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Conservatory Solar Coating Evaluation

Are Solar Coatings an alternative to blinds?

Conservatory blinds can be very expensive. An alternative may be to coat the roof with a thin layer of a special substance called a solar coating that reduces the amount of radiation from the sun that passes and keeps the conservatory cooler during the summer months. But what are they, do solar coatings work, what types of solar coating are available, will it tint the glass and how much will it cost compared to conservatory blinds?

Conservatory: What are solar coatings

A solar coating is an extremely thin film of material that is applied to one surface of the glass or polycarbonate in a conservatory - usually on the roof and on the exterior pane.

Conservatory: Do solar coatings work?

Yes. The technology is quite mature and has been installed not just on conservatories, but office buildings throughout the world. How well individual solar coatings work is a different question that I cannot answer.

Conservatory: How do solar coatings work?

The light that we get from the sun contains many more 'frequencies' than the visible light that we all see by. Ultra-violet has a frequency slightly higher than visible and infra-red which carries much of what we feel as heat has a frequency lower than visible. Certain materials attenuate, or reduce, the amount of energy contained at a specific frequency. For example black objects appear black because they absorb most of the energy being transmitted in the visible portion of the light spectrum (a name for the range of different frequencies). More clever than that is to design a material that will absorb ultra violet light and infra red but leave most of the visible light un-touched. A good material with let though most of the visible light but block the other solar radiation. How much visible light a pane of glass lets through is called its visible transmittance or Tv, which wants to be as high as possible (for example a figure of 1.0 means it lets all the visible light through, a reasonable figure is 0.7) and the solar heat gain coefficient (basically how hot it will get for a given amount of sunlight) needs to be as low as possible, say below 0.4. In the US these figures are quoted as part of the energy efficiency on windows sold. Because these coatings block infra red radiation they will also provide some level of insulation against heat escaping from the conservatory on a cold winters day.

Conservatory: What types of solar coating are available?

The following are proprietary conservatory and window solar coatings that we have found on the market worldwide.

CoolKote - This is a metallised PVC coating which "blocks 80% of solar heat" (probably mean infra red), "99% of ultra violet" and " Reduces glare by 70%". On a hot day figures provided suggest that the average temperature in the conservatory over a week remained around 23-24 Celsius after CoolKote had been applied yet up to 45 Celsius in a conservatory with no CoolKote applied. The readings were taken on 14 consecutive days, but they don't give an outside air temperature or anything to compare it against. A better way of doing it would have been to build two cold frames, one with a pane of plain glass in and one with CoolKote and then measure the temperature in them over a couple of months every day and show us what the temperature difference was. As it is the information they have provided us with on the site may be misleading - I can't really tell. CoolKote is a film that can easily be applied to you conservatory using soapy water - a bit like a very large bit of sticky tape. They say it shouldn't peel off, comes with a 10 year warranty but you should obviously avoid scratching it. It can be applied yourself or they can come and fit it. It can also be fitted at the time of your conservatory build or later by numerous conservatory manufacturers.

Celsius - This is a glass rather than an additional coating. That is it already has the coating applied or impregnated on the surface. Don't give any real details of what it is. It reflects "72% of total solar energy" which is apparently three times that of normal glass. It has a Tv of 0.45 which is low, but is only applied to the roof, obviously this would reduce the glare as they claim. Another benefit of the glass is that it apparently reduces the magnitude of any external noise but a factor of two. This is presumably a feature of the glass rather than the coating itself. I would have thought that you wouldn't notice that much as you still have all the side windows made of normal glass transmitting noise (albeit double glazed). It is claimed that it has some hydrophilic properties and so water and dirt just run of the roof in sheets and hence it needs less cleaning and because it reflects the heat back inside the conservatory the panes of glass are up to 5 Celsius warmer than otherwise, which reduces condensation. Again the other materials should do this.

Wonderglass - This is widely available in the states and just starting to become available here (I think). Now this is magnetron sputtering of up to 11 different coatings of material onto a glass sheet. Very impressive. It is supposed to be the worlds most energy efficient glass. It deflects away "85% of the suns solar heat", blocks "90% of Ultraviolet light". It has a hydrophilic coating to reduce cleaning and reduces glare. Because in a way it is much more high tech than the earlier competition they can have high solar heat rejection and still have a Tv of up to 0.72 (compared to plain glass at 0.9 and plain glass double glazing at 0.81)

Polycool - These are coated inserts. I've had a sample delivered and they are strips of concave polyester plastic with a metallised (sputtered e.g. high tech) coating on them. The inserts are designed to be slid up inside the gap between the polycarbonate roof panels. They can either be fitted by yourself or a fitter can come along. Looks fairly easy depending on access and how sprightly you are. Basically you remove the roof panel end caps and any tape from the conservatory roof (the end where it goes into the guttering) and slide the inserts up, cutting them to the correct length when fully inserted. You have a choice (mostly for aesthetic reasons rather than heat rejection) of  gold (gold coated) or silver (aluminium) colour film. Both types of film reduce the 'solar penetration and heat build up (via the roof)' by 85%. This they say can reduce the internal temperature of the conservatory by 40°F in high summer. In the winter and during the evening it can increase the U-value of your roof by 10-15% meaning it will lose heat more slowly.

Conservatory: Will it tint the glass?

• CoolKote: They say "Diffused light grey tint when seen from below"
• Celsius: They say "subtle blue tint in the glass "
• Wonderglass: They say "still remaining colour neutral"
• Polycool: Don't specifically say just "ambient light reduction is typically 5%"

Conservatory: Are solar coatings cheaper than blinds?

A 10m² conservatory roof space with roughly cost between £1300 and £1800 to cover with conservatory blinds. Whilst CoolKote costs between £595 and £680 to be installed by a supplier. Polycool will cost about £330 for the same size conservatory for a DIY fitting. The others that I have found are an integral part of the roof (and or windows) and I haven't seen any prices for using them instead of ordinary polycarbonate.

Summary

A solar coating could be cheaper than roof blinds and certainly should be considered as an alternative to blinds when specifying your new conservatory.

Further feedback: Anecdotal I know, but my brother-in-law paid a lot of money for pre-coated glass in the roof of his conservatory. I don't know exactly what make it is but again its not enough to keep the room cool and he ended up having a huge split air conditioning unit installed. That does the trick!

Last Updated: April 2008

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