Wind and solar power are the darlings of the green energy industry. Many manufacturers are scrambling for a piece of the action. But, Siemens AG is one of the only companies that can claim to be a leader in both technologies. It operates several plants near Chicago that assemble solar inverters and wind turbine mechanical drives.


“In the coming years, renewable energy resources are going to play a much bigger role in the energy mix,” claims Michael Weinhold, Siemens’ chief technology officer. “However, when it comes to harvesting renewable sources, fluctuations in their availability pose some challenges [which] can be overcome.

“There is no universal solution, because the power generation mix, demand for electric power, and the number and capacity of cross-border power lines differ from country to country,” adds Weinhold. “The most important consideration in connection with all renewable energy resources is that they must produce power at a competitive cost in the medium to long term and no longer be dependent upon subsidies.”

Solar Inverters

Solar energy is one of the fastest growing segments of the U.S. economy. The solar market grew 140 percent in the third quarter of 2011, compared with the same quarter in 2010. According to the Solar Energy Industries Association (SEIA), solar power in the United States now exceeds 3,650 megawatts, which is enough to power 730,000 homes. And, that number is expected to grow steadily in the years ahead as the technology quickly evolves.

While most companies are scrambling to produce solar modules, Siemens is concentrating on the less sexy equipment that converts sunlight into electricity after it’s captured by solar panels. Specifically, Siemens is focusing on solar inverters.

A solar inverter is one of the most critical components of a photovoltaic system. It converts the variable DC output from the solar panels to AC current so it can be put on the utility grid. Siemens’ SINVERT PVS family of inverters is ideal for large- and medium-sized solar power plants.

Solar power plants consist of thousands of solar modules spread out over acres of land. According to the SEIA, most utility-scale facilities are located in sunny climates, such as Arizona, California, Florida, Nevada and New Mexico. But, many solar farms are under development in other parts of the United States.

The three-phase SINVERT PVS inverters can achieve up to 98.7 percent peak efficiency levels when converting solar power from panel to grid. The devices are housed in air-conditioned inverter stations, which are strategically placed in multiple locations throughout solar power plants. A 20-megawatt installation would require about 40 inverter units.

The typical Siemens customer is a utility company or a renewable energy developer that is installing a large solar power generation project. The PVS inverters can be used to fit installations from 500 kilowatts up to 500 megawatts, but the size and scale varies from project to project. Up to four individual units can be clustered together to form 2,000 and 2,400 kilowatt systems.

Siemens assembles the SINVERT PVS family of inverters at its West Chicago, IL, plant. The 210,000-square-foot facility also builds motor control centers, enclosed motor starters, switchboards and control cabinets.

“We had two existing plants at this location, and converted one to support the manufacturing of solar inverters,” says Deron Jackson, motor control center business segment manager at Siemens Industry Inc. “The West Chicago location puts us close to our domestic customer base, and allows us to quickly fulfill our customers’ needs from a manufacturing and service standpoint.”

Siemens recently invested $10 million to upgrade its West Chicago operation, which consists of two buildings. Most of the investment involved new tooling and testing equipment.

“Before the plant upgrade, our challenge was managing 30,000 different metal parts within four product areas,” says Jackson. “We integrated new fabricating equipment into the plant, in addition to a new material handling system.”

Solar inverters are bulky devices that resemble mainframe computers. Each unit measures 83 by 103 by 29 inches and weighs 4,696 pounds.

Key components are a Siemens drive unit, an inductor and a machine control system. “Solar inverters are similar to a motor control center (MCC) in complexity, but it is a standard product unlike MCCs, which are engineered-to-order,” says Jackson.

“Since solar inverters are a standard product with relatively few options, they would be considered low mix [in our plant],” Jackson points out. “But, they are highly complex and demand fluctuates greatly due to the nature of power plant project timelines.”

Depending on the options selected, a 500 kilowatt inverter, which consists of an AC cabinet and a DC cabinet, can be fully assembled and tested in 80 to 100 hours. Key steps in the process include AC module assembly, DC module assembly, AC cabinet assembly, DC cabinet assembly, point-to-point testing, function test, load test and options testing.

The West Chicago assembly line consists of six workstations, with one operator at each. Solar inverters are manually assembled with screwdrivers, torque wrenches and pneumatic tools.

One side of the assembly line is devoted to the AC cabinet and its main component—the drive, which is imported from a Siemens plant in Germany. Assemblers on the other side of the line build the DC cabinet, where the main component is the conductor. The last workstation installs cabling and door panels.

Solar inverters are manually rolled from station to station, which are located just a few feet apart on the compact assembly line. Siemens eventually plans to install a conveyor to eliminate this physical movement.

Wind Turbine Gears

Like solar power, the U.S. wind industry represents not only a large market for power generation, but also a growing market for American manufacturing. According to the American Wind Energy Association, the U.S. wind industry installed enough turbines to generate 6,816 megawatts in 2011, which is 31 percent higher than 2010. All totaled, the United States currently has enough turbines to generate 46,916 megawatts of electricity, and additional turbines are under construction to produce more than 8,300 megawatts.

