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National Energy Research Laboratory (NREL)

The NREL is the only laboratory run by the United States government that is entirely devoted to renewable energy. The lab’s mission is to move technology for renewable energy from concept to commercial application. It falls under the control of the U.S. Department of Energy’s (DOE) Office of Energy Efficiency and Renewable Energy (EERE). NREL is located in Golden, Colorado and sits on a 327 acre campus. Fiscal year funding for 2010 was $536.5 million.

NREL is widely considered to be one of the most successful renewable energy initiatives worldwide. The lab has won over 50 R&D 100 Awards since 1982. It attracts top talent from across the globe. The following are some of the research initiatives at NREL.

U.S. Department of Energy SunShot Initiative

SunShot is a national collaboration with the goal of making solar energy cost competitive with other energy technologies by 2020. The goal is to reduce the installed cost of solar systems by 75%.  NREL is involved in research of high-efficiency PV cells using copper indium gallium diselenide (CIGS), cadmium-telluride, and silicon as part of the SunShot program. NREL is also engaged in research to use earth-abundant materials to produce thin-film PV cells that are tunable over a wide range of solar wavelengths, the use of amorphous silicon with organic materials to produce PV technologies that go beyond the Shockley-Queisser limit, and the modification of copper-oxide through alloy with sulfur, zinc, and magnesium to tailor band gaps.

National Center for Photovoltaics (NCPV)

This center is under the direction of the NREL and focuses on technology that can drive industrial growth in photovoltaics. NCPV has produced many breakthroughs in PV cells, the two most recent being:

  1. The production of solar cells that produce more electrons for current than there are photons hitting the cell.
  2. A miniaturized solar cell about the size of the dot made by a ball point pen.

 

The first of these breakthroughs is interesting from the stand point that a solar cell that produces more electrons than photons entering would have efficiency above 100%. In fact, the cell is capable of 114% efficiency. The technology is based on a process called Multiple Exciton Generation (MEG), which allows each photon that strikes a quantum dot (small semiconductor material) to produce more than one electron.

The second breakthrough produces triple junction gallium arsenide cells that are only 600 microns in diameter. Their small size allows them an efficiency rating of over 41%. They work by concentrating sunlight onto the cells to create intensity greater than 1,100 times that which falls on standard solar cells.

Cadmium Telluride (CdTe)

NREL has been invested in CdTe for over twenty years. In that time, they have helped to advance the technology of thin-film CdTe for large scale applications to efficiencies of 13%. While low for standard silicon panels, 13% is an outstanding conversion rating for thin-film. NREL recently demonstrated efficiencies in this category of 17%. Their current goals in this category are:

  1. Understand the failure mechanisms in CdTe cells so as to produce tests for determining reliability.
  2. Understand CdTe junction functionality so as to break through the 10% efficiency barrier.
  3. Produce materials for adjuncts to the CdTe layer in such cells that can withstand the high temperatures of production (650 oC).

Copper Indium Gallium Selenide (CIGS)

Like CdTe, NREL has been invested in CIGS for over 20 years. CIGS technology is the most efficient available for thin-film applications. The group set the world record in this class with conversion efficiency of 20%. There goals in this are:

  1. Understand how material choice and manufacturing processes affect performance and reliability of CIGS modules.
  2. Determine how to replace rare and/or expensive materials with Earth-abundant materials.
  3. Employ materials science to produce CIGS flexible cells that are reliable.

Silicon Materials and Devices

NREL engages in both basic and applied research involving the production of low-cost, high efficiency silicon solar cells. Recent achievements and ongoing research in silicon solar technology include:

  1. 19.3% efficiency in heterojunction solar cells
  2. Chemical vapor deposition of Si at 700 oC.
  3. Understanding nanoparticle silicon production and electronic properties.
  4. Understanding light-induced metabolic degradation in amorphous silicon:hydrogen combinations.
  5. Application of thin crystal silicon on cost-effective substrates

III-V Multijunction Materials and Devices

NREL invented the first inverted metamorphic multijunction (IMM) technology as well as the first multijunction PV cell. The III-V multijunction cells, which use gallium, indium, and phosphorus have reached efficiencies of over 40% and are widely used in space applications.

Manufacturing and Engineering

NREL invests a number of resources into understanding how to measure and characterize renewable energy products to determine everything from efficiency to potential usability to reliability. They test everything from raw materials to fully assembled products and even the manufacturing processes themselves. NREL is involved in all levels of solar energy production from acquisition of materials straight through research to consumer installation.

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