Block’s Indicator of Sustainable Growth

by Ray Block

By all accounts, geothermal resources in the world are immense. The Union of Concerned Scientists says that within 10 km (about 33,000 feet) of the Earth’s surface, the amount of heat contains 50,000 times more energy than all the known oil and natural gas reserves in the world.

Greater effort is now being made to exploit these resources, as the need to create low carbon economies becomes more urgent. Although there is a small volume of greenhouse gases involved, geothermal energy is available 24 hours a day, providing base load power at a price almost competitive with coal.

At September 2009, United States with the largest known geothermal resources in the world, is generating geothermal electric power in eight western states. California is the long time leader, with more than 40 geothermal plants providing nearly 5 per cent of the state’s electricity.

The state’s renewable energy requirement of 33 per cent by 2020 will spur more development. Nevada, the second largest geothermal producer has a 25 per cent renewable energy target by 2020, and this will also facilitate increased production. Soon another five states will also be generating electricity.

Total US installed geothermal capacity is currently 3.1 GW. Although representing less than 1 per cent of total US electricity capacity today, the aim is to reach at least 5 per cent of US power needs by 2020, and 10 per cent by 2030. The US Geothermal Energy Association says that 144 projects are now under development in 24 states, which could provide additional electricity capacity of 7 GW.

Up to $338 million in Recovery Act funding was allotted by the Obama Administration in 2009 for the exploration and development of new geothermal fields and research into advanced geothermal technologies. These grants matched on a one-for-one basis with private and non-federal cost share funds will support 123 projects in 39 states.

Conventional US geothermal resources on private and accessible public lands has a mean estimate of 33 GW, while the latest study by the US Geological Survey of geothermal resources in hot rock technology suggest an additional mean estimate of 518 GW available.

While the capacity factor in conventional geothermal production, (the amount of electricity produced) is at least 73 per cent, and may be only 30 per cent in hot rock technology, the overall resources are so large, that one day they may be able to supply much of the country’s electricity needs.

European geothermal resources are mainly in heating and cooling, directly exploiting the aquifers (Paris leads in low and medium energy resources), where the temperature ranges between 30 degrees C. and 150 degrees C. The second way is to produce heat using geothermal ground source heat pumps. The major European producers are Sweden, Italy, France, Hungary, Germany, Denmark.

The EU-27 country geothermal electricity target for 2020 is 6 GW, and for geothermal heating installed 39 GW. Outside the EU, Iceland with about 300,000 people is the geothermal standout,with 17 per cent of its electricity and 87 per cent of its direct heating from geothermal energy.

Everywhere on Earth, the deeper you go, the hotter it gets. Some of the regions are within the “Ring of Fire,” characterised by volcanoes, hot springs and fumaroles, (vents emitting hot gases), where the heat is close to the surface. These areas are around the rim of the Pacific Coast on the US and Canadian west coast – California, Nevada, Alaska, Hawaii, and down the Asian coast to include Japan, China, Philippines and Indonesia.

There is also the Mid-Atlantic Ridge, an underwater mountain stretching from Iceland and the Azores to Antarctica, the East African Rift Valley mainly around Kenya, the East Pacific Rise paralleling the west coast of South America, the Rio Grande Rift running up through New Mexico and Colorado and the Juan de Fuca Ridge (tectonic spreading centre off the coast of Washington state and the adjoining province of British Columbia.)

There are two additional levels of geothermal resources. One of these is a steady supply of milder heat available for direct space heating, at depths down to 200 metres or so, which is available in parts of Europe and North America.

There is also the very large resource at depths of 3 km to 10 km (about 2 to 10 miles), where enhanced geothermal systems (EGS), also known as hot rock technology, has opened up a virtual Pandora box of energy treasures. In addition to the US, Australia, France, Germany and Japan have R&D programs to make EGS commercially viable.

In the EGS process, a fractured reservoir is created at a depth where the rock is hot. Water is continuously injected down a well into the engineered fractures, where the water heats as it flows through. The water is then brought to the surface via production wells, and its heat is extracted to generate electricity in power plants. Finally, the water depleted of its heat, is re-injected to be heated again.

Susan Petty, President of AltaRock Energy, whose company is exploiting an EGS project in Oregon gave evidence to the US Senate Committee on Energy and Natural Resources in 2007.She discussed the economics of the cost of geothermal electricity at depths of 3 km, and temperature of 300 degree C.

Her experience is that EGS at current technology could be generated for a cost of about US$74 MWh. This price includes financing costs and amortising the capital investment of the well field, but before profit. With incremental technology improvement, the cost of power could be cut in half