When will our electricity come from the sea?
If you've ever struggled to walk across the deck of a boat as it rolls in a choppy sea, or tried to stand up against breaking waves at the beach, you'll have felt the might of the ocean.
It feels like there's a lot of power there too, so getting energy from the waves of the sea sounds as if it's got real potential. For World Service listener Michael McFarlane, it's a question that's been on his mind for years.
"I live in Jamaica and we are never very far from the sea… Electricity generation [here] is mainly based on fossil fuels," he says.
So why isn't the ocean powering Michael's home yet?
In order to tackle this question for the World Service programme Crowdscience, first, there was a language problem to unpick.
Deborah Greaves, Professor in Ocean Engineering and Director of the COAST Laboratory at the UK's Plymouth University explains: "We've tended to use "marine renewable energy" to describe wave and tidal energy…[it's] energy which can be extracted from the movement of the oceans in the marine environment."
Large tidal power generators already exist in selected locations around the world - the La Rance River estuary plant in Brittany, France, opened in 1966, and the world's current largest tidal power station is at Sihwa Lake in Gyeonggi Province, South Korea, costing 313.5 billion South Korean won (£212 million GBP or $263 million USD).
Expense is one factor that currently limits the worldwide number of tidal power plants. Environmental concerns are another, as some places with particularly strong tides are also sensitive ecosystems, such as estuaries.
And there's one more detail that's particularly relevant for listener Michael: As anyone who's been lucky enough to spend time on a beach in Jamaica knows, the tides there don't go in and out that much. It can be by as little as centimetres, compared with metres at a time in other locations around the world.
For our programme, this means we turn to wave power, which, as Prof Greaves tells us, is still in the early stages of development. "Wave energy on the other hand involves extracting the wave energy motion in a device, and there are a huge number of different approaches to how you can do this."
Out at sea, water doesn't always move as predictably as in a tide. Ocean waves are whipped up by winds, and can be all over the place, interacting from all directions. It's this irregularity and difference which means that energy can be harvested in many ways, and there are thousands of patents registered for a whole variety of different approaches.
You can get some idea from the devices' myriad of names, which include: The Limpet, the Frog, Mighty Whale, Wave Roller, Wave Dragon, the Oyster, and the Penguin. The latter bobs up and down in the sea like a real penguin does - although it looks a bit like a cartoon block of cheese - some names aren't totally representative.
But, variety and excellent names aside, what has the most potential to generate our electricity - wave or tidal? "There's more potential for wave energy in terms of the resource because the tidal resource tends to be located in specific positions round the coastline.
"So there's actually a greater potential for wave energy, but at the moment it's further off being commercially developed," says Deborah Greaves.
At the Coastal Ocean and Sediment Transport laboratory at Plymouth University in the UK, Professor Greaves oversees new wave power devices being tested in their giant Ocean Wave Basin. Over 100 cars could be parked inside the 35m long, 15m wide and up to 3m deep tank - if it weren't full of water.
And at one end, there are 24 paddles that can be individually controlled to generate waves approaching 1m in height. This means that a variety of waves can be created - from the sort of waves that you might see at the beach, to a much more mixed-up surface with different sized and timed waves from many directions, which the COAST team call a sea state.
As big as this sounds, this is only laboratory scale - it's not a patch on the open ocean, but it's where wave energy devices start out. Deborah explains: "We can only go up to a certain scale here...and so in order to really understand how your device is going to perform in the sea, and some of the additional challenges in installing it and getting it to survive in a marine environment.
"All of those things we can't test but they can be tested at larger scale at a nursery site in the sea."
FaB Test in Falmouth Bay is one such place. Heading out about a mile into the sea on a research vessel illustrated how this stage helps wave energy device developers move their models forward.
"It enables us to make sure that we have access to the devices... At the same time, this area here is providing us with very rough and extreme conditions. We have seen waves close to 10m," said Prof Lars Johanning of Exeter University, casually leaning on one leg and maintaining impressive stability whilst the CrowdScience team clung on to the boat rails and their microphones.
"In the real world as you've just experienced here... you've got waves from different directions, you've got a current, you've got wind, you've got salt water - so you've got corrosion," Prof Johanning explains.
"It's a small thing that goes wrong quite often unfortunately but it stops you from going further. Or of course then, you address it."
Prof Johanning tells us that the real challenge for wave energy devices is surviving extreme conditions. "You would like to have very nice looking waves from one direction if possible... very smooth and regular. That is not the real sea. The real sea is a bit different unfortunately so you have to overcome this. We can design for these conditions but we also have to make sure that it is cost effective."
Once safely off the boat and back in the car, we set off from the nursery site towards what we were affectionately terming as 'big school' for wave energy devices (much to our contributors' amusement). Here, standing on a glorious and very windy beach, we met Stuart Herbert, Commercial Director of Wave Hub Ltd.
"Wave Hub you can think of as a large electrical extension lead. So we have a cable which is 25km long - very thick cable - and it goes underneath the sand we're standing on and heads out to the sea and ends up about 10 miles off [the town of] St Ives," said Stuart.
Given the wind and wintry conditions, this was the closest we could get today - thankfully. Mr Herbert tells us: "[The conditions have been] as high as 15 metres in the last couple of years.
"Bigger is better to a certain extent but these devices have to survive out there… This site has an excellent wave resource and a good place where we can connect to the National Grid… There's other places like Australia, Western Ireland, Portugal, France, Spain also have very good wave resource."
So what does he think about listener Michael McFarlane's question: Could the energy of the sea provide us with all our electricity?
"What a fantastic question! And Jamaica has a good wave resource." A promising start. But what's the timeline, and could it happen?
"It has been estimated that there's more than twice as much wave energy out there than is required to power the whole world. However, capturing that wave energy, capturing this wild and unpredictable resource, is quite a challenge. It's going to take some time for these devices to get to a commercial stage where we can deploy them in multiple numbers all over the world.
"Would we ever get to a stage where we can power the whole world from wave energy? I have to be absolutely honest with you and say that's really not going to happen. There have been some estimates made that it could be 15-20% in the UK."
So, not all of our electricity then. But island communities could still make use of some wave power in the future, especially because, as Mr Herbert says, "A lot of island communities at the moment either have no power or get their power from expensive sources like diesel generators."
Michael was far from wrong in thinking that the sea appears to offer this vast resource of free power. But the challenge is making devices that can harvest the most energy from those unpredictable waves, in a cost effective manner, and survive the relentless bruising and battering of the environment.
As Stuart Herbert concludes: "Wind turbines have been around for at least 20 years... Wave energy is at least 10 years behind that. So 10 years from now I would imagine that we'll start seeing commercial arrays of wave energy devices producing really useful amounts of power."
BBC CrowdScience, Wave Power first airs on the World Service at 1132 GMT on Saturday 24th December. Listen online and download the podcast.