Dear Colleagues

Imagine deriving the entire power for a country from hot rocks a few kms below the earth’s surface. Read on about a clever (but very difficult) technology to extract energy from a virtually inexhaustible pollution free source, which as engineering professionals you need to be aware of, as you may be called to comment on.  However, as experts have pointed out, drilling into fractured granite is technically very challenging with no power produced commercially as yet.

Conventional geothermal power (which we are familiar with) relies on naturally occurring pockets of steam or hot water to generate electricity. In Iceland, one quarter of the power generated is from geothermal sources. The more interesting geothermal power plants are situated close to volcanically active parts of the world. Conventional geothermal power plants generate 10.7 GW of power – enough for 53m people worldwide (and provide 93,732 GWhours/year – thanks, Dave Kimble for the original correction). But this note is not about conventional geothermal power but the more interesting (and controversial) EGS ones.

Engineered geothermal systems (EGS) work in parts of the world which are not volcanically active, by drilling many kms down. Water is then injected down to these hot rocks situated kms deep and the hot water is brought back up to the surface, where the heat is extracted to generate electricity. The earth gets hotter the deeper you go. MIT have calculated that if only 2% of the thermal energy, in rocks 3-10kms below the US’s surface is tapped, it could provide all America’s power needs. But at this stage there are very few EGS plants worldwide. Naturally, there are the usual plans to build many plants in Australia, Britain, France and Germany with a predicted 160GW of geothermal capacity installed worldwide by 2050 (with half from EGS).

The great opportunity with geothermal power is minimal carbon dioxide, power is continuous (i.e. not intermittent like solar and wind power) – so good base load provision of power.

The concept of Hot Dry Rock (HDR) geothermal power emerged from Los Alamos National Labs in the USA. As noted earlier, this is effective any where, where hot, dry rocks are drilled and fractured. Cold water is injected in the one well, flows through the cracks in the rock and heats up. The hot water is brought up to the surface in a separate production well where a secondary working fluid with a lower boiling point is heated up. This then spins a turbine for electricity. The original water is re-injected back into the well.

Costs vary depending on the depth of drilling. A typical US geothermal well produces power at $0.10/kWh so quite competitive with traditional sources of energy esp. as there is a $0.02/kWh production tax credit in the USA (at least). However, due to its far greater depth and thus high drilling costs, EGS geothermal costs $0.19kWh. So uneconomic (unless in Germany where the renewable energy subsidy is a huge mindblowing $0.31/KWh).

The biggest challenges for EGS to overcome are the drilling technical challenges and creating the necessary underground reservoirs. An added fear for people are the resulting earthquakes that are caused. Mainly small tremors. But enough to worry people. One Swiss project was recently shut down as it resulted in a 3.4 magnitude earthquake cracking buildings in the region.

What can you do about this ?

• Discuss this technology with your peers
• Investigate how power sources such as this could be applied
• Look at how your area of technology (mining or oil and gas) could be applied to this field

Thanks to The Economist and the Dept of Energy for some interesting reading.

In considering this new pioneering technology (based on rocks), I  like the quote from Ruth Westheimer:

Our way is not soft grass, it's a mountain path with lots of rocks. But it goes upward, forward, toward the sun.

Yours in engineering learning