(Now this, this is content not meta – promoted by ek hornbeck)
re-posted from DailyKos
There is an energy source that is abundant, clean, renewable, and locally available. It’s also almost entirely untapped, even though the technology to tap a lot of it already exists. It’s enhanced geothermal, which involves tapping the Earth’s heat with deep mines (miles deep). A panel at MIT wrote about it, and I’m impressed. The full report (400 pages) is at this site this site
Geothermal energy, generally, means any use of the Earth as an energy source, mostly by utilizing heat differentials between parts of the Earth. A lot of this is already used. But this diary is about a particular type of geothermal which is largely unused. Namely, drilling very deep mines (miles deep) and using the heat differential to generate electricity.
Here’s what the panel of experts said:
1. EGS is one of the few renewable sources that isn’t intermittent.
2. EGS is available nearly everywhere in the USA
3. EGS has virtually no environmental impact (including CO2 release)
4. The technology exists to utilize it to generate huge amounts of electricity (on the order of 100 GWe, within a generation
5. This could be cost competitive for electricity and heat, given an outlay on the order of $1 billion over the next 15 years
On to the details (note that these details are based on the executive summary of the report…..if questions come up, I will try to find the answers in the main part of the report)
Part 1: Motivation and scope
The report covered three areas:
a) Magnitude and distribution of the EGS resource
b) Status and remaining requirements of EGS technology for commercially feasible development
c) Economic impact of EGS on the US energy supply to 2050.
The magnitude is huge – possibly sufficient to meet all of the needs for the USA for electricity. The distribution is widespread, EGS is available virtually everywhere in the USA.
Further technology is needed for EGS to be fully feasible, but none of this is insurmountable or radically new.
The economic impact could be very substantial, easily able to reach 100,000 MW by 2050 (which they state is 10% of total need).
Part 2: Definitions
Geothermal energy means the thermal energy stored in the Earth’s crust.
It is distributed between the constituent host rock and the natural fluid that is contained in fractures and pores at temperatures above ambient levels
. Taken this broadly, geothermal energy has been in use for a long time, but in restricted areas or for restricted uses. These uses generate about 110,000 MW of energy (10,000 MW of electricity and 100,000 MW of direct-use).
However, enhanced geothermal systems (EGS) involve engineered reservoirs created to extract heat from low permeability and/or porosity geothermal resources. This explicitly includes the drilling of deep wells (10,000 to 30,000 feet) through which water can be circulated and heated by contact with the rocks, and then returned to the surface in a closed loop.
Part 3: US geothermal resource base
The total amount of geothermal energy available in the USA to a depth of 10 km (about 6 miles) is stunningly large – more than 130,000 times the total energy use in the USA in 2005 (that is not a typo). Not all of this is economically extractable. However, a large amount of it is so extractable, and more will become so as technology develops. (The report gives a wide range of estimates, from 2% to 40%).
Further, although this resource is more abundant in the western states, it is available throughout the country.
For generating electricity, one must drill down to temperatures of at least 150 or 200 degrees (C); for some other uses (e.g. heating) temperatures of 100 to 150 degrees are adequate. These latter temperatures are (in most of the country) reached at between 3.5 km (in some areas of the Rocky Mountains) to 6.5 km (in much of the country). The higher temperatures appear to be at depths of 6.5 to 10 km.
Part 4 Cost
There are two broad areas to consider with regard to cost: Initial investment and continuing costs.
The cost of drilling a well depends on many factors, but principally on depth. The report estimates that a 3.5 km well would cost roughly $4 million, a 6.5 km well roughly $10 million, and a 10 km well about $20 million.
Ongoing costs are covered below.
Part 5 Environmental impact The report summarizes that the total environmental impact of EGS is much lower than fossil-fuels, and quite possibly lower than solar, biomass, or wind. Mostly, this is because nearly all of the work takes place underground, the surface equipment is quite compact, the general availability of EGS limits transportation costs, minimal discharges of nitrogen, sulfur oxides, and other particulate matter. The main environmental problem with EGS is groundwater use and contamination, possible seismic impact from drilling, and noise, safety, and land use effects of drilling. These are described, however, as manageable.
Part 6 Economic feasibility
The break even cost for EGS depends on many factors, as well, but the best projections are that it would start at about 10 cents per kilowatt hour, and drop to about half that in 15 years, before beginning to climb again.
There you go!
All the above is a summary of a summary. Mistakes are almost certainly mine 🙂
I should make it clearer that I am NOT an expert. I’m a statistician, not a geologist. I saw this mentioned and pursued it. Others here know more than I.
Also I thought I made this clear, but EGS is new stuff, no one is really doing it. There are OTHER kinds of geothermal, but this one is new