How to power the urban revolution

Our swelling cities consume enormous amounts of energy and generate over 80% of global carbon emissions. We need to make them more self-sufficient, but how?

As I’ve said before, Earth is experiencing a uniquely urban event. The migration of people to cities is by far the biggest humans have witnessed, and it is having far-reaching impacts on the planet's geology, biology and chemistry. In a time of dwindling resources and rising greenhouse gases, how will the Anthropocene's urban revolution be powered?

Hubs of living, industry and transport, cities consume a large proportion of global energy resources and generate more than 80% of global carbon emissions. However, cities also represent the tightest concentration of energy users, making them ideal targets for efficiency improvements.

Electricity generation in the Anthropocene is likely to become decentralised and user-owned. The large power stations that currently supply cities will continue to exist, but individuals and communities will increasingly generate their own energy – through rooftop solar-thermal panels or ground-source heat pumps to heat water and buildings, and photovoltaic panels and wind turbines to provide electricity, for example. In the next decade, photovoltaic paint, blinds and glass that can generate electricity from sunlight will be used for public and private buildings. Garbage produced by householders and office workers is also likely to be used onsite to generate combined heat and electric power for residential and commercial blocks.

Many cities have plans to become independent from their national grid in the next couple of decades – some towns and villages have already managed it.

The urban environment will also likely generate its own electricity and heat through passive measures, rather like crystal radios used to. Pavements, streets, stairs and corridors in buildings may be fitted with piezoelectric generators that charge up through footfall. Other innovative energy generators that are in development include in-shoe piezoelectric devices, phone chargers that work from body heat, lighting that relies on bioluminescent bacteria or algae. Pipes carrying water could be embedded in dark asphalt in pavements, roofs or streets to collect the solar thermal energy generated during the day. In Paris, for example, the heat from passing trains and from the bodies of waiting commuters in an underground Metro station is being used to heat the apartment block above it. 

Efficiency measures in the generation, transport and use of energy will need to be vastly improved so that, for example, waste heat is recovered from boilers and stored or used elsewhere, leakage is reduced with insulation and improved materials, and automated ”smart” controls regulate energy use throughout buildings, from switching off lights in unoccupied rooms to adjusting heating and cooling systems. (I'll be discussing smart networked cities in my next column)

Decentralised and renewable energy production, which is often erratic or (in the case of solar or tidal) depends on the time of day, require a smart grid that is far more flexible than the 20th-century ones used in most cities today. A smart grid relies on sensors and feedback mechanisms to detect customer demand and adjust the load accordingly. For example, at peak demand – 7am when people all switch their kettles on – standby generators or storage devices can be brought online, while some gadgets, such as refrigerators or air-conditioning systems can be automatically dialled down or switched off for a short time.

Off the grid

Most countries are looking to adopt smart grids in the coming years, partly because they are far more efficient and so use less energy, but also because they allow for renewable energy integration – monitoring and sensing demand and supply in real-time and balancing loads accordingly – and for individual householders to feed their excess electricity back to the grid. Grid upgrades are essential – even large cities like New York have been experiencing crippling blackouts – but are expensive and disruptive, and resisted by energy-intensive industries such as cement works, which prefer “baseload” power plants. Currently, the intermittent nature of wind and solar generation is overcome by relying on back-up from plants powered by fossil fuels, nuclear or falling water (hydroelectric).

However, energy storage and distribution solutions are becoming increasingly urgent. Storing energy locally that buildings produce for later use will eventually be far more efficient than feeding it into the grid and using the grid as the energy store. There are plenty of options but none is perfect. Batteries are improving every year, with the most likely grid-scale option being liquid metal batteries, which are still at the prototype stage. Using the energy to compress air or steam, which can then be released and converted to electricity is another option. Others are looking at using energy to split water, creating hydrogen for storage, which can then be burned as a fuel when needed. Another option is to store the energy in the fast spin of a friction-free flywheel – the energy is then accessed by using the flywheel to turn a rotor in an electric generator, which slows the wheel.

In the Anthropocene, people will also have to curb the use of energy-guzzling electronics, or use renewable recharging methods – in Britain alone, electricity consumption from domestic appliances has doubled since the 1970s. Quick fixes, such as fitting low-energy lighting (20% of a building’s energy is consumed through lighting), and improving insulation are likely to become mandatory through policy tweaks to building regulations and property sales and rental codes. These are small steps, but we may see the day when all new buildings must be self-sufficient energy generators, with scores of neighbourhood grids running cooperatively in a networked city grid.

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