A Smaller Array That Saved More
How a consumption-led design beat a bigger system quoted elsewhere on a west-facing roof in West Bridgford.
Template case study • Replace with a real project before publishing
A west-facing roof pushes generation later into the afternoon — closer to when this household actually used electricity. Treated as a disadvantage by the quote they already had, it turned out to be the reason the smaller system won.
At a glance
- Location: West Bridgford, Nottinghamshire
- Property type: 1930s semi-detached
- Roof: West-facing main pitch, chimney to the south end
- Annual consumption: 4,100 kWh, with a heavy evening profile
- System installed: 3.8 kWp array, hybrid inverter, 9.5 kWh battery
- Timescale: Surveyed in March, installed over two days in April
How the job went
The quote they already had, what the survey changed, and what we installed instead.
The challenge
The owners had a quote from another installer for a 6.4 kWp array with no storage — as many panels as the roof would carry. Both work full time and the house is empty until six, so almost everything that system generated would have been exported at the going rate and bought back a few hours later at four times the price.
What we found on survey
Two things. The chimney shaded the southern end of the main pitch from roughly two o’clock onwards for much of the year, which the earlier quote had not accounted for and which would have dragged down a string wired straight across. And the half-hourly data showed a pronounced evening peak: over sixty per cent of household consumption fell between four and eleven at night.
A west-facing roof is often treated as a disadvantage. Here it was closer to an asset, because it pushes generation later into the afternoon — nearer to when this household actually needed it.
What we designed and installed
A smaller array than the one quoted, laid out to keep the chimney’s shadow off a single string, with optimisers on the three affected modules only. A hybrid inverter so solar and battery run as one system. And a 9.5 kWh battery sized against the measured evening load rather than a round number, on a time-of-use tariff so it also charges cheaply overnight through the winter.
The result
- Self-consumption modelled at around 78%, against roughly 30% for the larger array without storage.
- Lower capital cost than the system originally quoted, and a shorter modelled payback.
- The house rides through the evening peak on stored generation for most of the year.
- Overnight charging carries the winter months when the array contributes little.
What this job shows
Three things worth taking from it, whatever your own roof looks like.
More panels is not more saving
Once you are generating more than you can use or store, the extra output earns the export rate only — typically a fraction of what you pay to import. The payback on that last increment is far longer than on the first, which is why the bigger quote was the worse buy.
The roof you have is rarely the problem
A west-facing pitch is usually written up as a disadvantage. Here it pushed generation later into the afternoon, closer to when the house was actually occupied, and that made it an asset. Orientation only matters in relation to when you use electricity.
Storage is what moved the number
The array on its own would have exported most of its output. Pairing a smaller array with a battery sized against the evening load is what lifted self-consumption, and self-consumption is the figure that shows up on the bill. Try the model on the home page or read sizing your system.
Approved installers — accreditations held by Qualis Energy Limited
FAQs
Is a west-facing roof a problem for solar? +
Not necessarily. A south-facing roof produces the highest annual total, but a west-facing one pushes generation later into the afternoon, closer to when many households actually use electricity. Total generation and useful generation are different numbers, and only one of them appears on your bill.
Why would a smaller array save more than a bigger one? +
Because once you are generating more than you can use or store, the extra output earns the export rate only — typically a fraction of what you pay to import. A smaller array with a well-sized battery can keep a far higher proportion of its output in the house.
What does self-consumption of 78% mean in practice? +
It means roughly three-quarters of everything the system generated was used in the house rather than exported. Without storage, a typical figure is nearer thirty per cent. That difference is where the saving comes from.
Would the same logic apply to your roof?
Send us your annual kWh figure and a photo of the roof and we will model it honestly — including the case for spending less than you were expecting to.