In addition to being a leading supplier of blades and nacelles, Siemens is the largest producer of wind turbine gear drives in the United States. It operates two plants in Elgin, IL, that specialize in mechanical drives.

One facility produces the gears and components needed for wind turbines and other mechanical drive applications, such as large mining shovels, marine propulsion drives and water screw pumps. Siemens acquired the 150,000-square-foot plant in 2005, when it purchased Flender Corp., and recently renovated it for lean production.

The heart and soul of a wind turbine is its three-stage gearbox and drivetrain. The hub of three rotor blades is connected to a gearbox via low-speed and high-speed shafts that drive a generator contained within a nacelle. The generator converts the energy into electricity and then transmits it to a power grid.

Most wind turbines are designed for a 20-year life cycle. As a result, the gearbox and drivetrain system must be strong enough to handle frequent changes in torque caused by changes in wind speed. The whole system must be carefully aligned to minimize wear from constant vibration and temperature extremes.

To ensure reliability and quality, Siemens manufactures all of its own gears, pinions, rotors and shafts. Couplings and motors are imported from a Siemens plant in Germany. “We go to extremes to address robustness, such as our in-house heat-treatment facility and metrology lab,” says Arnout Kant, mechanical drives business unit manager at Siemens Industry Inc.

Siemens recently built a $20 million assembly plant that is located several miles away from Kant’s component factory. Products are shipped between the plants several times a day.

The newer facility is divided in half, with two ‘sister’ operations sharing the footprint and separated by a parts warehouse. One side of the long assembly hall is operated by Siemens Drive Technologies. The other side is run by Winergy Drive Systems Corp., a joint-venture between Siemens and Winergy AG.

“The layout of the factory is similar to our sister plants in China and India,” says Jacob Schiff, plant manager. “We use the same equipment, which makes all three plants extremely flexible.

Approximately 70 percent of the Siemens side of the plant is devoted to assembling and testing wind turbine gearboxes. But, it’s not uncommon to see assemblers at some workstations also building products for the mining industry.

Because of large gears and heavy-duty drive-shafts, the typical gearbox weighs more than 2,000 pounds. "However, the weight can vary greatly with size," says Schiff. "We commonly assemble gearboxes exceeding 20 tons." Because of that weight, overhead travelling bridge cranes run the entire length of the facility. In addition, workstations are equipped with jib cranes, hoists and rotating turntables to address ergonomic issues.

Wind turbine drives are manually assembled in limited volumes on a project by project basis. Siemens' operators use various mechanical tools and measurement instruments to assemble gearboxes. "Standard items [include] calipers, dial indicators, torque wrenches, filing stones and dead-blow hammers," says Schiff. "[We also use] design tools and fixtures for achieving special fits or preload forces."

Large fasteners, such as M36 bolts, are used to hold assemblies together. Maintaining torque control on the large bolts, and the interaction of adjacent bolts when fastening heavy flanges together, is a key challenge faced by assemblers.

Siemens gearboxes are assembled with lean manufacturing principles. "The assembly steps are designed for one-piece flow (wherever possible) with line balancing across operational steps," explains Schiff. There are seven key steps used to assemble gearboxes: parts wash; component subassembly; housing preparation; loading the housing; exterior assembly; testing; and coating.

Parts wash involves the removal of machining oil and protective coating from the gearing.

Subassembly involves the preparation of various components, such as planetary carriers, bevel gear-pinion sets, gears and shafts. "The process typically involves shrink fitting, in which gears or other components are heated to specified temperatures to allow expansion," says Schiff. "While hot, the components are fitted with other cooler components, allowing the temperature to neutralize and thereby achieve a shrink fit."

Housing preparation involves some gearbox designs that call for interior lubrication systems. This requires pipe fitting within the housing.

Loading the housing is the process of placing the components and subassemblies inside the gearbox. "The process varies greatly, depending on the style of the housing," Schiff points out. "Single housings require specific knowledge of the insertion sequence and method due to the tight nature of the fit. Split housings offer a simpler approach, as the gearing can be laid into one side, then closed up with the mating half."

Exterior assembly involves basic components, such as sensors, external lubrication lines, fans, guards and couplings. More complex final assembly steps include motor connections, base plate mounting and external cooling units.

Testing is the next step in the production process. This includes various test and inspection protocols, such as monitoring sound, vibration, temperature, oil pressure and oil purity.

The final step is the coating process. "This typically includes a primer and a finish coat for protection of the unit," says Schiff.

“We have focused on implementing the Siemens Production System to streamline work flow and material flow, in addition to standardizing tools and assembly processes,” adds Schiff. “Our on-time delivery has improved, and we’ve reduced the average hours per unit time from 180 to 120 hours.”

Other recent improvements in the plant include visual work instructions and a “3I program” that emphasizes ideas, innovation and implementation.