Richard M. Swanson

The promise of concentrators

This paper addresses the issue of why concentrator systems have not gained a significant market share. The history of concentrator development is reviewed, and the status of existing concentrator efforts outlined. A critical look at the requirements to propel concentrators to a prominent market role in large-scale power production is presented. Various concentrator and flat-plate PV system approaches are compared by computing the expected cost of energy, and conclusions are drawn as to what the best course of action will be. Concentrator systems are projected to be the lowest-cost, lowest-risk PV option for medium and large PV power plants. Copyright

A mirror-less design for micro-concentrator modules

The authors present a novel nonimaging optics design for a flat-plate concentrator PV power system. The design consists of a conventional primary/secondary lens combination, but uses aspheric and TIR (total internal reflection) lens components in the primary to reduce the focal length and, hence, the thickness of the whole module. Ray tracing simulations indicate that an acceptance angle in excess of /spl plusmn/2.6/spl deg/ can be achieved, which makes this design suitable for light-weight, low-cost tracking systems. The design also has the advantage of being mirror-less, avoiding all manufacturability and reliability issues associated with metallization processes as faced by previous low-profile designs.

Editorial: Toward 100 Gigawatts of Concentrator Photovoltaics by 2030

In this editorial, we report on the conclusions of a concentrator photovoltaics (CPV) industry group convened in July 2012 to develop pathways to large-scale CPV deployment, specifically targeting the installation of 100 GW of CPV in the United States by 2030. The group identified technical and financial barriers to this goal and developed a corresponding set of recommendations for overcoming these barriers. These recommendations focus on technical improvements at the system and cell levels and on activities needed to support the commercialization.

Simulation and characterization of high efficiency back contact cells for low-concentration photovoltaics

Herein, the performance of low-cost crystalline silicon solar cells under low to medium levels of concentration is explored. Simulations and experimental results are shown for concentrations up to 20 suns. An efficiency of 23% at 9 suns is achieved on a 34.5 mm x 125 mm solar cell using SunPowers standard production process. Low sensitivity of cell performance to illumination profile and position is also demonstrated.

Developments in Silicon Solar Cells

Silicon solar cells are undergoing rapid development resulting in increasing performance and reduced cost. This paper discusses the major and efficiency limitations and cost elements of silicon solar cells, and shows how these are being improved. A roadmap to achieving grid electricity cost parity by 2012 through halving the installed cost of photovoltaic systems will be outlined.

High-efficiency, point-contact silicon solar cells for Fresnel lens concentrator modules

Point-contact silicon solar cells have been developed for Fresnel lens concentrator modules. The cells have an area of 1.21 cm/sup 2/ on a 12/spl times/12 mm die. The design incident flux on the cell is 22.3 W/cm/sup 2/. A new cell design and process have been developed to insure a high efficiency and a large fabrication yield, and to eliminate hazardous materials and pyrophoric gases. The new process is very safe and benign to the environment. Also, a new passivation technique for the front surface has been discovered which makes the point-contact cell fully stable under steady-state concentrated sunlight. No degradation has been observed so far after more than 200 days of exposure behind Fresnel lenses providing an incident power density of 36 W/cm/sup 2/. An improved anti-reflection coating and an improved light trapping, giving an average effective number of passes of the infra-red light greater than 25, are part of the developments. The best cell shows an efficiency of 26% under 100 suns (AM1.5D, 25/spl deg/C). The typical cell efficiency is greater than 25% at 200 suns. The cells are easily solderable due to a double-level metallization and three large copper pads. The cells are now produced in large quantities in a pilot line located in a Class 100 clean room which has a capacity of 7.5 MW per year of concentrator solar cells.<<ETX>>

Single-wafer integrated 140 W silicon concentrator module

A wafer-scale-integrated (WSI) module of back-side contact (BSC) solar cells has been developed for central receiver or concentrating dish applications. Two parallel strings of five series-connected BSC cells on a single 4 in silicon wafer, mounted on a cold plate, form a 6 cm*6 cm monolithic module producing more than 140 W under 20 W/cm/sup 2/ at operating temperature. The best measured efficiency is 20.8% at around 7 W/cm/sup 2/ and at 39 degrees C cell temperature. At 25 degrees C, the monolithic module is 22% efficient at 5.8 W/cm/sup 2/.<<ETX>>

Recent developments on the flat-plate micro-concentrator module

We develop a novel 300-Sun concentrating photovoltaic (CPV) module. A non-imaging optical design based on a compact total internal reflection (TIR) lens enables a very low profile module, similar to a flat-plate module. This paper presents some recent advances in the development of this module. These advances concern the two main components of the system, the optics and the cell, as well as their integration inside a complete module. The manufacturing cost of the entire system is estimated and compared to conventional Fresnel lens-type systems. This comparison accounts for actual cell temperatures under operating conditions, evaluated through thermal experiments.

Straight talk about concentrators

This paper addresses the issue of why concentrator systems have not gained significant market share. Various concentrator and flat-plate PV system approaches are compared by computing the expected cost of energy. Based on this result, some conclusions and recommendations for the concentrator industry are presented.

Degradation of surface quality due to anti-reflective coating deposition on silicon solar cells

We find that the front surface quality on back contacted silicon solar cells is degraded by the evaporative deposition of an anti-reflective coating. The degradation is most severe when an e-beam evaporation is performed, but there is still significant degradation with thermal evaporation. The surface recovers some after a forming gas anneal but is still degraded compared to before the evaporation. The degradation overwhelms and negates any forming gas anneal performed prior to the evaporation. The degradation is greatly reduced if the surface is not textured. We discuss the application of these results to our high efficiency silicon solar cells.