A Greener Future for Renewable Energy Supply Chains

According to Environment America, U.S. wind and solar energy generation has more than tripled over the past decade. And that trend is headed sharply upward: BloombergNEF’s base-case forecast projects annual U.S. renewable energy installations will average 102 gigawatts (GW) over the next decade—quadruple the 26 GW averaged since 2014.

That’s a lot of new capacity coming online—and a lot of construction material that will be used to build it. Concrete, in particular, plays a significant role in building such installations. And as one of the leading sources of man-made greenhouse gas emissions, concrete’s carbon footprint must be lowered to make these renewable energy projects truly “green” from a life-cycle perspective.

Concrete is used extensively in wind farms. Most U.S. wind turbines sit on a spread foot foundation that can consume up to 400 tons of concrete per megawatt installed. Today’s taller wind turbines, with a capacity of 10 MW or more, not only require ever-larger concrete foundations, but also typically require the turbine tower itself to be made from concrete (rather than steel). 

Concrete is similarly used in solar projects for foundations to support panel arrays; as ballasts to anchor solar panels in ground-mounted installations or on rooftops; and as piles to anchor solar panels in difficult terrain. The Crescent Dunes concentrated solar power project in Nevada not only uses concrete foundations to anchor its more than 10,000 heliostat mirrors, but also incorporates a reported 9,100 cubic yards of concrete in its power tower (roughly 900 concrete trucks’ worth).

As noted, concrete has an emissions problem—one that stems almost wholly from the manufacture of portland cement, a standard component of virtually all concrete mixes. Manufacturing one ton of cement generates approximately 0.8 to 0.9 tons of CO2 emissions. However, if that ton of cement is replaced with one ton of fly ash to produce concrete, virtually all of those cement-related emissions are avoided.

Fly ash—a by-product of coal combustion—has been specified for decades in the U.S. to help improve fresh concrete’s workability and strengthen hardened concrete’s lifespan and resistance to water and chemical ingress. Now, as climate concerns have emerged, its utility in lowering concrete’s carbon footprint has redoubled its value as a construction material.

Alert readers will note the irony that renewable energy’s rapid growth is displacing coal plants’ production of the very industrial by-product—fly ash—that can help lower the carbon footprint of the concrete used to build wind turbines and solar arrays. Fortunately, while coal plants indeed continue to retire, the U.S. has hundreds of years of fly ash stored in landfills and impoundments around the country—surplus ash that was not used in concrete or other applications during the industry’s heyday.

The American Coal Ash Association estimates that approximately two billion tons of ash is available nationwide to be harvested and used to help meet the concrete sector’s aggressive net-zero-carbon targets. Utilizing those two billion tons of fly ash in concrete production would thus avoid the release of almost two billion tons of CO2 into the atmosphere—the equivalent of removing every gasoline-powered car in the United States from the road for two years and is the equivalent of India’s annual CO2 emissions – the world’s 3rd highest. 

Ash harvesting is growing quickly and is helping to provide specifiers with lower-carbon concrete in areas of the country where coal plant retirements have left ready-mix producers with little access to fly ash fresh from the power plant. Indeed, the rise of ash harvesting promises a more reliable supply of ash, as its availability is unaffected by seasonal or other variations in the operation of coal plants.

For five years, Eco Material has been harvesting ash from a landfill in Pennsylvania and beneficiating it (improving its characteristics in preparation for sale). Ash harvesting is now integral to our business plan, and operations are underway at two harvesting sites in Georgia that are expected to produce approximately 1.2 million tons of ash annually once they are fully operational. We have several other harvesting projects underway in the Gulf Coast, Midwest and Texas. WE are also upgrading some of these ashes to our Green Cement products which relace even more highly polluting Portland Cement in concrete mixes.

Substituting a portion of the cement used to produce concrete with fly ash is a proven method by which to decarbonize concrete. Harvesting and beneficiating previously disposed ash is ensuring that this valuable resource will be available for many decades into the future as concrete producers aim for a net-zero-carbon industry. All builders of infrastructure are encouraged to incorporate it in their concrete to lower the carbon footprint over the life-cycle of their projects.