2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 225 -
Electrical Power Generation by Solar Organic
Rankine Cycle with Flat-Plate and Evacuated-
Tube Solar Collectors as Heat Source
C. Thawonngamyingsakul
*
and T. Kiatsiriroat
**
*
Graduate School, Chiang Mai University,
(Thailand)
**Department of Mechanical Engineering, Faculty of Engineering, Chiang Mai University,
(Thailand)
Abstract
--This paper presents potentials of electrical
power generation by solar organic Rankine cycle with two
types of solar collectors, flat-plate and evacuated-tube, as
heat sources. The required electrical power was 10 kW. The
flat-plate solar collectors with
R
F
WD
= 0.682,
R L
F U
= 4.5392
W/m
2
K and the evacuated-tube solar collectors with
R
F
WD
=
0.5,
R L
F U
= 1.6 W/m
2
K were used in the system and the
area of each type was between 300 and 800 m
2
. The organic
Rankine cycle (ORC) was operating with R245fa and the
evaporating temperature of the ORC was between 75 and 85
o
C. The weather conditions of Chiang Mai and Ubon
Ratchathani were taken as the input data of the calculation.
It could be found that the maximum yearly power
generations from the flat-plate solar collectors at Chiang
Mai and Ubon Ratchathani were 21.7 and 20.9 MWh,
respectively while the evacuated-tube solar collectors were
28.93 and 28.11 MWh, respectively. The values of levelized
electricity costs (LEC) from the flat-plate solar collectors at
Chiang Mai and Ubon Ratchathani were 35.03 and 37.31
Baht/kWh, respectively while the evacuated-tube solar
collectors were 27.07 and 27.28 Baht/kWh, respectively.
Index Terms
-- Solar
Organic
Rankine
Cycle, Electrical
Power Generation, Solar Collector, Levelized Electricity
Cost
I. N
OMENCLATURE
c
A
Collector area (m
2
)
crf
Capital recovery factor
Cm
Chiang Mai
p
C
Specific heat (kJ/kg.K)
Eva
Evacuated-tube solar collector
net
E
Annual net electricity (kWh)
Flat
Flat-plate solar collector
R
F
Heat removal factor
h
Enthalpy (kJ/kg)
IHE
Internal heat exchanger
T
I
Total solar radiation on tilted surface (W/m
2
)
invest
k
Total investment of the plant (Baht)
&
o m
k
Operating and maintenance cost (Baht/year)
m
Mass flow rate (kg/s)
S
M
Mass of water in thermal energy storage (kg)
Q
Heat rate (kW)
__________________________________
This work was supported by the Office of the Higher Education
Commission, Ministry of Education, Thailand
under the Project
“Development and Upgrading of Renewable Energy and Its
Applications”
.
t
Time (s)
T
Temperature (K)
U
Overall heat transfer coefficient (W/m
2
.K)
Ub
Ubon Ratchathani
L
U
Overall heat loss coefficient (W/m
2
.K)
v
Specific volume (m
3
/kg)
W
Power (kW)
th
K
Thermal efficiency
WD
Optical efficiency of collector
II. I
NTRODUCTION
In recent years, the applications of renewable energy
such as biomass, wind energy, geothermal energy and
solar energy for electricity generation become more
important because of the potential in reducing
consumption of fossil fuels and relaxing environmental
problems. According to the study of solar energy
potentials of Thailand [1], the yearly map of direct
normal solar radiation reveals that the regions which
receive the highest solar radiation are in the central region
covering parts of the provinces of Singburi, Nakhon
Sawan, Lopburi, Chai Nat and the lower part of northeast
area covering parts of the provinces of Nakhon
Ratchasima, Chaiyaphum, Roi Et, Yasothon, Surin and
Ubon Ratchathani. These regions receive yearly direct
normal solar radiation in the range of 1,350-1,400
kWh/m
2
-yr.
At present, concentrating solar power (CSP)
technology can be exploited through three different
systems: the parabolic trough system, the tower system
and the dish/Stirling engine system. All the CSP
technologies will be appropriate for countries having high
direct normal solar radiation. Investment and electricity
generation costs for CSP technologies at high direct
normal solar radiation (>1,700 kWh/m
2
) are shown in
Table I [1]. It could be seen that the parabolic trough
system afforded the lowest investment and the electricity
generation cost. Department of Alternative Energy
Development and Efficiency [1] also investigated the
potentials of the three CSP technologies in Thailand. The
values of levelized electricity costs (LEC) of the
parabolic trough system was found to be the lowest
which was 9.77 Baht/kWh. However, Ketjoy and
Rakwichian [2] studied techno-economic feasibility of a
solar parabolic technology for power generation in
