Inverters, panels and racking are the big three when it comes to solar components. But there’s another rock star solar component that is often overlooked: Linear actuators.
If you’re not sure what a linear actuator is, that’s okay. Most of the time, when I tell people I work in the field of linear actuators, they respond with a blank look. Still, despite their low profile, linear actuators make a significant impact in solar arrays.
Generally, electric linear actuators in solar applications are used in tracking sun position. The actuator angles the solar panels to follow the sun, helping to maximize efficiency.
Before low-cost electric actuators came along, the only choices for angling solar panels were actuators using hydraulic or pneumatic technology. Both of these options can be costly and environmentally unfriendly. Electric actuators changed all that. Additionally, electric actuators can lift upwards of 2,000 lb. When defining support structures for solar arrays, a rule of thumb is to figure 3 lb/ft2 of solar array, so there are few solar panel arrays that can’t be automated with this electric technology.
![solar actuator]()
Electric Is Efficient
Switching from a hydraulic actuator system to an electric version is likely to reduce power consumption. This reduction can be as much as 80%, and savings can sometimes be seen in less than 12 months. The reason becomes clear by considering the components that make up a hydraulic system.
A hydraulic system that positions a solar array via a hydraulic cylinder requires a hydraulic pump to move its hydraulic fluid. Additionally, the electric motor driving the pump must be sized correctly to make the installation energy efficient; if the pump motor runs excessively, its energy use can be significant.
Similar arguments apply for pneumatic positioning systems. Pneumatic systems require an air compressor to supply system air. The size and inherent energy efficiency of the compressor can impact the overall energy use of the positioning system. Moreover, the air (or other gas) used as a pneumatic working fluid is compressible. So it converts some of the energy applied by the air cylinder into heat, making these systems less energy efficient than hydraulic systems with their incompressible working fluids.
Cheap Actuators Can Cause Component Failure
Electric actuators generally have fewer parts than equivalent hydraulic and pneumatic options. An electric actuator system mainly consists of the motor/actuator, the control system and mounting hardware. Typical linear actuator systems incorporate some kind of dc motor. In recent years, the dc brushless motor has become widely used in actuators, but step motors and dc brush motors can be found in actuators as well. Actuators powering super-large loads might incorporate ac induction motors instead (such as when driving a lead screw to operate a large valve in a refinery).
The basic positioning mechanism of a typical linear actuator consists of an electric motor that turns a lead screw. The nut on the lead screw typically attaches to the apparatus that the actuator is meant to position. The resolution of the actuator positioning is largely set by the pitch of the lead screw–the finer the pitch, the finer the resolution of the move.
A standard linear actuator typically has a motor in a separate enclosure attached to the side of the positioning mechanism (usually a lead screw). Side attachment generally means the motor drives the lead screw via either a belt or a chain. Alternatively, the motor may be attached to the end of the actuator, in which case it generally turns the lead screw directly.
In addition to these typical configurations, it’s possible to find linear actuators set up in several other ways. For example, some units use a motor shaft whose inner diameter is enlarged to such a degree that the motor shaft is hollow. The drive screw passes through the center of the motor, and the nut attaches to the motor itself. Here the positioned apparatus attaches to the end of the screw. Similarly, the motor can be made with a small outside diameter but with its pole faces stretched lengthwise so the motor can still exhibit high torque though it fits in a small diameter. This type of configuration makes it possible to devise actuators in special form factors.
Finally, some linear actuators also incorporate limit switches at the end of their rated length. The limit switch actuates to signal overtravel, i.e. that the actuator has extended beyond its normal operating distance. Thus the limit switch serves as a safety measure.
In contrast, an equivalent hydraulic system contains these same components plus a pump, a fluid reservoir, a fluid filter system and a control valve— as well as hoses for the hydraulic fluid. Similarly, pneumatic positioning systems add an air compressor, compressed air storage (called an accumulator), control valves and air hoses.
Electric Is Good For The Environment
Hydraulic actuators push on a fluid to create motion. Today most ordinary hydraulic fluids are based on mineral oil. Natural oils such as rapeseed (also called canola oil) are used as base stocks for fluids where biodegradability is important.
But hydraulic fluids can also contain numerous chemical compounds that include oils, butanol, esters, polyalkylene glycols, organophosphate, silicones, alkylated aromatic hydrocarbons, polyalphaolefins, corrosion inhibitors, anti-erosion additives and so forth. In locales that are environmentally sensitive, these can create concerns about contamination in the event of a fluid leak.
Spilled hydraulic fluid is generally not considered a hazardous waste in the eyes of regulators such as the Environmental Protection Agency, but there can be exceptions. For example, some older hydraulic fluids contained polychlorinated biphenyls (PCB) so they could handle high-temperature applications such as die-casting. Hydraulic fluid containing more than 0.5% non-dissolved PCB material or more than 50 parts per million total concentration of PCBs is considered a hazardous material regulated by the EPA under the Toxic Substance Control Act (TSCA) and Resource Conservation and Recovery Act (RCRA). PCB waste disposal must be in a TSCA-compliant incinerator, TSCA/RCRA-compliant chemical waste landfill, or through some alternative method that the EPA has approved. And hydraulics that have contained PCBs at a concentration exceeding 1,000 parts per million must be flushed with a solvent before they can go to a land fill or be otherwise disposed of. The drained liquid and solvents must be disposed of like other PCB wastes.
To avoid environmental concerns, some hydraulic systems may use water-based fluids. But these can leave the actuator subject to surface corrosion and improper sealing can encourage development of bacteria.
Of course, the only fluids used in electric actuators are light lubricants for the moving parts. These are used in small amounts and do not constitute a contamination hazard. Most actuators today are lubed at the factory and need no additional lubrication over their operating life.
Hopefully, as we are propelled into a future where alternative means of energy will only be explored further, using technologies that promote harm reduction and increased efficiency will not only be seen as a sensible transition–but a necessary one.
By: Matthew Edwards of Progressive Automations, a 12-V actuator manufacturer and distributor based in Richmond, British Columbia.
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