Proponents of clean energy have long seen the oceans as a great hope for the future. Ocean waves carry tremendous power, and could, in theory at least, provide much of the world's electricity.
But while other sources of renewable energy - such as wind and solar - have been widely adopted in recent years, wave energy has been slow to take off.
But that's changing. Scottish engineers will soon deploy an offshore "wave farm" in Portugal.
They have also signed a deal to build an even larger farm in Scottish waters.
Construction of the wave farm in Portugal has been underway for the past year in a busy shipyard in the Portuguese coastal town of Peniche.
Engineers are building large devices called the Pelamis system. They are massive, red, steel tubes that look like rounded train cars.
"Pelamis is actually the name of a surface swimming sea snake, which is quite an apt description for the machine when you see how it moves," says Max Carcas, who runs business development for the Scottish firm Ocean Power Delivery.
The firm has already deployed a prototype system around the Orkneys off the coast of Scotland.
These train-like tubes will eventually be linked together, four in a row, with the rows deployed in parallel to each other. More rows can be added to create more electricity and the rows of tubes are connected to the power grid via a single cable. Together, the hinged "snake" will be 140m (460ft) long.
The machine points into the direction of the oncoming waves.
The wave farms will produce electricity for thousands of homes
"A bit like a ship at anchor or a flag on a flagpole, it self orientates into the waves," said Mr Carcas.
"Waves then travel down the length of the machine and in doing so each of the sections, each of these train carriages, moves up and down and side to side."
These snake-like movements push hydraulic fluid through generators to produce electricity.
The plan is to place 30 of these devices five kilometres out to sea.
The machines will be anchored to the seafloor, and large cables will deliver the energy back to shore. The wave farm is expected to supply enough energy for 15,000 households.
On paper, it sounds simple.
Pelamis resembles a sea snake
But there is a reason why these devices are not being used widely around the world: the technology is still in the early development stages.
The machines are relatively ineffective at capturing energy, and are expensive.
Also, the energy produced is not cost competitive with electricity from other sources.
But Mr Carcas argues that wave energy holds a lot of promise considering it is still in its infancy.
"There's never been a new energy technology that's been economic out of the box.
"What gives us tremendous hope with this technology is that our opening costs are substantially below where wind power started 20, 25 years ago."
Wind power has reduced its cost by 80% since, as the technology has been deployed and optimised, he says.
"So, we think we've got a very compelling case for policymakers to put in place the right market enablement mechanisms."
And such "market-enablement mechanisms", in other words subsidies, are what Portuguese policymakers are providing.
The Portuguese government has agreed to pay a premium, called a "feed-in tariff," for wave energy to help kick-start the technology.
Engineer Teresa Pontes, from the National Institute of Energy, Technology and Innovation in Lisbon, says there are several reasons why the ocean is an ideal source of energy for Portugal.
"We have very good waves. We have a very long coast compared to the size of the country, and we have a population that is mainly located along the coast.
"So it's a match of conditions: natural, structural, and also political in this case."
Ms Pontes says wave energy could someday supply 20% of Portugal's power. Wave energy could also provide substantial electricity up and down the European coast, as well as along the west coasts of Australia, New Zealand, South Africa, and the United States.
Sean O'Neill, president of a Washington DC trade association called the Ocean Renewable Energy Coalition, says: "The total potential off the coast of United States is 252 million megawatt hours a year.
"That's equal to about six-and-a-half percent of our total capacity in the United States, equal to all the dams that we have in the US right now."
In the US, small wave energy projects - using different technologies from the one in Portugal - are currently being tested off New Jersey and Hawaii, and another project is being planned for Oregon.
But Europe is far out in front when it comes to embracing wave energy.
The European Union has proposed a commitment to generate 20% of its energy from renewable sources by the year 2020.
But technological and economic hurdles are likely to keep wave power from becoming a major source of energy in the near term, says Matti Vaino, who heads the European Commission's Energy and Environment unit in Brussels.
"At the moment, the big increases in renewable energy have not been in the wave area.
"Obviously they have been mainly in wind but also in the better use of biomass, and a little bit in solar.
"I would not expect that wave energy would be in the next couple of years making the major breakthrough."
But wave energy will have a small breakthrough in the next few months when the three Pelamis machines will be deployed in the ocean off the Portuguese coast this spring.
And there are further near-term projects in the works for England, Scotland and Spain.
Jason Margolis is technology correspondent for The World, a BBC World Service and WGBH-Boston co-production.