It’s rare these days that one reads about new geothermal technology (there have been only three geothermal posts in all of GPB history), so I like to highlight new developments when I see them.

Recent Department of Energy awards for small clean tech businesses included one to Cool Energy, a Boulder, Colorado, company that has developed a new Stirling engine that converts low temperature heat energy into electricity.  The grant will support a demo program to build the company’s first 20kW prototype engine and use it to generate electricity from untapped heat from distributed geothermal sources.

Cool Energy owns at least eight U.S. patents and patent applications, including U.S. Patent No. 7,617,680, entitled “Power generation using low-temperature liquids” (‘680 Patent).  The ‘680 Patent is directed to systems and methods of generating power through the use of thermodynamic engines and liquid cryogens (materials having a low-temperature boiling point).

The core innovation of the patented invention is recited in independent claim 1:

1.  A method of generating power, the method comprising:

providing a liquid cryogen in thermal communication with a thermodynamic engine to maintain a temperature differential across the thermodynamic engine with a heat source;

running the thermodynamic engine to convert heat provided in the form of the temperature differential to a nonheat form of energy;

collecting cryogen-vapor produced by vaporization of the liquid cryogen; and

combusting the cryogen vapor to generate additional energy.

This basic cycle is described in detail in the ‘680 Patent, and the different positions of the Stirling engine at the major steps of the cycle are illustrated.

FIG. 3 of the ‘680 Patent shows an embodiment of the invention in which the thermodynamic engine (304) is in an ambient environment (300).  The temperature differential is established by providing a cryogen (308), on one side of the engine (304).  Exemplary cryogens have a boiling point less than -150ºC and include liquid nitrogen, helium, liquid hydrogen, carbon monoxide, and argon.

The temperature differential across the thermodynamic engine (304) may be used to extract energy (312).  The conditions of the ambient environment (300) may be manipulated to improve efficiency, such as increasing the temperature differential with an external heat source (328).

The temperature differential may also be boosted by combusting vaporized cryogen with a combustion unit (310), which receives vapor from the cryogen source (308) by a direction mechanism (316).  An oxidation source (320) may be provided to promote burning.  Waste heat generated by combustion of cryogen vapor may be used to locally increase temperature on the hot side of the engine through mechanism (324).

According to the ‘680 Patent, the efficiency of energy extraction depends on the size of the temperature difference across the engine, and “the overall energy output of the combination is increased by energy E₂ 314 to provide total energy generation E₁+E₂.”

Cool Energy’s press release says the demo project will use the recoverable heat from co-produced liquids (presumably, the cryogens discussed in the ‘680 Patent) at oil and gas wells.

Fenix Energy (Fenix) is a Vancouver-based company that provides geo-exchange systems.  Geo-exchange, also called geothermal heating and cooling, means tapping into the energy stored under the Earth’s surface and using it as a heating and cooling source.

According to this Cleantechies piece, because Fenix’s technology uses vertical drilling that minimizes disruption to existing surroundings, it can be deployed in urban environments and particularly in green buildings.

Fenix owns at least one international patent application, Publication No. WO 2012/109759 (‘759 Application), entitled “Low headroom confined space geoexchange drilling system and method.”   

The ‘759 Application is directed to a low headroom drill apparatus (100) comprising a rotary drill head motor (101) supported on a drill mast (103), which is itself supported by a drill rig base frame (112) including floor supports (106).   The drill mast (103) can be elevated by an actuator (116) to a vertical drilling position. 

An axial drive means (114), shown in FIG. 1 as a chain and sprocket hydraulic motor drive, drives movement of the motor (101) in an axial drilling stroke to advance or withdraw the drill rod string (102) through the ground below a floor slab (110) of a building.  The drill rig base frame (112) may include transport brackets (118) to facilitate movement of the drill rig apparatus (110).

The drill mast (103) is of a length less than the maximum headroom of confined space in which the drill system (100) is being used, such as 6-7 feet in a parking garage or basement or 7-9 feet in an office building.  This enables use of the system without the need for any sub-excavation below the bottom floor of the building or other measures to provide sufficient vertical clearance for the drill mast (103). 

Max Headroom

According to the ‘759 Application, the invention is particularly well suited for use in multi-story buildings with vertically oriented geo-exchange piping and in smaller areas with strict headroom limits.

The Cleantechies article also noted that Fenix recently completed a geo-exchange installation at a building in Ontario after the first three floors were in place, and because the system is so unintrusive, other work such as plumbing, electrical and glazing occurred in parallel with the drilling process.

Potter Drilling, LLC (Potter) is a Redwood City, California-based company that develops drilling technology for various applications, including geothermal energy production.

