On paper, power towers look great. So why are they shutting down?

One reason is current solar power tower heliostat fields are limited to 1500°F maximum because of flat heliostats. This new adaptive optic heliostat innovation creates higher temperatures 2500°F, which now allows for greater industrial applications, such as using the sun to manufacture cement, steel, fuel, and broad field of chemical manufacturing, along with green electric power generation.

Simply adding mirrors to a heliostat field to produce a higher central tower temperature has the problem that the 0.5-degree angular width of the sun causes the reflected light leaving the heliostat mirror to expand by 0.5 degree. This causes the reflected spot on the tower to be larger, or less concentrated with each added heliostat row. Distant heliostats become difficult to accurately hold the spot on the tower.

Engineers have tried to increase tower temperature by using parabolic shaped heliostat mirrors to focus the sunlight into concentrated spot. This solution works well when the sun is directly behind the tower. Yet, the parabolic mirror produces a large, aberrated, less concentrated, smeared spot on the tower as the sun moves away from the heliostat parabolic optical axis. Only a small percentage of the heliostats in the field produce a small focus on the tower while the remaining heliostats produce highly aberrated spot thus elevated tower temperature is not reached. Bending the reflector makes the right corrected optical shape anywhere in the field.

Last year a welded steel version of the adaptive heliostat was built and patented by the University of Arizona then successfully tested at the National Solar Thermal Test Facility, Sandia National Lab. Sandia reported successful test results for the entire day of heliostat tracking of the sun across the sky. However fabricating then adjusting the initial shape of the mirror steel support frame was labor intensive.

Ferrocement is a thin wall reinforced concrete layered with continuous small diameter steel mesh that can be woven into a fabric to create the perfect flexible surface. The labor of tying the layers of mesh together is minimized by stretching the wire over the mold. Ferrocement’s most notable characteristic is greater elasticity and resistance to cracking. This simple construction technique from molds is the next step in mass production. It could make power towers more efficient and globally ubiquitous.

The heliostat mosaic of mirrors are glued to the ferrocement support structure that has 2 passive mechanical cam operated actuators which continuously deform and bend the mirror into a dual concave radius (saddle shape) throughout the day. The heliostat mirror keeps a parabolic shape when the sun is directly behind the tower.

This new robust passively activated ferrocement adaptive optic heliostat invention allows the entire field of heliostats to simultaneously produce a small, concentrated focus on the central tower, thus creating higher temperatures. This opens a whole new paradigm of industrial applications previously unachievable with sunlight.

More efficient lower cost concentrated solar power is the future for humanity’s clean energy and saving the planet.