2012 International Congress on Informatics, Environment, Energy and Applications-IEEA 2012
IPCSIT vol.38 (2012) © (2012) IACSIT Press, Singapore
Solar Photovoltaic/Thermal (PVT) Test-bed
Toh Peng Seng1*, Jiang Fan2* and Goh Leag Huab
a
b
Grenzone Pte Ltd, Singapore
School of Electrical and Electronic Engineering, Singapore Polytechnic, Singapore
Abstract. Solar photovoltaic/thermal (PVT) system that combines solar PV system with solar thermal
system into one makes more effective use of solar energy when converting solar energy into both electrical
energy and thermal energy. This paper addresses a solar PVT test-bed in Singapore where the different types
of solar PVT systems developed in Singapore are installed and tested to investigate their performance under
the tropical weather conditions.
Keywords: solar termal; photovoltaics, solar photovoltaic/thermal (PVT).
1. Introduction
The conversion of solar energy to electrical or thermal energy has been practised for many years. The
most popular used solar energy collectors are flat plate solar panel for solar thermal system and flat plate
solar PV module for solar electricity. Comparing to solar PV and solar thermal technology, hybrid solar
photovoltaic/thermal (PVT) technology that produces both electricity and thermal energy under sunlight
simultaneously is relatively new. A PVT collector, the most important component in a hybrid PVT system,
is basically composed of solar PV cells/module mounted on top of heat absorber. The hybrid PVT collectors
are divided in two groups[1-4]:
•
Liquid PV/T collectors that normally produce both hot water and electricity.
•
Air PV/T collectors that are usually building-integrated by installing on facade or roof of
a building to provide warm ventilation air as well as electricity.
In a tropical country like Singapore, water PVT system is more adequate for medium-temperature
domestic applications with temperature ranging from 45°C to 55°C. In applications, a water PVT collector
can be divided into two categories, eg. (1). glazed PVT collector and (2). unglazed PVT collector. Fig. 1
illustrates the basic structures of glazed and unglazed PVT collectors. A glazed PVT collector with glass
cover, can produce more thermal energy but has slightly lower electrical yield, while an unglazed PVT
collector without glass cover produces less thermal energy but more electricity[5-6]. As seen in Fig. 1b, an
unglazed PVT collector has simpler structure and consists of solar PV cells or PV module on top and thermal
absorber below. It delivers relatively lower thermal energy due to more heat convection loss on its front
surface and possesses lower total conversion efficiency than a glazed PVT collector[6-7]. Main advantages
of an unglazed PVT collector over a glazed PVT collector are simpler structure, easier to fabricate and lower
cost. The simplicity of low-cost unglazed PVT collector is balanced by generally lower thermal
performance[8-10] due to high thermal resistance between liquid and PV cell (laminate layers, adhesive bond,
irregularities in flatness of absorber, possible air traps or dry contacts, heat exchanger configuration); white
* Dr. Toh Peng Seng. Tel.: +65 65790560; fax: +65 65790561
E-mail address: tohpengseng@grenzone.com
* Dr. Jiang Fan. Tel.: +65 68790629; fax: +65 67721974
E-mail address: jiagnfan@sp.edu.sg
gaps between PV cells in commercial PV modules results in reduced absorption of solar radiation at aperture
area.
Fig. 1.
collector
Basic structure of liquid PVT collector: (a). glazed PVT collector and (b). unglazed PVT
With increasing concern about depletion of fossil fuels, high dependency of energy import and global
climate change, Singapore Economic Development Board(EDB) sets aside project funding for development
of new solar PVT collectors and research on feasibility of PVT systems in tropical region. One of main tasks
is to set up a test-bed to investigate the performance of new PVT collectors developed by local company.
This paper presents performances of four different PVT systems installed at the test-bed.
2. Site for the PVT Test-Bed
The solar PVT test-bed was set up on the rooftop of 5-storey teaching block in Singapore Polytechnic as
shown in the Fig.2. There are no any other obstacles on the site except a 10 meters high wind turbine. Fig. 3
depicts the shadows at point A of test-bed in a year. As can be seen from the figure, the site selected for
PVT test-bed has no shadows all over a year except some afternoon time after 5pm between March and April,
August and September respectively.
Fig. 2 Layout of the site selected for solar PVT test-bed
(a)
(b)
Fig. 3 Measurment of shadows in situ: (a). shadow change in the first half year and (b). shadow change in the second
half year
Owing to the negative temperature coefficients of PV cells, PV modules are normally installed in such a
way that a certain air gap behind PV modules must be maintained to dissipate the heat of solar cells by
natural ventilation. In a hybrid PV/T collector, the PV cells/modules are directly mounted on the top of
thermal absorber. Although there is no air gap behind solar cells/module, the fluid flow beneath the PV cells
will cool PV cells faster than natural air ventilation of a normal PV installation and improve the power
output of PV cells. To explore the impact of cooling effect of PVT collector on PV cells, we also installed
two PV systems, one a-Si PV system and another mc-Si PV system, to compare the performance of PV cells
of PV module and PVT collectors respectively.
