Two Harrow semis on the same street can get quite different solar quotes, and much of the difference has nothing to do with the panels. Roof shape, scaffolding, the inverter, a battery and, on the hill, planning all move the number. This guide works through a solar quote for a typical Harrow semi using published national figures, then sets out what makes a local quote go up or down. For what an installation involves in the borough, see our page on solar panels in Harrow.
We do not print our own prices. Every figure below belongs to the Energy Saving Trust, DESNZ, PVGIS or HMRC, and each is labelled. Where a number is our own arithmetic on theirs, we say so. The aim is to give a Harrow household a yardstick to hold any quote against, ours included.
Why the example is a semi
Semi-detached houses are Harrow’s single largest housing type: 37.1% of the borough’s 89,642 households lived in one at the 2021 Census, ahead of purpose-built flats at 26.2% and terraces at 16.9%. In North Harrow the share is 54.0% and in Kenton West 64.7%, and 58.8% of Harrow households own their home. A semi with its own pitched roof and an owner who can say yes is the most common starting point here, so it is the one we work through.
Two national figures, measuring different things
The Energy Saving Trust says a typical domestic system is around 4.5 kWp, about 12 panels covering 20 to 30 m² of roof, and costs around £7,600 installed. DESNZ’s solar cost data for the 2025/26 financial year, drawn from 264,742 installations and excluding batteries, gives a median of £1,546 per kW for systems of 4 to 10 kW and £1,595 per kW for systems up to 4 kW. For domestic retrofits, which are nearly 90% of domestic installs, the mean is £1,651 per kW for 4 to 10 kW and £2,109 per kW up to 4 kW.
The worked example
Take a Harrow semi with room for a 4.5 kWp array. On DESNZ’s median, 4.5 × £1,546 comes to about £6,957; on the retrofit mean, 4.5 × £1,651 comes to about £7,430 (our arithmetic). Both sit close to the Trust’s £7,600. Now suppose the semi has a hipped roof and only 4 kWp fits. On the up-to-4 kW median that is about £6,380, but on the retrofit mean for that band it is about £8,436 (our arithmetic). A smaller array does not mean a proportionally smaller bill, because scaffolding, the inverter and the electrical work cost much the same either way.
On generation, our PVGIS 5.3 run for Harrow town centre gives about 3,965 kWh a year from 4 kWp facing due south at 35°, or 991 kWh per kWp; scaled to 4.5 kWp that is roughly 4,460 kWh (our arithmetic). For scale, Ofgem’s typical household uses 2,500 kWh a year. The nearest Met Office station with a sunshine record, at Northwood, averaged 1,556 hours a year over 1991–2020. An east or west slope makes less than these figures.
The VAT window
Residential solar installations are zero-rated for VAT until 31 March 2027. From 1 April 2027 the rate reverts to 5%. On a £7,600 job, 5% would be £380 (our arithmetic). That is a real difference but not a reason to rush a decision; our guide to VAT on solar panels and batteries sets out what counts as a residential installation.
What moves a Harrow quote
The roof. Hips, dormers and chimney stacks decide how many panels fit. In North Harrow and Kenton West, where semis are the majority of homes, the shape of the semi’s roof is usually what sets the array size, and the worked example above shows what a smaller array does to the price per kW.
Planning on the hill. Five of Harrow on the Hill’s eight conservation areas, Harrow Park, Harrow on the Hill Village, South Hill Avenue, Mount Park Estate, and Roxborough Park and The Grove, carry Article 4 directions. Where a direction catches panels, a planning application adds time and sometimes changes the design. Below the hill, roof slopes are usually permitted development.
Who owns the roof. In Greenhill ward, which takes in the town centre, 69.0% of households live in purpose-built flats, so freeholder consent comes before any price.
The network. Harrow town centre is in UK Power Networks’ Eastern area. An inverter above 16 A per phase, 3.68 kW, needs a G99 approval before work starts rather than a G98 notification; that is paperwork, not normally a cost to you unless the supply needs upgrading.
A battery. The Energy Saving Trust puts a 5 kWh system at around £4,600 and says fitting it with the panels costs less than a separate visit later. Our page on battery storage in Harrow covers that side.
The house itself. In the Harrow West constituency the median detached house scores 58 on its EPC, in band D. For a house like that, insulation may be the better first spend, and we will say so.
Payback, honestly
The Energy Saving Trust’s payback table, with export payments included and fuel prices as of July 2026, puts a London home at about 9 years for its typical system. It is the Trust’s figure on its assumptions. Export rates are set by each supplier, must be above zero and change at short notice, which is why we never print one. Our guide to solar panel payback time in the UK shows how to work the sum for your own bills.
Group buying, then and now
Harrow residents know the group-buying route well: in the 2021 and 2022 Solar Together London rounds, 285 committed to panels, more than in any other London borough. The scheme, now Switch Together, says it is not active in Harrow at the moment. An independent quote is the comparison point either way. Harrow is part of our solar panels in North London coverage, and you can ask for a survey through our contact page.
Sources: Energy Saving Trust, Solar panels: costs, savings and benefits explained (updated 27 August 2026) and Battery storage (updated 19 August 2026); DESNZ, Solar PV cost data (May 2026, 2025/26 financial year); PVGIS 5.3, European Commission Joint Research Centre (PVGIS-SARAH3 2005–2023; 4 kWp, 35°, due south, 14% losses; Harrow run 15 October 2026); Met Office, Northwood long-term averages 1991–2020; Ofgem, typical domestic consumption values from 1 July 2026 and Smart Export Guarantee; HMRC, VAT Notice 708/6; ONS Census 2021, TS044 and TS054, Harrow and its wards, via Nomis; ONS, Energy efficiency of housing, EPC records to March 2025; London Borough of Harrow, Harrow on-the-Hill conservation areas and Living Harrow: Climate and Nature Strategy 2023–2030; Energy Networks Association, EREC G98 Issue 2; Switch Together, Harrow page. Totals, scaled generation and the VAT difference are our arithmetic.