In Japan, a smelly waste product is being reimagined as a potential clean fuel of the future that is powering cars and tractors.

We're being eyed suspiciously by dozens of cows. Their breath fogs cartoonishly from their nostrils.

It's a brisk morning in snowy Hokkaido, an island in the north of Japan. The cold air carries the distinct scent of cow manure – a smelly yet familiar side-effect of the region's thriving dairy industry. Accounting for 20% of the country's landmass, this island is the second-largest in Japan. It's also home to over a million cows, which produce over half of the country's milk and dairy products.

We are visiting one farm in Hokkaido that wants to transform the source of the pungent aroma in the air into something valuable. They are turning cattle manure into hydrogen.

When it is burned, hydrogen does not emit carbon, making it an attractive alternative to fossil fuels. There are widespread hopes it could be used as a sustainable fuel to heat homes and power cars, trains, aircraft and ships in the future.

But the most common way of producing hydrogen today involves using methane – a fossil fuel piped up from deep underground, meaning it is still associated with significant carbon emissions. Hydrogen can also be produced by splitting water using electricity, but this can be expensive and is only low carbon if renewable sources of electricity are used.

The Shikaoi Hydrogen Farm, however, is using a different source – a waste product that there is no shortage of on Hokkaido. Around 20 million tonnes of cow manure is generated in Hokkaido annually. If not treated correctly, it can be an environmental burden, producing significant methane emissions as well as affecting water quality if allowed to leak into streams and rivers. So can it instead be used as a source of sustainable energy?

"This project to produce hydrogen from livestock manure originated in Japan and is unique to this place," says Maiko Abe from Air Water, one of several companies involved in the hydrogen farm project. We are visiting the facility in Shikaoi, a town in central Hokkaido, to film an upcoming episode of the BBC's TechXplore focusing on Japan. "Shikaoi accounts for 30% of Hokkaido’s cow waste and urine, so it has great potential for renewable energy."

Launched in 2015 by Japan’s Ministry of the Environment, the project aims to convert agricultural by-products into hydrogen to supply the local, rural community in a circular economy. The cow excrement and urine is collected from local dairy farms before being fed into a anaerobic digester at a central facility. Here bacteria break down the organic waste to produce biogas and a liquid fertiliser. The biogas is then purified into methane that is used to manufacture hydrogen.

The plant now has a hydrogen production capacity of 70 cubic metres (18,500 gallons), with an onsite fuelling station that can fill around 28 vehicles fitted with hydrogen fuel cells per day, says Abe. Although the fuel can be used by cars with fuel cells, the plant's fuelling station has been specially designed to accommodate agricultural vehicles such as tractors and forklift trucks. These farm vehicles are difficult to electrify with batteries due to their size and the type of work they do. The hydrogen-powered vehicles are used around the farms' sites, reducing the emissions that would otherwise be created by using other fuel sources.

Cattle-made-hydrogen is also stored in canisters that are transported to provide power and heat to other facilities in the area, including a local sturgeon fish farm and the nearby Obihiro Zoo.

But hydrogen isn't without its problems. It needs to be stored in high-pressure tanks as a gas, and can be........

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