Tapping the power of the ocean

Marine-based heat exchange plants are becoming more viable as oil costs rise. Two multinational engineering firms step up to the challenge of bringing 'Ocean Thermal Energy Conversion' to market.

Two multinational engineering firms are going head-to-head to bring online the first scaled-up model of an ocean-based heat exchange system, known as OTEC, standing for 'Ocean Thermal Energy Conversion'. Heat exchange is a tried and tested form of power generation on land, but a viable OTEC system would open up a major new potential source of energy.

OTEC relies on a minimum temperature difference of 20°C between warm surface water and the much cooler water at depths below 1,000 metres. The warm water is flash-evaporated in a vacuum chamber which drives a turbine.

Modern OTEC systems create desalinated water as a by-product. The waste cool water, pumped from the nutrient-rich deep ocean, can be used in biotechnologies and aquaculture. A major advantage to OTEC over other renewables is its potential to generate a large constant base load energy supply.

OTEC has been around since the 1970s, when the US military and Lockheed Martin first flirted with the technology in response to the decade's oil price spikes.

As oil stabilised, OTEC went out of favour, but with the cost of energy as it is now, it could once again become a viable competitor in the global energy market.

The two engineering companies, DCNS Group and Lockheed Martin, are both seeking investment for 10MW plants, to be constructed in 2015. Lockheed Martin is working with Makai Ocean Engineering to build a 10MW plant off the coast of Hawaii, with plans to scale up to 100MW by 2020, if it proves successful.

France's DCNS Group is planning a 10MW facility off the coast of Martinique, which could also come onstream in 2015.

The major engineering challenge for a large OTEC plant is the construction of a 1km long tube with an unusually wide diameter of 10m, which must survive for decades or more in the harsh conditions of the ocean. Whilst the fuel of OTEC is free, the capital costs of such a facility could total $1billion.

But both companies remain optimistic. "We believe OTEC is poised to become a leader in reliable, secure and clean energy generation, because it provides base load power which is scalable to hundreds of megawatts", said Dan Heller, Vice President of Lockheed Martin New Ventures.

- Green Futures