Patented Calibration


A figure from one of our many patents in heliostat calibration and control

To direct sunlight (referred to as flux in the CSP industry) at a target hundreds of meters away, we have to know the position of the sun, the position of the tower and the position of the actuated mirror, or heliostat, to great precision.

There can be hundreds of thousands of heliostats at a single plant and accounting for each one is a significant challenge.  Our competitors have avoided this challenge by deploying fewer, larger, and more expensive heliostats which are difficult to install and monitor.

Our control software, Spectra, accepts the challenge head-on, massively parallelizing the problem, and using novel, patented algorithms to identify each heliostat as it is installed, and to prepare each heliostat for tracking by calibrating it to milliradian accuracy.

Precise Control


Using our control system to celebrate the 4th of July at Sierra.

That’s right: our control system points our heliostats with milliradian accuracy.  For example, a 2m-wide beam of light is being directed to a point on a thermal receiver absorber panel 300m away. We need less than 1/10th of a degree of accuracy if we don’t want to spill our light off of the receiver.  And we do it.  With such fine individual heliostat control, we can create intricate flux distributions on our thermal receivers allowing for a wide variety of applications.  We can control for superheat, salt temperature, peak flux or delivered power, our patented throttling algorithm gives us the unprecedented precision we need to respond to the necessary environmental and plant conditions.

Large-Scale Optimization

The techniques for our high performance in the field required many years worth of research, experimentation, and testing via large-scale simulation and optimization.  We optimize everything: heliostat range of motion, thermal losses, receiver aim-point selection, control group selection, and which heliostats to use at every minute of every day in every plant around the world.  Our models of instantaneous and annual performance have been validated time and time again, giving us the confidence (and the tools) to move forward with project bidding, winning, and construction.


Our SCS5 heliostat performing a pointing test.