April 22, 2014

The spring 2014 issue of The Bridge, a publication of the National Academy of Engineering, focuses on emerging issues in Earth resources engineering, including three articles co-authored by Stanford scientists Roland Horne, Mark Zoback and Sally Benson:

Geothermal energy: An emerging option for heat and power

By Roland Horne, professor of energy resources engineering aand deputy director of the Precourt Institute, Stanford University

     Jefferson Tester, professor of chemical & biomolecular engineering and director of the Cornell Energy Institute, Cornell University

Summary: Geothermal energy has experienced a renaissance in the past 10 years as many new technologies and countries have joined the industry. The technology for generating electricity and deploying district heating from high-grade hydrothermal systems is relatively mature and reliable. Technologies for geothermal heat pumps are also mature and are being deployed at increasing rates in the United States and Europe. The use of innovative hybrid and combined heat and power plants, lower resource temperatures and enhanced reservoir stimulation methods are making geothermal energy accessible in a much greater variety of places. At a number of field test sites in the U.S. and elsewhere, enhanced geothermal systems technologies are being demonstrated at a scale that is approaching commercial levels and, if operated long enough to prove sustained production, would enable the deployment of a substantially increased fraction of the huge geothermal resource base, which for the U.S. amounts to about 14 million exajoules.

Shale gas: Development opportunities and challenges

By Mark Zoback, professor of geophysics, Stanford University

      Douglas Arent,  executive director of the Joint Institute for Strategic Energy Analysis, National Renewable Energy Laboratory

Summary: The development of shale gas resources in an environmentally responsible manner presents a critical opportunity to take a major step toward decarbonizing the global energy system. There is much concern about inexpensive natural gas crowding out renewable energy sources, such as wind and solar, but fast startup and efficient combined-cycle natural gas plants will complement such renewable energy resources by providing reliable backup power regardless of the time of day or weather conditions. It is therefore important for countries around the world to implement energy policies that allow for the effective development and use of natural gas while continuing to deploy renewable energy sources.

Carbon capture, utilization and storage

By Sally Benson, professor of energy resources engineering and director of the Precourt Institute, Stanford University

      S. Julio Friedmann, deputy assistant secretary for coal, Office of Fossil Fuel, U.S. Department of Energy

Summary: Control technologies for reducing CO2 emissions from industrial sources and fossil fuel–fired power plants are an important component of achieving sufficiently large and rapid emission reductions over the coming decades. Carbon capture with storage in deep geological formations is the only currently available control technology likely to be deployable at scale within this time frame, but it will require the work of engineers, scientists, and social scientists to resolve important challenges. Today, more than 20 Mt/yr of CO2 are captured from anthropogenic sources and injected underground, and there is a pipeline of projects that will raise this amount by 50 percent within the next few years. But this is still far short of the fiftyfold scale-up needed, and a variety of challenges must be addressed to achieve the necessary progress. Costs for capture are too high, particularly in the absence of regulatory drivers for carbon capture, utilization and storage (CCUS). Outstanding technical issues related to large-scale storage (e.g., pressure management, wellbore leakage, and storage capacity) will require a combination of R&D and commercial experience before they are fully resolved. Nontechnical aspects are perhaps even more important: access to capital for plant construction, regulatory issues, and public support for CCUS must also be a top priority for policymakers and industry leaders. Above all, sustained support from governments, industry and academia is critical for continuing progress in this important CO2 emission reduction technology.