Enhanced Geothermal Systems - The "Killer App" of the Energy World
Google surprised the audience at the National Clean Energy Summit in August by pronouncing that “enhanced” geothermal energy could be the “killer app” of the energy world. In September, Google and General Electric jointly announced an effort to more fully develop this potentially unlimited resource.
What exactly is “enhanced” geothermal energy? Why has it excited such giants as General Electric and Google? And, will it live up to expectations?
Traditional geothermal energy relies on naturally occurring pockets of steam and hot water beneath the earth. Geothermal power plants on the surface use the steam from 1 to 2 miles below the surface to run turbines and generate electricity. In order to be economic, large geothermal plants are usually built where the heat is relatively near the surface and where the temperatures of the hydrothermal resources are generally warm (between 300 and 700 degrees Fahrenheit). These plants produce, on average, for about 30 years and, depending on their location, are competitive with the prices from traditional fossil fuels plants. However, large scale geothermal resources seem quite hard to come by or the resources are located at uneconomic depths. Consequently, traditional geothermal power plants produce less than .0035 of total electric generation in the US and less than 1 percent world-wide.
“Enhanced” geothermal however, taps into the earth’s unlimited hot rock. Those rocks are then fractured, water is circulated through the system, and the resulting steam is used to produce electricity in a conventional turbine.
A 2006 report on Enhanced Geothermal Systems (EGS) by MIT (sited by Idaho National Laboratory and Wikipedia) concluded that it would be affordable to generate 100 GWe (gigawatts of electricity) or more by 2050 in the United States alone, for a maximum investment of 1 billion US dollars in research and development over 15 years.
The MIT report calculated the world's total EGS resources to be over 13,000 ZJ. Of these, over 200 ZJ would be extractable, with the potential to increase this to over 2,000 ZJ with technology improvements - sufficient to provide all the world's present energy needs for several millennia. The key characteristic of an EGS (also called a Hot Dry Rock system), is that it reaches at least 10 km down into hard rock. At a typical site two holes would be bored and the deep rock between them fractured. Water would be pumped down one and steam would come up the other. The MIT report estimated that there was enough energy in hard rocks 10 km below the United States to supply all the world's current needs for 30,000 years.
What then are the impediments to this seemingly unlimited resource? First, the depth of these holes are daunting. There are technological challenges involved in drilling wide bore holes to depths of 4,500 meters (about 2.8 miles) as well as the difficulty involved with breaking (fracturing) rock over large volumes. Second, drilling to such depths is currently very expensive. Conventional oil and gas wells drilled to 15,000 feet generally cost tens of millions of dollars. Each enhanced geothermal plant would require two holes.
Google is relying on several potential breakthroughs to advance EGS. On the cost side, Google expects that the economies of scale will bring project costs down in line with coal-fired plants. On the technology side, Google has invested in new hard rock drilling technologies and in companies involved in EGS research and development.
Certainly, the injection of GE as a participant in enhanced geothermal lends tremendous credibility to Google’s efforts. The only question in my mind is whether any one approach is truly the “killer app” in the energy world.
Renewable Portfolio Standards: An Avenue for Fostering Alternative Energy Projects
Government’s response to the focus on climate change must be holistic and visionary. One regulatory avenue for fostering alternative energy projects that assist in the battle against climate change is a Renewable Portfolio Standard (RPS). At its core, an RPS is a requirement that retail electricity suppliers purchase a certain percentage or quantity of renewably generated energy. Currently 25 states and Washington DC have mandatory targets for retail electricity purchases and 4 states have non-binding goals. In 2007 the House of Representatives passed an RPS, but the US Senate did not.
While most RPS programs share a common goal of encouraging the production of renewably generated energy, they vary in terms of purchase goals, timeframes for compliance and eligible technologies. Wind, solar, and geo-thermal are eligible under most of the RPS programs, but eligibility criteria varies widely with respect to other technologies and fuel sources such as bio-mass, landfill-gas, municipal solid waste, hydropower, and fuel cells. While the advantages in terms of climate change impacts associated with renewably generated energy may seem obvious (no emissions), less obvious may be the results stemming from the expansion of several states’ RPS programs into non-renewable areas.