Potter specializes in novel drilling systems that don’t require contact between the drill assembly and the rock in order to make holes in the geological formation.  Specifically, the company’s key innovations involve a process called spallation, which uses high intensity fluid streams to fracture rock surfaces. 

A common problem that arises during deep drilling is that non-uniform stresses are created around the borehole, which cause the rock around the hole to break out; this can make a circular hole become non-circular.  Pieces of rock can fall into the hole, causing the drill or casing to get stuck.  This phenomenon is aptly named “breakout.”

Potter’s drilling processes take a proactive approach to this problem by intentionally creating non-circular boreholes to avoid inadvertent and uncontrolled breakout.

In addition, Potter developed a technology to produce non-circular boreholes for ground source heat pump (GSHP) applications where it is desirable to separate the tube carrying water down the hole from the tube carrying water back up in order to reduce heat exchange between the different temperature streams. 

Potter owns U.S. Patent Application Pub. No. 2008/0093125 (‘125 application), entitled “Method and system for forming a non-circular borehole”, which describes some of the company’s drilling technologies for creating shaped boreholes.  

One of those is particle drilling for GSHP applications, which uses particles in an air stream to cut the rock.  This technology is being developed by a spinoff company called Ground Source Geothermal.

I talked to Dr. Tom Wideman, Potter’s CTO, who told me (no pun intended I think) that the company’s “most groundbreaking” technology is hydrothermal spallation.

Hydrothermal spallation uses hot water to cut through rock.  According to the company’s web site, hydrothermal spallation was invented and patented by Potter’s co-founder Robert Potter and Jefferson Tester of MIT. 

Potter is the exclusive licensee of U.S. Patent No. 5,771,984 (‘984 patent), which is owned by MIT and directed to apparatus and methods of excavation by hydrothermal drilling. 

The ‘984 patent covers a jet housing (602) rotatably mounted to a flow pipe assembly support (604).  The jet housing (602) contains two or more combustion chambers (610).  

Jet housing (602) contains passageways (614) for cooling water, passageways (616) for the fuel and passageways (618) for the combustion air.  It also has a central conduit (620) for the escaping combustion gases and returning flakes of rock. 

The hot fluid products of thermal combustion are jetted downward onto the rock though nozzles (612) located near the outer circumference of the bottom of the drilling apparatus.

This Clean Technica piece calls Potter’s hydrothermal spallation drill the “Holy Grail” of geothermal because of the promise that it can drill faster, deeper and cheaper than prior drilling systems. 

Potter is continuing its spallation innovation and patenting.  Wideman described Potter as an “IP-rich company” and told me the company has multiple recently-filed patent applications in the pipeline.

 

Last month Google.org announced investment of over $10 million in geothermal technology.  Specifically, the web search company’s investment arm will give $6.25 million to Sausalito California-based geothermal company AltaRock Energy (AltaRock), $4 million to Redwood City, California drilling technology company Potter Drilling (Potter) and almost $500,000 to the Southern Methodist University Geothermal Lab (SMU) (see greentech media piece here)

Although the United States trails other countries in some renewable energy sectors such as solar, wind and biofuels, it is the world leader in geothermal energy.

The particular technology Google.org is funding is EGS, or enhanced geothermal systems, which involve drilling deep holes into hot rock in two locations and injecting water into the cracks in the first location.  Steam pressure forces the resulting super-heated water up through the holes in the second location, and that heat is used to run a turbine and produce electricity.

According to AltaRock’s web site, the company owns a portfolio of EGS patent applications and holds exclusive licenses for related intellectual property.  However, searches of the U.S. Patent & Trademark Office database for AltaRock as assignee yielded no results, and AltaRock did not respond to an e-mail inquiry about its patent portfolio.  A similar search for SMU also came up empty.

The good news for AltaRock continued this month as it reached a deal with building products and real estate firm Weyerhauser Company to develop geothermal projects in northern California, Oregon and Washington.

 

Potter owns a patent application directed to drilling systems and methods for geothermal heat pump applications.  U.S. Patent Application Pub. No. 2008/0093125 (‘125 application) describes a method for creating more stable bore holes by making the holes non-circular.

According to the ‘125 application, elliptical, oval or eccentric shaped holes prevent portions of the rock formation from breaking apart from the bore hole wall.  Non-circular bore holes also facilitate installation of piping for heat pumps and provide improved geometry for heat exchange.

In addition to funding clean technologies, Google is developing its own.  Last month Google Inc.’s U.S. Patent Applicaton Pub. No. 2008/0209234 (‘234 application) published. 

The ‘234 application describes a floating platform-mounted computer data center with an electrical generator and cooling units.  The data center of the ‘234 application gets its electricity from wave power and is cooled by the sea water upon which it floats.