To date, 3 PVT collectors developed by Grenzone Pte Ltd have been used to build 4 PVT systems to
study the operational performance in tropical region. In addition, 2 PV systems were also installed in the testbed for comparison of PVT system with normal PV system. The layout of PVT test-bed upon completion of
installation is shown as in Fig. 4.
3. Structures and Operations of PVT Systems
Three different structures introduced in the test-bed are (1). a-Si stand-alone PVT system, (2) a-Si
natural circulation grid-tied PVT system, and (3). a-Si & mc-Si forced circulation grid-tied PVT systems.
The schematics of three types of PVT systems are illustrated in Figs. 5a, 5b and 5c respectively.
Fig. 4. New layout of the PVT test-bed after installation of all systems; 1). 93Wp unglazed a-Si PVT system ; 2).
768Wp unglazed a-Si syphon PVT system ; 3).1.532kWp unglazed a-Si PVT system ; 4).1.8kWp glazed mc-Si PVT
system ; 5). 1.024kWp a-Si PV system and 6). 1.2kWp mc-Si PV system
(a)
(b)
(c)
Fig. 5 The structures of three PVT systems in the test-bed: (a). Stand-alone forced circulation PVT system; (b). Gridtied natural circulation PVT system and (c). grid-tied forced circulation PVT system
The opeerational perrformances of
o all systems are monito
ored and recoorded by a central data lo
ogger that iss
networked with distribuuted data looggers of eaach PVT and
d PV system
m. To obtaiin the accurrate data forr
t central daata logger coollects both thermal
t
and electrical
e
parrameters from
m all system
m
performance analyses, the
every one minute.
m
Fig. 6 summarizzes the perfoormance of th
hree a-Si PV
VT systems ssince they weere installed..
As can be seen from Figg. 6a, 1.532kkWp PVT syystem shows the best perrformance annd its averagee conversionn
%, while 7688Wp syphon PVT system
m presents thee lowest convversion efficciency(<20%
%)
efficiency iss around 41%
that may bee caused by the poor heaat transfer beetween the collector
c
andd water tankss or by not high
h
enoughh
water tempperature prodduced in an unglazed PVT
P
collecto
or. The 933Wp PVT ssystem is th
he first PVT
T
prototypingg system insttalled in the test-bed andd has been operating
o
successfully foor 18 month
hs to providee
valuable exxperimental results
r
for thhe developm
ment of later PVT collecttors/systems. Its averagee conversionn
efficiency is 34.66%[9--10]. Fig. 6b presents the monthly
y average hoot water tempperatures in the tanks off
s
It is
i apparent from
f
the figuure that two forced circulation PVT ssystems are able to meett
three PVT systems.
the temperaature range from
fr
45°C too 55°C in moost of time of
o a year. Thhe average hhot water tem
mperature forr
93Wp PVT
T system is 45.96
4
°C, whhilst that of 1.532kWp PVT
P
system is 43.94 °C. Like comm
mercial solarr
thermal sysstem, there iss still a needd to install electrical
e
heaater in waterr tanks as baack-up sourcce when low
w
irradiance weather
w
persiists as shownn in January 2011
2
in the figure.
f
(aa)
(b)
Fig. 6 perfoormance of thrree a-Si PVT systems: (a). system
s
converrsion efficienccy & (b). averrage hot waterr Temp in the
tanks
4. Concllusions
This paaper presentss a test-bed set
s up in Sinngapore for research on the operatioons and perfformances off
different typpes of solar photovoltaic
p
c/thermal (PV
VT) systems in tropical region.
r
Four PVT system
ms consistingg
either a-Si PV
P modules or mc-Si PV
V modules have
h
been deeveloped andd installed att the test-bed
d. Long term
m
experimentss on three a-S
Si PVT systeems turned out
o that all three a-Si PVT
T systems aree stable and reliable, twoo
forced circuulation a-Si PVT
P
systemss possess goood operational performannce to meet tthe adequate temperaturee
range for troopical domesstic applicatiions and havve realised 34
4.66% of connversion effiiciency for 93Wp system
m
and 41.46%
% of conversiion efficienccy for 1.532kkWp system respectivelyy, but thermaal syphon un
ngalzed PVT
T
system mayy not be suiitable for tropical applications. More research work is undderway to study
s
on thee
performance of glazed mc-Si
m
PVT and
a also to develop
d
otheer type of PV
VT system liike CIGS PV
VT collector..
o fluid flow in PVT colleector on operration of PV cells is also ongoing.
The investiggation of coooling effect of
5. Acknoowledgmeent
The autthors would like to exprress their thaanks to Econ
nomic Devellopment Boaard(EDB), Siingapore forr
the project funding
f
and Singapore Polytechnic annd Grenzonee Pte Ltd andd for their suppport to the project.
p
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