Performance Analysis of Hybrid Photovoltaic Thermal (PV/T) Solar Collector by Varying PV Panel and Cooling of Glass Cover

INTRODUCTION TO SOLAR ENERGY

Energy consumption increases very rapidly as the world developing. Conventional sources are not able to fulfill the today energy needs. Fossil fuels are the main conventional sources for energy production till now. The two main limitations of fossil fuels: Limited in quantity and environment pollution makes the world think for alternative energy sources. Renewable energy sources eliminate the weaknesses of conventional sources. But because of less knowledge about these sources and high initial cost of the conversion systems limits the use of these resources. From the renewable energy resources, solar energy has a huge potential for the fulfillment of today energy needs. The total solar radiation energy falling on earth atmosphere is 1017 watts Amount of solar radiations reaches earth is 1016 watts, this is 1000 times more than the world energy need. So if 5% of this energy is utilized, this is 50 times of world energy demand.

In Solar water heater water is heated by the use of solar energy. Solar heating systems are generally composed of solar thermal collectors, a fluid system to move the heat from the collector to its point of usage. Fig 1.1 shows the different parts of solar water heater. The system may use electricity for pumping the fluid, and have a reservoir or tank for heat storage and subsequent use. The systems may be used to heat water for a wide variety of uses, including home, business and industrial uses. Heating swimming pools, under floor heating or energy input for space heating or cooling are more specific examples.

Fig 1.1: Solar water heater

Solar collectors are the devices used to convert solar energy into heat energy. Solar collector with associate absorber (absorb the solar radiation) collects and converts the solar energy into heat energy that can be used in many applications. Fig.1.2 shows the working principal of solar collector.

In the Fig 1.3 some collectors are given which are used for to convert solar energy into heat energy with their approximate working temperature range.

Flat-plate collectors are very common and are available as liquid based and air-based collectors. These collectors are better suited for moderate temperature applications where the demand temperature is 30 0C - 70 0C and/or for applications that require heat during the winter months.

The air-based collectors are used for the heating of buildings, ventilation air and crop-drying. In this type of collector a flat absorber plate efficiently transforms sunlight into heat. To minimize heat escaping, the plate is located between a glazing (glass pane or transparent material) and an insulating panel. The glazing is chosen so that a maximum amount of sunlight will pass though it and reach the absorber. Figure 1.3 represents the constructional features of flat plate collectors.

WHY PVT COLLECTOR IS REQUIRED

These systems combine a photovoltaic cell, which converts electromagnetic radiation (photons) into electricity, with a solar thermal collector, which captures the remaining energy and removes waste heat from the PV module. Photovoltaic (PV) cells suffer from a drop in efficiency with the rise in temperature due to increased resistance. Such systems can be the engineered to carry heat away from the PV cells thereby cooling the cells and thus improving their efficiency by lowering resistance.

The electricity conversion – efficiency of a solar cell for commercial application is about 6-15 %, more than 85% of the incoming solar energy is either reflected or absorbed as heat energy.

In order to write the energy balanced equation the following assumption have been made. • The heat capacity of photovoltaic/thermal (PV/T) collector has been neglected in comparison with the heat capacity of water in the storage tank. • There is no temperature stratification in the water of the storage tank due to forced mode of operation. • One dimension heat conduction is good approximation for the present study. • The system is in quasi-steady state. • The ohmic losses in the solar cell are negligible. The energy balance equations for each component of (PV/T) solar water heating system are as follows, (i) For Solar Cells of PV Module (Glass-Glass) (ii) For Blackened Absorber Plate Temperature Below the PV Module (Glass-Glass) (iii) For Water Flowing Through an Absorber Pipe Below the PV Module (Glass-Glass) The energy balance of flowing water through absorber pipe is given by, The rate of thermal energy available at the end of absorber PV module (glass-glass) is evaluated as, (iv) The Rate of Thermal Energy Available at the End of First Collector Following Tiwari [12], the rate of thermal energy available from the first flat plate collector can be evaluated as, An expression for the rate of thermal energy available at the end of second collector will be as follows On solving the Eqs. (4), (5) and (6) we get, Where and (vi) Energy Balance for Complete Water Heating System The rate of thermal energy available at the outlet of second collector is fed into insulated storage tank, and then the energy balance of whole system will be, The above equation can be solved by assuming Tfi = Tw, due to perfectly insulating connecting pipes. Using Eq. (7) the tank water temperature can be obtained by as, Where, and

(vii) Energy Analysis The energy analysis is based on the first law of thermodynamics, and the expression for total thermal gain can be defined as, Overall thermal output from a PV/T system = thermal energy collected by the PV/T system + (Electrical output / çpower) where, çpower is the electric power generation efficiency for a conventional power plant. This is so because electrical energy is a high-grade form of energy which is required for operation of DC motor. This electrical energy has been converted to equivalent thermal by using electric power generation efficiency as 0.38 for a conventional power plant . In the case of withdrawal from tank the thermal energy output from the tank can be written as,

Series connected glass cover was used in collector. Thermal losses through the collector backs are mainly due to the conduction across the insulation (thickness of bottom side insulation 6 cm and side liquid tube made of copper material. The distance between glass cover and absorber plate is 3 cm and thickness of collector is 10 cm.

