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How facades and pavements in European cities are used to harvest clean energy

American flag on the boat near the cityPhoto by Chris Barbalis on Unsplash

The façades and sidewalks of buildings in Dutch and Italian cities are transformed into intelligent surfaces with energy recovery and equipped with sensors to power, heat and cool spaces and even monitor roads.

Europeans have grown accustomed to seeing solar panels on the roofs of buildings. But there are many other artificial surfaces in our cities and towns that could be used to harvest energy, including construction surfaces.

"In Europe, the number of square meters of available construction space is comparable to that of roofs," said Dr Bart Erich of the Netherlands Organization for Applied Scientific Research. He is leading a project called ENVISION, which studies technologies to recover energy from building surfaces.

The project team estimates that there are approximately 60 billion square meters of building facade in Europe - prime property to achieve the European goal of an energy-neutral built environment by 2050.

The companies and researchers involved in the project have set themselves the challenge of making the apartments have positive energy, which means that the buildings produce more energy than they use. The idea is to integrate four new technologies in the facades of buildings to recover heat or electricity.

One of the technologies is the photovoltaic windows which recover electricity. They have stripe characteristics in the glass, making them suitable for stairs or windows where you want light to enter, but full transparency is not necessary.

Another approach uses a special paint that absorbs 40% -98% of sunlight, depending on the color. Painted panels are then attached to special heat pumps. "(These) can generate heat or hot water," said Dr. Erich.

The system also keeps the panels at a fairly stable temperature even on hot summer days, which makes it effective in collecting heat. This technology was tested in a school gymnasium in Almere, the Netherlands, where it was used to heat the gymnasium and for hot water.

There are also colored glass panels with heat recovery technologies. These can be used decoratively on the facades of buildings.

The fourth technology uses special ventilated windows to cool a building in summer. "The glass is transparent and collects near infrared radiation (from sunlight)," said Dr. Erich.

By moving the air through the channels inside the glass, the heat is removed. It cools because, like a blind, glass filters the sun's energy. Often a lot of light is reflected outside, contributing to the warming of cities and the demand for air conditioning.

Smarter surfaces

Many of us see everyday surfaces as something that should just be tough. Professor Cesare Sangiorgi, materials engineer at the University of Bologna in Italy, believes that we should expect more from these surfaces and that we can create a new type of urban environment with more intelligent surfaces. "We are looking to create more livable urban spaces and surfaces," said Professor Sangiorgi, who is leading a project called SaferUp.

The project is helping scientists at the start of their careers to study how to improve the roadways and roads on which we pedal, drive and walk. Most sidewalks contain no technology and are similar to what has been used for centuries, but European scientists aim to revolutionize this situation.

In the United Kingdom, researchers from the University of Lancaster, including one at SaferUp, are creating intelligent roads by installing electromechanical devices. When crushed by traffic, they transform mechanical energy into electricity. Under normal traffic conditions, this could generate enough energy over a one-kilometer stretch to light about 2,000 street lights or power sensors that monitor traffic volumes. Field trials are planned for 2021.

'In Europe, there is a similar number of square meters of building space available as attic space.'

Dr Bart Erich, Dutch Organization for Applied Scientific Research

Scientists at the University of Perugia in Italy are designing intelligent cement sensors that can be placed on roads or bridges. "Small particles change resistance to electric current when they are bent or deformed by the passage of an (a) vehicle," said Professor Sangiorgi. This is called the piezoelectric effect - it occurs when mechanical stresses are exerted on certain materials, such as ceramic.

"You need certain electronic components, but the material itself could then detect the weight, speed or number of vehicles passing through it and report the condition of the material (which constitutes a bridge)," said the Professor Sangiorgi. In the future, this information may be downloaded to the phone or laptop of a safety engineer during road or bridge inspections. This could avoid catastrophic failures, such as the collapse of the highway bridge in Genoa, Italy, in April 2018, by improving the monitoring of the wear of these structures.

Cool cities

Futuristic roads are also designed to better manage the heat. Today, many cities suffer from higher temperatures in summer than the surrounding countryside as buildings and sidewalks release heat from the sun at night.

This heat island effect causes more illness and death, especially when heat waves strike. Scientists at the University of Perugia are developing lighter colored surfaces that absorb much less heat than black asphalt. This takes advantage of phosphorescent materials, which can store and then emit light. Special materials shine blue or yellow even when mixed with concrete. The temperature of this sidewalk is lower than that of regular urban surfaces.

The sidewalk glow lasts an hour or two after sunset because it releases energy from the sun, says Dr. Anna Laura Pisello, materials scientist at the University of Perugia in Italy. "It can save energy on street lighting," she said. The Italian sidewalk test began last year on the campus of the University of Perugia and is expected to be used in the city later this year.

The surface of the asphalt can reach a peak at 70 ° C during the summer heat waves. Heating causes it to warp and crack, which increases maintenance costs and shortens the life of a surface. In Germany, a SaferUp scientist is working with others to develop a network of pipes integrated into the pavements to dissipate heat. "Pipes can get geothermal energy to heat the pavement when there is ice, or take groundwater to cool a pavement when it is too hot," said Professor Sangiorgi.

For new facades, Dr. Erich said that normally building facades do not earn money for owners, but colored glass panels, for example, should provide a return on investment in 15 years. As with coating technologies, the first step is to build prototypes in the laboratory, then test and present them in the real world. Other demonstrations of painted panels with energy recovery, transparent and colored glass will be integrated into the buildings in the near future to present the future facades. PV glass is tested in a utility building in Austria, ventilated panels and windows in a building at the University of Genoa and colored heat sensors in apartments in the Netherlands.

In the near future, Europeans will be walking on smarter sidewalks with sensors and electronics inside. If they look up, they can admire attractive building facades that silently recover the energy of sunlight while cooling the cities around them.

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