Solar tile links protection of historical buildings with power generation

Solar power is all the rage among Italian home-owners since the new electricity feed-in law "Conto Energia" entered into force this year. Unlike the previous law to promote the use of solar energy, the new act focuses on small units and therefore directly ad-dresses end consumers. And they are happy to install solar modules on their roofs. In Italy, a country blessed with just as much sunshine as Spain or Greece, that is a lucrative business. But not everyone who wants to is allowed to install conventional solar panels on their roof - the authorities for the protection of historical monuments have so far refused their approval.

One look at a city like Venice shows why. The lagoon city wreathed in myth is characterized by roofs made of light-brown clay pantiles, which are laid with alternate convex and concave surfaces uppermost. Dark-colored solar cells would stand out amid the sea of tiles and disfig-ure the idyllic Renaissance scenery. As a result, the city that features on the UNESCO World Heritage List might lose its magical attraction for tourists around the globe. The Italian com-pany REM S.p.A has found a solution to this dilemma  solar tiles made from plastic with in-jection-molded PLEXIGLAS® cover panels. The so-called "TechTiles" have the appearance of traditional clay tiles, but contain powerful solar cells, or alternatively, solar heating mod-ules for heating water. The tiles' collector surfaces are much smaller than conventional solar panels, because the historical roofs can only be used to generate energy despite monument protection regulations if their optical impression is preserved. A roof oriented toward the south with a size of 18 square meters and an inclination of 30 degrees thus produces 1,650 kilowatt-hours per year (see table) under the Southern Italian sun. That is enough energy to cover five sixths of the annual power consumption of a one-person household in Germany.

From antiquity to the solar age

There are no reliable records confirming when fired clay tiles were invented and by whom. All we have is a report by the Greek poet Pindar, who attributes the invention of the roof tile around 450 BC to the Corinthians. The curved shape now common in the Mediterranean region dates from the Middle Ages and has not changed much up to the present day. Now, with the new model from REM S.p.A., this shape is entering the solar age and thereby bridging the gap between tradition and progress.

Climate change and rising energy prices are also issues that concern the protection of historical monuments in Germany. Christoph Mohr, Curator at the Office for the Preservation of Historical Monuments in the German Federal State of Hesse, declares: "We welcome initia-tives that try to reconcile the aesthetic aspect of protecting historical buildings with new technologies for power generation. We are waiting for products that combine both, making it pos-sible to use solar collectors that are suitable for protecting monuments from a structural engineering viewpoint." These products have to be both functional and attractive. "Tiles with solar collectors have to fit inconspicuously into historical architecture. Only then can one speak of an intelligent fusion of design and technology." The solar tile also convinced the jury of the Well-Tech Design Award, which conferred first prize for the tile last year.

Classic outside, high-tech inside

Although the suitable tile shape has not yet been found for each country, it certainly has for Italy. All the solar tile has in common with its medieval predecessor are the color and the shape. The modern version makes use of plastic rather than clay. The center of the overtile contains the solar cells or solar heating modules, concealed beneath a transparent panel. The solar tile was invented by Roberto Corvaglia and Sante Bortoletto at REM, who explains the principle: "Two factors are essential for optimal energy generation  powerful solar cells and a cover panel with high transmission." Light transmission was the decision criterion for the inventors when choosing the material: "We use PLEXIGLAS® for the panel because it transmits over 90 percent of light, much more than other plastics. Those are not so UV-resistant either, and turn yellow in the course of time," Corvaglia says. He and Bortoletto used a trick to prevent the dark solar cells from being visible through the transparent panel: "We added a fine texture to the inside of the sheets. They still let in sunlight, but obstruct the view from outside. That's how we prevent the black solar cells from spoiling the clay-colored im-pression of the tile," Corvaglia explains. From a distance, the high-tech version looks no dif-ferent from traditional tiles. But the sheet has to do more than look good, it has to be tough too. Bortoletto says: "Not even hailstones are a problem, PLEXIGLAS® stands up to those as well."  

Working hand in hand with roofers

The panel receives additional stability through a cross strut, which means the tiles can be walked over without any problem for easier installation. Roofers are grateful for another fea-ture of this technology too: the simple clip-on connection means the solar tiles can be installed without help from electricians. For especially fast roofing, the solar tiles are also available as prefabricated roof modules with an insulating layer and supporting surface. Nevertheless, each tile functions separately. If one fails, all the others continue to produce electricity.

South and north of the Alps

TechTiles are not just for the sun-drenched Mediterranean, they are also of interest for Northern Europe too. But the shape would need to be different. In Germany, the plane tile ("beaver- tail") is widespread. "We are already planning to produce different shapes for use north of the Alps," Corvaglia says. In the near future, the solar tile might also transform historical roofs in Northern Europe into miniature power plants.