International Journal of Mining, Metallurgy & Mechanical Engineering (IJMMME) Volume 2, Issue 4 (2014) ISSN 2320–4060 (Online)
Thermal Analysis of a Solar Energy System with
Storage Tank in Different Weather Conditions
Kyoung Hoon Kim1 and Chul Ho Han2

non-concentrating and concentrating. The flat plate solar
collectors are usually permanently fixed in position and
therefore need to be oriented approximately. Farahat et al. [9]
developed an exergetic optimization of flat plate solar collectors
to determine the optimal performance and design parameters of
these solar to thermal energy conversion systems. Çomaklı et al.
[10] investigated the optimum sizes of the collectors and the
storage tank to design more economic and efficient solar water
heating systems. Tang et al. [11] constructed and tested two sets
of water-in-glass evacuated tube solar water heater for
comparative studies of performance. Gallego et al. [12]
investigate the modeling of phase change material storage tank
in a solar cooling plant and Palacios et al. [13] investigated
thermal mixing caused by the inflow from one or two round,
horizontal, buoyant jets in a water storage tank.
In recent years the research on the conversion of low-grade
heat from sources such as geothermal heat, waste heat, lowtemperature solar thermal heat, etc. into electrical power or
low-temperature energy conversion has received a lot of
attention [14]-[15]. A thermal storage system is employed to
store the collected solar energy and provide continuous power
output when solar radiation is insufficient. Wang et al. [16]
presented a regenerative organic Rankine cycle (ORC) to utilize
the solar energy over a low temperature range using flat-plate
solar collectors. Delgado-Torres and García-Rodríguez
[17]-[18] carried out a theoretical analysis that the thermal
energy required by a solar ORC is supplied by means of
stationary solar collectors. Gang et al. [19] proposed a new solar
thermal electric generation system with regenerative Organic
Rankine Cycle for use of low-temperature source.
In this paper the effects of weather conditions on the transient
thermal performance of the collector system with heat storage
tanks are parametrically investigated. The important system
variables are investigated on the summer and winter solstices
with variations of system parameters such as the monthly
average daily total radiation on a terrestrial horizontal surface or
the maximum temperature of a day.
Abstract—A storage tank in a solar system plays an
important role for the improvement of performance of solar
energy systems by providing thermal capacitance to alleviate
the solar availability and load mismatch and improve the system
response. In this paper a transient performance analysis is
carried out for a glazed solar flat plate collector system with
heat storage tanks in different weather conditions. Results show
that the system parameters such as the monthly average daily
total radiation on a terrestrial horizontal surface or the
maximum temperature of a day affect greatly on the
performance of solar energy system.
Keywords— solar, flat plate collector, storage tank, transient
performance, weather condition.
I. INTRODUCTION
B
powerful nuclear fusion reaction, the Sun produces
staggering amounts of energy and much of that energy is
dispersed in space. The energy intercepted by the Earth over a
period of one year is equal to the energy emitted in just 14ms by
the Sun. The Sun releases an enormous amount of radiation
energy to its surroundings and when the energy arrives at the
surface of the Earth, it has been attenuated twice by both the
atmosphere and the clouds. After the thermal energy is collected
by solar collectors, it needs to be efficiently stored when later
needed for a release. Thermal storage is one of the main parts of
a solar heating, cooling, and power generating system and it
becomes of great importance to design an efficient energy
storage system. [1]-[5].
The collection of solar energy and energy storage with
auxiliary heat by solar heat storage tank are very important for
the performance of solar energy system. The state of the art on
solar thermal applications with the focus on the two core
subsystems of solar collectors and thermal energy storage
subsystems has been recently reviewed [6]-[7]. Cruz-Peragon et
al. [8] presented a general methodology to validate a collector
model with undetermined associated complexity.
The solar collectors may be categorized as two types of
Y
II. SYSTEM ANALYSIS
The schematic diagram of the system is illustrated in Fig. 1.
Flat plate collectors (FTC’s) are used to collect the solar
radiation. The main components of a flat-plate collector are
cover, heat removal fluid passageways, absorber plate, headers
or manifolds, insulation and container. The thermal storage tank
is employed to store the collected solar energy and to provide
Kyoung Hoon Kim1 is professor in the Department of Mechanical
Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk
730-701, Korea (phone: 82-54-478-7292; fax: 82-54-478-7319; e-mail:
khkim@kumoh.ac.kr)
Chul Ho Han2 is professor in the Department of Intelligent Mechanical
Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk
730-701, Korea (phone: 82-54-478-7393; fax: 82-54-478-7319; e-mail:
chhan@kumoh.ac.kr), corresponding author
111
International Journal of Mining, Metallurgy & Mechanical Engineering (IJMMME) Volume 2, Issue 4 (2014) ISSN 2320–4060 (Online)
where θ and θz are incident angles on the tilted and horizontal
surfaces, respectively, β the tilt angle of the collector, and ρ the
reflectance of ground.
The incident solar flux absorbed in the absorber plate is
determined as
the stable power output when solar radiation is insufficient.
Water is used in both the solar energy collector system and the
thermal storage system. The modeling of the thermal
performance of the system is as follows [2], [5].
The average hourly total (beam plus diffuse) and diffuse
radiations on terrestrial horizontal surface I and Id, respectively,
can be determined from the monthly average daily total
radiation on a terrestrial horizontal surface H as follows [2]:
Hd
 1.390  4.027 KT  5.531KT2  3.108KT3
H
rd 
Id


