Heliostat, a perfect reflection of the sun

A heliostat is one of the key components in an STE tower technology plant. Heliostats are mirrors that track the sun on two axes. These systems are configured around a tower, which has a solar receiver in its upper section.

They are designed to redirect the solar energy that the Earth naturally receives and to concentrate it onto a single point in the upper part of the tower where the solar receiver is located, which reaches a high temperature. This heat is capable of generating steam that turns a conventional turbine, producing clean electricity. Research into new designs and materials leads to higher levels of efficiency in the electricity production cycle, while reducing the cost of STE plants that use this technology.

There are four key elements to a heliostat – the mirror or facet; the metal structure on which it is supported; the dual-axis solar tracking system; and the foundations that anchor it to the ground. These elements make STE technology for tower plants flexible and adaptable compared to other solutions, since the solar field can be adapted to sites that are gently sloping and can reduce the effects of seasonality.

However, solar concentrating heliostats should not be confused with conventional photovoltaic modules. Although at first glance they look similar, they rely on very different concepts – photovoltaic solar power and thermal solar power.

” Heliostats can have different designs depending on the geographic and environmental requirements of the plant, as well as its size.

Both products are used in a solar field; they have a similar shape and dimensions; and they both use the sun as a source of energy, but how do they use solar radiation? The key difference is this: photovoltaic panels absorb the solar radiation while heliostats reflect it. Photovoltaic panels produce energy directly through a physical reaction that excites the electrons in a semi-conductor material. However, heliostats are a mechanism for concentrating solar energy – they are essentially mirrors. Heliostats can have different designs depending on the geographic and environmental requirements of the plant, as well as its size.

As part of its commitment to innovation, Abengoa is constantly researching and developing new heliostat concepts to reduce their cost and weight and to increase their overall resistance.

The latest model developed by Abengoa –the ASUP 140 heliostat– offers an innovative solution and is 140 m² in size. It incorporates an innovative facet concept that combines highly-reflective 2 mm glass with a foam support to improve its load-bearing capacity. ASUP 140 has been used in projects such as Atacama 1 in Chile, reducing the cost of the solar field by 30 % thanks to an optimized structure that minimizes the need for materials.

Ana Velasco Ortega,
Abengoa Solar Products.