National Renewable Energy Laboratory (NREL)

A solid-state optical system invented by the National Renewable Energy Laboratory (NREL) measures solar cell quantum efficiency (QE) in less than a second, enabling a suite of new capabilities for solar cell manufacturers.

QE is a measurement of how cells respond to light across the solar spectrum, but traditional methods for measuring QE had been too slow, limiting its application to small samples pulled from the production line and analyzed in laboratories. NREL’s technique, commercialized by Tau Science as the FlashQE™ system, uses a solid-state light source, synchronized electronics, and advanced mathematical analysis to parallel-process QE data in a tiny fraction of the time required by the current method, allowing its use on every solar cell passing through a production line.

The FlashQE system uses an array of light-emitting diodes (LEDs), each emitting a different wavelength of light. The LEDs illuminate the cell simultaneously, rather than the serial approach of the conventional system. The key to the technology is that all the LEDs are flashed on and off at different frequencies, thereby encoding their particular response in the solar cell. High-speed electronics and advanced mathematics cleverly extract the encoded information to reveal a full-spectrum QE graph of the cell. A wide variety of information is gathered in less than a second—information about the ability of the front surface of the cell to absorb high-frequency light, the quality of the thin-film surface coatings, the ability of the middle region of a cell to absorb a wide range of wavelengths, how well the back surface absorbs lower-energy light, and the ability of the back surface to collect electrons.

Some of this is new information for manufacturers. Solar cell manufacturing lines test each cell to determine useful cell parameters, such as how much current and voltage is generated. But conventional tests give no information about how the cell responds to each color of light in the solar spectrum. Flash QE's ability to also test for each cell’s response to color allows crucial extra information to be fed back into the production line. It does it so fast that cells of the same current and the same response to particular colors can be sorted into bins. From these sorted bins, spectrally matched modules can be made to optimize the energy produced throughout a day.

NREL’s ingenious approach, in which parallel processing allows all of the QE data points to be measured simultaneously to produce a QE graph in 1 second, is more than 1,000 times faster than the industry’s current state-of-the-art technique.

The National Renewable Energy Laboratory (NREL) has patented and licensed a catalyst that reforms tar into syngas, a breakthrough that can accelerate the process of getting biomass ready for fuel synthesis and use as a drop-in fuel. The process also can help reduce greenhouse gases because the biomass that is used in fuel gets combusted into carbon dioxide, which is food for future biomass. The result is that 90 percent of carbon emissions get recycled into new biomass.

Syngas is a mixture of hydrogen and carbon monoxide—the building blocks of fuels and chemicals—and it is generated by heating particles of biomass with steam and air in a turbulent, “fluidized” mixture to gasify it. But the making of syngas creates tars and other undesirable components. The tars can foul the refining process, so must be removed from the syngas before the fuel is synthesized. NREL researchers ultimately found a catalyst that could neutralize those tars.

The researchers knew they needed a fluidized material that could move around in the reactor and provide more efficient contact of the catalyst with the gaseous fluid. NREL enlisted help from a Colorado neighbor, CoorsTek, to help develop a catalyst support that would work in the fluidized bed of a gasification reactor.

The resulting catalyst support is made by taking all the raw materials and grinding them in water to form a high-solids solution. The particles in the solution are approximately one micron in diameter. The solution is spray-dried by atomizing the liquid in very hot air, forming droplets. The tiny droplets are little round pellets of ceramic; each one is formed when numerous particles from the solution adhere together. Then the material is fired, giving it strength. But the porous surface of the ceramic is not totally sealed, so the catalyst components can "soak in."

Once the support structure was identified, NREL created the catalyst by mixing the ceramic particles with a solution of nickel, magnesium, and potassium salts. When this was heated, a chemical reaction occurred and the catalytic metals stuck onto the ceramic surface, forming a catalyst that can be used in gasification reactors.

The new Energy Systems Integration Facility (ESIF) at the National Renewable Energy Laboratory (NREL) is meant to investigate new ways to integrate energy sources so they work together efficiently, and one of the key tools to that investigation, a new supercomputer, is itself a prime example of energy systems integration. NREL teamed with Hewlett-Packard (HP) and Intel to develop the innovative warm-water, liquid-cooled Peregrine supercomputer, which not only operates efficiently but also provides hot water to the ESIF, meeting all of the building's heating needs.

Peregrine is the first installation of the new HP Apollo Liquid-Cooled Supercomputing Platform, and it provides the foundation for numerical models and simulations that are enabling NREL scientists to gain new insights into a wide range of energy systems integration issues. This innovative high-performance computer (HPC) can do more than a quadrillion calculations per second as part of the world's most energy-efficient HPC data center.

