New medium scale, lower-temp geothermal electric

[spinningmagnets]

The Chena hot spring near Fairbanks, Alaska has a lot of 165F (74C) shallow geothermal water within easy reach, and also plenty of 40F (4C) surface water to use for a condenser.  

Since water boils at 212F, they decided to try a new design that uses a common R134a refrigerant in a secondary loop that boils and condenses within these parameters to power a conventional high-RPM turbine. The turbines not only draw power from the pressure supplied to their inlets, they also derive significant power from the partial vacuum drawn by the condenser.

The hot water is drawn from a 700 ft well, and discharged to the surface. The cold condenser water is supplied without a pump from an elevated natural reservoir and it is also discharged to the surface.

Their previous power supply was a bank of Diesel-generators that consumed an average of 1,000 gallons of fuel a day. The diesel power was provided at $0.30/Kwh, and the cost of power from new plant is $.07/Kwh.

The $2.2 million project is rated at 400 Kw, and was put together in two 6-month construction cycles due to severe winters. Its modular nature allows for easy expansion as the city's electrical needs increase.

I believe this is a major development, because the lower heat requirement of this type of plant makes solar-generated electricity more cost-effective. Also, the major components are readily available as they were adapted from existing large refrigeration components by the Carrier corp.

Nuclear power (though improved) is still effectively blocked, and the new "cleaner" coal plants take about 5 years to build.

http://www.yourownpower.com/Power/#How%20it%20Works%20...

http://en.wikipedia.org/wiki/1%2C1%2C1%2C2-Tetrafluoroethane

[BigBreaker]

Google "organic Rankine".  While not common, the engineering of the technology you describe is well understood.

Water is cheap, has a huge heat of vaporization and boils at a relatively low temperature compared to typical fuel combustion.  Few other working fluids have such a trifecta of features.  But other fluids are perfectly servicable and if the driving temperature is near or below 212 degrees, they become more desireable.  In this case the heat is low grade but nearly inexhaustable... it makes sense to use something that boils at a lower temperature.  They are running an air conditioner in reverse and extracting the energy.

I wish they reinjected the ground water and used a pure hydrocarbon (iso-butane) or ammonia for the working fluid.  R134a is healthier than R12 but still far nastier than it needs to be.

[zeusmorg]

  Hmm, makes one think, wonders just how difficult it would be to scale to home power generation, using solar heated water, ground loop for condenser cooling,(with air in winter).

Now it's just figuring out where to scrounge the usable components. I'm sure a lot could be salvaged from a window A/c unit. Probably the most difficult thing would be building the turbine, and figuring out the sizing of all the components.

Well, at least it's food for thought.

[spinningmagnets]

My first choice is two wind-gens first, and then to add PV as I can afford it (when I retire), but...

Vaporising and condensing cycles have many similarities to steam engines. I cant help but to believe a vertical two-cylinder motorcycle engine (Triumph/Yamaha 650?) could provide a few Watts just for fun.

Over at "builditsolar.com" one of the best projects is a backyard shed that has one of its long sides oriented for maximum winter sun collection. Water is trickled over home-made collectors that drain to an underground insulated storage pit.

The hot water is used for a floor radiant heat system in the house, but if I already had more hot water than I needed, I can't help but to wonder if it would be worth scrounging some junk to make a R134a "steam engine" to get a few extra Watts into the battery when there's no wind.

Certainly more trouble than its worth, but better than spending my retirement shopping with the wife for more shoes...

[jonas302]

Now thats the way to figure payback on these projects

Have fun

[Tritium]

This could be used in many oil wells both producing and spent as well as some dry holes that have a downhole temperature sufficient for vaporization of the refrigerant. I have 2 dry holes with temps around 155 degrees F very near my house on my property so this is very interesting to me.

Thurmond

[DamonHD]

Possibly if there is that small an amount of energy and a small temperature differential to work with, eliminating moving parts and using a solid-state Peltier/Seebeck device might be worth thinking about.

I have no idea how expensive or effective it would be...

Rgds

Damon

[spinningmagnets]

Minersville (West of Beaver, Central Utah) found out there's enough geothermal heat near enough to the surface to drill wells and run a steam-turbine electric plant. Exploratory drilling leases have also been signed for parts of Nevada and Arizona.

The hot ground water was found to have an average temperature of 260F. Although water is well known to boil at 212F (at sea level) when you raise its contained pressure (inside a steam engine) the waters temperature must be raised much higher for it to boil.

The new geothermal plants use boiling and condensing Freon, which even while under pressure, will still boil at the fairly low temperature of 180F.

California has built several experimental solar water-steam generation plants (SEGS, Mojave desert) in order to establish the best design, should this type of plant be chosen for duplication elsewhere.

One problem encountered is not only the greater temperature needed to boil pressurized water (a constant input of over 300F), another concern is the high volume of surface water that needs to be evaporated in the process of spray-cooling the exterior of the condensers (radiators) so the spent steam will condense back into a liquid.

Pressurized Freon needs much less heat to boil (180F), and much less water to condense. This type of system using "Freon-Steam" is called an "Organic Rankine Cycle" (ORC). Although I don't know of any ORC generators that use solar heat for power, it is only a matter of time.

http://thefraserdomain.typepad.com/energy/2008/01/raser-technolog.html

[spinningmagnets]

Since the previous postings, I have occasionally done searches on smaller home-scale ORC units. Here's some:

http://www.keelynet.com/orc1.jpg

Matteran one-HP ORC, single piston motor

http://www.redrok.com/images/sterl2hp.jpg

Matteran 2-HP ORC on pop-up trailer, uses a turbocharger turbine

http://www.mchp.eu/rankin1.jpg

European company "Inergen" claims to have sold several thousand 1Kw refrigerator-sized ORC units. Uses methane or propane for boiling Freon, can be configured to use waste heat as hot-air/hot-water co-generation. Uses a scroll-style compressor run backwards as a freon motor. Advertised as a "Green" back-up generator.

http://www.redrok.com/images/sterl2hp.jpg

redrok solar power site, many links, big section on home-steam and home-ORC, recommends scroll-style compressors as motors. Has pics and info on available automobile scroll compressors.