H d 24
S  I b Rb  b  I d Rd  I b  I d Rr  d
where (τα)b and (τα)d represent the transmissivity and
absorptivity product for beam and diffuse radiation on the
collector plate, respectively.
The total loss coefficient UL is consisted of the bottom, the
top and the side loss coefficients:
(1)
cos(h)  cos(hss )
 2hss 
sin(hss )  
 cos(hss )
 360 
(2)
U L  Ub  Ut  U s
I
r   rd    cos(h)
H
Then, the useful energy of the collector Qu, is given by:
Qu  mwC p T fo  T fi 
H
H0

(11)
(12)
(4)
I T  I b Rb  I d R d ( I b  I d ) Rr
where Ap is the total absorption area of the collector, mw, Cp, TL,
and Tfo are mass flow rate, specific heat, inlet and outlet of water,
respectively.
In this system a sensible heat storage tank is used to store the
collected solar energy. For the simplicities, it is assumed that the
water in the insulated storage tank is completely mixed with the
water flowing back into the tank from the collector and from the
heat load. Then the energy balance in the storage tank can be
obtained as follows [16]:
(5)
where Ib and Id are the hourly beam and diffuse radiation that the
collector receives, and Rb, Rd, Rr are defined as tilt factors for
beam, diffuse and reflection radiations, respectively, whose
values are given by:
VC   VC   dTdt
cos( ) sin( ) sin( L   )  cos( ) cos(h) cos( L   ) (6)

