Solar power generation continues to increase, with forecasts from BloombergNEF (BNEF) calling for global solar generation to make up 22% of the world’s electricity by 2050, up from about 2% today. BNEF has said solar and wind will account for almost 50% of the world’s power generation by midcentury, becoming more economically viable than natural gas and coal by 2030.
Several factors are spurring this growth, including regulatory policy, more corporate demand for clean energy, and technological innovation that continues to reduce the cost of renewables. Energy analysts have said that utility-scale solar projects are being built at 90 to 95 cents per watt, which was inconceivable only two years ago. And analysts say that cost will soon fall below 85 cents per watt.
At the same time, concentrating solar power (CSP) technology is increasing in energy density and overall output. One key to innovation is the performance of tracking gear drives that enable heliostats to focus more sunlight on receiver towers (power towers) more reliably.
Considering the enormous scale of a typical CSP plant, even a fractional improvement in heliostat aiming accuracy can prove quite significant. The Timken Company’s Cone Drive technology enables precise tracking of the sun’s movements, balances heliostat performance and system cost, and helps with the need to reduce long-term maintenance spending.
The technology is being proven at the Ivanpah Solar Electric Generating System (Figure 1) project in the Mojave Desert in California. Ivanpah, developed by BrightSource Energy, is one of the world’s largest CSP installations. Timken’s double-enveloping worm gear technology is helping power the 377-MW complex, which began operating in 2013 and was recognized as POWER’s Plant of the Year in 2014. The cone drive operation ensures Ivanpah’s nearly 174,000 sun-tracking heliostats are carefully calibrated to optimize energy capture.
Taking Aim at Ivanpah
BrightSource’s expansive site uses dual-axis drives for heliostats to reflect solar beams onto receiver towers where molten salt is superheated to nearly 1,000F, in turn powering steam cycles that drive electricity-generating turbines. Absolute precision is paramount to ensure the sun’s light stays tightly focused on the towers—targets measuring no more than three square meters in size at a distance up to 2,000 feet away.
At Ivanpah, harsh conditions make aiming accuracy even harder to achieve. Desert windstorms can pack peak gusts of 190 miles per hour while assaulting the site with sand and debris. For a heliostat to maintain its exact position and offer dependable performance despite these challenges requires a special feat of mechanical engineering.
Heliostats saw extensive research and development in the 1980s with the azimuth-elevation tracking pedestal type emerging as the predominant design (also known as an azimuth-altitude design, where the heliostat operates on a primary vertical axis and secondary horizontal axis). Today, this design remains the most common in commercial CSP plants and is preferred for its high range of motion and optical efficiency.