IN south Denmark, the ferry Ellen sails quietly from Fynshav to the island of Æro in the west Baltic Sea without trailing even the slightest puff of diesel fumes in her wake.

Powered entirely by batteries charged while in harbour using electricity generated by wind turbines, the 196ft ferry easily covers 22 nautical miles (25 miles), between charges – Ardrossan to Brodick is about 14 miles – while carrying up to 200 passengers and 30 cars.

Green and clean, it has been said the only oil on board – other than what’s used to keep the gearbox greased – is used for cooking chips in the onboard cafe.

Built at a cost of €21.3 million (£185m) – partly funded by the European UnionCommission – stacked floor to ceiling in its engine room are 840 lithium-ion batteries with a capacity of 4.3MWh – roughly the annual electricity usage of a typical UK household.

And, unlike diesel ferries pumping out noxious fumes, it is expected to reduce CO02 emissions by 2,000 tonnes a year.

All of which may sound like cutting-edge ferry travel – and for users of CalMac’s ageing fleet, it may even sound positively space age. Yet Ellen has been operating for two years and is far from the only battery-driven ferry operating in Nordic waters.

The world’s first electric car ferry, MV Ampere, was launched in 2015, and carries up to 260 passengers and 160 cars on a 20-minute route across Norway’s longest and deepest fjords.

Also, two months ago, the world’s largest all-electric ferry, Basto Electric – with capacity for 600 passengers and 200 cars – began operating on a route across an Oslo fjord.

In a sign of its commitment to emission-free ferry travel, Norway’s government has now said ferries operating on the Bodo and Moskenes route – the country’s longest ferry connection – must be hydrogen-powered from 2024.

In comparisonCompared to all of that, CalMac’s three diesel-hybrid ferries appear just a bit outdated, never mind the continuing crisis affecting its broken-down diesel-fuelled MV Loch Seaforth, its ageing vessels and the long-running saga of the construction of two overdue and over-budget new ferries.

As Norwegians cruise towards green hydrogen, questions in the UK swirl around the decision to fuel the delayed vessels with marine diesel and liquefied natural gas (LNG) that needs to be imported from the Middle East and transported by lorry from south England.

With pressure growing to curb marine emissions, the UK Government’s climate-change commitment aims to cut carbon emissions by 78 per cent by 2035 and, with the COP26 spotlight shining bright, some may wonder how we are ever going to catch up.

“Norway is the exemplar,” says Diane Gilpin, founder and chief of Smart Green Shipping, a consortium looking to fit retractable aluminium sails to vessels that can work with fossil or green fuel, driving down costs and creating a lower, or zero, carbon journey.

“We’re behind, but not woefully behind. The key thing is that the Prime Minister has said shipping emissions are to be included in the domestic carbon budget – until now, any emissions around the waters of the UK were included in the global shipping budget. That has provided a stimulus in the UK to figure out how to de-carbonate shipping.”

She believes Scotland, with its technical expertise, engineering heritage, plethora of ferries and plenty of wind power, is perfectly placed to pioneer new forms of low-carbon, marine technology.

“There’s a great opportunity for small and mighty maritime nations to identify lucrative technology solutions that can be designed and developed on the Clyde and then the solutions can be exported worldwide.

“The Department for Transport estimated that almost half the world’s ships would be fitted with wind-assist devices by 2050.

“There are lots of different possibilities,” she continues. “You have wind turbines that produce more electricity than a community can consume. It could be converted to hydrogen that could be used as a shipping fuel in different ways – within a battery or liquid fuel.

“That’s excellent, but it’s more expensive than current fossil fuel. Combine that with wind – so half the power is from wind and the other half from this ‘green’ fuel, and you’re putting a green ship on the water.”

She adds: “Scotland has a real opportunity – wind technology could be developed in Scotland to give it that niche that could if it moves quickly to develop it.”

Smart Green Shipping is currently involved in “detailed conversations” with Scottish Enterprise and private investors and is working with Clyde-based naval architects and marine engineers Malin on its FastRig proposition.

