Scott M. Paap

Cost analysis of flat-plate concentrators employing microscale photovoltaic cells for high energy per unit area applications

Microsystems Enabled Photovoltaics (MEPV) is a relatively new field that uses microsystems tools and manufacturing techniques familiar to the semiconductor industry to produce microscale photovoltaic cells. The miniaturization of these PV cells creates new possibilities in system designs that can be used to reduce costs, enhance functionality, improve reliability, or some combination of all three. In this article, we introduce analytical tools and techniques to estimate the costs associated with a hybrid concentrating photovoltaic system that uses multi-junction microscale photovoltaic cells and miniaturized concentrating optics for harnessing direct sunlight, and an active c-Si substrate for collecting diffuse sunlight. The overall model comprises components representing costs and profit margin associated with the PV cells, concentrating optics, balance of systems, installation, and operation. This article concludes with an analysis of the component costs with particular emphasis on the microscale PV cell costs and the associated tradeoffs between cost and performance for the hybrid CPV design.

Cost analysis for flat-plate concentrators employing microscale photovoltaic cells

Microsystems Enabled Photovoltaics (MEPV) is a relatively new field that uses microsystems tools and manufacturing techniques familiar to the semiconductor industry to produce microscale photovoltaic cells. The miniaturization of these PV cells creates new possibilities in system designs that may be able to achieve the US Department of Energy (DOE) price target of

Decentralized nonimaging micro-optical concentrator

1/Wp by 2020 for utility-scale electricity generation. In this article, we introduce analytical tools and techniques to estimate the costs associated with a concentrating photovoltaic system that uses microscale photovoltaic cells and miniaturized optics. The overall model comprises the component costs associated with the PV cells, concentrating optics, balance of systems, installation, and operation. Estimates include profit margin and are discussed in the context of current and projected prices for non-concentrating and concentrating photovoltaics. Our analysis indicates that cells with a width of between 100 and 300 μm will minimize the module costs of the initial design within the range of concentration ratios considered. To achieve the DOE price target of

Micro chiplet printer for micro-scale photovoltaic system assembly

1/Wp by 2020, module efficiencies over 35% will likely be necessary.

216 cell microconcentrator module with moderate concentration, ±4° acceptance angle, and 13.3 mm focal length

A novel non-imaging micro-concentrator concept and its development in Sandia National Lab’s microsystems-enabled photovoltaics (MEPV) program are described in this paper. Key notions of the compact 2-element optical concentrator are toroidal lens surfaces that decentralize the focused beam and a reflective cone structure that enhances light collection and illumination onto micro-scale solar cells (e.g., ~100’s microns in diameter). The optical configuration therefore provides a low-intensity, hot-spot-free illumination pattern on the receiver while achieving a concentration-acceptance angle product (CAP) over 1. Designs taking into account practical factors (such as fabrication capabilities, misalignments) achieve a 400X geometric concentration with a ±2.4° (90% of peak) acceptance angle (CAP = 0.84) and a 600X geometric concentration with a ±2° acceptance angle (CAP = 0.85), allowing low cost, mass production using injection molding. Development and experimental evaluation of a baseline prototype module is also described.

Guiding optimal biofuels

The micro-CPV concept uses an array of micro unit cells (or elements) such that the material usage, weight, and the required structural strength can all be scaled down favorably. Unfortunately, one of the essential unfavorable scaling factors is the assembly cost due to the many micro scale components that must be deposited, positioned, oriented, and connected over large areas. By using a dynamic electric field template, we successfully demonstrate chiplet printing - assembling a desired solar cell chip at a designated location with well controlled orientation. Xerographic printing systems utilizing this method can be extended to provide high-throughput, on-demand heterogeneous assembly of micro-CPV systems.

Biochemical production of ethanol and fatty acid ethyl esters from switchgrass: A comparative analysis of environmental and economic performance

We report on a demonstration prototype module created to explore the viability of using microscale solar cells combined with microlens array concentrators to create a thin, flat-plate concentrator module with a relatively large acceptance angle for use with coarse two-axis tracking systems designed for flat-plate, one-sun modules. The demonstration module was comprised of an array of 216 cell/microlens units and was manufactured using standard tools common to the integrated circuit, microelectromechanical system (MEMS), and electronics assembly industries. The module demonstrated an acceptance angle of ±4°, an optical concentration level of 36X, and a focal depth of 13.3 mm. The acceptance angle and focal depth of the system successfully demonstrated adequate performance for integration into a system using a coarse two-axis tracker for flat-plate modules. To fully take advantage of this system approach, significant future work is required to reduce optical losses, increase cell and module efficiency, reduce the focal length to approximately 5 mm, and increase the concentration level to greater than 100X while maintaining an acceptance angle of at least ±2°.

Wafer-level Integrated Micro-Concentrating Photovoltaics

In the current study, processes to produce either ethanol or a representative fatty acid ethyl ester (FAEE) via the fermentation of sugars liberated from lignocellulosic materials pretreated in acid or alkaline environments are analyzed in terms of economic and environmental metrics. Simplified process models are introduced and employed to estimate process performance, and Monte Carlo analyses were carried out to identify key sources of uncertainty and variability. We find that the near-term performance of processes to produce FAEE is significantly worse than that of ethanol production processes for all metrics considered, primarily due to poor fermentation yields and higher electricity demands for aerobic fermentation. In the longer term, the reduced cost and energy requirements of FAEE separation processes will be at least partially offset by inherent limitations in the relevant metabolic pathways that constrain the maximum yield potential of FAEE from biomass-derived sugars.