Abstract— Building integrated photovoltaic thermal solar collector (BIPVT) has been designed to produce both electricity and hot water and later integrated to building. The hot water is produced at the useful temperatures for the applications in Malaysia such as building integrated heating system and domestic hot water system as well as many industrial including agricultural and commercial applications that require low grade heat (>50ºC). An experiement study of a BIPVT collector involving a specially designed absorber collector has been performed for heat transfer enhancement. The results of performance and efficiency including the photovoltaic, thermal and also the combination of both are discussed and analyzed. Results at solar irradiance of 904 W/m2 shows that the combined efficiency of 60 %, electrical efficiency of 11% at mass flow rates of 0.041 kg/s. Keywords— BIPVT collector, hot water heating system,

thermal and electrical efficiency.

I. INTRODUCTION

ALAYSIA received approximately 4.0 - 8.0 hours of sunlight every day which lead to almost 4000 - 5000

Wh/m² of mean monthly sunlight rays (Sopian et al. 1992). These amounts of solar energy can be useful for plenty of purposes by improving its efficiency and cost effectiveness. There are two types of known solar energy systems that can generate electricity effectively, which are, thermal and photovoltaic system. However, priority is given more to photovoltaic system since that it is easier to manage and can produce electricity directly from the sun.

Recently, photovoltaic system has been integrated to the building either on wall or on roof, hence indirectly, reducing its overall costs of the system. This system is known as Building Integrated Photovoltaic (BIPV) and can be install for individual usage or in large scale.

Photovoltaic system that integrated with the building leads to a temperature rise on the panels, causing the photovoltaic's efficiency decrease. Under Standard Test Conditions (STC),

Manuscript received May 19, 2011: Revised version received xxx. A. Ibrahim, M. Y. Othman, M. H. Ruslan, S. Mat, A. Zaharim and

K.Sopian is with the Solar Energy Research Institute, Universiti Kebangsaan Malaysia, 43600 Bangi Selangor, MALAYSIA.

(E-mail: adnan@vlsi.eng.ukm.my*, myho@ukm.my, hafidz@ukm.my, sohif@ukm.my, azami.zaharim@gmail.com and ksopian@vlsi.eng.ukm.my)

operation's temperature was fixed on 25ºC. It is noted that the building integrated photovoltaic system used in areas such as Malaysia accumulate up to 60 ºC - 80 ºC. This temperature raises and causes the module to lower it efficiency level. Hence, it is crucial to reduce the operational temperature in order to get optimum efficiency throughout the system. The researches in this photovoltaic/thermal have been increased recently. Generally, photovoltaic/thermal collectors can be divided into two types:

• Solar water heating and photovoltaic cells combination. • Solar air heating and photovoltaic cells combination. Both types of these collectors can be identify from the

medium type used as a heat transferring fluid, which is, either water or air. Choosing the collector is much depending on the type of system and usage suitability. Usage of solar collector is determined based on the collector overall efficiency and output temperature produced. Prior factors that determine thermal efficiency is that heat transferring process between absorption plate and fluid flow medium inside the collector. The most important parameter in this heat transferring process is the absorber's surface area that exposed to the medium and the coefficient of the heat transfer for the involving medium. While the electricity efficiency of the photovoltaic cell was influenced by the temperature of the cells itself, electricity efficiency will decrease as the heat increasing. This means that optimum result will only achieved as long the system operates in a lowest temperature. Thermal efficiency will also rise if the PVT collector is allowed to operate at a lower temperature. However, optimization needs to be performing to ensure the system operating in a suitable efficiency with the required output temperature from the collector for other purposes can be determined.

Solar energy technology can be broadly classified into a hybrid systems; photovoltaic energy system and thermal energy system. Hybrid photovoltaic thermal system inherited all the advantages of PV technology. The advantages such as works on noiseless environment; do not produce any unwanted waste such as radioactive materials etc, highly credibility system with life span expectation is between 20 to 30 years and very low maintenance system are considered an attractive features for PVT system (Ibrahim et al. 2009a).