cos( z )
sin( L) sin( )  cos( L) cos( ) cos(h)
1  cos( )
2
(7)
 1  cos(  ) 
Rr   

2


(8)
Rd 

 FR Ap S  U L T fi  Ta 
The hourly radiation falling on a tilted surface is given by
Rb 
(10)
(3)
where h the hour angle, and KT is the monthly average clearness
index defined as
KT 
(9)
L
p w
p t
 Qu  Qh  (UA)t TL  Ta 
(13)
where ρ, V, Qh are density, volume, and heat load, respectively,
and subscripts w and t denote water and tank, respectively.
solar
insolation
Tfo
flat-plate
collector
heat
storage
tank
mw, TL
pump
Figure 1. Schematic diagram of the system.
112
Qh
International Journal of Mining, Metallurgy & Mechanical Engineering (IJMMME) Volume 2, Issue 4 (2014) ISSN 2320–4060 (Online)
III. RESULTS AND DISCUSSIONS
1.1
The numerical simulation of the solar flat plate collector is
presented in this section by using the mathematical models
established above. Seoul in Korea (N37.6º, E127º) is selected as
the case city, and the summer and winter solstices are selected as
the case days. The basic data for the simulation are similar to
those in [16] and [5]; β = 34.27º, L1 = 1.1m, L2 = 1.6m, L3 =
0.2m, M = 2, Np = number of plates = 300, ki = 5 W/mK, δi =
0.05 W/mK, hf = 320 W/m2K, Do = 0.015m, Di = 0.0135m, W =
0.12m, δp = 0.0005m, kp = 385 W/mK, ρ = 0.5, Vw = 2.5 m/s, εp
= 0.1, εg = 0.88, n = glass refraction index = 1.526, Kec =
extinction coefficient = 0.037, αn = absorptance of the plate at
normal incidence = 0.91. Nt = number of storage tank = 3, Do =
external diameter of storage tank = 2.1m, Di = inner diameter of
storage tank = 1.7m, Ht = height of storage tank = 2m, δp = tank
wall thickness = 0.0006m, δi = insulation thickness = 0.2m.
Here, it is assumed that the daily maximum and minimum
temperatures occur at 4:00 and 14:00, respectively.
H
heat loss of storage tank [kW]
1.0
2
av
[MJ/m day]
SS
WS
15
0.9
0.8
6
20
8
25
10
30
12
0.7
0.6
0.5
0.4
0.3
0
4
8
12
16
20
24
solar time [h]
Figure 3. Plot of heat loss from tank with time on the summer and winter
solstices for various monthly average total radiations.
3.1 Effects of monthly average daily total radiation
The plate temperature is plotted against solar time in Figure 2
on the summer solstice (SS) and winter solstice (WS) for
various monthly average daily total radiations on a terrestrial
horizontal surface, Hav’s. The plate temperature increases with
increasing the daily total radiation. And it can be seen from the
figure that as the time increases the plate temperature increases
and reaches a maximum value and the decreases, however, the
time for the maximum plate temperature is later than the time for
the maximum solar radiation.
With the assumption that the mass flow rates of fluid in the
collector tubes and the heat load are assumed to be fixed, the
transient heat loss from the storage tanks are plotted in Figure 3.
The heat loss decreases with time until about 8 O’clock which is
later than the sunrise time. Then the heat loss increases with
time due to the solar insolation and the temperature elevation
inside the tanks. Finally the heat loss decreases with time due to
the decrease in solar insolation. The heat loss on the winter
solstice is greater than the summer solstice due the greater
temperature difference between the inside tank and ambient.
Figure 4 shows the temperature variations of tanks on
summer and winter solstices. The temperate inside tank
decreases with time until about 8 O’clock, mainly due to the
decrease in the ambient temperature. After the temperature
increases until about 16 O’clock, the temperature decreases
with time again even before sunset time, since the heat input due
to solar insolation becomes lower than the heat load. It can be
seen from the figure that the tank temperature increases with
increasing the daily total insolation.
The variations of the collector efficiency are plotted in Figure
5 with time for various numbers of the tanks. The collector
140
2
o
plate temperature [ C]
140
H
WS
130
SS
SS
120
110
2
[MJ/m day]
15
6
20
8
25
10
30
12
av
[MJ/m day]
WS
15
o
av
temperature in tank [ C]
H
130
100
90
80
70
120
110
6
20
8
25
10
30
12
4
8
100
90
80
70
60
60
50
50
7
8
9
10
11
12
13
14
15
16
0
solar time [h]
12
16
20
24
solar time [h]
Figure 2. Plot of plate temperature with time on the summer and winter
solstices for various monthly average total radiations.
Figure 4. Plot of temperature in tank with time on the summer and winter
solstices for various monthly average total radiations.
113
International Journal of Mining, Metallurgy & Mechanical Engineering (IJMMME) Volume 2, Issue 4 (2014) ISSN 2320–4060 (Online)
1.0
SS
WS
15
0.8
0.7
0.6
6
20
8
25
10
30
12
