MRS Bulletin


Other Renewables

Hydropower, Geothermal, and Ocean Energy

Ralph E.H. Simsa1

a1 Massey University, New Zealand, and International Energy Agency, France


Some forms of renewable energy have long contributed to electricity generation, whereas others are just emerging. For example, large-scale hydropower is a mature technology generating about 16% of global electricity, and many smaller scale systems are also being installed worldwide. Future opportunities to improve the technology are limited but include upgrading of existing plants to gain greater performance efficiencies and reduced maintenance. Geothermal energy, widely used for power generation and direct heat applications, is also mature, but new technologies could improve plant designs, extend their lifetimes, and improve reliability. By contrast, ocean energy is an emerging renewable energy technology. Design, development, and testing of a myriad of devices remain mainly in the research and development stage, with many opportunities for materials science to improve design and performance, reduce costly maintenance procedures, and extend plant operating lifetimes under the harsh marine environment.

Ralph E.H. Sims can be reached at the Renewable Energy Unit of the International Energy Agency, Paris, tel. +33–1–4051–6563. He remains director of the Centre for Energy Research, School of Engineering and Advanced Technology, College of Sciences, Private Bag 11222, Massey University, Palmerston North, New Zealand; tel. +64–6–3505288, fax +64–6–3505604, and e-mail

Sims is professor of sustainable energy at Massey University, New Zealand. Over a 35-year career working in renewable energy, he has served on various boards, is a fellow of the NZ Institute of Professional Engineers, and a Companion of the Royal Society of New Zealand. Sims also was a lead author in the IPCC 3rd Assessment Report—Mitigation (2001) and is the coordinating lead author for the energy supply chapter of the 4th Assessment Report (2007).