If You Can’t See A Solar Panel, That Doesn’t Mean It’s Not There

In the shift away from fossil fuel energy sources, there has been a huge expansion in solar power. We’ve seen solar thermal plants in the desert and photovoltaic panel farms covering huge areas of land, but perhaps the most potential comes from placing the panels on rooftops. In some parts of the world this is encouraged through a system of subsidies, as is the case in Italy. But what if your building is part of a protected world heritage site such as the Roman city of Pompeii? The answer comes in the form of traditional roof tiles that hide their photovoltaic elements under a polymer skin that looks for all the world like a traditional Roman pan tile. As is so often the case with such products, the manufacturer’s description page is cagey about the details in the name of protecting their invention. What they do tell us is that the tile uses conventional solar cells mounted underneath the polymer layer, which is described as “opaque at the sight but translucent to sun rays“. This sounds like an inherent contradiction, so naturally, we’re intrigued as to how it works.

A clue comes in its claimed properties, one of which is that it has photocatalytic self-cleaning. This implies the presence of a titanium dioxide film which generates oxygen free radicals from air in the presense of light. Titanium dioxide is ubiquitous as a white pigment and food colouring, but it also has interesting colour properties in thin films, being used in iridescent and reflective effects. If we wanted to make a guess as to how these work, we’d expect them to use a carefully selected dye whose spectral profile doesn’t interfere too much with that of the solar cells, along with the colour effects bestowed by a titanium dioxide thin film.

However they work, these tiles are a fascinating bit of technology and we’d love to know more. It’s certainly not the first solar roofing innovation we’ve brought you.

45 thoughts on “If You Can’t See A Solar Panel, That Doesn’t Mean It’s Not There

  1. I don’t understand the point of having theses super expensive, low efficiency and hard to install PV modules.
    Before needing theses, we should already have every industrial building and parking lot covered. Theses are not some historical heritage and need energy during the day (think super market and factory). While private homes have smaller roof space, PV need to be well integrated, energy needs during early morning and late evening.

      1. And how do you convince non-technical bureaucrat that yes, you complied with the order, those “ordinary looking tiles” are in fact, solar panels in disguise.

        They’d probably still fine you for not putting solar up because the panels aren’t visible.

    1. One point is to produce the energy at the point of consumption, so you don’t need to double up on the transmission infrastructure. For example, a mall covered in solar panels would produce more peak power than it consumes, so the utility connection has to be oversized to accommodate the peak outflow. A solar panel at home would be sized more according to the consumption of the home itself – which reduces demands on the infrastructure.

      The major advantage is reducing the fluctuation in power output by spreading the panels over a wider area. If all the panels are concentrated in single spots, clouds cause large variations in power output. Likewise, the orientation of the panels can be randomized more evenly to spread the hourly production peak.

      1. Indeed, orientation can really matter.

        The energy company that turned out to be the best contractor to fit solar on our roof suggested filling the basically western facing side as much as the south for that reasoning – we didn’t as cost to energy generated isn’t in favour of that and our peak use tends to be more in the middle of the day anyway. But still a nice idea that may get done eventually.

        Solar tracking if you can manage it, even only a few degrees worth can really add up!

      2. The way these subsidies work is to make you hook to the infrastructure, and rebate you for your part of the electricity. Can’t have customers escape centralized markets…

    2. Using this logic you should not be surfing this web site for entertainment or any reason if you’re not already a billionaire. Wasting time with something if you can… Whatever

  2. I haven’t seen numbers, but I assume both these and the more traditional glass panels when integrated as a roof cover loose efficincy due to worse heat dissipation. Cooling is very important for silicon devices and these 10-15 cm of moving air below the panels is hard to overestimate.

  3. >What they do tell us is that the tile uses conventional solar cells mounted underneath the polymer layer, which is described as “opaque at the sight but translucent to sun rays“. This sounds like an inherent contradiction, so naturally, we’re intrigued as to how it works.
    It’s not terribly crazy. Making the surface matte so reflections are dispersed and absorbing blue and green light can help maintain the illusion of a reddish opaque surface. If I remember correctly, cells work better in the green region of the spectrum, so they don’t need to be reflected out anyways.
    Of course, it is less efficient than just letting everything through, and it looks more expensive than traditional panels, but other users have already commented on that.

  4. How do I interpret “Oxygen free radicals”?
    Are those radicals without any ogygen in them, or are those “free radicals” made of Oxygen?

    Does this also imply it’s an Ozone generator?
    If Titanium dioxide with sunlight is able to separate O2 into two O’s then some of those O’s are likely to combine with another O2 to make an O3.

    Sometimes I wish I had learned a bit of chemistry at school when I was young…

    1. Free radicals that enter the human body (air, food, drink) can make their way into cells and damage chromosomes and accelerate development of cancers. Ingestion of free radicals is discouraged for that reason.
      Unless one is currently undergoing radiation therapy for a cancer,
      then consumption of free radicals can further damage the cancer cells affected by the radiation.

      Yeah, I don’t have a direct answer to your question.

    2. Free radicals containing oxygen. Usually people talk about superoxide formation from the promoted electrons and oxygen at the photocatalyst interface.
      No it doesn’t unless trace ammounts of ozone are enough for something to be an ozone generator. I wouldn’t expect any appreciable quantity, if any, reaction rates for this sort things are really low, but there are studies that indicate the formation of ozone from illuminated TiO2 surfaces in the presence of nitrogen oxides or something if you want to bother getting past an ACS paywall.

