Wave Energy Enjoys Breeze at its Back

Wave energy holds enormous potential, but is far less further along in its development than other renewable energy sources such as wind turbines and solar panels. But some projects are emerging that tackle many of the daunting challenges engineers face such as wave variability, corrosiveness of seawater and environmental concerns.

The potential is huge: in wave rich areas, 100-200 megawatts of power in theory could be generated for every kilometer of coastline. But even if that happens, such potential won’t be achieved for years if not decades. Indeed, wave energy projects are starting out much, much smaller.

For example, a wave pilot project on the Douro River in Portugal will generate about 750 kilowatts promising enough power for about 750 homes. That’s comparable to the optimal output of a wind turbine with a rotor sweep of about 140 feet. And the Norwegians have one third scale model of a system that could generate 2.5 megawatts, comparable to largest wind turbines with about an 80 meter rotor sweep, according to MIT professor Chiang Mei, who has studied ocean wave energy since the seventies. Mei is working with Portuguese academics and scientists on the Douro project by performing numerical simulations that predict wave forces and behaviors.

“Our objective is not to come up with one design of our own. We try to analyze many designs and ask what is the size, shape and energy extraction rate, how do you space them and what is the power takeoff system. We develop methods to simulate designs,” Mei said in a phone interview.

According to a MIT press release, the Douro River project is described as follows:

“They plan a pilot-scale version of a facility called an oscillating water column, or OWC. Situated on or near the shore, an OWC consists of a chamber with a subsurface opening. As waves come in and out, the water level inside the chamber goes up and down. The moving surface of the water forces air trapped above it to flow into and out of an opening that leads to an electricity-generating turbine. The turbine is a design by A.A.Wells in which the blades always rotate in the same direction, despite the changing direction of the air stream as the waves come in and out.”

The major technical hurdle is to overcome the variability of the waves, according to Mei.

“Ocean waves come in at different frequencies…which depends on the wind. Either you [must] have [a machine with] many different frequencies or you use a control system to adjust your power takeoff system. That’s the challenge,” he said. “Also, when waves are too strong, you have to shut off the engine to protect the machine. Wave amplitude changes at night.”

Wave frequency isn’t the only challenge, either. There are environmental concerns, lack of government support and the absence of standards which are essential to commercialization of any complex technology.

“There are no standards even though wave energy has been studied for years. There has been no national effort on this so far,” says Mei, who says the two basic wave energy machines include the floating body type or the buoy and snake which run parallel to the coastline (while he does not know Steven Chu, he is optimistic the science background of the energy secretary-elect could provide a federal boost for wave energy).

“The buoy and snake can block navigation,” he says. However, the Norwegians have developed arrays that have a 10-meter radius and are spaced 50 meters apart. “At least fishing boats can go through and an array is more likely to be environmentally acceptable,” says Mei.

While wave energy faces many technical and economic challenges, there is one overriding force working in its favor.

“Sooner or later, petroleum will become less available. Waves have so much energy. Letting them sit there without using it is does not make sense.”