A Pilot Study of the Building Integrated Photovoltaic Thermal (BIPVT) Collector for

Commercial Applications in Malaysia

A. Ibrahim, M. Y. Othman, M. H. Ruslan, S. Mat, A. Zaharim and K. Sopian

M

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ISBN: 978-1-61804-022-0 139

Thermal Storage Tank Water

Storage tank

Data Logger 24ch

Converter/

Inverter

Load

V

• Pyranometer • Thermocouples • DC Current

transducer • DC Voltage

transducer • Flowmeter • Thermostat

Auxiliary Heater

DATA ACQUISITION

SYSTEM

Grid connected

PV/T water collector

Water out

A

Numerous researches and development programs have been carried out to improve the applications of solar energy systems. Several design of photovoltaic thermal solar water based collector has been proposed in the past. Among the first was Martin (Wolf 1976) who analysed the performance of combining the heating and photovoltaic power systems for residences and conclude that the system was technically feasible and cost effective. Beside Wolf, research on PV/T water based collector bas been conducted by Florschuetz, extending the Hottel-Whillier model to the analysed the combination of PV/T flat plate collectors with the traditional hot water system and PV panel to minimize the usage of the installation area. It is proven that by combining the system, the installation area produced more energy per unit surface area than a separate system (Florschuetz 1979).

Zondag examined the various concepts of combined PV-thermal collector technologies and conclude that the design of the channel below the transparent PV with PV-on-sheet and tubes design gives the best efficiency overall (Zondag 2008). Bergene performed theoretical examination of a flat plate solar collector model that integrated with solar cells, concludes that the system combination of both produced approximately about 60-80% efficiency (Bergene et al. 1995).

Performance simulation of PV/T collectors with seven new design configurations of absorber collectors design has been studied by (Ibrahim et al. 2009b) and conclude that the best design configuration is the spiral flow design with thermal efficiency of 50.12% and cell efficiency of 11.98%.

The aim of this paper is to develop and test the efficiency of the BIPVT collector for the building integrated systems for Malaysia applications where the system required to operate with an output temperature between 40ºC to 60ºC which later suitable range for domestic usage.

II. BIPVT COLLECTOR EXPERIMENTAL SETUP

The outdoor experiment on the BIPVT collector has been performed at Solar Energy Research Institute Solar Park (SERI), Universiti Kebangsaan Malaysia to determine the ability (efficiency) of the collector to convert the sunlight to heat and electrical energy. The collector, as shown in Fig. 1 is made of a rectangular hollow tube of stainless steel material with dimension of 12.7×12.7 mm.

Fig. 1: The design of absorber collectors in parallel tested outdoor for BIPVT collector applications

The collector, which assembled using a TIG welding method, consist of a single unilateral channel for the water to flow in and out underneath the standard photovoltaic panel with the size of 1 m high x 0.65 m length and 0.3 m thickness. Thermal insulator as in Fig. 2, is packed underneath the collector to prevent heat from escaping further and provides more uniform temperatures throughout the system.

Fig. 2: The assembly view of the BIPVT collector

A standard photovoltaic panel represented as a flat plate

single glazing sheet of polycrystalline silicon with single glazing sheet has been laminated and bonded with a high temperature silicone adhesive and sealant. Once sealed and watertight, the collector is attached to the bottom side of photovoltaic panel and encapsulated in a Polyvinyl resin and formed a complete BIPVT collector system with the size of 815 × 628 x 30 mm.

As shown in Fig. 3, ambient temperature and other temperatures are measured using K-type thermocouple. Solar radiations from the sun are measured by Eppley pyranometer for intensity. Mass flow rates for the collector is set from 0.034, 0.039 and 0.041 kg sec 1 and connected direct to data acquisition system which later link to the computer. The full schematic diagram of data acquisition system comprised of the BIPVT collector, water storage tank with auxiliary heater, data acquisition system and converter/inverter that link to the load. The grid connected system is an additional to the system.

Fig. 3: The Schematic diagram of BIPVT system

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III. BIPVT COLLECTOR SYSTEM EFFICIENCY

The efficiency of thermal and cell for the BIPVT collector is evaluated based on the Hottel and Whillier equations (Hottel H. C et al. 1958). In these equations the mass flow rates can be calculating based on:

.

m = ρAVav

where: .

m = The mass flow rate, ρ = the density of the medium drain input area and Vav = the water velocity.

The thermal efficiency of the collector is expressed as: (Vokas et al. 2006)

( )T

ai

LRPVRthG

TTUFF

−−= ταη

where: FR = heat removal efficiency factor, ταPV = average

transmittance-absorptance of the collector, UL = overall collector heat loss coefficient (W/m2 ºC), Ti = fluid inlet temperature (ºC), Ta = ambient temperature (ºC) and GT = solar radiation at NOCT

For temperature-dependent electrical efficiency of the PV

module, )( eη (Tiwari et al. 2006), the expression given is:

( )[ ]rcre TT −−= βηη 1

where: ηe = electrical efficiency, ηr = reference efficiency of

PV panel (ηr = 0.12), β = temperature coefficient (ºC 0.0045ºC-1), Tc = temperature of the solar cells (ºC), and Tr = the reference temperature.

