A test case for heat mining
September 26, 2017 by Denis Pombriant
There’s a compelling opportunity presenting itself in Arizona for a low-cost test case for EGS or using heat from the Earth’s crust to generate electricity in a conventional electric plant. The Navajo Generating Station, in Page, Arizona is the West’s largest coal-fired power plant and it is also tailor-made for a simple experiment. In February 2017, the utility consortium that owns the 2,250 MW generating station announced that it would close the plant in 2019 (decades ahead of its end-of-life), taking coal-mining jobs and a revenue source for the Navajo Nation with it.23
While it’s good to remove that much coal pollution from the world it’s hard on the local economy, and although the mining jobs won’t come back, converting the plant, which sits on top of a good geothermal gradient, to EGS could be important in several ways.
- Keeping 2,250 MW of nonnuclear generating capacity on line would be important to satisfy regional power needs, and if this capacity was not needed, it could be directed to other uses like producing fresh water.
- Converting the plant to geothermal would keep some local jobs and the available power would help make the area more competitive for a variety of industries.
- It would generate some new jobs. Short-term jobs would be found in constructing the geothermal wells.
- Proving the concept at this site would provide needed impetus to further develop underground heat gradients for EGS power generation elsewhere in the west. And if the idea works as planned, more plants using EGS could be built elsewhere in the west.
- Finally, keeping the plant opened will save existing jobs.
So, there are good reasons to consider converting the plant to geothermal generation, especially given its impending closure. The cost is limited to drilling, fracking, and some plumbing to convert the plant—far less than building a new power plant from scratch. Several interlocking events have to take place to turn the idea to reality but the timing is good.
For example, the plant will continue operating until its scheduled shutdown in 2019. During this time the utility consortium that owns the facility would need to engage with drilling companies to bore test wells to gauge the heat gradient xxx and sample the rock in the stimulation area. These wells are typically 2 to 3 km deep, which sounds like a lot but it’s similar to some gas wells, so the technology exists.
A stimulation area is the place where drillers use hydraulic fracturing to increase the porosity of the rock so that water can flow through the fractured and very hot rock to absorb heat. This water would be conveyed to the surface through another well completing a circuit in which cold or used water is sent into the stimulation area and hot water is brought up to steam turbines that drive generators on the surface.
Due to the tremendous pressure at great depths, hot water from such wells is much hotter than the boiling point of water at sea level, 100 degrees centigrade. Often the temperature underground can vary from as low as 150 degrees centigrade to more than 300 degrees. When this superheated water reaches the low pressure of the surface it expands rapidly and this expansion drives steam turbines.
Hot water from Earth’s crust is already being used for power generation for instance, in California’s Sonoma Valley where 13 generating stations are producing over 600 MW of electricity. Naturally, this power is pollution free and renewable so it makes sense, given the world climate situation, to try this experiment. If it works as expected, this experiment could set up the inter-mountain states as an energy producer comparable in size to some of the oil producers.
Think about that. A large area of the continent containing many states (the intermountain area) where relatively little commerce occurs due to rough terrain and sparse population could become one of the greatest energy sources in history. The energy would be clean and it’s not necessary to disturb the natural beauty of the area to get to the energy.