
Howey is Professor of Engineering Science at Oxford, where he runs the Battery Intelligence Lab and co-founded Brill Power. His research focuses on battery modelling and ageing for electric vehicles, grid and off-grid power systems.
The House Retrofit
Three years ago, Howey undertook a substantial home refurbishment that included the solar-and-battery install at the centre of this talk. The house itself is fairly typical of the UK housing stock: nearly a century old and poorly insulated. The measure that impressed Howey most was not the solar installation but the external wall insulation, which he estimated reduced gas use by 30-40% while making the house substantially more comfortable. During installation he measured a 2°C difference between insulated and uninsulated sections of wall.
The solar and battery system consists of thirteen solar panels providing around 4 kWp and a 10 kWh battery installed in a garden shed. The panels are connected to micro-inverters, which cope better with partial shading and carry a 25-year warranty.
What the Data Shows
Over three years, the panels produced roughly 90% of the household’s annual electricity demand, but hardly at the right time. Howey consumes about half of what he generates and exports the rest, importing power back from the grid during the winter. Cycling energy through the battery is about 95% efficient, with losses of 100 kWh a year, “a full charge in my electric car,” as he put it.
In summer, the house runs essentially off-grid apart from EV charging, exporting surplus power during the day. In winter, solar generation drops and the household relies on cheap overnight electricity from the grid. The EV accounts for around a third of electricity consumption: “thirsty,” but flexible, since charging can be shifted to cheaper times.
Was It Worth It?
Using the Octopus Go tariff, Howey highlighted a paradox: because the export price and the cheap overnight import rate are only around 4p/kWh apart, the sensible move is to charge the car overnight on cheap grid electricity and export the daytime solar generation rather than use it directly. He also flagged the negative wholesale prices that now appear on sunny, windy days – a phenomenon he called a market failure, though one attendee countered that negative prices are a feature rather than a failure, helping the grid absorb surplus generation that might otherwise lead to the curtailment of renewables.
Set against a sensible base case, the system saves about £500 annually, giving a payback period of roughly twelve years – about the same period for which the battery is warrantied. Whether that represents a good investment depends heavily on battery longevity: if the battery lasts only ten years, the internal rate of return falls below zero.
If these systems are to pay, Howey saw three routes: cheaper hardware, exemplified by Germany’s market for plug-in “balcony” solar; smarter control through rolling-horizon optimisation and third-party aggregators trading household assets into wholesale markets; and squeezing more revenue through price arbitrage – charging when power is cheap and discharging when it is expensive.
A striking finding was that solar without a battery may be the better investment for most households. On Howey’s figures, removing the battery cut annual savings by only around 20% while roughly halving the capital cost – a finding worth pausing on, given that solar-plus-battery is the more common choice for households installing today.
Relatedly, the biggest change in his thinking was on vehicle-to-grid, which he had previously resisted on battery-health grounds but now regards as convincing. His car holds 77 kWh, nearly eight times his home battery. Scaled across the UK’s 1.5 million electric vehicles, this represents a substantial storage resource.
Beyond the Home
Howey also connected his household experience to wider challenges facing the UK electricity system. He argued that renewable curtailment in Britain is often driven more by geography than timing. Rather than reflecting periods of excess generation, it arises because electricity cannot be transmitted efficiently between regions, forcing renewables to shut down in one area while fossil-fuel generation continues in another. This reinforced his broader argument that the main constraint may be market and network design rather than hardware.
Conclusion
Howey’s verdict was that “the hardware is ready; the market is still under construction.” He argued that the UK market, as currently designed, does not adequately reward the flexibility that Clean Power 2030 will require, with questions around locational pricing, market reform and saturation risk still unresolved.
What stood out to me was Howey’s admission that he had not run a discounted cash flow analysis before installing his system, despite having the expertise to do so. Moreover, 0% VAT and the major refurbishment already under way reduced his effective capital costs considerably. Over three years of operation, he has learnt to run his system more effectively – exporting solar, shifting EV charging to cheap overnight rates, and pushing the battery harder through forced discharge – and yet the payback remains marginal. If that is the experience of a battery expert with every advantage, the challenge for the average homeowner is considerably steeper. Accessible decision tools covering capital costs, tariff switching, charging cycles and aggregator options would help households without specialist knowledge make informed decisions – but the more uncomfortable implication of Howey’s data is that many of those households, by buying solar-plus-battery, may be buying a more expensive system than the evidence justifies.