Another day, another round of unearthing more investments from the secretive Quercus Trust.

The firm, funded by math whiz-turned-multimillionaire David Gelbaum, has now plunked down money into at least 47 technology companies, according to our latest count, and all but one of them are focused on green technology. The exception is Evolution Robotics, which produces visualization and navigation system for robots. This could come in handy for hazardous waste cleanup.

With 47 investments, Quercus has now one of the largest portfolios – in terms of sheer number of companies – in venture capital. The size of its investment and management team is unknown. Other than Gelbaum, the only other VC associated closely with the Trust is David Anthony, who makes investments in parallel with Quercus from his firm 21 Ventures.

By contrast, Foundation Capital, one of the more successful greentech firms, has ten publicly announced green investments and most revolve around two discrete themes – smart grid and green buildings. Three members of the firm concentrate on greentech.

We published an article on the firm in November that identified 34 companies that had received money from the firm, and found three more right afterward. Although some were small public companies, most were small, private or early-stage outfits. Readers like Scott Miller of Q Advisors and our own research have unearthed ten more since then.

The investments span the gamut of green. While most of the investments have been in solar (14 so far), Quercus has also put money in water (Colorep), biofuels (LiveFuels), batteries (Firefly Energy), wind (Magenn) and hydrogen (Nanoptek.).

Some of the companies in the trust seem more in the science experiment stage and were founded only a few months ago. Others, however, are already signing major alliances deals. The firm is one of the principal investors in GridPoint, the smart grid software company that has raised over $200 million and is working on the high-profile SmartGridCity initiative with Xcel Energy. ReGen Power Systems was founded in the mid-1990s.

Some of these companies, however, seem to be touting technologies and ideas for markets that have already attracted a number of startups.

Entrepreneurs who have received money from the trust say Gelbaum is not investing in these companies as a way to evangelize green or as a form of charity. The Los Angeles Times calculated in 2004 that he had given at least $250 million to environmental causes. He wants to make money from his investments. Nonetheless, some add that Gelbaum may well contribute the profits to environmental causes.

How many investments has the firm made? We have no idea. Quercus does not issue press releases, and it does not list its phone number. (Phone numbers on SEC forms lead to its law firm.) Anthony declined to comment. There are likely others. Interestingly, four of the newly discovered investments are in Israeli companies: 21 Ventures invests a substantial portion of its capital in Israeli firms.

And the new list includes:

BioPetroClean: Out of Tel Aviv University, BioPetroClean designs bacteria cocktails for purifying water or cleaning oil spills. The company competes against 212 Resources and Altela for oil refineries, mines and other industrial customers who need to recycle water in local operations.

3GSolar. Another Israeli outfit. 3G makes a photovoltaic dye that it says is 40 percent cheaper per watt than silicon. The efficiency, however, is far lower: The company hopes to get to 7 percent. It will primarily be aimed at off-grid power in emerging markets. Konarka, one of the early photovoltaic dye companies, has been trying to get to mass acceptance for years. It primarily sells to the military.

Advanced Telemetry: A software developer, it makes a console that dynamically tracks gas, water, solar and other electricity consumption and provides recommendations for efficiency. This has become a crowded market in the past two years with several companies, such as Tendril, already in trials with large utilities. Advanced lists alliances with only a few companies and organizations. One, Zensys, has been falling behind ZigBee to become a standard in home automation.

ETV Motors: Formed this year, ETV wants to make the EP3, a power system for electric cars that includes a battery, a battery charger, and a system to let those two parts communicate efficiently.  The company doesn't list its address, but job board ads have ETV seeking employees in Israel.

Lightwave Power: The company is actually part of a new wave of companies that are getting into solar without necessarily making solar cells. Instead, they are concentrating on films or other additives that will improve the performance of cells.

ReGen Power Systems: A 12-year old Massachusetts company, ReGen has a Stirling engine that converts factory waste heat into power. The Stirling operates at lower temperatures (200 to 400 Celsius) than most waste heat systems. It competes with ElectraTherm, which has a similar product, as well as Recycled Energy Development, one of the giants in the field. The waste heat market has also attracted several companies with thermoelectric materials, which directly convert heat into power with semiconductors. (Promethean Power, another Quercus company, has a thermoelectric device.) Cypress Semiconductor is trying to get into this market.

TBT Group: It specializes in piezoelectric materials. When these materials are bent or vibrate, they create minute amounts of power. Piezoelectrics have been studied extensively at Georgia Tech. Germany's EnOcean has already commercializes a few devices on these principles.

Technospin: The company has created a small wind turbine with blades shaped more like an airplane propeller. For homes and off-grid commercial centers. It has been around since 2004. In the past 15 months, investors and entrepreneurs have started to revive the small wind category.

Variable Wind Solutions: The company makes components that monitor the speed of wind turbines to stabilize the output for grid operators and utilities. It is from, you guessed it, Israel.

LaunchPoint Technologies: An R&D lab for hire. It has worked on, among other projects, Maglev trains, pressure sensors, and an electronic rail system where the engine is actually in the track.

Graphene Energy: Founded in December 2008, the company hopes to make ultracapacitors out of graphene, sheets of pure, crystalline carbon. It is the brain child of Rod Ruoff, a professor at the University of Texas, and Xin Zhao. Some believe that ultracapacitors, which store energy and can potentially charge far faster than batteries, could charge electric car batteries while the cars tool down the road or replace batteries entirely.

Tags: batteries, biofuel, energyefficiency, environment, gelbaum, gridpoint, quercus, smartgrid, solar, ultracapcitors, vcinvestments, water, wind