In cities across the world, people are waking up to the need to reduce their reliance on fossil fuels. The impact they have on the environment and their unsustainable nature mean that alternative sources of energy are increasingly in demand.

Could the answer to how we shift to renewable power, and meet the energy demands of today’s world, be as simple as using the spaces our cities already afford and mining wasted energy we already produce? Current thinking suggests so.

But what options are available, and do they represent real alternatives to the methods of generating energy we currently use, or are they too quirky to ever become mainstream, commercial products?

The path to renewables is paved with kinetic energy

Eventually our vision is for this technology to be powering our cities

Imagine walking down the street and producing the energy that powers the lights and buildings that surround you. This may seem farfetched, but Pavegen Systems are working to make this a reality.

The UK-based company has developed paving tiles that capture kinetic energy from people who step on them. The energy which is then produced can be used to power the surrounding environment. Laurence Kemball-Cook, the founder of Pavegen, explains how the technology “can power a range of applications including lighting, signage, wireless communications and sound systems”.

The product is best supported when placed in areas with the highest possible footfall; the company describes how “train stations, airports, sports stadiums, offices, schools and public spaces” are all ideal settings for the stones. To this end, the company has already installed 200 tiles into a football pitch in Rio de Janeiro, 51 tiles at London’s Heathrow Airport and 14 tiles outside a train station in Saint Omer, France.

Kemball-Cook is unabashed when asked about Pavegen’s potential. As part of his Ted talk,Turning Our Cities Into Human Power Plants, he said: “Eventually our vision is for this technology to be powering our cities.”

To achieve this goal he does acknowledge the technology will have to be “commercial, reliable and there when you need it”, and in order for the technology to have mass-market appeal, Pavegen will also need to be affordable. Kemball-Cook has said that in the last five years his team has dropped the cost of production by 90%.

He said: “We’re constantly improving the tile to reduce manufacturing costs and amplify power output; we have a new iteration of the tile launching in 2016 that will bring us a step closer to commercialisation. This is further emphasised by the large-scale, permanent projects taking place over the next few months.”

In addition to capturing energy though steps, Pavegen are working on a version of the tile that could be used for road surfaces. This version of the tile would generate renewable electricity from vehicles breaking on the road. However, they are not the only company to be developing this technology.

Scandinavian research organisation SINTEF and the Norwegian University of Science and Technology have been developing “power roads” that harvest wasted energy from cars. Berit Laanke, from SINTEF Building and Infrastructure, imagines that they will be able to extract energy from new automotive technologies, such as electric cars, by capturing the excess energy they produce.

The system used to capture energy from cars would be similar to Pavegen’s “footfall” technique. Cars would have to exert pressure on the road surface, which would then capture and store the energy in much the same way as Pavegen does with human steps.

Wind turbines under city bridges

Under-bridge turbines can help to bring decentralised wind power to urban areas where it was considered not suitable because of the turbulence caused by buildings

Capturing kinetic energy isn’t the only way of moving cities towards renewable power. According to research by teams in the UK and Spain, wind turbines located under bridges could provide a way of utilising the space available in cities and turning them into sources of energy. Power output would vary depending on the bridge in question, but two medium-sized turbines could produce as much as 0.5MW of power which would be the equivalent to the average energy consumption of 250 homes.

At that rate the idea would have a long way to go to match offshore wind farms. In the UK, capacity in offshore stands at around 4.2GW, and one turbine can produce enough energy to power 3000 homes.

Zahir Dehouche, course director of Sustainable Energy Technologies and Management at Brunel University, said: “It’s a very interesting concept, under-bridge turbines can help to bring decentralised wind power to urban areas where it was considered not suitable because of the turbulence caused by buildings.

“Under-bridge turbines can help to reduce the levelized cost of electricity generated from this decentralised wind system, which could be a good opportunity for the traditional energy providers to invest, particularly as electricity suppliers are obliged to have a certain proportion of their electricity from renewable sources.”

However, Dehouche does note that bridges would need good exposure to prevailing winds and average wind speed of 6m/s or greater for turbines to be effective.

Although the researchers claim that the application of wind turbines under cities is as viable for rural areas as it is for major cities, clearly the project has a greater chance of gaining commercial backing if it is successfully incorporated into cities across the globe. However, there are examples of technologies in development that could provide the means to generate energy regardless of location.

Heating houses with ‘nerd power’

We are trying to make this a product that can be installed in thousands of homes

A Dutch startup company called Nerdalize has created a novel way of heating homes using the heat generated from computer servers. Its story began when co-creators Mathijs de Meijer and Boaz Leupe were renovating a run-down house and accidentally broke the thermostat.

“Mathijs was working on his laptop and after really trying everything to stay warm, he said: ‘Well, you know what, how about we take 100 laptops, put them into one of the rooms and then we’ll have nerd-heat heating our house?'” said Florian Schneider, who co-founded the company with the pair, in an interview with the BBC. “That was more of a joke — and then very quickly turned into, ‘Wait, maybe this is not such a stupid idea after all.'”

From this simple idea, Nerdalize eventually designed the Eneco eRadiator, while working with one of the biggest energy suppliers in the Netherlands: Eneco. The eRadiator replaces the hot water contained in a traditional radiator unit with a computer server. By installing servers in people’s homes, instead of large centralised data centres, the heat generated can be used to keep homes warm as well as for their original function.

The servers are connected to each other via the internet and produce heat by performing complex calculations for a variety of companies and knowledge institutes, such as research for Leiden University Medical Centre.

Schneider is sure that Neradlize does have a product with mass market appeal. He said: “We are trying to make this a product that can be installed in thousands of homes, making it easy to install, maintain and make the business case even more attractive to the users.

“One thing that helps in making this work is joining forces with partners, as well as other parties, that provide high speed internet infrastructure.”

Whether in cities or further afield, there are interesting renewable energy options. Considering the 2020 EU target for the UK is that 15% of its energy comes from renewable sources, alternative options may become more prevalent as we draw closer to that date.

For these ideas to become mainstream however, they would have to move away, in the public’s consciousness, from being considered as offbeat options and become genuine alternatives to the way we currently produce energy.