Solar Energy Technology at ARPA-E

J. Zahler
U.S. Department of Energy,
United States

Keywords: solar, ARPA-E, DOE

Summary:

The Advanced Research Projects Agency-Energy (ARPA-E) at the U.S. Department of Energy provides R&D funding to technologies that could fundamentally change the way we use, generate, and store energy. ARPA-E’s mission is to advance early-stage energy innovations that will create a more secure, affordable, and sustainable American energy future. ARPA-E funds two focused programs in the areas of solar energy systems and materials FOCUS and MOSAIC and funds other related projects through its OPEN programs. The objectives of these programs will be reviewed and representative projects from each program will be presented. FOCUS (Full-spectrum Optimized Conversion and Utilization of Sunlight) was conceived to address the intermittency of renewable generation technologies, specifically photovoltaic (PV) modules, which lack the ability to store and dispatch energy. On the other hand, concentrated solar power (CSP) is capable of storing multiple hours of thermal energy for dispatch at a later time to meet the needs of the grid. However, while thermal energy storage is relatively inexpensive, full CSP systems are significantly more costly than PV systems. The FOCUS program is based on the assumption that hybrid solar energy systems that harness part of the solar spectrum for direct electricity generation using PV converters, with the remainder used to generate heat, will result in the highest efficiency, lowest cost solar energy conversion system featuring integrated thermal-energy storage. Dr. Howard Branz, the ARPA-E program director who initiated the FOCUS program, summarized the approach as “no photon left behind. The FOCUS program was announced in the summer of 2013 and resulted in thirteen projects. MOSAIC (Microscale Optimized Solar Cell Arrays with Integrated Concentration) objective is to cost effectively combine the enhanced harvesting efficiency of concentrated photovoltaics (CPV) with the low cost and form-factor of flat-panel conventional Si PV modules. CPV systems demonstrate significantly higher energy conversion efficiency than conventional Si PV modules and have the advantages of increased energy production per unit of module area and reduced balance of systems costs. However, CPV systems have historically suffered from system complexity, the need for external mechanical tracking, and the need for high direct normal incidence (DNI) light found in limited geographies such as the desert southwest of the United States. The MOSAIC program is founded on the assumption that shrinking the optical and PV elements of CPV technologies will confer numerous advantages while addressing historical limitations of CPV systems. For instance, miniaturization reduces the total material required and associated BOM cost, while allowing passive cooling of the PV elements. Additionally, miniaturization enables the use of scaled micro-electronic and opto-electronic fabrication and assembly technologies, reducing the cost and complexity of manufacture. Shrinking the module form-factor also allows for the incorporation of internal tracking mechanisms enabling fixed-tilt CPV installations, such as rooftops. Other concepts include the incorporation of PV elements for collection of diffuse light, which would allow the systems to be deployed in new geographical regions that exhibit low-DNI, such as the northeast of the United States. Program Director Dr. Mike Haney initiated MOSAIC in the fall of 2014, which resulted in eleven projects.