OCEAN ENERGY TRAWLERS
Francis J. M. Farley
We are facing a severe power shortage and may be on the verge of runaway global warming. Oil and coal produce greenhouse gases. Fracking for methane is a disaster; when burnt it produces carbon dioxide (a little less than oil and natural gas). But there is always leakage from the mines and methane has 60 times more greenhouse effect than carbon dioxide. On top of that the geological damage will bring unpredictable consequences. Onshore wind turbines are ugly. Off shore wind is expensive, both to install and to maintain. Nuclear accidents are rare; but when they happen, devastating. So what can we do?
The restless oceans are full of energy. A new way to harvest this resource is with ocean energy trawlers. A special ship goes out to sea; once on station it deploys a string of floating wave energy converters which generate electricity. This is used on board to electrolyse sea water, producing hydrogen which is collected in large tanks. After a few weeks the ship picks up its machines, goes back to port and offloads the gas to a regular power station. Hydrogen is green: when burnt it just turns into water, lovely water, no greenhouse gases at all. With a minor modification you can even drive your car on hydrogen ...... no fumes, no smell !
Britain is the world leader in wave power. But there are problems. The machines must be anchored where the waves are strong but in storms they get too strong: anchors drag, cables snap. Electrical connections to the shore are tricky: they must be buried to avoid damage. Maintenance in rough water is hazardous and often impossible. Wave power is fickle, it varies from day to day, hour to hour, not matching the demand. In northern Scotland where the waves are good, few people are living. A high power grid connection must be provided
to the cities further south. All these factors add to the cost.
Ocean energy trawlers avoid these obstacles. A small crew on board maintains the machines. There is no connection to the shore. No environmental questions, no problems with fish or coastal shipping. The captain keeps out of storms. He goes where the waves are good and delivers the hydrogen wherever needed, with attractive export potential. Wave variations from day to day do not matter; the harvest rolls in step by step and when the ship is full you deliver the load. In summer time, it just takes a little longer.
Is it feasible? Yes! Every step in the process uses known technology. Can we afford it? Maybe. A small trawler with wave energy converters on board could pick up a couple of megawatts and generate 36 tonnes of hydrogen in a month. Using the price of natural gas, that is worth about 36,000 euros at the power station, enough to pay for the trawler and the crew. A bigger ship could carry more wave energy converters. When it gets to the right area, it deploys them in a long interconnected line . It could pick up about 40 megawatts and deliver twenty times more fuel; 720,000 euros per month is good fishing.
How does it compare with natural gas? Natural gas in Europe costs 359 euros per tonne. Tonne for tonne, hydrogen produces 2.8 times the heat. So hydrogen fuel is worth 1000 Euros per tonne in the market, and free from carbon.
Electrolysis of seawater also produces oxygen. This is used in engineering and medicine and is worth at least 100 Euros per tonne. For each tonne of hydrogen you get 8 tonnes of oxygen so this can almost double your income.
Hydrogen is hard to store and transport. You need massive pressure vessels. A better option is sodium, a soft silvery metal, lighter than water; you can cut it with a knife. Sodium ingots are easy to store and deliver. Put it into water and hydrogen bubbles off. On the trawler you can electrolyse a molten sodium salt and turn the power into sodium: it's a standard process.
Everyone talks about the "hydrogen economy"; using hydrogen instead of coal, oil and natural gas. But it is hard to store. The "sodium economy" might be more practical. Imagine buying capsules of sodium at the gas station ...... fill 'er up; I'll have 20 kilos. Yes, sodium can catch fire and you need to take precautions. But the same applies to gas and petrol. We just have to learn the right procedure.
How many trawlers would we need? How big should they be? Lots of small ships, or a few large ones? How do you make small wave machines so the trawler can pick them up? What is the best technology? All these questions have to be addressed. And where would they go?
The best waves are off west Africa where the trade winds blow. Regular smooth and serene for most of the year, with no shipping to get in the way. The Bay of Biscay is also good. Where the Atlantic swell meets the continental shelf the waves get shorter and steeper, which is good for wave energy. Those unpredictable Scottish waters looks less attractive.
Ocean energy trawlers can make something else ..... water! Instead of producing hydrogen or sodium for power stations, use the energy to desalinate seawater. This is a standard process. The trawler can then deliver fresh water to the many countries in hot climates that are desperately thirsty. In Israel fresh water is worth 0.55 Euros/tonne. Our small trawler could produce 5,000 tonnes of fresh water per day, which is worth 2500 Euros. Cruise the Indian ocean for a week, deliver water to Yemen and pocket the cash.
Something like 40 of these larger 40 MW trawlers could bring in the fuel for a large power station. They would surely cost less than another nuclear reactor. So if this takes off there would be a substantial fleet of ocean energy trawlers, made by British industry and manned by British sailors. We would not depend on foreign gas, or shale gas, or whatever. England would be green and unpolluted. Britannia would rule the waves.