heat loss of storage tank [kW]
0.9
collector efficiency
0.8
2
Hav [MJ/m day]
0.5
0.4
0.3
0.2
0.1
0.7
0.6
0.5
o
Tmax [ C]
SS
0.4
0.0
WS
30
10
25
5
20
0
15
-5
0.3
7
8
9
10
11
12
13
14
15
16
0
4
8
solar time [h]
Figure 5. Plot of collector efficiency with time on the summer and winter
solstices for various monthly average total radiations.
o
plate temperature [ C]
SS
WS
30
WS
10
25
5
20
0
15
80
Tmax [ C]
80
o
SS
24
o
90
o
[ C]
temperature in tank [ C]
90
20
from the figure that the plate temperature has a peak value with
respect to time and the peak time increases with increasing the
maximum daily temperature.
The transient heat loss from the storage tanks are plotted in
Figure 7. The heat loss decreases firstly with time and then
increases with time, and finally decreases with time. Therefore,
there exists a local minimum and a local maximum value of the
heat loss with respect to time. It can be observed from the figure
that the time for the local minimum value decreases with the
daily maximum temperature and the time for the local maximum
value increases with the daily maximum temperature.
The temperatures in tanks on summer and winter solstices
are plotted with time in Figure 8 for various daily maximum
temperatures. The temperature in tanks increases with
3.2 Effects of daily maximum temperature
The plate temperature is plotted against solar time in Figure 6
on the summer solstice (SS) and winter solstice (WS) for
various daily maximum temperatures. Here, the daily average
minimum temperature is assume to be lower than the maximum
temperature by 10℃. The plate temperature increases with
increasing the daily maximum temperature. And it can be seen
max
16
Figure 7. Plot of plate temperature with time on the summer and winter
solstices for various daily maximum temperatures.
efficiency is defined as the ratio of the useful heat gain to the
solar insolation on the tilted plate surface. The collector
efficiency becomes zero at sunrise and sunset times and has a
peak value with respect to time. It can be observed from the
figure that the peak efficiency increases with the total daily
insolation and the peak time decreases with the total daily
insolation.
T
12
solar time [h]
-5
70
60
30
10
25
5
20
0
15
-5
70
60
50
7
8
9
10
11
12
13
14
15
0
16
4
8
12
16
20
24
solar time [h]
solar time [h]
Figure 8. Plot of plate temperature with time on the summer and winter
solstices for various daily maximum temperatures.
Figure 6. Plot of plate temperature with time on the summer and winter
solstices for various daily maximum temperatures.
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International Journal of Mining, Metallurgy & Mechanical Engineering (IJMMME) Volume 2, Issue 4 (2014) ISSN 2320–4060 (Online)
[3]
0.6
[4]
0.5
collector efficiency
[5]
0.4
[6]
0.3
o
[7]
Tmax [ C]
0.2
SS
0.1
WS
30
10
25
5
20
0
15
-5
[8]
0.0
[9]
7
8
9
10
11
12
13
14
15
16
[10]
solar time [h]
Figure 9. Plot of collector efficiency time on the summer and winter
solstices for various daily maximum temperatures.
[11]
increasing the daily maximum temperature. It can be observed
from the figure that there exists also a local minimum and a local
maximum value for the temperature in tanks with respect to time,
and the time for the local minimum value decreases with the
daily maximum temperature, however, the time for the local
maximum value increases with the daily maximum temperature.
Figure 9 shows the variations of the collector efficiency with
time for various daily maximum temperatures. It can be seen
from the figure that the peak efficiency increases with the daily
maximum temperature and the peak time for the collector
efficiency decreases with increasing the daily maximum
temperature.
[12]
[13]
[14]
[15]
[16]
[17]
IV. CONCLUSIONS
This paper presents the transient thermal performance
analysis of solar flat plate collector system with thermal storage
tank. The important system variables including the collector
plate temperature, heat loss of the tank, temperature in the tanks,
and the collector efficiency are parametrically investigated for
various the monthly average daily total radiation and the daily
total maximum temperature. Results show that the system
parameters such as the monthly average daily total radiation on
a terrestrial horizontal surface or the maximum temperature of a
day affect greatly on the performance of solar energy system.
[18]
[19]
ACKNOWLEDGMENT
This research was supported by Basic Science Research
Program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Education, Science and
Technology (No. 2010-0007355).
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