Solar energy has slipped so readily into the vernacular that one is easily confused. Genuine solar technology uses direct sunlight to create thermal heat and can provide 90% of hot running water in high summer and about 55% annually. However, what interests most people is photo-voltaic (PV), a rather different ‘solar’ technology using daylight- sunny or overcast-to create electricity.

PV is also the only renewable-energy fitting that, once installed, requires negligible intervention while generating income: you sell your excess to your local supplier and to the National Grid, to which you remain connected (see www.gov.uk/feed-in-tariffs for details). ‘Efficient quality panels tend to pay for themselves over a shorter period than, say, ground-source heat pumps: one installation I saw created £3,500 of electricity a year,’ says independent house-finder Colin Mackenzie. However, he warns: ‘Aesthetics can rule against PV unless you can place them somewhere unobtrusive-assuming the house isn’t listed.’

The time over which you can recoup your PV investment depends on the increasingly cut-throat competition between suppliers, on geography- the sunnier south of England is where installations are more prevalent-and on the helter-skelter slide of government subsidy FIT (Feed In Tariffs). FIT is fixed for 20 years, index-linked and, importantly, stays with the property, not the individual. Households that boldly installed PV before 2011 continue to be rewarded with 43.3p per unit for energy sold back.

But take-up was wrongly estimated by Gordon Brown: people joined the scheme in throngs and, as a result, by 2012, FIT had dramatically halved. A 4kw system installed last autumn for £6,000-£8,000, with annual output of 3,400kWh, should be powering the house and returning £877 in its first year, with £17,000 profit over 20 years. Unfortunately, FIT has since been further reduced-properties registering a 4kw system between July 1 and September 30, 2013, will receive just 14.9p per unit, and a mere 6.85p if energy performance is certificated ‘E’ or below. That could be an issue for older houses, which may also need energy-efficient boilers and loft insulation.

However, the good news is that, as with mobile phones, suppliers keep slashing hardware costs, so long-term annual return on investment is about 10%. And there are other advantages: Malcolm and Susan Brenton are retired professionals producing small-scale beef and pork in Surrey. They operate several freezers and installed PV on a barn roof in 2011 to reduce bills and make better use of their capital. It quickly became clear to them that the ranks of cold-callers in the PV world are not always tuned in to bespoke requirements. ‘Most salesmen work hard to tell you there’s an eight-year payback,’ said Mrs Brenton. ‘We had trouble conveying to them that payback wasn’t an issue for us; we wanted to know if we could take money out of our savings and put it on the roof to make money-which it does.’

She adds: ‘Our other concern was for hardware guarantees. A neighbour who bought a Chinese-made converter has already got through three. We considered buying one from Germany and Austria, where they’ve used this technology for considerable time.’

Getting the fittings right is crucial: in particular, complicated, steeply pitched roofs need special thought. Optimum performance is achieved when panels are south-facing at 30°; steeper than 50°, and performance declines. East or west locations shouldn’t be discounted-they can perform to 85% of the capacity of a south-facing panel. The largest domestic system is usually 4kw, determined by most houses having a single-phase connection to the Grid (those with space for bigger systems need network operator permission).

A 4kw system ideally needs 28sq m (300sq ft) of space free from shade by trees or chimneys. Rain will keep panels clean, although output is affected by dirt, so bear in mind ease of access for annual inspections. Although quality panels last 50 years, the inverter-which can go in the loft-will need replacing at least once within the 20-year contract span.

One cautionary note: there is nothing ‘free’ in PV installation. ‘Roof-rent’ schemes provide your electricity with no outlay, but you have to use most domestic appliances in daylight hours to get full benefit, the renter installer receives your FIT payments, and may handcuff you to an unappealing contract. Plus, if you decommission the panels for roof repairs, you could end up having to compensate the installer.

Aesthetics and PV go hand in hand at the White House in Tonbridge, Kent: the panels are discreetly placed in the gully between the two pitched roofs. £2.5m through Savills (01732 789700)

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