The next stage is to fit the sails on to a working merchant ship to prove that the automated, retractable, recyclable technology works in the real world.

“We have a huge energy transition challenge, but there’s no silver bullet,” she says. “However, people now recognise we can’t wait any longer – we are in a climate emergency.”

There are obstacles to overcome. Writing in The Herald recently, Kevin Hobbs, chief executive of Caledonian Maritime Assets Ltd, which owns ferries, ports, harbours and infrastructure across the west coast of Scotland, the Firth of Clyde and Northern Isles, warned: “The feasibility of fully electric ferries will depend largely on the grid capacity of the islands they serve.

“Ferries will need to plug in and charge at each port, and if an island’s electrical capacity cannot support this without disrupting the energy supply to residents and businesses, then it’s a less feasible option. It will potentially require solid investment in the islands’ energy generation infrastructure or enhanced grid interconnectors.”

The logistics of powering ferries using new technologies is being hammered out in Orkney, where the European Marine Energy Centre is preparing to begin testing the world’s first hydrogen-fuelled ferry on the 25-minute, Kirkwall-to-Shapinsay route. It will initially use locally produced hydrogen to run some of its auxiliary systems with plans to eventually operate the vessel entirely on the “green” energy.

Neil Kermode, managing director of EMEC, believes the ferry could be fully hydrogen powered by this time next year.

“It’s not about, does hydrogen work?”

he says. “We know it does. It’s about how we get it working in a marine environment, how to store it, what skills are needed, training. All of that needs to be worked out.

“When it comes to electric ferries, we are lagging behind some of the stuff being done in Norway.

“A lot of the climate talks in the past excluded shipping and aviation from national plans, but now everyone is on board. We can’t just say it’s not our problem.

“It would have helped if it had started 20 years ago, but there’s no point crying over spilt milk.”

He adds: “Scotland has about 50 ferries, they put a big carbon footprint down for us all. Ferries last 25 to 30 years and we have to be careful that, when we replace them, we replace them with vessels that will serve us well in 30 years’ time.”

But it’s not only ferries to the islands that carry a carbon cost: could electric-powered flight be closer than we think?

In mid-July, American aviation company Ampaire will operate a series of low-carbon test flights between Caithness and Orkney using a hybrid-electric aircraft called the Electric EEL.

Seven round trips are planned across a 35-mile route between Wick and Kirkwall, as part of a £3.7m project, Sustainable Aviation Test Environment (SATE).

As well as testing different types of low-carbon aircraft – using electric, hydrogen and sustainable aviation fuels – the project also aims to identify the operational infrastructure needed to support them, and will examine using drones to deliver essential items such as medical supplies to remote health centres.

The low-carbon flights could whizz passengers form Caithness to Orkney in a mere 20 minutes.

Electric-powered flight is certainly gathering pace. In America, Bye Aerospace’s eFlyer 800 combines sleek private-jet style looks, room for eight people and a 575-miles range thanks to a grid of electric cells spanning the airframe.

Another US developer, Regent, is working on a 10-passenger zero-emissions part plane-part boat, that can depart a harbour on a hydrofoil before lifting off the water to hit speeds of up to 180mph.

Closer to home, a six seater electric plane said to be Europe’s largest emission-free aircraft completed its first UK test flight in June last year.

Powered by hydrogen, the Piper Malibu flew several short journeys from Cranfield Airport in Bedfordshire, as part of a project funded by the UK government.

As for how we travel around the islands in the future, Kermode is clear: it will be different.

“At the end of the day we don’t have a choice,” he adds. “We can’t keep burning carbon-based fuels.

“We know we will have to change that secret is to find a way to be more efficient and do it as cheaply as possible.”

Alex Cross, head of engineering, performance and policy at CalMac, said: “CalMac has made significant reductions in our carbon footprint through changing the way we operate, but the long-term nature of shipping assets means investment decisions made now will impact well into the future.

“Whatever the future solution is for transport, it is clear renewable energy will play a major part - whether it is used for the production of hydrogen or ammonia, or for the provision of clean energy to charge battery-operated ferries.”