As HPC systems are scaling up by orders of magnitude, energy consumption and heat dissipation issues are starting to stress the supporting systems and the facilities in which they are housed. But unlike most other computers that are air-cooled, Peregrine is cooled directly with warm water, allowing much greater performance density, cutting energy consumption in half, and creating efficiencies with other building energy systems. Peregrine’s warm-water cooling system eliminates the need for expensive data center chillers and heats the water to 103°F, allowing it to help meet building heating loads. At least 90 percent of the computer’s waste heat is captured and reused as the primary heat source for the ESIF offices and laboratory space. The remaining waste heat is dissipated efficiently via evaporative cooling towers.

The ESIF is designed to address the key challenge of delivering distributed energy to the grid while maintaining reliability. It’s a complex problem involving systems within systems and leveraging Big Data—and the Peregrine serves as a powerful new tool in NREL’s ongoing work to find a solution. But although it's a cutting-edge facility, the ESIF is not some esoteric experimental building tucked away from the public. It was designed for partners—and since it opened for business, NREL’s world-class facility has attracted many commercial partners.

Not surprisingly, the capabilities of the ultra-efficient HPC data center are placing NREL in the spotlight. It earned a 2014 R&D 100 Award and helped the ESIF earn R&D Magazine’s 2014 Laboratory of the Year award and the Energy Department's 2013 Sustainability Award.

Optimizing solar-cell technology can be a complex job, requiring expertise in material science, physics, and optics to convert as much sunlight as possible into electricity. But despite this complexity, a simple fact is key to making a high- performance solar cell: any sunlight reflected off the cell can’t possibly be converted into electricity.

Manufacturers have tried to minimize the reflection of sunlight off of solar cells by first chemically etching micrometers-deep structures into the surface of solar cells and then depositing one or more thin anti-reflection layers. Unfortunately, the equipment and processes for these conventional methods add significant cost to the solar cell, and the cells still absorb only 93-97 percent of the sunlight.

To address this problem, scientists at the National Renewable Energy Laboratory (NREL) have invented the “black silicon” nanocatalytic wet-chemical etch, an inexpensive, one-step process that literally turns the solar cells black, allowing them to absorb more than 98 percent of incident sunlight. The process costs just a few cents per watt of solar-cell power-producing capacity.

To etch the silicon, a wafer is immersed in a solution that contains chloroauric acid, which is composed of hydrogen, chlorine, and gold. Tiny nanoparticles of gold instantly form and act as a catalyst for chemical reactions, producing a nanometer- scale porous surface on the cell wafer. The nanoscale pores—on the order of a billionth of a meter in diameter—are much smaller than the wavelength of the incident light, so they suppress reflection across the full spectrum of sunlight. As the tiny holes deepen, they make the metallic gray silicon appear increasingly dark until it becomes almost pure black, absorbing nearly all frequencies of sunlight. The surface becomes riddled with minute pores of varying depths with no sharp interfaces that would reflect light, creating a highly absorbent silicon wafer.

Using a closely-related process that employs lessexpensive silver nanoparticles, NREL has made a black silicon cell with a validated 18.2 percent conversion efficiency— about the same efficiency as a typical crystalline silicon solar cell with a more costly antireflective coating.

At 100°F, NREL’s black silicon etching process takes less than a minute. In contrast, the etching process that prepares silicon wafers for conventional antireflective coatings takes 8–30 minutes, and applying the coatings adds even more processing time.

Gearbox failures have a significant impact on the cost of wind farm operations. To help minimize gearbox failures, in 2007 the National Renewable Energy Laboratory (NREL) initiated the Gearbox Reliability Collaborative (GRC), which consists of wind energy manufacturers, project owners, researchers, and consultants.

Gearbox deficiencies are the result of many factors, and the GRC team recommends efficient and costeffective improvements in order to expand the industry knowledge base and facilitate immediate improvements in the gearbox life cycle. The GRC combines analysis, field testing, dynamometer testing, condition monitoring, and the creation of a gearbox failure database.

NREL and other GRC partners have been able to develop improved processes for the design, testing, and operation of wind turbines to increase gearbox reliability. In contrast to private investigations of these problems, the GRC quickly shares its models, data, and findings among its participants, including many wind turbine manufacturers and equipment suppliers. Ultimately, the findings are made public for use throughout the wind industry. This knowledge is resulting in increased gearbox reliability and an overall reduction in the cost of wind energy.

The GRC started with a representative gearbox design, which was then redesigned to the best industry standards as of 2007. Two heavily instrumented gearboxes were built based on this design. One was mounted in a wind turbine and tested in the field, while the other was tested on a dynamometer, which simulates the loads experienced by a typical wind turbine, but on a compressed time scale. This effort built an understanding of how selected turbine loads and operational events translate into bearing and gear responses.

Based on all the lessons learned from the past five years, the GRC has now produced a new and improved design, which is projected to yield an operating lifetime of 12 years, more than triple that of the previous redesigned gearbox. This new design, shown in the illustration below, will be built and tested in the same way as the previous iteration, and again, all results will be shared first with the GRC members and eventually made public.