Five ideas for more climate-friendly buildings

In hot regions such as the Greek islands, white is the wall colour of choice. And this is not just for aesthetic reasons, of course. After all, white reflects sunlight, thereby ensuring that the rooms inside do not become unbearably hot. US researchers now claim to have developed the whitest wall paint ever created: it is said to be able to reflect more than 98 percent of the incident sunlight. The measurements taken by the scientists show that this results in a surface temperature, even in the noonday heat, which is 4.5 degrees lower than the surroundings, falling even more sharply to 10.5 degrees at night. “If you were to use this paint on a roof with an area of 90 square metres, the estimates indicate a cooling performance of ten kilowatts,” says Xiulin Ruan, Professor of Mechanical Engineering at Purdue University in the US. “This performance outstrips that of the central air conditioning plants used in most houses.” This ultra-white paint is said to be about as durable as conventional wall paint. And it should also bring benefits to its immediate surroundings. This is because, when facades heat up less strongly, this also helps to temper the effect of the urban heat islands which the residents of big cities are increasingly having to contend with.

The main purpose of insulation material is normally to keep homes from losing their heat. In a new departure, the material being worked on by researchers at the Universities of Halle-Wittenberg and Leipzig is designed to store summer heat and release it again at night or in the winter. This invention is based on what is known as a latent heat store. Changing the aggregate state from solid to liquid allows it to absorb heat. When the material hardens, the stored heat is released again. This is the same principle as that used by hand-warming cushions in the winter. Once integrated into thermal insulation board, this new material should be able to store up to 24 times more heat than conventional concrete or plaster, the researchers have calculated. To date it has only been produced in small quantities in the lab – mainly from eco-friendly materials. In the future it might be used to make sweeping improvements to the energy footprint of buildings, in both winter and summer. Not only that, but it could also be used as passive cooling to improve the efficiency of solar power or battery systems.

Early photovoltaic technology was a clever but costly business, and yet electricity generated by the sun has now become the cheapest way of generating electricity. 90 percent of today’s solar cells use the metalloid silicon to convert solar energy. Scientists and corporations are, however, increasingly working on organic solar modules. These make use of hydrocarbon compounds to generate electricity. In short, they use plastic. The benefit of this is that the solar films used are not only a lot thinner and lighter: they are, above all, flexible.  They are therefore basically suitable for all surfaces on which the use of rigid and heavy modules is impossible. The films produced by Heliatek in Dresden, for instance, have already been used on the roofs of lightweight structures, biogas plants and wind turbine towers. Thanks to their semi-transparent property, however, they can also be used in glass facades or windows. And, as the proponents of the technology emphasise, they can be produced with less energy and material, thereby reducing the costs. Although this sounds like a no-brainer, it does come with a few downsides. Whereas silicon cells can achieve a service life of 40 years, the life expectancy of organic cells currently falls short of this, at “only” 25 years. And they are still a good ten percent less efficient that their silicon-based relative. In other words, you need more space to harvest the same amount of energy – thereby taking the lower production costs out of the equation to some extent. The organic solar cells therefore still have some catching up to do before we are likely to see them attached to every windowpane at some point in the future.