by Chris Kulczycki
Mon Nov 21st, 2005 at 04:19:18 AM EST
From the front page -- DoDo
Excuse the bad surf lingo; it's an American thing. But this is about wave energy, not tidal energy; that was last week. Who doesn't love to watch waves crash against a rocky coast or surfers riding a perfect wave? And who doesn't love the feeling of a heeling sailboat bashing to windward in a steep chop, other than the fellow with his head over the transom?
|Waves are formed by wind's friction over the surface of the water. They can travel incredible distances. That huge roller in Huntington Beach may have started as a ripple off the Hawaiian coast. Waves are pure energy moving through the water, energy that could be turned into electricity. Anywhere there are waves; there is free sustainable power. All we have to do is figure out how to capture it. Thanks to recent research that's starting to happen.|
To learn of its potential, of working European and other prototypes, and where research is heading, dive below the fold!
The map below shows annual average wave power in kilowatts per metre of crest width for various sites around the world. Any area over 15kW per metre can generate power at competitive prices.
And here is a map showing wave potential in Europe:
Why Wave Energy
Wave energy has several advantages over wind, solar, and even tidal power.
· Energy density is very high.
· Wave energy is available most of the time; the ocean is rarely `flat'.
· Many more potential sites are available. It is far less dependent on geography.
· Generation plants can be miles from land and not be an eyesore.
· No valuable real-estate is required,
· A 100MW plant requires only about 1 square mile.
· Being modular, it is easy to increase or decrease capacity.
There are several ways to convert wave energy to electricity. Below I'll outline some of the most promising methods.
Power from Sausages
One of the world's first wave generation stations is in Portugal. The technology they use is Pelamis Wave Energy Converters, affectionately known as sea sausages, and manufactured by Ocean Power Delivery LTD of Edinburgh. They are huge hinged tubes, about 120m long, the size of five boxcars, that float (tethered) on the surface of the ocean. As they are flexed by waves they generate electricity. Large fleets of sausages could be anchored in an area and connected to an underwater cable bringing the power to shore. 33 sausages generating 22MW will eventually make up the Portuguese fleet if all goes as planned.
From Ocean Power Delivery's site:
The Pelamis is a semi-submerged, articulated structure composed of cylindrical sections linked by hinged joints. The wave-induced motion of these joints is resisted by hydraulic rams, which pump high-pressure oil through hydraulic motors via smoothing accumulators. The hydraulic motors drive electrical generators to produce electricity. Power from all the joints is fed down a single umbilical cable to a junction on the sea bed. Several devices can be connected together and linked to shore through a single seabed cable.
Bobbing for Electricity
Several companies have developed buoys that generate electricity. They bob in the waves activating a sort of piston connected to a generator. Ocean Power Technologies, Inc.
makes the buoys shown below.
AquaEnergy Group, Ltd also makes wave powered generating buoys. But these use a hose pump; pressurized seawater is directed into a conversion system consisting of a turbine driving an electrical generator. They are planning the installation of their first offshore power plant in Makah Bay, WA, USA, with a goal of initial power delivery on one megawatt of capacity by the end of 2006.
Wavgen of Scotland manufactures the LIMPET (Land Installed Marine Powered Energy Transformer) is a shoreline energy converter. The first unit is sited on the island of Islay, off Scotland's west coast and providing grid power. Another station is planned for the Faroes Islands. This second plant will utilize tunnels cut into the shore's steep sea cliffs. This first drawing is from their site:
Here's another, better, drawing:
Wave Energy Of Norway has installed and is testing another type of wave powered generation scheme. The first installation is on shore, but it could also be incorporated into breakwaters or even floating barges. The concept is a little more complicated; this is from their site:
The Seawave Slot-Cone Generator (SSG) concept is an wave energy converter based on the wave overtopping principle utilizing a total of three reservoirs placed on top of each other, in which the potential energy of the incoming wave will be stored. The water captured in the reservoirs will then run through the multi-stage turbine for electricity production. Using multiple reservoirs will result in a high overall efficiency.
The SSG gives the advantage to harness the wave energy in several reservoirs placed one above the other, resulting in high hydraulic efficiency. The SSG is built as a robust concrete structure with the turbine shaft and the gates controlling the water flow as virtually the only moving part in the mechanical system.
The SSG is flexible with regard to range of application. It can be utilized as a floating or a fixed offshore installation or a shoreline installation integrated in a breakwater installation. The SSG can be utilized for:
· Production of electric power
· Production of hydrogen by use of electrolysis
· Production of clean drinking water by use of osmosis
Like any new technology, there are many small players and prototypes floating around. But as plants are built the best designs will quickly be adopted. For the most part these are simple and robust systems that are easy to install and maintain. Some designs are predicted to deliver power at costs well below even wind and tidal generation. Several developing countries have expressed an interest in building them. Being modular and easily scalable they are perfect for village and island micro-grids, or large national grids.