The meteoric rise of renewable energy has consequences for our electricity supply. While coal and gas fired power stations can generate electricity whenever you need it, renewables are intermittent by nature. So we need a backup plan for when the wind stops or the sun goes down.
All over the world, engineers and scientists are racing to solve one key problem; how to safely and efficiently store electricity at a huge scale but at a low cost. The quest is producing some truly remarkable ideas and this episode details three of them.

Rehearsals briefly resume amid uncertainty over the band's future. Following a productive meeting with Harrison, the Beatles agree to abandon the idea of a live show and relocate to their Apple Corps studio to formally record the new album. Billy Preston, a musician the group met in Hamburg, joins in on the sessions on electric piano.

Can new emission-free electric planes replace our polluting airliners and revolutionize personal transportation in our cities? The film takes a ride in some quiet, energy-efficient, prototypes that are vying for success as electric flight takes off.
The race is on to stop the climate emergency and we're seeing more and more people really paying attention to their carbon footprint. Aviation is a fast-growing offender, but is it too slow to respond. Could rapid progress in electric technology change the equation?

We face one of the greatest challenges in the history of humanity, to eliminate the fuels that have driven progress and technology for over a century, while our thirst for energy only grows. The sun is the biggest source of energy in the solar system. It's like a nuclear reactor in the sky, and it provides endless power. If we can harvest just fractions of this, it can power all our consumption. Innovators are searching for new ways to capture more of the sun’s power, and make it available through the night, everywhere.

As tides rise and fall twice a day, vast amounts of water swirl around the earth. This is a huge energy source that's currently largely untapped. An estimated 3000 gigawatts are available to be harvested globally, enough to power a third of the earth's homes. Yet compared to wind and solar, the technology needed to harness tidal power is still in its infancy. The power of the ocean’s tides is the last great untapped energy source on Earth. From sub-sea kites to floating platforms, teams of engineers are racing to perfect the technology to harness the vast flows of water.

Dr George McGavin and Dr Zoe Laughlin set up base camp at one of the UK's biggest sewage works to investigate the revolutionary science finding vital renewable resources and undiscovered life in human waste.
Teaming up with world-class scientists, they search for biological entities in sewage with potentially lifesaving medical properties, find out how pee can generate electricity, how gas from poo can fuel a car and how nutrients in waste can help solve the soil crisis. They follow each stage of the sewage treatment process, revealing what the stuff we flush can tell us about how we live today, and the mind boggling biotechnology being harnessed to clean it, making the wastewater safe enough to return to the environment.