Sustainable and renewable sources of energy are growing in popularity as they become more cost effective and fossil fuel emissions continue to cause environmental concerns. A popular form of renewable energy is wind turbine generators (WTG). WTGs are not only growing in numbers of installed turbines, but the nameplate capacities are getting larger because of the increased nacelle (generator) and rotor sizes.
In 2012, the average nameplate capacity was 1.94 megawatts (MW) with a rotor size of 307 feet, according to the U.S. Department of Energy. Today’s installations range from 2.7 to 4.5 MW with 417-foot to 476-foot rotors. The foundations supporting WTGs are already large and traditionally have cast-in-place gravity foundations that use massive amounts of concrete and rebar and require more soil excavation.
The WTG foundation’s main role is to transfer the loading from the turbine to the ground and provide stability for the WTG to rotate and generate power. Innovations in the design of the WTG foundation continue to emerge as the WTGs become larger. One innovation developed by Hanson for the WTG foundation is the use of soil anchors rather than the traditional gravity foundation. Soil anchors transfer the loading to the mass soil layer, rather than relying on the weight of the concrete and overburdening the gravity foundation.
A soil anchor foundation can reduce the size of the foundation footprint up to 50%. The smaller foundation size does not just reduce the cost — it also helps reduce emissions. An anchored foundation will have less excavation, soil backfill, concrete and reinforcement. Assuming a 3 MW turbine at a hub height of 361 feet with good soils, the excavation and backfill is reduced by 85% and the concrete and reinforcement is reduced by 80% and 50%, respectfully.
The reduction in emissions due to the smaller foundation footprint for the example above is 177.23 metric tons of carbon dioxide equivalent, a 72% reduction compared to a standard foundation. The largest reduction in emissions comes from the raw materials used to construct the foundation. The image below shows the total emissions for gravity and anchored foundations.
If you want to learn more about anchored foundations, reach out to Steven McRory at smcrory@hanson-inc.com and Matt Heyen at mheyen@hanson-inc.com.