What is wave energy?

Wave energy is an irregular and oscillating low-frequency energy source that can be converted to a 60-Hertz frequency and can then be added to the electric utility grid. The energy in waves comes from the movement of the ocean and the changing heights and speed of the swells. Kinetic energy, the energy of motion, in waves is tremendous. An average 4-foot, 10-second wave striking a coast puts out more than 35,000 horsepower per mile of coast.

Waves get their energy from the wind. Wind comes from solar energy. Waves gather, store, and transmit this energy thousands of miles with little loss. As long as the sun shines, wave energy will never be depleted. It varies in intensity, but it is available twenty-four hours a day, 365 days a year.

Ocean wave energy technologies rely on the up-and-down motion of waves to generate electricity. The first wave-power patent was for a 1799 proposal by a Parisian named Monsieur Girard and his son to use direct mechanical action to drive pumps, saws, mills, or other heavy machinery. Installations have been built or are under construction in a number of countries, including Scotland, Portugal, Norway, the U.S.A., China, Japan, Australia and India.

Where are the best waves?

Generally, extreme latitudes and west coasts of continents. View global wave atlas (based on satellite data) and another world wave map

The world’s first commercial wave energy plant, .5 MW, developed by WaveGen is located in Isle of Islay, Scotland.

Here is wave data from the National Data Buoy Center or the Army, or the Scripps West Coast wave data system. You can also try http://www.nodc.noaa.gov/General/wave.html or http://www.globalwavestatisticsonline.com/ for a fee. It has been estimated that the total available US wave energy resource is 23 GW- more than twice as much as Japan, and nearly five times as much as Great Britain.

What is the impact on the environment?

Unlike dams, wave power structures that are equally long-lived promise comparatively benign environmental effects. Wave power is renewable, green, pollution-free, and environmentally invisible, if not beneficial, particularly offshore. Its net potential (resource minus “costs”) is equal to or better than wind, solar, small hydro or biomass power.

What are the anticipated wave energy cost?

It has been estimated that improving technology and economies of scale will allow wave generators to produce electricity at a cost comparable to wind-driven turbines, which produce energy at about 4.5 cents kWh.

For now, the best wave generator technology in place in the United Kingdom is producing energy at an average projected/assessed cost of 7.5 cents kWh.

In comparison, electricity generated by large scale coal burning power plants costs about 2.6 cents per kilowatt-hour. Combined-cycle natural gas turbine technology, the primary source of new electric power capacity is about 3 cents per kilowatt hour or higher. It is not unusual to average costs of 5 cents per kilowatt-hour and up for municipal utilities districts.

What are some of the devices that harness wave energy?

There are three basic methods for coverting wave energy to electricity:

  1. Float or buoy systems that use the rise and fall of ocean swells to drive hydraulic pumps. The object can be mounted to a floating raft or to a device fixed on the ocean floor. A series of anchored buoys rise and fall with the wave. The movement “strokes” an electrical generator and makes electricity that is then shipped ashore by underwater power cable
  2. Oscillating water column devices in which the in-and-out motion of waves at the shore enter a column and force air to turn a turbine. The column fills with water as the wave rises and empties as it descends. In the process, air inside the column is compressed and heats up, creating energy the way a piston does. That energy is then harnessed and sent to shore by electrical cable.
  3. “Tapered channel” or “tapchan” systems, rely on a shore-mounted structure to channel and concentrate the waves, driving them into an elevated reservoir. Water flow out of this reservoir is used to generate electricity, using standard hydropower technologies.

Why ocean wave energy?

With acknowledgement to Capital Technology, Inc.”While lagging behind wind and solar in commercial development, ocean wave power is a more promising resource than either:

  • Because waves originate from storms far out to sea and can travel long distances without significant energy loss, power produced from them is much steadier and more predictable, both day to day and season to season. This reduces project risk;
  • Wave energy contains roughly 1000 times the kinetic energy of wind, allowing much smaller and less conspicuous devices to produce the same amount of power in a fraction of the space;
  • Unlike wind and solar power, power from ocean waves continues to be produced around the clock, whereas wind velocity tends to die in the morning and at night, and solar is only available during the day in areas with relatively little cloud cover;
  • Wave power production is much smoother and more consistent than wind or solar, resulting in higher overall capacity factors;
  • Wave energy varies as the square of wave height, whereas wind power varies with the cube of air speed. Water being 850 times as dense as air, this results in much higher power production from waves averaged over time;
  • Estimating the potential resource is much easier than with wind, an important factor in attracting project lenders;
  • Because wave energy needs only 1/200 the land area of wind and requires no access roads, infrastructure costs are less;
  • Wave energy devices are quieter and much less visually obtrusive than wind devices, which typically run 40-60 meters in height and usually requiring remote siting with attendant high transmission costs. In contrast, 10 meter high wave energy devices can be integrated into breakwaters in busy port areas, producing power exactly where it is needed;
  • When constructed with materials developed for use on off-shore oil platforms, ocean wave power devices (which contain few moving parts) should cost less to maintain than those powered by wind;

Even though wave energy is at the very beginning of the manufacturing learning curve, capital costs per net kw are already down in the range of wind energy devices, and below solar. In areas of higher power costs, such as diesel-based communities not connected to the grid, investment returns from wave energy projects are potentially very attractive. In 1909, ocean wave power was used to light lamps on the Huntington Beach Wharf until a storm carried the apparatus out to sea. Long-term reliability of the OWC technology has now been demonstrated, with one device in India still going strong after 10 years of continuous operation.”

View a video explaining wave energy: