'Where is the physics guy KP?

What do you think about Geothermal as a partial answer to heat pollution?'

Sawzaw, I'm on a different time zone to most of the rest of you guys (Bruce, Amos etc) hence you'll get comments from me at seemingly random times. Plus I spent much of the weekend digging a car out of a foot of snow in Northern Scotland.

Two points.
1. Geothermal is good. I know people with experience on ground source heat pumps, and who certainly wouldn't build/buy a new house without one. They work well with underfloor heating, which means you don't have radiators taking up wall space. I don't have experience of heat pumps with cooling/conditioning systems as air con is less essential at 55 North...
Main issue with ground source heat pumps is having enough space to drill the holes, especially if you are in town. In much of America, that shouldn't be a problem as you have a lot more room!

In the longer and bigger picture geothermal energy could be very important for the US. There is a technology called 'hot dry rock' or 'enhanced geothermal' where a fluid is pumped into fractured subsurface rocks. The fluid can be used directly for heat or indirectly for electricity. MIT have estimated the US could install 100GW of this technology by 2050 (total US electricity demand is between 650-750GW). Geothermal using existing technology seems undeveloped and there is at least 10GW of buildable plants see
US Geothermal Power Could Top 10 Gigawatts.

Here is a summary I wrote about the current status of various renewable technologies (apologies if I put this up before, its been a long thread!)
Current Status of Renewables

2. Regarding your worry about heat pollution, I think that on a global scale all renewables are good. Let me explain without any maths.

Heat pollution will only warm the planet if the heat wasn't there to start with! So a coal fired plant creates a lot of excess heat (about 45%) that goes into the atmosphere. Where did the heat energy come from? From the chemical energy in the coal, which has been locked up for 250 million years. So burning that coal suddenly is going to release heat that wasn't there before (at least for 250 million years). And there could be a 'global warming' effect.

But think about a wind or wave power plant. Was it is doing, is just concentrating energy that is already there in the atmosphere or oceans of the planet. The waves are already pounding away and the wind is already blowing. Ultimately that energy comes from the heat supplied by the sun - no sun, no atmospheric circulation, no wind. So in a wind/wave plant we are taking a little of the earth's heat, concentrating and transforming it to a convenient form (generally electricity). We are not producing heat that wasn't there before, so on a global scale wind/wave/solar plants are not going to warm up the planet. To get heat from a wave plant, we are in effect cooling the ocean slightly, so it all balances out.

As you have pointed out, all these technologies have waste/inefficiencies. There could well be local heat pollution - in fact there is almost certain to be somewhere, whatever technology you use, but that's a different story and its not going to warm the plant as a whole.

I think you could make the same argument for nuclear. What you are doing is concentrating heat that was already there in the earth (radioactive ores produce heat) and using that to make electricity and creating waste heat. The heat will be coming out into the air (or into the cooling water that nuclear plants) use rather than into the earth's crust so there will be some heat capacity issues but the total amount of heat released will be same. However, I'm more of a chemist than a physicist so I'll check that out some time.

Finally, I am encouraged that both you and Bruce are both (as he puts it) 'all in favor of geothermal, tidal, and hydroelectric power'. I'd guess that Bill D and Amos are as well. So essentially, despite the near 1000 posts of argument here, there is actually a consensus there. Some people might say 'build renewable plants because of global warming' some might say 'build renewable plants to avoid pollution' and some might say 'build renewable plants so we don't have to get oil from the Middle East'.

I just worry that the need to get on and build the things gets obscured by the politics of everything. We know/expect that there are lots of interested parties and vested interests, but the actions that need taking seem fairly clear - build renewable plants, encourage energy efficiency at home and in offices, inflate your car tyres properly. And the nice thing is that some of this is stuff that individuals can do as well as governments and corporations.

If this thread is going to carry on, I'd like to see people trying to aim for a consensus rather than just keep posting quotes that support their arguments - and I'm not looking at anyone in particular there.

cheers KP

PS It amuses me how the most argumentative threads among US Mudcatters are the political ones whereas the Brits get all het up about the definitions of folk music. Do you think I could start an inclusive thread along the lines of 'Obama supports 1954 definition' or 'Palin likes Show of Hands'? :)