In search of low-cost wave energy

Costs will remain high until technology stabilises and there is serious scaling up in capacity. The potential is huge for India and the world

One of the least used forms of renewable energy is wave energy from the ocean. Waves generate a lot of power. If this can be harnessed and converted into electricity, it is also endlessly renewable. Unlike solar or wind, it’s 24x7 under most weather conditions.
 
Although the idea has been around for a long time, it remains a low-key research area. The first attempts to use waves go back to 1799 when French polymath, Pierre-Simon Girard, invented a water turbine and filed patents. Modern experiments were pioneered by Yoshio Masuda in the 1940s. Masuda, a commander in the Imperial Japanese Navy invented a buoy that used oscillating water columns (OWC).

 
The OWC is a simple concept. The Masuda buoy had a floating chamber with a trapped column of air, and a hole below the waterline. The water level inside oscillated up and down due to wave motion, compressing / decompressing the air column. This moved a piston, generating electricity. More sophisticated turbines based on the OWC concept are very much in use nowadays.
 

Many other ingenious concepts have also been utilised. The Salter Duck is another commonly seen float, which uses a pendulum that bobs back and forth. There are hydraulic rams, which work by creating pressure differentials in a dual valve (or multi-valve) system. As a wave peaks, it forces water into the ram. One valve closes and the other opens, creating higher pressure that forces water up against gravity to move a turbine. As the wave ebbs, pressure eases, the second valve closes, while the first valve re-opens and the turbine moves again.

 
Other generators use motion by for example, putting together a string of oscillating buoys, anchored in shallow water. Wave attenuators are long segmented floats placed perpendicular to the length of waves. As the floats flex due to waves, the motion is converted to electrical power.

Another concept is a submerged “carpet” converter made from flexible material (such as rubber). The carpet flexes and bends with wave motion. The movement is used to drive a piston.
 
“Overtoppers” are inclined ramps, which work like floating hydro-electric dams. When a wave peaks, the water climbs the ramp and fills a reservoir. The water is then drained off, using hydro turbines. 

 
Wave energy depends on local geography, wind factors and the mathematics of the interactions among multiple waves. There are several computer models that study these variables to judge where wave power will be consistently at ideal levels.
 
Conversions to power can be surprisingly high, with claimed conversion rates of 80-90 per cent of kinetic energy to electricity for some devices. However, wave energy is expensive for multiple reasons. It requires tricky engineering to take power, and transmit it somewhere useful through the sea. Wave converters also incur high repair and maintenance costs. Sea water is corrosive and bad weather often damages and destroys installations.

 
There are also serious environmental concerns, as always, with any new technology. Wave converters could damage the marine environment in many ways. They can also cause noise pollution that upsets marine life (sound is amplified and travels much faster in water). Since seawater is also a good electrical conductor (unlike air), the converter and the transmission system have to be carefully though through and insulated, adding to the challenge.
 
There are experiments happening all over the world, with wave energy installations in Europe, Australia, the US, West Indies and Australia. India’s only major wave energy pilot project was located in Vizhinjam, Kerala and run by IIT, Madras. But it was decommissioned a few years ago. Unlike with solar, wind or biogas, there’s no mission target for wave power.

 
The US Department of Energy has an interesting ongoing Waves to Water competition offering $2.5 million in prizes. Competitors have to produce clean desalinated water using only ocean waves as power source. They must submit concept, technical design, build a prototype, and demonstrate it in an open water testing competition. This would be win-win.
 
As of now, wave energy is very expensive with many technologies developed to somewhere between proof of concept and pilot projects. Costs will remain high until technology stabilises and there is serious scaling up in capacity. If a technology scales, waves may even be cheaper and more reliable than wind or solar.

 
The potential is huge, for India and for the world. India with its 7,500 km coastline and islands, could generate anywhere upto 60 Gigawatts of wave energy. The US Dept of Energy estimates that upto 65 per cent of the US’s power needs could be met by waves.