The overall efficiencies (combined efficiency) ηpvt is used to

evaluate the overall performance of the system: ηpvt = ηth+ηe

IV. RESULTS AND DISCUSSION

The experiment on BIPVT collector system has been performed on 30 December 2009. Fig. 4 shows the temperature distribution for the BIPVT collector taken at mass flow rate of 0.039 kg/s and data were collected and gathered from 08:00 to 17:00 respectively. It is noted that from the experiment shows that the water inlet temperature reaches 53.2ºC, plate temperature of 70.3ºC and ambient temperature at 37ºC.

Fig. 4: The temperature distribution of the BIPVT collector taken at mass flow rate of 0.041 kg/s.

As shown in Fig. 5, the efficiency and the irradiance of the

collector versus time. The result shows that the system is time dependence based on solar irradiance and noted that the peak of solar irradiance on that particular day was at 13:30 at 904 W/m2. The temperatures of the collector remain unchanged even though the solar irradiance recorded to fall and this shows that the BIPVT collector has the capability of retain the heat.

Fig. 5: Efficiency and irradiance versus time for BIPVT collector

Fig. 6 show the dependence of electrical, thermal and combined BIPVT collector efficiency on the mass flow rate respectively.

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Fig. 6: Efficiency of photovoltaic (PV), thermal (T) and combined versus mass flow rate

V. CONCLUSIONS

Results indicates that the electrical and thermal production of a BIPVT collector increases with decreasing temperature of ambient. The collector is considered to be a closed loop system, it is worthwhile to deliver the hot water out of the collector for other purposes and cold water should be kept as low as possible. A trade-off between increasing of electricity production and producing hot water is thus necessary. The experiment proved that the BIPVT system has a potential as an alternative method of energy production for commercial applications in Malaysia.

ACKNOWLEDGMENT

The authors would like to express their gratitude to Universiti Kebangsaan Malaysia and the Ministry of Science, Technology and Innovation Malaysia for sponsoring the work under project Sciencefund 03-01-02-SF0039.

REFERENCES

[1] Bergene, T. and O. M. Lovvik (1995). "Model calculations on a flat-plate solar heat collector with integrated solar cells." Solar Energy 55(6): 453-462.

[2] Florschuetz, L. W. (1979). "Extension of the Hottel-Whillier model to the analysis of combined photovoltaic/thermal flat plate collectors." Solar Energy 22(4): 361-366.

[3] Hottel H. C and A. Whillier (1958). "Evaluation of Flat-Plate Solar Collector Performance." Trans. of the Conference on Use of Solar Energy 2: 74.

[4] Ibrahim, A., G. L. Jin, R. Daghigh, M. H. M. Salleh, M. Y. Othman, M. H. Ruslan, S. Mat and K. Sopian (2009a). "Hybrid photovoltaic thermal (PV/T) air and water based solar collectors suitable for building integrated applications." American Journal of Environmental Sciences 5(5): 618-624.

[5] Ibrahim, A., M. Y. Othman, M. H. Ruslan, M. A. Alghoul, M. Yahya, A. Zaharim and K. Sopian (2009b). "Performance of photovoltaic thermal collector (PVT) with different absorbers design." WSEAS Transactions on Environment and Development 5(3): 321-330.

[6] Sopian, K. and M. Y. Othman (1992). "Estimates of monthly average daily global solar radiation in Malaysia." Renewable Energy 2(3): 319-325.

[7] Tiwari, A. and M. S. Sodha (2006). "Performance evaluation of hybrid PV/thermal water/air heating system: A parametric study." Renewable Energy 31(15): 2460-2474.

[8] Vokas, G., N. Christandonis and F. Skittides (2006). "Hybrid photovoltaic-thermal systems for domestic heating and cooling--A theoretical approach." Solar Energy 80(5): 607-615.

[9] Wolf, M. (1976). "Performance analyses of combined heating and photovoltaic power systems for residences." Energy Conversion 16(1-2): 79-90.

[10] Zondag, H. A. (2008). "Flat-plate PV-Thermal collectors and systems: A review." Renewable and Sustainable Energy Reviews 12(4): 891-959.

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