Geothermal energy?

[extragoode]

Originally Posted by LostCause

1.) Low availability of source heat. You either have to build over a volcanically active area or drill extremely deep wells.


- LostCause

How is this different from oil? Nobody says it's impractical to drill a big deep hole when there's oil down there, but if it's just a bunch of essentially heat, oh well then why bother!

[LostCause]

I believe you would have to dig ~35 miles deep before the earth would be hot enough to boil water. I've forgotten the exact rate at which the earth increases in temperature with depth, but I believe 212F is achieved around 35 miles based on a brainstorm I did awhile back.

35 miles is at the very limits of contemporary drilling technology. I also can't imagine the technical hurdles of capturing low-energy steam from such a depth. Liquids with low boiling points could lower the drilling depth needed, but efficiency and total recoverable energy would probably be extremely low.

The only comparable energy source to fossil fuels that I know of are: radioactive ore, hydrogen (w/ fusion reactor), and the sun.

Like with any source of wealth, whether it be money or energy, the first generation generates it, the second enjoys it, the third squanders it. Wealth isn't easy to come by and unfortunately, I think we are the third generation.

- LostCause

[DifferentPointofView]

Wait.. Since when was this thread moved to saving at home!? I put this in off topic. This probably explains why we're talking about using geo to heat our homes.

This isn't what I was talking about in the first place! i was talking about how if Iceland could potentially power HALF The earth just from Geothermal, why not have the US put some near it's volcanic hot spots?

I also originally was thinking about using Geothermal to generate Electricity. Hydrogen could cheaply be made if it was made using geothermal electricity, so the possibility is even more possible to build hydrogen cars, and Maybe Honda's hydrogen car might be more popular.

I'll have to ask Darin about the movement.

[Otto]

Why not use a conventional heat pump, but simply immerse the heat exchanger in ground water or a pond or lake if you have one nearby? That way, you would not necessarily need the fan or fan motor to circulate over the heat exchanger: Advection would do the work.

Water is ~800 times denser than air, so has ~800 times more heat in it for a given volume. Around here, the ground water ambient temperature is ~50 degrees F in January.

My lot fronts on a small lake, so I could put slinky coiled tubing in the lake for heat exchangers. However, the soil has natural conduits for groundwater, which runs by gravity flow to the lake. So, I'll build the house with a french drain around the perimeter to intercept the groundwater flow, then use that water in a small basin and immerse the heat exchanger there: 50 degree ground water will come to me via gravity flow, for free. No pump or motor needed.

And, a well-insulated building needs much less heat or air conditioning from any source than a poorly insulated one. Best to go with passive solar architecture, well insulated, for modest demand on HVAC.

[Otto]

Originally Posted by extragoode

How is this different from oil? Nobody says it's impractical to drill a big deep hole when there's oil down there, but if it's just a bunch of essentially heat, oh well then why bother!

Some smart people have made two proposals regarding old oil wells. I propose doing both, simultaneously:

1. Use the existing but non-economic holes for geothermal purposes by pumping water down them to capture geothermal heat.

2. Add microbes to eat up the oil residue, making natural gas in the process, which can be bottled and burned for energy.

[dremd]

Originally Posted by Otto

Some smart people have made two proposals regarding old oil wells. I propose doing both, simultaneously:

1. Use the existing but non-economic holes for geothermal purposes by pumping water down them to capture geothermal heat.

2. Add microbes to eat up the oil residue, making natural gas in the process, which can be bottled and burned for energy.

NOW there is an Idea. I really don't know what the temp is at the bottom of a well. A local guy is putting windmills on abandoned offshore platforms, I'll try ask him next time I see him, sounds right up his alley. FYI the initial reason for the oil rig windmills is that it is easier to get permits to build an oil well than to build a windmill, then he realized that there were plenty of pre-existing oil wells sitting abandoned.

[dremd]

Originally Posted by Otto

Why not use a conventional heat pump, but simply immerse the heat exchanger in ground water or a pond or lake if you have one nearby?

If you had the slightest flow I think it would work well, but I don't know how much advantage you would get over Diesel Johns setup.

[Otto]

Originally Posted by dremd

If you had the slightest flow I think it would work well, but I don't know how much advantage you would get over Diesel Johns setup.

As I understand it, slow flow is better than fast flow vis a vis heat exchange--slow gives more exposure time on the fins, so is more complete & efficient.

I thunk of this after looking at the basement of a neighbor's house across the lake. His house is pier and beam foundation, and a spring flows under the house in wet (winter) season, such that ground water @ ~50 degrees is channeled through a ~3" PVC pipe at a rate maybe ~4X what you'd get filling your bathtub at full blast. In other words, plenty. So, I figure you could stick a conventional heat pump down there, but remove and discard the fan and its motor, with the heat exchanger immersed in a box with Mother Nature providing the ground water via gravity flow over the fins. The water then goes on its merry way to the lake, as always.

This saves the need for trenches, slinkies, fluid pumps, etc. and is quiet. The freon inside the heat exchanger does not know or care if there is air or water on the out side of the fins.

Installation of a french drain would intersect whatever subsurface water seeps or "pipes" there may be in the earth, and then channel such water away from the foundation while using its heat. So, french drain instead of trenches and slinkies.

[Otto]

Originally Posted by dremd

NOW there is an Idea. I really don't know what the temp is at the bottom of a well. A local guy is putting windmills on abandoned offshore platforms, I'll try ask him next time I see him, sounds right up his alley. FYI the initial reason for the oil rig windmills is that it is easier to get permits to build an oil well than to build a windmill, then he realized that there were plenty of pre-existing oil wells sitting abandoned.

If the well is more than a few feet below the frost depth, the well temp will be whatever local ground temp is in your area. Around here, that's ~50 degrees, but in most of the US somewhat warmer.

Bugs have always known this, and all hibernating animals that simply burrow down to acceptable temperature level in winter.

I'm glad your friend is doing windmills on defunct oil platforms. You might also ask him if his windmills use vortex generators to enhance efficiency. VGs make major improvement in lift/drag of airplane wings, which operate in the same Reynolds numbers and general aerodynamic range as windmills. Should get more power out of the windmill at lower windspeeds, or even make them productive at windspeeds previously too slow for the windmill. Might help with noise reduction, too, which is often a major gripe from the neighbors.

[Big Dave]

Two different things are being discussed.

True geothermal energy is using volcanic heat to generate electricity.

Water source heat pumps use ground heat to heat/cool a heat pump.

The first one is very mature technology. Geothermal heat and power have been around since the nineteenth century. It is indeed free heat, once you get past the initial cost, but there is a very limited set of usable resources and almost all of them have been developed.

Water source heat pumps are a big issue here on the frozen steppes because we have a very high water table. I can sink a 100ft well and slide a heat exchange loop down it and provide a heat sink to easily run a 5 ton (60,000 BTU/hr) heat pump. That is overkill for AC (three tons does a decently insulated 2,000 sq. ft. home) but needs help for heating. In the Midwest you need 5 BTU per hr per sq ft and that is iffy. You also need auxiliary heat to make up the difference and warm up the supply air to the 104 degrees that people like. Heat pumps are notorious for their 95 degree supply air that makes people feel cold. Water source heat pumps are very efficient and suffer no seasonal loss of efficiency.

Water source heat pumps have a future but geothermal is too site-dependent for widespread use.