Renewable Energy from the Sea
The water (hydrologic) cycle
The ocean can produce thermal energy from the sun's heat and mechanical energy from the tides and waves.
Less directly, the ocean also plays a part in producing hydropower. Water constantly moves through a vast global cycle, evaporating from lakes and oceans, forming clouds, precipitating as rain or snow, and then flowing back down to the sea. The energy of this water cycle, which is driven by the sun, can be tapped to produce electricity or for mechanical tasks like grinding grain. Hydropower uses a fuel—water—that is not reduced or used up in the process. Because the water cycle is an endless, constantly recharging system, hydropower is considered a renewable energy.
This ocean thermal energy conversion center in Hawai‘i used the heat stored in the ocean to generate electricity.
Ocean Energy Basics
The ocean that surrounds Hawai‘i has long sustained its people, and today new technologies are being developed that will enable us to tap the ocean as a source of energy for future generations. As the world's largest solar collectors (covering 70% of the Earth's surface), oceans absorb thermal energy from the sun. They also produce mechanical energy from the tides and waves. Even though the sun affects all ocean activity, the gravitational pull of the moon primarily drives the tides, and the wind powers the ocean waves.
There are different types of ocean energy that can be applied in various ways. Learn about the following technologies on the DOE Web site:
Ocean Energy in Hawai‘i
In experimental deployments, cold water from the ocean depths has shown promise as a cost-effective alternative to traditional air-conditioning systems. The Natural Energy Laboratory of Hawai‘i Authority (NELHA), a state agency dedicated to energy and ocean-related research, education, and environmentally sound commercial activities, has experienced the economic benefits of this technology firsthand. Since NELHA began using a small-scale deep seawater air-conditioning system to cool three of its research compound buildings, it has reportedly saved up to as much as $4,000 a month in energy costs.
At the Natural Energy Laboratory of Hawai‘i Authority, cold seawater (43°F) is pumped from 2,000 feet below the ocean's surface and then converted to energy used to cool laboratory buildings.
Hydropower Basics
Hydropower is using water to power machinery or make electricity. When flowing water is captured and turned into electricity, it is called hydroelectric power or hydropower. There are several types of hydroelectric facilities, all powered by the kinetic energy of flowing water as it moves downstream. Turbines and generators convert the energy into electricity, which is then fed into the electrical grid to be used in homes, businesses, and industry.
To learn more about hydropower technology, visit the DOE Web site:
Hydropower in Hawai‘i
In Hawai‘i, hydropower is not new. On the Big Island, the Wailuku River hydropower plant near Hilo has been generating electricity since 1993. The Wailuku River plant is the largest in the state, but there are also smaller plants on Hawai‘i, as well as on Kaua‘i and Maui. Although these hydropower plants are small in comparison to many mainland facilities, they have furnished power to sugar mills and to the three island utility companies for many years. Additional hydropower projects on the islands of Hawai‘i, Kaua‘i, and Maui are under discussion.
