Our Technology

Practical Solar designs and manufactures the world’s most reliable, cost effective and high-performing heliostat: the PSI-1KW. Practical Solar is the only company that can realistically show its heliostats will reliably run without failure for half a century, anywhere on Earth. Practical Solar also makes a thermal receiver – read more about it here.

Heliostat Specifications

Heliostat Price List

Heliostat Features

Practical Solar is proud that its heliostats were used to test the solar panels that will fly on NASA's mission to the Sun next year. These panels needed to be tested at the very high solar flux that they will experience when flying close to the Sun's surface.

Practical Solar heliostats were used to test the solar panels that will fly on NASA's mission to the Sun next year.

Heliostat Features

Demonstrated Reliability

Because heliostats contain moving parts, operate completely exposed to the natural elements, and are expected to operate for decades with only minimal maintenance, it is fair to question long-term reliability. Below is a description of our heliostat technology as it relates to reliability and calculation of mean time between failure (MTBF).

Practical Solar heliostats incorporate powdered steel technology gear trains. These gears are very rugged and low cost, costing only about 10 percent that of machined gears. Because the sun travels across the sky so slowly and isn’t out at night, the duty cycle of the gear drive system is less than 0.5 percent. Therefore, it is possible to greatly accelerate wear testing of the gear drive by running them at close to 100 percent, allowing the equivalent of decades’ worth of wear to be simulated in only weeks and months. Continuous testing of the gear train lasted two years. We have determined that there is negligible gear wear over the equivalent of 100 years of normal operation. Essentially, gear life is infinite in this application.

Practical Solar heliostat gear trains are driven by small permanent magnet, brushed DC motors (two per heliostat). We set up special life test fixtures to accelerate testing of these motors by many times. Many motors were tested simultaneously, from different production lots. The motors were run under as close to actual real life conditions as possible, and also under much heavier loads and higher speeds than real world conditions. The motors were then taken apart and inspected for brush, commutator and bearing wear. We found that after the equivalent of 20 years of normal operation the carbon brushes had only lost about 15 percent of their length, the commutator was only slightly worn, and the sintered bronze sleeve bearings showed only slight wear. Not a single motor out of hundreds tested ever failed.

Because of the extreme gear reduction from the motor to the mirror drive shafts, the torque that can be produced is huge. If the mirror support frame is mechanically prevented from moving as it might if buried in snow, the torque generated could be enough to damage the gear train. The electronic motor drive circuitry includes electronic torque limiting. There is also a mechanical slip clutch on each axis to prevent external loads, such as high wind gusts, from doing damage to the gear train.

The mirror frame is extraordinarily stiff in every direction, but light weight. It’s constructed of 5052 aluminum alloy, an extremely corrosion resistant material. The frame is fastened with 270 stainless steel rivets. The mirror frame is impervious to all weather conditions worldwide, including areas with high pollution levels and acid rain. Finite Element Analysis was used extensively to determine worst case wind loads.

The entire mechanical mechanism, and electronics, is sealed for life. There are no exposed mechanical elements such as lead screws or motors, as is common with many heliostat designs.

Practical Solar heliostats use a mix of analog and digital circuitry. The parts count is quite modest, and all components are rated over the industrial temperature range. Capacitors, resistors, diodes, transistors, and integrated circuits are hugely current and voltage derated. Multilayer boards have been avoided to eliminate interlayer via failures. There are no electrical connectors inside the sealed unit, only solder connections.

The failure of a single heliostat in a field of 100 heliostats only reduces the energy output of the field by 1 percent. If a heliostat field failure is defined as an energy output decline of 5 percent then five heliostats would need to fail. If heliostats fail at random times and are generally quite reliable (high MTBF) then the effective MTBF of the entire field is much higher than the MTBF of the individual heliostats. With ongoing and continuous accelerated life testing, an MTBF of many decades of continuous operation can be achieved in a heliostat array of many individual Practical Solar heliostats. A MTBF of 50,000 hours for a deployed heliostat array in commercial building HVAC applications is a conservative estimate based on past life testing.

Finally, a test field of heliostats has been running in the Boston area since 2006. Periodically, these heliostats are taken apart and inspected, and then returned to the test field. This ongoing test confirms the results of the accelerated life testing done in the lab.

Extraordinarily High Positioning Accuracy

Positioning accuracy of reflected light onto the desired target needs to be very high in concentrated solar energy applications. The mirror frame is positioned up/down (altitude) and left/right (azimuth) to continuously reflect sunlight to the thermal receiver, as the sun moves across the sky. The PSI-1KW heliostat design employs two proprietary high-accuracy rotary position encoders, equivalent to a 3200-line encoder. This allows the reflected beam of sunlight to be positioned to within 20 centimeters, at a distance of 50 meters from the target. Encoders with such accuracy commonly cost hundreds of dollars each. Practical Solar has reduced the cost to less than $10 per axis. Twelve individual mirrors are fixed to each frame. Each mirror is permanently tilted to a slightly different angle, allowing different focal lengths on individual heliostats in a heliostat array. Using multiple mirrors on a single frame, and high performance encoders, allows for highly concentrated focus on small targets.

Extraordinarily Low Electrical Power Consumption

Almost all heliostat designs employ stepper motors, or brushless DC motors to drive their mirror frame. The electrical power requirements are significant. Our design incorporates two very small brushed DC motors, driving extremely high reduction ratio gear trains. The PSI-1KW average power consumption is one-tenth of a watt (12V@0.008A), and delivers a thousand watts, a ratio of 10,000 to one. We can power 100 heliostats with a single 2-conductor 18-gauge unshielded cable. Power and communication share this simple cable, from heliostat to heliostat. (Each heliostat has a unique name, so it only responds to commands addressed to it.) A single, modest size photovoltaic panel, charging a single 12V car battery, can power a large array of PSI-1KW heliostats. A very important feature in remote locations.

Focal Lengths

The reflective surface is comprised of 12 individual mirrors, mounted to the mirror frame in a 3 x 4 array. Each individual mirror is 305mm square x 2mm thick. Reflectivity is 90 percent. The design of the mirror frame allows each of the 12 mirrors to be tilted a precise amount, so that the entire reflective surface has a desired focal length. This allows a very tight focus, and high solar concentrations. Any focal length from 10 meters to a 100 meters can be specified by the customer. The focal length is stamped on every frame.

Powerful and Versatile Software

Practical Solar software works on any computer that runs any version of the Microsoft Windows operating system. A single low-end laptop can control a field of one to thousands of individual PS-1KW heliostats. There are two main modules in the software suite: “PS-1KW Heliostat Array Trainer” and “PS-1KW Heliostat Array Controller”.

Heliostat electronics

PS-1KW Heliostat Trainer is used setup individual heliostats in a field of heliostats. Our heliostats have incredible accuracy and repeatability, but don’t know where true south is, and don’t know the verticality of the mounting pole. This software, coupled with simple tools, and two technicians, can setup a hundred heliostats a day.

Heliostat Trainer software

PS-1KW Heliostat Array Controller issues commands to the heliostat array based on the setup data determined by the PS-1KW Heliostat Trainer software. It also interfaces to the Measurement Computing line of DAQ devices to allow input from the user such as temperature, pressure, and meteorological data to influence the commands to the heliostat field. Practical Solar can quickly develop custom solutions to your particular solar thermal application using these inputs.

Heliostat Array Controller software

Practical Solar software includes a suite of diagnostic tools.

Heliostat Performance Predictor software