Ah Sylvia,

Who suggested attaching a solar thermal generator to a hot-rocks source?

The point is that if human beings had agreed that we would never get to the moon, we would never have got there because nobody would have tried. So an 'it will never work' attitude doesn't really get us anywhere does it? The same could have been said of many technological advancements. I'm sure battery storage will increase. And there are so many other available technologies to use and develop.

The point of building new systems and testing new ideas, is that while they may not be viable currently, they will never be viable unless they are trialled and further developed. Coal power stations, steam engines, nuclear power plants, the internal combustion engine all went through long development stages and have continued to be developed to this point. And history tells us that people said 'it will never work, let's continue riding horses and burning wood!' Closer to home, piping water from Perth to Kalgoorlie was never going to work either!

BTW I note that you didn't respond regarding combined heat power stations...these are far more efficient than the conventional coal and gas power systems. Just shows that with a little vision and a willingess to invest, you can make things happen.

A basic economics concept is opportunity cost - to be viable, the risk-adjusted rate of return must be at least equal to the best return on alternative investments. Geothermal would be in use now if it were viable; unless, for example, it is not viable only because the pollution costs of other sources are not priced. If, e.g., the effective cost to the community of CO2 emissions is $20/tonne, this could be corrected either by imposing a carbon tax or by a compensatory subsidy to geothermal production. That doesn't require any "new" economics. If geothermal isn't viable on that basis, at current and projected prices, then it's not in our interests to pursue it. Of course, changes in relative prices (cf the rapid rise in oil prices) might make it viable in future, subject to the various reservations voiced in other posts.

These hot rock power sites are, of course, another example of nuclear power (what do you think makes the rocks hot?), and presumably will be rejected by the greenies on the basis that nothing that can be f use may be approved. It's all hot air as far as I am concerned.

As far as I have read, the Hot rocks system has yet to even achieve energy neutrality, and even if it is, the huge volume of water consumed is still likely to make this environmentally unfriendly.

The proof of the pudding is that no one is putting serious money into this and if it really was the answer to our prayers, the hot rocks areas would be swarming like a gold rush.

So far, the hot rocks are a hole into which money is poured.

I would love to believe that a solution is in sight, but I am not yet ready to suspend reason like Kevin Cox.

In previous posts there do seem to be a considerable number of misconceptions. In particular on the danger of radon, thermal efficiency and even the effect of removing the heat.

Concerning the unjustified statements, one of great concern is the issue of radon from high heat production granites. It is not the abundance of heat producing elements that is the most critical, but the presence of an insulating layer of cover rocks so that the miniscule amount of heat generated is trapped and held for millions of years. There have been three hot rock projects that have measured radon emissions from granites during water and steam production Cornwall UK in the 1980's, Soultz France in the 1990's and the Cooper
Basin project in 2005. All three had relatively similar abundances of radiogenic elements in the granites and all three showed radon emission levels below background levels in many areas of the world where radon is not considered a problem.



Another concern is that of taking all that heat out of rocks 4-5 km underground. What will be the effect at the surface? The expectation is that there will be no effect. . In the granite the rock is 300ºC, but just 50km to the north, still beneath the Cooper Basin but in metamorphic basement rocks the rock is only 150ºC at the same depth.
It is true that the thermal efficiencies of power generation at 200ºC is relatively low, but it is incumbent on geothermal companies to prove that drilling, heat extraction and power conversion is an economically viable process. Now that some good results have been achieved it is looking less likely that the process is going to fail, particularly since the cost of other energy sources is now going through the roof, including coal without carbon capture and storage. With CO2 pollution taxes likely to be soon upon us and with the prospects of them increasing in time hot rock geothermal is looking more and more attractive.

For those interested in what the company has got to say, see http://www.geodynamics.com.au/IRM/content/home.html