  5. My expectations got downgraded a fair bit when it comes to those boutique solar tiles. I mean, even Solar Roof is pricey for what it delivers, and these look-alikes are only relevant in places where it’s listed buildings or nothing.
    So, I guess be happy it’s not solar-friggin-roof-glaze… but with our luck, some company will integrate LEDs in them and give you a discount for harassing your neighbors with ads supplementing the glare of street lights.

    1. ps. Ha, now I see how could work:
      1) listed buildings would require expensive specialty solar roof tiles to match style.
      2) EU legislation will make installing a PV system mandatory concomitant with roof repairs and restorations.
      I see what you did there, industry.

    2. I would not go as far as saying for listed building or nothing. Being able to get power locally is a good thing, even if the payback time is going to be longer it will still get there, and then there is the human factor – the big ol rectangles of solar cells with air gaps all around them bolted to what is basically a few runners on the roof really isn’t very nice to look at. You can use those same flat panels and make a pretty structure, but that requires architecture from the ground up to do so, where replacing slate or tile with faux-slate that happens to be solar still looks good. Keeping the S.O. and neighbour approval factors up – which from what you hear about the USA’s HAM’s finding putting up a small radio mast impossible…

  6. If mounted to a north/south axis, they could produce power throughout the day.

    But since we are discussing historical Italian buildings, how many you seen oriented to the cardinal directions? B^)

    1. That is assuming it is functioning as a singular cell – if it is two split down the middle the curvature is basically all eliminated and provides two panels well angled to catch the sun efficiently through a much wider period of time than a flat panel – more surface area of panel potentially too.

  7. A friend of mine trying to renovate his NYC apartment and needed to install a grating for an air conditioner. The historic committee said the grate had to match the existing brick wall. It took him two years to determine what the average color of a brick wall was and get permits and sign offs and stuff. Maybe in Italy there aren’t insane historic-preservation hoops to jump through. I kinda feel like just putting up regular old solar cells would not offend me one bit, but obviously a historic preservation committee would never agree. These things seem to be a kind of, sorta worth it compromise.

    1. I sincerely hope if has changed now, but I remember a case in Aspen, Colorado, where a concerned citizen claimed that rooftop solar was a “political statement” and therefore was not allowed to be visible from the street. Too bad if that was the part of the roof that faced South.

      I’m still trying to dig out the original article – I read it in a printed newspaper back in 2007 ish.

    1. The idea is 100% plausible, so while I’d not suggest buying them yet with so little detail there is still a reasonable chance this is, or will be when its ready, a legitimate product…

  8. Are these to replace original Roman roof tiles? Or to add a new but old-looking roof to a Roman structure that cutrently has no roof?

    Either way this is not heritage, history or preservation, but building a Disney-style replica.

    There is a frequently forgotten difference between preserving the *look* of historical materials, and preserving the materials themselves.

    1. Very good observation and distinction. We used to belong to a .. society in the north east to support craftspersons. There was actually a society of historic mill workers that would do the upkeep and fabricate new parts as needed using historic methods and materials. We got to know a millwright pretty well- nothing Disney about it. It kinda struck me that one guy could just make all the stuff to keep a perfectly good windmill operating. And I mean operating in the sense of using windmill to make enough flour to sell to tourists to make enough money to keep going

    2. There is also a point you have to allow new methods and materials to be used if you wish the historic buildings to actually survive – if it is impossibly expensive to run or maintain the building because of that insistence on only 100% historic methods and materials the building will be left to rot, and eventually fall down.

      Far better to preserve the look and feel as much as possible while keeping the building useful than insist upon historically accurate (or even as sometimes happens actual historical salvage) materials.

      Also even a Disney-style replica can be perfectly justified, artistic merits are entirely subjective – it will be to some peoples taste. So why shouldn’t they be allowed to have their personal blend of cartoon fairytail nonsensical elements in the design?

  9. I would like to raise another question. Since it it is a polymer skin; what is its ability to hold up against UV? I seen so many products break down, start cracking etc. Even products that are UV resistant are due to pigment preventing the penetration of UV. The surface is still damaged over time. For example, the gray electrical conduit over time can develop a white powdery appearance. But it can be cleaned to remove the residue and be gray again. Then I wondered if it has protection, how much efficiency did it cost? If the surface is damaged, will it impact its appearance and efficiency? I seen the clearcoat on automobiles crack and peel.

    1. A very good thought, I don’t expect it will matter hugely though – the skin breaks down over (hopefully anyway) many years, and if the breakdown rate is actually a problem can always go up there every 5 years or whatever for the deep spray clean and new surface treatment giving another heap of life to it.

      Really should be cleaning solar panels fairly often anyway if you want to get good performance, so having to have somebody in (if you are not doing it yourself) shouldn’t be all that bad.

      As for what the efficiency cost is, that will depend on exactly what type of solar cell is in these things – different compositions work best at different wavelengths, so as long as you pick the composition that works with the right wavelengths the polymer does pass well it won’t be cost free, but aught to be pretty good still.

    2. That should not be a problem: once the tiles are approved, you can install them. Problem might be, when after years the coating has peeled off and replacement is needed, you might be forced to source new tiles in solar cell blue to preserve the look of the old ones.

      Other question: how is the wiring of the tiles done?

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