SerpApi.Org
As Britain rides out its third heatwave of the year, the cost of running fans and air conditioning is mounting for those with them.
Meanwhile, those without cooling devices may be glad to skip the bills but could be looking enviably at any neighbours with air con and eager to find ways to make their homes less stifling.
One relatively cheap method that has cropped up among the many claimed ways of cooling down your home is solar window film.
So could this really be a viable money-saving alternative to expensive shutters that lets your home still get lots of natural light? This is what you need to know.
How does solar film work?
Solar window film is a flexible, transparent sheet that you can smooth straight on to a thin layer of glass, like a window or door.
The metal and ceramic layers in the sheet block sunlight from getting into your home by reflecting or absorbing 99 per cent of UV rays.
And it can cost as little as £15 per square metre if you apply it yourself. Some of the UK stores you can buy it from include Amazon, Abode Window Film, The Window Film Company, and Purlfrost.
But beware following a recent rise in search trends, prices could increase.
When shouldn’t I use it?
You should avoid using solar window film if you have triple-glazed windows as it can create thermal stress.
Thermal stress can result in fogging between the panes, seal failure or glass cracking.
You should also avoid the product if you have low-E coated double glazing. You can check the compatibility with the specific film.
Does it work better than curtains and blinds?
Apparently so. This is because it allows you to still get lots of natural light into your home without the excess heat or the UV rays.
This keeps your home cool in the summer and cuts down the glare caused by sunlight. The film even enhances privacy when you buy it with a reflective or tinted finish.
Which type of window is it best for?
Solar window film is best for double glazing. But what works for toughened and non-toughened differs slightly.
You can use any kind of solar film including reflective or dark tints with toughened double glazing.
Neutral films or lighter films tend to go best with non-toughened double glazing.
What do the experts have to say?
Cliff Elwell, Professor of Building Physics at UCL, says while it might save you money on running fans or aircon in summer, the challenge with solar window film is what it compromises in winter.
He said: ‘UK energy demand from homes is winter dominated due to heating. Modern double glazing has low-e glass, the aim of which is to reflect infrared heat (heat radiation) back into the room. This helps keep the room warm. In the summer it does the same thing, and this time it helps keep the radiated heat out.
‘However, we don't want to stop the visible light from getting in as this has an impact not only on how nice it is to be in the room for the light quality, but also the heat gain.
'In the winter we want this and it significantly reduces bills for most homes. Any film that stops visible light coming in could reduce the 'free heat' in the winter.
‘In the summer we have the opposite concern; we want to keep heat out. Most of this, considering only radiation rather than conduction through higher temperatures and air exchange (ventilation), comes in the form of visible light.
‘It is best to completely stop it entering the home and the best way to do this is with shading, such as awnings or simply hanging a sheet over a window.
'You can remove these when you want the heat to come into the home. The old sheet method may not be very tidy, but it is highly effective and free for most.
‘If you chose to put a film on the window to reduce the visible light coming in, you would reduce the heat coming in. This is good in the summer and bad in the winter.
‘On balance, I would expect you to lose out financially by applying such films because we aren't cooling most homes in any case. But if someone is really struggling with overheating and can't have shade, it could improve the internal temperatures.
‘You might also apply a film to filter the light, with minimal impact on the visible spectrum but cutting out the IR and perhaps the UV too. This is basically doing the same as the low-e glass, so if you already have that, there shouldn't be much difference.
‘If you don't have low e-glass, this technology should help in both summer and winter. The downsides would be whether it comes back off again cleanly, whether it goes on nicely (no bubbles) etc.’
In agreement, David Shipworth, Professor of Energy and the Built Environment at UCL, said: ‘It all comes down to how much it costs you to cool your home. Most people don’t have AC in the UK so they won’t be saving much money - they will just be more comfortable.
‘Solar window film won’t be as good as external shading but not everybody can do that. Internal blinds (like Venetian blinds) with a reflective white surface that you close when the sun is on the windows also help - but it’s best to stop the sun hitting the window in the first place if you can.’
