GEOTHERMAL ENERGY is an attractive source of abundant baseload electricity with low emissions. To date, however, geothermal facilities have been deployed only where naturally occurring heat, water and rock permeability allow easy energy extraction.
Enhanced geothermal systems is a new approach: with adequately deep drilling, every country could potentially access an almost unlimited energy resource. Enhanced geothermal systems allow the use of the heat within the Earth in a wider range of locations than existing geothermal resources – where there is insufficient naturally occurring steam or hot water and where the permeability of the Earth’s crust is low.
Enhanced geothermal systems don’t require natural convective hydrothermal resources but seeks to enhance or create geothermal power from hot dry rock sites through ‘hydraulic stimulation’, pumping high-pressure cold water down an injection well into the rock. This increases fluid pressure in the naturally fractured rock, mobilising shear events that enhance permeability – a process known as hydro-shearing, which is very different from hydraulic tensile fracturing used in the oil and gas industries. Geothermal power could be extracted in a larger number of locations that could be developed to function as baseload stations producing 24-hour-a-day power, much like conventional power plants.
The Earth’s innate heat offers an essentially inexhaustible energy supply, if it could be tapped for electricity production. The estimated enhanced geothermal resource base in the United States alone is some 13,000 times the current annual consumption of primary energy. Using reasonable assumptions regarding how heat would be mined from stimulated enhanced geothermal reservoirs, the extractable portion still amounts to 2,000 times the annual consumption, according to a study led by the Massachusetts Institute of Technology and commissioned by the U.S. Department of Energy (The Future of Geothermal Energy , January 2007).
A 2011 report by the International Energy Agency estimated that geothermal generation could reach 1,400 terawatt hours per year – as much as 3.5% of worldwide electricity – within four decades, replacing the creation of almost 800 million tonnes of carbon dioxide.
While some technical challenges need to be overcome to make enhanced geothermal systems a common alternative energy source globally, most of the difficulty stems from a lack of sufficient engagement by business and government to make a significant impact. Instead, recent efforts have focussed on small-scale projects. Major barriers to the technology’s expansion have been the high front-end capital costs of geothermal projects, and a lack of investor confidence due to the paucity of available drilling data – only a small number of wells have been drilled worldwide to date. The technology needs to be sufficiently de-risked to overcome the natural conservatism of private capital. Until this occurs, exploration of the resource will be limited to isolated, government-supported development. Engagement by major financial and energy players will be needed to make cost projections attractive to investors.
Uncertainty in geothermal projects mostly centres on the lack of understanding of the size and characteristics of individual resources before drilling begins. Some questions around the local environmental impacts of engineered geothermal systems also need to be studied and better understood. Technical issues are largely around the ability to create a closed water circuit, the avoidance of mineralisation and channelling (leading to localised cooling) and the integrity of rock fracturing. All these problems, however, are considered surmountable over time.
The Equinox participants were extremely enthusiastic about the potential of enhanced geothermal systems. To reduce the technical and financial risks of large-scale engineered geothermal technology, they called for the establishment of a public-private partnership that would roll out up to 10 commercial-scale, 50 megawatt demonstration projects worldwide. These would be internationally collaborative efforts, marrying industry and government partners.
These projects would help reduce risks and uncertainties for drilling by bringing down the learning curve. Drilling into larger amounts of the geothermal resource base would likely result in greater economies of scale for delivered power. And that would translate into lower average costs per well – not only for wells per field, but wells drilled regionally. This learning-curve approach has been applied successfully for oil and gas drilling technologies. It may also lower prospecting and surveying costs by sharing information. If all data derived from the projects were to be made publicly available to facilitate transfer of drilling technologies and expertise internationally, it would build confidence between government and private investors.
Large-scale demonstration projects are a potentially powerful means of building confidence and improving technological understanding to encourage the uptake of new technology. These would not only establish whether projects are technically feasible, but also de-risk the construction and operation of ‘commercial-scale’ facilities.
This is part of a series on a blueprint to address the world’s looming energy crisis.