The water tank is provided to collect the heated water. The capacity of tank is 30 litres with protecting insulation. Four valves are provided for circulation of water in collector. There are two valves for water inlet and outlet and other two valves are provided on liquid tube to measure the mass flow rate and maintain water overflow. All valves are made from brass material. Two plastic pipes are used for circulating the water between water tank to collector and collector to water tank by using pump and the pipes of pump are joined with tube by clamping. The D.C pump of 12 Watt is used in the collector. The collector water is circulated by pump. In this system, 8 switches thermocouple is used to measure the different temperature of collector. The angle protector is provided in PVT collector construction to set the angle using angle protector. It is made from M.S. bar.

Preliminary measurements determined that first fractions of solar radiation at about 9:00 AM of local time. Distillate output and temperature augmentation in the time span before 9:00 AM and after 5:00 PM proved to be negligible. For this reason, the following parameters will be measured in an interval of one hour from 9:00 AM local time to 5:00 PM. Parameter to be measured ► Solar Radiation [W/m2] ► Water inlet temp [°C] ► Water outlet temp [°C] ► Ambient temperature [°C] ► Heat gain(Q) ► Thermal efficiency(ηTH) ► Overall efficiency(ηOVER)

Q= heat gain m= mass flow rate Cp = specific heat 4.187 TO= Outlet water temp (°C) T1= inlet water temp (°C)

The electrical output of the FP-PVT, the and the solar PV module was calculated using equation where P is the electrical output (W), I is the measured current (A) and V is the measured voltage (V). The electrical conversion efficiency of the two systems was calculated using equation , where Ac is the area of the collector aperture and G the incident solar radiation (W/m2) on aperture. The total instantaneous output of both PVT collectors was calculated by adding the thermal and electrical output and the overall efficiency calculated using equation

Fig 6.1 show relation between local time (Hr) and Insolation (w/m2). All the figures show that, Insolation increases from morning 9:00 AM to 1:00 PM noon due to increase of solar radiation and

(w/m2) and lowest sunshine hours obtained during morning 9:00 AM of 360 (w/m2).

Fig.6.3 shows relation between Local Time (Hr), insolation (watt/m2).and thermal efficiency of solar collector. average highest thermal efficiency gained by solar collector at 1 PM of 17.82 % and least at 9 AM 5.82% .

Fig.6.4 shows relation between Time (Hr), Insolation (w/m2) and Temperature difference of water outlet and inlet. In all the figures, they show that, by increasing insolation temperature difference is also gained by water and water temperature increase. Due to increase of water temperature at outlet, difference of water temperature at inlet and outlet is increase. It is very desirable for design of any collector. Average temperature difference gained at 1 PM of 18 °C.

Fig.6.5 shows relation between Local Time (Hr), insolation (watt/m2).and thermal efficiency of solar collector. Average highest thermal efficiency gained by solar collector at 9 AM of 19.03 % and least at 5PM 6.90 %

cooling .here also shows that the overall efficiency is higher than the without cooling. Average increase of overall efficiency of 12.46 % by the with cooling compared with the without cooling of glass cover of the hybrid solar collector.

Following points were concluded from the dissertation work of single and double flat plate collector with photovoltaic panel. • This system is not only used to heat the water but also increase electrical efficiency, improvement in PV panel and also increase overall efficiency of flat plate collector. • Solar insolation is increase from morning 9 am to 1 pm noon and decrease after 1 pm in hybrid solar collector. • Hybrid solar collector with mono crystalline panel Thermal efficiency is 11.13 % and with poly crystalline panel is 11.56 %,hence the With poly crystalline panel possess slightly higher thermal efficiency compared with mono crystalline panel used in hybrid solar collector. • Overall efficiency of hybrid solar collector with Mono crystalline is 12.79% and with Poly crystalline is 13.48 %, hence hybrid solar collector with Poly crystalline panel possess higher overall efficiency (combination of thermal and electrical) compared with Mono crystalline panel. • Overall efficiency of hybrid solar collector with glass cooling is 15.40 % and without glass cooling is 13.48 %,hence hybrid solar collector with glass cooling possess higher overall efficiency compared with without glass cooling.

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Assistant Professor, Mechanical Department, KITRC, Kalol, Gujarat, India mkpatel9027@gmail.com