Energy and Exergy Analyses of Solar-Driven ORC Integrated with Fuel Cells and Electrolyser for Hydrogen and Power Production

Abstract

Hydrogen as an energy carrier is an excellent storage medium for harvesting renewable energies which are characterized by hourly fluctuations and intermittence. In this paper a system that integrates an organic Rankine cycle (ORC), electrolyser, hydrogen storage in metal hydrides, and a fuel cell is analyzed thermodynamically for on-demand power generation from solar energy. The system is destined to small-scale applications such as roof-top solar power at low concentration and total collector area of the order of 100 m². This will ensure the heating and power needs of an average residence throughout the year. Compound parabolic concentrators are used as vapor generator integrated with an ORC heat engine with cyclohexane working fluid. A small capacity thermal energy storage system is used to keep the working fluid hot during nighttime and eliminate the need of system warm-up in the mornings. The ORC is made to operate continuously and steadily during the daylight to produce power with a solar multiplicity factor of 3. A fuel cell system is used to generate power on-demand from the stored hydrogen. A part of the rejected heat is recovered and used for cogeneration. The system efficiency is determined based on thermodynamic analysis and proved to be attractive.

Nomenclature

A :

Area, m²

BVR :

Built-in volume ratio

C :

Concentration ratio

$\dot{E}$ :

Energy rate, kW

I :

Irradiance, W/m²

n :

Refraction index

r :

Radius, m

T :

Temperature, K

U :

Overall heat transfer coefficient, W/m² K

CPC:

Compound parabolic concentrator

FC:

Fuel cell

HR:

Heat recovery

ORC:

Organic Rankine cycle

PEME:

Proton exchange membrane electrolyser

PIC:

Power inverter and control center

SR:

Solar receiver

SYS:

Overall system

TMS:

Thermo-mechanical storage

θ :

Half acceptance angle

η :

Energy efficiency

ϕ :

Rolling or involute angle

0:

Reference state

1:

Initial

b:

Base

i:

Inner

loss:

Losses

o:

Outer, orbiting

T:

Tilt surface