# Theoretical Analysis of the Performance of a Solar Chimney Coupled with a Geothermal Heat Exchanger

• A. Dhahri
• A. Omri
• J. Orfi
Chapter

## Abstract

The use of solar energy to generate electric power is suggested as a promising technology. Specifically, the solar chimney power plant which generates electricity from free solar energy using air natural convection flow has gained interest during the last few decades. In this chapter, a numerical analysis of the performance of a solar chimney power plant using steady-state Navier–Stokes and energy equations in cylindrical coordinate system was presented. The fluid flow inside the chimney was assumed to be turbulent and simulated with the k–ε model, using FLUENT software package. The computed results were in good agreement with the experimental measurements of the Spanish Manzanares power plant. Besides, some theoretical models were proposed taking into account the air kinetic energy difference within the solar collector. The numerical model was then coupled with a mathematical model for a geothermal heat exchanger to investigate the option of coupling solar and geothermal sources for a continuous day and night operation. Several scenarios were proposed and assessed. The results particularly focused on the effects of the main geometrical parameters of the collector, the weather conditions as well as the effectiveness of the heat exchanger on the air mass flow rate, the temperature rise within the collector, and the overall performance of the combined renewable energy plant. The results show the benefits of the hybrid solar–geothermal plant compared to the single solar chimney plant for day and night periods.

## Keywords

Solar energy Solar chimney Numerical model Electric power Geothermal energy

## Nomenclature

A

Area (m2)

Acoll

Solar collector area (m2)

Dtube

Tube diameter (m)

G

g

Gravitational acceleration (ms−2)

h

Heat transfer coefficient (Wm−2K−1)

$$\dot{m}$$

Mass flow rate (kg s−1)

ntube

Tube number

R

T

Temperature (K)

V

Airflow velocity (ms−1)

## Greek Symbols

λ

Thermal conductivity (W m−1 K−1)

μ

Dynamic viscosity (kg (s m)−1)

ρ

Density (kg m−3)

τ α

Transmittance-absorbtance product

## Subscript

c

Solar collector cover

e

Environment or external

f

Fluid

i

Internal

m

Average

r

Storage reservoir

s

Soil or solar

w

Geothermal water

w, in

Heat exchanger inlet

w, out

Heat exchanger outlet

1

Solar collector inlet

2

Solar collector outlet

ΔT

Temperature increase (K)

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