Some scientists estimate that by 2050 two-thirds of the world's population will live in cities, so they are looking, along with some technology companies, for producing renewable energy coming from the urban furniture that surrounds us. Is it realistic?
Taking into account new materials, inventions and devices that are being developed, no one can say that this is an unreachable goal.
Another very different thing is if feasible from an economic point of view and if it is really an alternative for existing energy producers.
1. Energy cement
Cement mixtures made with wastes from power plants could serve to build, for example, buildings that serve as batteries.
This concrete compound of potasiogeopolimétrico (KGP) is cheaper than ordinary cement and can store electricity.
According to the researchers, a bright six meters high, built with KGP and equipped with a small solar panel, could contain enough energy to feed all night.
"We have shown that KGP cement mixes can be used to store and release electricity without the need to add anything that is costly or dangerous," says Lancaster University professor Mohamed Saafi, who leads the survey.
Buildings with KGP could be used in cities to meet their electrical requirements.
2. Windows from solar panels
New materials also help make solar panels cheaper and more profitable.
Solar energy is the most common source of renewable energy in cities because the cost has fallen from US $ 4 per watt that cost a decade ago to US $ 0.50 worth now.
In the United Kingdom, for example, more than one in three companies are already producing part of their electricity, mainly using roof-mounted solar panels.
But building silicon-based solar panels is a big energy bill because it requires temperatures above 1400ºC or higher and the silicon must be 99.9999% pure.
Now materials such as perovskite have been created that can make the panels much thinner, cheaper and operate at much lower temperatures, says Nitin Padture, a professor of engineering at Brown University in the United States.
Being partially transparent, could also be used for windows.
The downside is that most of them contain lead, a very toxic metal, but a choice suggested by Professor Padture and his team is replace the cable with titanium.
"Titanium is fairly common, but no one ever thought of using it to replace the lead in the perovskite solar panels," he says.
"We do not want to replace the existing silicon technology, but to improve it".
3. Urban wind turbines
When we talk about the wind, the other most common source of renewable energy, conventional turbines do not work well in areas with many buildings, because wind directions vary greatly.
But researchers Nicolas Orellana and Yaseen Noorani have created one global wind turbine to end the problem. The O-Wind Turbo, which won the James Dyson 2018 in the UK, is a global device that turns when the wind hits him from any direction.
Another solution is provided by the Turkish company Devici Tech. This is the use wind generators vertical along the roads they can use the energy produced by cars when they are in circulation.
The company claims that the Enlil turbines, already tested in Istanbul, can meet the energy needs of up to two homes and also integrate solar panels and seismic sensors.
But there are some inventions that, despite their work, have proven to be no profitable at all.
4. Photovoltaic roads
In France, for example, Colas was a pioneer in the construction of photovoltaic roads. It has been installed extensively across the country as well as in some areas of Japan and the United States.
The first construction took place on a 1-mile monolithic route in Normandy, in the north-east of the country.
There are doubts as to whether, in the case of photovoltaic roads, solar panels are really useful because, when in a horizontal position instead of being inclined towards the sun, they can do not receive so many sun rays. In addition, motion, snow or mud can block them.
In 2014, a small bicycle strip of 70 meters was built in Amsterdam for $ 3 million. It produced 3,000 kilowatts per hour (kWh) of electricity in the first year, but for this money, 65 million kWh of electricity could be purchased on the open market.
5. Action for movement
Another technology that seeks to justify itself in commerce is piezoelectric. It is a type of energy that when compressing certain materials such as quartz, it flows through them.
Therefore, cars and lorries traveling on special road surfaces equipped with piezoelectric devices could produce energy. Pedestrians could do this on special pavements.
In 2009, Isowian company Innowattech experimented with streets that capture energy, and now an American company, Pyro-E, wants to test similar technology on a small section of road in Fresno, California.
But although these works are technically viable, they are today costly.
Some estimate that in the United States one kilometer of two-way street would require 13,000 piezoelectric devices to add US $ 400,000 to construction costs.
Even without considering construction or installation costs, it will take about 12 years to recover this amount.
The UK company Pavegen has been developed electrified pavements which can produce two to four pairs of energy with each step given over them.
Its footpaths, which cost about US $ 2,700 per square meter, have been installed in 200 locations around the world.
The number can be quite high, but also expensive solar collectors when they first entered the market.
"We believe that people, not just technology, will be the ones who will improve our cities," says Laurence Kemball-Cook, founder and CEO of Pavegen.
The idea, they hope, is that people can help build sustainable cities with renewable energy.
The technology is, it is now cheaper to reduce costs.
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