Research Papers

Stirling Engines for Distributed Low-Cost Solar-Thermal-Electric Power Generation

[+] Author and Article Information
Artin Der Minassians1

Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, CA 94720artin.der.minassians@gmail.com

Seth R. Sanders

Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, CA 94720artin.der.minassians@gmail.com


Corresponding author.

J. Sol. Energy Eng 133(1), 011015 (Feb 14, 2011) (10 pages) doi:10.1115/1.4003144 History: Received September 11, 2007; Revised August 14, 2010; Published February 14, 2011; Online February 14, 2011

Due to their high relative cost, solar-electric energy systems have yet to be exploited on a widespread basis. It is believed in the energy community that a technology similar to photovoltaics, but offered at about $1/W, would lead to widespread deployment at residential and commercial sites. This paper addresses the feasibility study of a low-cost solar-thermal electricity generation technology, suitable for distributed deployment. Specifically, we discuss a system based on nonimaging solar concentrators, integrated with free-piston Stirling engine devices incorporating integrated electric generation. We target concentrator collector operation at moderate temperatures, in the range of 120°C to 150°C. This temperature range is consistent with the use of optical concentrators with low-concentration ratios, wide angles of radiation acceptance which are compatible with no diurnal tracking and no or only a few seasonal adjustments. Therefore, costs and reliability hazards associated with tracking hardware systems are avoided. This paper further outlines the design, fabrication, and test results of a single-phase free-piston Stirling engine prototype. A very low loss resonant displacer piston is designed for the system using a very linear magnetic spring. The power piston, which is not mechanically linked to the displacer piston, forms a mass-spring resonating subsystem with the gas spring, and has a resonant frequency matched to that of the displacer. The design of heat exchangers is discussed, with an emphasis on their low fluid friction losses. Only standard low-cost materials and manufacturing methods are required to realize such a machine. The fabricated engine prototype is successfully tested as an engine, and the experimental results are presented and discussed. Extensive experimentation on individual component subsystems confirms the theoretical models and design considerations. Based on the experimental results and the verified component models, an appropriately dimensioned Stirling engine candidate is discussed.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Schematic diagram of the solar-thermal-electric power generation system

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Figure 2

Efficiency of solar collector (Schott ETC 16 (3)), Stirling engine, and system as a function of temperature for a representative system. The dot indicates the point of optimal system efficiency.

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Figure 3

Simplified schematic diagram of the conceived Stirling engine

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Figure 4

Simulation results of the single-phase free-piston Stirling engine thermodynamic behavior. (a) Wall, instantaneous, and average temperatures on hot and cold sides. (b) Expansion space, compression space, and total engine chamber volume variations. (c) Pressure variation. (d) p-V loop of the thermodynamic cycle.

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Figure 5

Schematic diagram of the displacer piston design

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Figure 6

(a) Fabricated displacer piston with embedded linear motion ball bearing and permanent magnet arrays. (b) Stationary magnetic array that provides the linear spring function for the displacer. Compare with Fig. 5.

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Figure 7

Fabricated heat exchanger shown with the etched fins and copper tube inserts

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Figure 8

Fabricated power piston shown with the low-carbon steel body and Nd–Fe–B permanent magnets attached to one end

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Figure 9

Ring-down characteristic of the displacer piston

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Figure 10

Gas hysteresis loss characteristic of the fabricated Stirling engine prototype

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Figure 11

The Stirling engine experimental setup

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Figure 12

Measured engine pressure and volume variations. Compare with Fig. 4.

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Figure 13

Measured p-V diagram of the engine

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Figure 14

Power balance diagram of the fabricated prototype. All the measured powers (in W) are noted on the diagram.




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