Research Papers

Hybrid Solar System for Decentralized Electric Power Generation and Storage

[+] Author and Article Information
Nico Hotz

Department of Mechanical Engineering and Materials Science,  Duke University, 303 Hudson Hall, P.O. Box 90300, Durham, NC 27708-0300nico.hotz@duke.edu

J. Sol. Energy Eng 134(4), 041010 (Sep 24, 2012) (8 pages) doi:10.1115/1.4007356 History: Received December 11, 2011; Revised July 20, 2012; Published September 21, 2012; Online September 24, 2012

The present study investigates the feasibility, efficiency, and system design of a hybrid solar system generating electric power for stationary applications such as residential buildings. The system is fed by methanol and combines methanol steam reforming and proton exchange membrane (PEM) fuel cells with solar collectors to generate the required heat for the steam reforming. The synergies of these technologies lead to a highly efficient system with significantly larger power densities compared to conventional systems and generate tremendous advantages in terms of installation and operation costs. The present investigation describes the entire proposed system and its components and presents first analytical, numerical, and experimental results of a larger project to prove the feasibility of such a system by analyzing first a bench test demonstrator generating around 10 W of electric power and finally a prototype for an entire single-family household. It is shown that the methanol-to-electricity efficiency of the entire system is above 50%.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Schematic of the hybrid solar-powered system

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Figure 2

Schematic of the hybrid reformer with integrated catalyst

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Figure 3

Reformer efficiency depending on the solar irradiation (200–1000 W/m2 ) for inlet flow rates varying from 0.19 to 15.1 mg/s methanol input per gram of catalyst

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Figure 4

Reforming efficiency, reformer temperature, and CO mole fraction of product gas depending on the solar irradiation (200–1000 W/m2 ) for inlet flow rates varying from 0.19 to 15.1 mg/s methanol input per gram of catalyst

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Figure 5

Daily distribution of electric power load, electric output by the fuel cell, and generated hydrogen for a single-family household during an average day in summer in central California

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Figure 6

Volumetric flow rates, electric power, and specifications of system components for single-family system in summer. Values for flow rates and electric power are shown as averages and (in parentheses) as maximum per hour. The averages are calculated for 11 h of sunshine (evaporator to PROX), 8 h of compressor operation, 16 h of discharging of the gas tank, and 24 h of fuel cell operation.

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Figure 7

Schematic of exergy flow through the entire system. Unless noted otherwise, all values show the exergy transfer during an entire day in summer (units: kWh).



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