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.

In this mind-bending series, Professor Jim Al-Khalili explores the vast range of size in the universe, from tiny atoms to gigantic, interconnected galaxies.
In the first episode, Jim will enter the world of objects that are too tiny to glimpse with the naked eye. Starting with the smallest insects, he moves on to encounter living cells with amazing superpowers and confronts some of humanity's deadliest enemies in the form of viruses. Going smaller still, he encounters wondrous new nanomaterials such as graphene, discovered by physicist Andre Geim. These are revolutionising engineering, medicine, computing, electronics and environmental science. Finally, Jim comes face to face with the fundamental building blocks of the world around us – atoms – and reveals why understanding the science of the 'small' is crucial to the future of humanity.

In the second episode, panic strikes the community as a full-blown catastrophe looms. Locals mobilize to confront the authorities and protest the nuclear power industry.
Twenty-eight hours after the accident began, the lieutenant governor appeared at a news briefing to say that the plant's owner had assured the state that 'everything is under control'. Later that day, Scranton changed his statement, saying that the situation was 'more complex than the company first led us to believe'. There were conflicting statements about radioactivity releases. Schools were closed and residents were urged to stay indoors. Farmers were told to keep their animals under cover and on stored feed.

In the third episode, during cleanup at the plant, insiders claim that cost-cutting measures and intimidation tactics create a danger war force than the accident itself.
Several state and federal government agencies mounted investigations into the crisis, the most prominent of which was the President's Commission on the Accident at Three Mile Island, headed by chairman John G. Kemeny. The investigation strongly criticized Babcock & Wilcox, Met Ed, Graphics processing unit, and the Nuclear Regulatory Commission for lapses in quality assurance and maintenance, inadequate operator training, lack of communication of important safety information, poor management, and complacency.
Kemeny said that the procedures and that the control room were greatly inadequate for managing an accident.

Our frozen planet is changing. In this final episode, we meet the scientists and people dedicating their lives to understanding what these changes mean, not just for the animals and people who live there, but for the world as a whole.
Our journey begins in the Arctic, where every summer huge quantities of ice calve from the edges of Greenland’s melting glaciers. On top of the ice cap itself, glaciologist Alun Hubbard descends into a moulin to try to understand the mechanisms that are driving this historic loss of ice.
Elsewhere in the Arctic, it’s not just land ice that is disappearing. In the Gulf of St Lawrence, Canada, biologists are trying to find out how the loss of sea ice will impact the lives of baby harps. In Arctic Russia, with the loss of summer sea ice, more and more polar bears are arriving on the island of Wrangel. Here, a local ranger and scientists are braving the hungry bears to assess their future survival.
Loss of sea ice impacts not just wildlife but people too. In the remote community of Qaanaaq, Greenland, local Inuit hunters are finding the ice too dangerous to travel and hunt on, risking their traditional way of life. And these changes happening in the Arctic have the potential to affect people far beyond. On Alaska’s open tundra, bubbling lakes hint at the gases being released from the previously frozen soil, including the potent greenhouse gas methane.
There is one place where the full scale of a melting Arctic can be best witnessed - from space. Based in the International Space Station, astronaut Jessica Meir looks down at forest fires across Europe and reflects how our changing weather patterns are interconnected.
Rapid ice loss is also happening across the high mountains of the planet’s continents. Glaciologist Hamish Pritchard uses a sophisticated helicopter-strung radar system to try to quantify how much ice is left in the previously uncharted glaciers of the Himalayas. It’s important as, downstream, some 1.2 billion people rely on glacial meltwater as their primary source of fresh water.
Finally, in Antarctica, we meet Bill Fraser, who has dedicated 45 years of his life to studying the Adelie penguin. Over this period, he has witnessed changes in weather conditions and the extinction of entire colonies. These ‘canaries in the coal mine’ are a sign that all is not well, even in the remotest place on earth. And changes here have the potential to affect all of us, so an international group of scientists is on an urgent mission to assess the stability of a huge body of ice known as the Thwaites ice shelf. If this plug of ice melts and slips into the ocean, it will raise global sea levels, impacting coastal communities across the planet.
The unprecedented changes our scientists are witnessing may be profound, but there is hope that, through a combination of technology and willpower, there is still time to save what remains of our frozen planet.

Voyager, the most ambitious space mission in history. They're the first probes to truly explore half the planets in our solar system: Jupiter, Saturn, Uranus and Neptune. These went from dots of light in the sky, to real worlds. The Voyager missions have ventured far beyond where other probes have explored. They're the first spacecraft to taste interstellar space, exploring further than any human made spacecraft has gone before. They are the greatest space mission ever. The legacy of Voyager is our remnant, it is our memory. It is a sampling of humanity that is out there now among the stars. And if they last until the death of the Universe, as the final stars fade, and everything goes dark, they will be humanity's final statement: ‘We were here.’
In the last episode of the season 10, experts explore the ultimate, ongoing mission of the Voyager spacecrafts.