If we take into account the new materials, inventions and devices that are developed, no one can say that this is an unattainable goal.
Another very different thing is if they are feasible from an economic point of view and if they are really an alternative to the energy generators that already exist.
These are five revolutionary inventions that have already proven their effectiveness,
Cement mixtures made from power plant waste could be used to build, for example, buildings that function as batteries.
This potassium electrolyte cement compound (KGP) is cheaper than ordinary cement and can store electricity.
According to the researchers, a six meter high light pole made with KGP and equipped with a small solar panel could contain enough energy to feed all night.
"We have shown that KGP cement mixtures can be used to store and release electricity without the need to add anything that is expensive or dangerous," says Lancaster University professor Mohamed Saafi, head of the research.
Buildings made with KGP could be used in cities to meet their electrical demands.
Windows made of solar panels
The new materials also contribute to making solar panels cheaper and more profitable.
Solar energy is the most common source of renewable energy in cities because the cost has dropped from US $ 4 per watt that cost a decade ago to US $ 0.50 which is worth now.
In the United Kingdom, for example, more than one in three companies already produce part of their electricity, mainly using solar panels positioned on the roofs.
But the production of silicon-based solar panels is a great waste of energy because it requires temperatures higher than 1400 ° C or higher and the silicon must be 99.99999% pure.
Now materials such as perovskite have emerged that can make panels much thinner, cheaper and work at much lower temperatures, says Nitin Padture, an engineering professor at Brown University in the United States.
Being partially transparent, they could also be used for Windows.
The drawback is that most of them contain lead, a highly toxic metal, but an option suggested by Professor Padture and his team is the replacement of lead with titanium.
"Titanium is quite common, but nobody had thought about using it to replace lead in perovskite solar panels," he says.
"We are not trying to replace the silicon technology that exists at the moment, but to improve it."
Urban wind turbines
When it comes to wind, the other most common source of renewable energy, conventional turbines do not work well in areas with many buildings because wind directions vary widely.
But researchers Nicolas Orellana and Yaseen Noorani have created a spherical wind turbine to solve the problem. Its O-Wind turbine, which won the James Dyson Prize in 2018 in the United Kingdom, is a spherical device that rotates when the wind hits it from any direction.
Another solution is provided by the Turkish company Devici Tech. It is about using vertical wind turbines along roads that can use the energy generated by cars while driving.
The company claims that its Enlil turbines, already being tested in Istanbul, can meet the energy needs of up to two houses and can also incorporate solar panels and seismic sensors.
But there are some inventions that, despite the work, have proven not to be profitable at all.
In France, for example, the engineering company Colas was a pioneer in the construction of photovoltaic roads. He installed several across the country, as well as in some areas of Japan and the United States.
The first construction was on a single lane route of 1 kilometer in Normandy, in the north-east of the country.
There are doubts about the fact that, in the case of photovoltaic roads, solar panels are really useful because, being in a horizontal position rather than inclined towards the sun, they may not receive as many sunrays. In addition, heavy traffic, snow or mud can block them.
In 2014, a small 70-meter cycle path was built in Amsterdam for $ 3 million. It produced 3,000 kilowatts (kWh) of electricity in its first year, but for that money, 65 million kWh of electricity could have been purchased on the open market.
Energy to movement
Another technology that seeks to justify commercially is piezoelectric. It is a type of energy that, when some materials are crushed, like quartz, flows through them.
Therefore, cars and trucks traveling on special road surfaces with piezoelectric devices could generate energy. Pedestrians could do it on special sidewalks.
In 2009, the Israeli company Innowattech experimented with roads that capture energy and now an American company, Pyro-E, wants to test similar technologies on a small stretch of road in Fresno, California.
But although these projects are technically feasible, they are currently expensive.
Some estimate that a two-way street kilometer would require 13,000 piezoelectric devices in the United States, which would add $ 400,000 to construction costs.
Even without considering the costs of production or installation, it will take about 12 years to recover this amount.
The British company Pavegen has developed electric floors that generate two to four joules of energy with each passage that passes through them.
Its sidewalks, which cost about US $ 2700 per square meter, have been installed in 200 locations around the world.
The figure could be quite high, but also expensive solar panels when they entered the market for the first time.
"We believe that people, not just technology, will be the ones that will improve our cities," says Laurence Kemball-Cook, Pavegen's founder and CEO.
The idea, they hope, is that people can help create sustainable cities with renewable energy.
Technology is, now it is cheaper to lower costs.