Sausalito, California-based AltaRock Energy has capitalized on the alternative energy craze with a bid to make Enhanced Geothermal Systems (EGS) a viable alternative to fossil fuel-based power. Eventually, AltaRock claims that it could supply 20% of all U.S. energy. But Altarock, which began a demonstration project in 2008 at The Geysers, an area located 70 miles north of San Francisco, has had its share of setbacks. The project was temporarily halted in September due to safety concerns. Once the demonstration project is back on track, expect AltaRock to expand quickly, as the company has over $26 million in backing from Google.org, Vulcan Capital, Kleiner Perkins Caufield & Byers, and Advanced Technology Ventures. Last month, AltaRock also received $25 million from the U.S. Department of Energy--the single largest grant to a geothermal company from the government.

This Al Gore-backed startup plays to the growing corporate desire to keep track of CO2 emissions for both carbon regulation and CSR purposes. The company's flagship product, Hara Environmental and Energy Management (EEM), is a software-as-a-service solution that keeps track of resources consumed by an organization, including energy, waste, carbon, and fossil fuels. Hara has garnered the confidence of major customers like Coca-Cola and the City of Palo Alto, which claims that the software will save $2.2 million and cut greenhouse gases by 15% over the next three years. Last month, Hara announced that it raised a total of $20 million from investors including Kleiner Perkins Caufield & Byers, Jafco Ventures, and Nth Power.

Lithium-ion battery makers may still cater to a niche market, but demand is about to explode as the next generation of hybrid electric vehicles roll off production lines. Imara, a Menlo Park, California-based startup, hopes to lead the charge with a lithium-ion battery that delivers a high power-to-weight ratio and long life cycle. Imara has a head start over its competitors--compared to major lithium ion manufacturer A123, Imara's batteries offer 20% more power and 60% more energy density (range between charges). The company has thus far raised over $19 million from investors including Nth Power and Battery Ventures. And this past September, Imara announced that it has started up production at a manufacturing facility capable of producing 8 million cells each year for customers in the power tool, outdoor power equipment, and transportation markets.

Residential and commercial buildings are responsible for 38% of all CO2 emissions, and much of that comes from the construction process. At the same time, the green building market is expected to grow between $96 billion and $140 billion by 2013. Enter Integrity Block, a startup that manufactures the sustainable answer to the standard concrete block. Integrity Block's building blocks are made out of a proprietary soil composite that contain 50% recycled content and require 40% less energy to manufacture. The startup only began shipping its blocks in 2008 and has already received a number of accolades, including a Green Log Home Award, Green Dot Award, and a selection as a BuildingGreen Top 10 Product. Integrity Block also garnered $2.7 million in funding last year in a round led by Navitas Capital.

This San Francisco-based startup merges metal with origami to make cheap and efficient sheet metal-based products. The company cuts "smiles" (tabs) into thin pieces of sheet metal so that the material can be folded into complex structures using as few components as possible. According to IO, an oven made with its process can be constructed from just four components, compared to the standard seven. By minimizing the amount of materials necessary, IO claims that it cuts 20% off the cost of appliances and car parts.

Instead of selling completed products, IO sells intellectual property and collects royalties from companies that buy its services. So far, IO is on track for success--the company has raised $32 million and big names like Whirlpool and Eaton have signed up for IP rights.

We don't all drive electric vehicles quite yet, and in the meantime, SOMS Technologies thinks its high-efficiency engine oil filter can seriously cut down on oil use. It may not be the sexiest green tech innovation, but its the first major upgrade to the standard oil filter since the 1970s. The microGreen filter, which purportedly lasts for 30,000 miles (10 times the recommended range for standard oil filters), saves on oil use by up to 70% and improves fuel efficiency by up to 5% thanks to a microfilter that captures particles down to 2 microns. SOMS has already raised $900,000, and the startup recently announced a pilot program with TruGreen, the largest lawn care services company in the U.S, to provide its microGreen filter to the company's fleet. SOMS also sells its filter through its Web site.

As utilities continue to roll out smart meters as fast as possible, eager energy management companies attempt to quench the growing thirst for their wares. One of the most promising (and well-funded) startups is Tendril, a 5-year old company that has raised over $40 million for its suite of energy management hardware and software solutions. Among Tendril's products: a smart thermostat, web-based energy portal, in-home energy display, smart outlets, and cell-phone apps that let customers keep track of energy use and remotely turn appliances on and off. Now that GE has announced a partnership with Tendril to develop software that connects smart appliances to the grid, don't be surprised if you find Tendril's products in a home near you.

Like it or not, incandescent light bulbs are being phased out. When all is said and done, we'll be left with mercury-filled CFLs and expensive-yet-attractive LED bulbs. Oree, an Israeli startup, its trying its hand in the LED market with a flexible, credit-card sized bulb that the company claims is cheaper and more efficient than competing LEDs. The bulb is ideal for office and general building use, where flat LED lighting could be an invaluable energy-saving tool. Oree has raised $11 million from investors including Genesis Partners, Kreos Capital, and Silicon Valley Bank.

Another major entrant in the burgeoning green building material industry is Calstar, a Foundation Capital-backed startup that makes low-energy, low-CO2 bricks from sand and fly-ash--a byproduct of burning coal. The bricks look and feel like standard clay bricks, and are expected sell for comparable prices. There's just one hitch: no one knows how well fly-ash bricks hold up in the long-term. Calstar will find out soon, though. The company started production at its Newark pilot plant last month. If all goes well, production at Calstar's Wisconsin plant will begin in December, and 12 million bricks will be produced in 2010.

Founded in 2007, this Los Gatos, CA-based startup claims that it has developed a process to turn CO2 from sources like coal power plants into replacement for Portland cement. As interest in carbon capture and storage increases, Calera offers up what it says is the best carbon sequestration technique in existence--a process that sequesters half a ton of CO2 for every ton of cement manufactured. Calera isn't the only company working on carbon-sequestering cement. Carbon Sciences and Carbon Sense Solutions are working on their own processes, but Calera has one distinct advantage: $50 million in backing from Khosla Ventures. The company already has a pilot plant set up in Moss Landing, California, and the California Department of Transportation has expressed a desire to test out the cement.