The growing green building sector has drawn in a number of startups promising to bring new energy efficient and eco-friendly formulations of traditional building materials to market (see The Year in Green Building and New $100M Green Building Fund Launches).

San Francisco startup CleanBoard, however, wants the $17 billion drywall industry to know that its "zero carbon footprint" product won't be any different than the gypsum drywall they've been seeing for decades – except that it will be made using the heat of the sun.

CleanBoard founder Rod MacGregor has been manufacturing drywall in China and importing it to the United States under the Bedrock Building Materials brand since 2005.

Now his new company has developed a system of using mirrors to collect and concentrate the sun's rays on a heat collector, which then heats a transfer fluid that will be used to heat drywall ovens to up to 200 degrees Celsius. Excess heat transfer fluid will be stored in pressurized chambers for up to 24 hours, to make drywall at night or on cloudy days.

It's a bit likesolar-thermal plants being built by BrightSource Energy or Ausra, except that the heat is used directly, instead of using it to boil water and spin a turbine to make electricity, MacGregor said.

"We only want heat to power an oven," he said. CleanBoard, which is privately funded, has developed the patent-pending technology itself and plans to have a Southern California plant making test amounts this year and be in full production in 2010, he said.

Using solar-thermal power for these kinds of "industrial process" heat needs – especially those at lower temperatures – has long been a potential sideline for solar thermal power plants. But a 2008 report by the International Energy Agency found that there was a lot more opportunity for solar-thermal in industrial heat than the 25 megawatts of power then in use for it worldwide.

Think of a sheet of gypsum drywall as "a brick of energy," MacGregor said. Making drywall uses about 1 percent of the U.S. industrial energy supply, which represents about one-third of the country's total energy usage, he said.  In the case of drywall, energy represents nearly half the costs of a finished sheet, he said – "The rest is mud and paper."

CleanBoard's solar-thermal system should be able to deliver heat for baking drywall at an equivalent cost of about $3 per million British thermal units, or BTUs, MacGregor said. Getting the same amount of energy out of natural gas hasn't been that cheap in the United States since late 2001, and has cost more than $6 per million BTUs over the past year.

Drywall is one of a growing number of building materials that startups are trying to make "greener," by reducing the energy used to make them or replacing materials with more sustainable ones.

They include Los Altos, Calif.-based Integrity Block, which makes building blocks from rammed earth, Carlstadt, N.J.-based Hycrete, which makes waterproof concrete, and Sunnyvale, Calif.-based Serious Materials, which makes its own version of environmentally friendly drywall.

One way companies can claim greater environmental sustainability is by buying carbon offsets, or paying for projects around the world that reduce greenhouse-gas emissions by a certain amount – a method that some critics call greenwashing (see Carbon Offsets: To Define or Not to Define?).

CleanBoard is already buying carbon offsets to allow it to sell a "zero carbon footprint" drywall at prices close to those for premium drywall, MacGregor said. Once the company's solar-thermal drywall plant is up and running, the company will use that solar heat to do away with most of the company's greenhouse-gas emissions related to energy use, and buy offsets for the remainder, he said.

MacGregor expects production to be about 2 million square feet in 2010, 10 million square feet in 2011, and 100 million square-feet of drywall a year at top volume. He expects he'll be able to find a market for the material for Leadership in Energy and Environmental Design (LEED)-certified buildings, which make up a growing part of many builders' portfolios (see Green Building: Cheaper Than You Thought).

CleanBoard also improves its environmental profile by using 100-percent recycled gypsum from construction waste and the calcium sulfite that's a byproduct of coal-fired power plant smokestack scrubbers, MacGregor said.

Still, the fact that CleanBoard is using gypsum, a product that's originally mined in open pits, differentiates it from other "eco-friendly" drywall makers. Serious Materials, which raised $50 million in 2007, uses a low-heat chemical process to make its EcoRock drywall material out of non-gypsum sources using less than one-fifth the energy of the traditional stuff.

Kevin Surace, Serious Materials' CEO, noted in an email that using solar power to dry gypsum is an idea that's been around for decades, whereas his company has come up with a new means of making drywall from new materials.

"Industrial processes should be redesigned from scratch to simply use less energy, period, not just use solar to waste energy on very old material science," he said. Serious Materials' drywall also beats its gypsum counterpart on strength, mold resistance and other qualities outside of energy efficiency, he said.

Still, Marc Porat, chairman of Serious Materials and founder of another green building startup, CalStar Cement (see Here Comes the Green Brick), said he supports different ways to make more environmentally friendly building materials.

"I don't see competition as being other green companies," he said. "I see competition as being the energy challenge and climate change."