The variety of RPS programs has allowed for many designs and policies to be demonstrated. Although not technically renewable, combined heat and power, energy efficiency and demand side energy efficiency have found their way into several of the RPS programs. By reducing demand for electricity, air emissions from current fossil fuel fired power plants is reduced to the extent that power is not needed. Arguably, the impact from reducing the demand of one megawatt of power, should have the same air emissions impact as the creation of one megawatt of renewably generated power and as such the nexus to demand management and energy efficiency in an RPS becomes self evident. Energy efficiency, demand management, and renewable energy should co-exist in an RPS and are a fundamental part of the future of our energy delivery system. As states continue to adopt and refine RPS programs, policy makers should bear in mind what this future of a sustainable energy delivery system may look like.
The US Department of Energy (DOE) has promoted (in part) a vision of the future that includes a hydrogen based energy delivery system that begins with small-scale distributed generation (DG) systems fueled by hydrogen. These DG systems provide stationary power and may also dispense hydrogen for hydrogen-fueled vehicles. DOE has funded several projects that evaluate the potential for the generation of wind-to-hydrogen, solar-to-hydrogen, geothermal-to-hydrogen and hydro-to-hydrogen, hydrogen generation systems. The common denominator is that renewably generated electricity is used to power an electrolyzer to generate hydrogen. Renewably generated hydrogen is the future. To bridge the gap to the future, however, Renewable Portfolio Standards should be developed that include hydrogen generated from fossil fuels.
One notable Wind-to-Hydrogen (also Solar-to-Hydrogen) demonstration funded by DOE is in Hawaii at the Kahua Ranch test site. There, the wind turbine has been configured to produce 48VDC, the solar array has been redesigned to produce 48VDC and each of these generation sources is connected to 24 battery cells allowing 48VDC short term electricity storage. The electricity is used to power an electrolyzer that generates hydrogen which is then stored in a low pressure hydrogen storage tank. When electricity is needed the hydrogen is used to run a 48VDC Plug Power Gencore Fuel Cell system.
Fuel cells utilize hydrogen and hydrogen-rich fuels to generate electricity and useful heat in a remarkably efficient way. A fuel cell is an electrochemical device that combines hydrogen and oxygen to create electricity heat and water. Because the conversion of hydrogen occurs without combustion, fuel cells do not produce the emissions normally associated with combustion such as carbon dioxide, oxides of nitrogen, carbon monoxide and particulates. Fuel cells are secure, reliable and high-quality power at the point of demand, with some systems able to provide high quality thermal energy as well as electric energy. Because many renewables like wind and solar produce intermittent power, a natural symbiotic relationship exists since fuel cells have the ability to generate electricity regardless of weather conditions. Fuel cells can act as a power storage technology converting off-peak generated wind and solar energy to peak power. Clean power that emits virtually no pollution during the power generation is a natural complement to intermittent renewable technologies such as wind and solar.
Introducing fuel-neutrality for fuel cells into every RPS in the short term will provide a bridge to renewably generated hydrogen. Currently, supplies of renewably generated hydrogen are scarce and the delivery systems not readily available. Simply put, today’s fuel cells that use existing fossil fuels (much more efficiently and cleaner than any combustion engines) can also use hydrogen from renewable sources as they become cost-competitive and the production and delivery of renewably generated hydrogen catches up with the demand. In this manner, the use of hydrogen from the conversion of hydrocarbons is seen as a temporary expedient to the long-term development of fuel cells. Moreover, even when they run off of fossil fuel derived hydrogen, the inherent efficiencies of the fuel cell systems, and the lack of combustion is an incremental advancement in the fight against climate change.
The vision of the future displayed in the Kahua Ranch project will only be advanced in the short term if fuel cells that utilize hydrogen reformed from fossil fuels are made a part of any federal RPS. At its core, a RPS should promote technologies that have a legitimate chance of substantially lowering pollution, reducing stress on the utility grid, spurring economic development, increasing our energy independence and fostering demand for hydrogen production and delivery systems that will eventually be renewably generated.
Initially, it may sound counter intuitive, but by allowing hydrogen generated from fossil fuels in any RPS, a critical component to generating the demand for renewably generated hydrogen will be in place and our path toward a more sustainable and energy independent future will be advanced. This model is not without precedent. New York, Pennsylvania, Connecticut, Minnesota, Colorado, Maine all include fuel cells as renewable resources regardless of the fuel supplied.
