Hybrid Photovoltaic Solar Thermal Collector System

Hybrid Photovoltaic Solar Thermal Collector System

M. Mahesh Babu 1, A. Rama Krishna2, J. Naga Raju3

1. BVC Engineering College

2. Professor, mechanical engineering department, BVC engineering college, JNTU Kakinada, India

3. Asst professor, mechanical engineering department, Malla Reddy College of engineering, JNTU Hyderabad, India

Abstract The hybrid photovoltaic/thermal (PV/T) collector is an integration of single-crystalline silicon cells into a solar thermal collector. The product is able to generate electricity and hot water simultaneously.

The solar radiation increases the temperature of PV modules, resulting in a drop of their electrical efficiency. By proper circulation of a fluid with low inlet temperature, heat is extracted from the PV modules keeping the electrical efficiency at satisfactory values. The extracted thermal energy can be used in several ways, increasing the total energy output of the system. Hybrid PV/T systems can be applied mainly in buildings for the production of electricity and hot water and are suitable for PV applications under high values of solar radiation and ambient temperature.

The results showed that PV cooling can increase the electrical efficiency of PV modules by 2 to 4% and thermal efficiency by 4 to 6% there by, increasing the total efficiency of the systems. Improvement of the system performance can be achieved by the use of an additional glazing to increase thermal output, a booster diffuse reflector to increase electrical and thermal output, or both, giving flexibility in system design.

1. INTRODUCTION

   A solar thermal collector is a solar collector specifically intended to collect heat: that is, to absorb sunlight to provide heat. Although the term may be applied to simple solar hot water panels, it is usually used to denote more complex installations. There are various types of thermal collectors, such as solar parabolic, solar trough and solar towers. These type of collectors are generally used in solar power plants where solar heat is used to generate electricity by heating water to produce steam which drives a turbine connected to an electrical generator. More than 80% of the solar radiation falling on photovoltaic (PV) cells is not converted to electricity, but either reflected or converted to thermal energy.This leads to an increase in the PV cells working temperature and consequently, a drop of electricity conversion efficiency, of about 36% loss per oC. In view of this, hybrid photovoltaic and thermal (PV/T) collectors are introduced to simultaneously generate electricity and thermal power. The hybrid photovoltaic/thermal (PV/T) collector is an integration of single-crystalline silicon cell into a solar thermal collector.The PVT system is able to generate electricity and hot water simultaneously.

2. EXPERIMENTAL SET UP OF THE HYBRID PVT COLLECTOR

   1. Constituent layers of the hybrid PVT collector

      Fig: layers of PVT collector

   2. polycrystalline silicon cell

      Total No. of units (36), Area (0.67sq.m), Emissivity (0.8),

      Cell conversion efficiency (14.5%),

   3. Solar collector

   Absorber material (Cu.) Absorber type (Flat box)

   Absorber module size (1.8 x 0.8 x 0.02 m3) Front glazing thickness (4mm)

   Total effective area ( 2 m2) Thermal insulation thickness (10 mm)

   (irreversible damage) degradation due to excess temperatures. Design considerations for cooling systems include low and uniform cell temperatures, minimal power consumption by the system.

   A. Proposed Cooling System

   We proposed a water cooling system for the following reasons

   There is a substantial temperature rise along the cells due to the low heat capacity of air.

   The coolant liquid is water is anti-corrosive and can be used to the optical concentration.

   Specific heat capacity of water is high so that it can absorb the heat from any surface.

   Low cost investment and water is easily available and can be served as thermoelectric system.

   IV. EXPERIMENT PROCEDURE

   1. Remove water from the tank by opening drain cork.

   2. Refill the water by opening storage tank valve.

   3. Connect all sensors to micro controller.

   4. For every 30 minutes note down following readings

      1. Inlet water temperature

      2. Out let water temperature

      3. Solar radiation

      4. Voltage from panel

      5. Current from panel

         V. CALCULATIONS

         1. water tank:

            Specifications:

            Type: cylindrical horizontal Length (1.2 m)

            Diameter (0.3 m)

            Water-storage capacity (100 liters) Thermal insulation thickness (30 mm)

         2. Storage battery

            Rated voltage (12 V) No. of Units (4)

         3. Converter

         Rated input-voltage (48 V) Rated output-voltage (220 V)

         Maximum output-power (1000 W)

3. DESIGN OF THERMOSYPHON COOLING SYSTEM FOR PHOTOVOLTAIC CELLS

TIME IN HOURS

8:00

9:00

10:00

11:00

12:00

1:00

2:00

3:00

4:00

Cooling of photovoltaic cells is one of the main concerns when designing concentrating photovoltaic systems. Cells may experience both short-term (efficiency loss) and long-term

Energy input to solar collector = H Ac

Energy output from solar collector = M (ToTi) Energy input to PV panel = H Ap

Power output from solar panel = V I

Thermal efficiency, T = M Cp (ToTi) / H Ac Electrical efficiency, E = (V I) / (H Ap) Total efficiency, O = T + E

Where

Ac: Collector area (m2) Ap: PV panel area (m2)

H : Solar radiation (W/m2)

M: Mass of water in water tank (kg/s) Ti:Collector inlet water temperature(oC)

To : Collector outlet water temperature(oC)

1. GRAPHS

   100

   TEMPERATURE VARIATIONS OF

   PV PANEL

   50

   TEMP,0C

   0

   TOP

   BOTTOM

   PANEL EFFICIENCY VARIATIONS

   10

   9

   8

   7

   6

   EFFICIENCY5

   4

   3

   2

   1

   0

   VARIATION OF IRRADIATION WITH

   RESPECT TO TIME

   SOLAR

   1500

   1000

   PV PANEL

   ALONE

   PV AT BOTTOM

   PV AT TOP

   IRRADIATION,

   W/m2 500

   8:00

   9:30

   2:00

   3:30

   5:00

   0

   11:00

   12:30

   irradiation

   8:00

   9:00

   10:00

   11:00

   12:00

   1:00

   2:00

   3:00

   4:00

   5:00

   TIME IN HOURS

   TIME IN HOURS

   INDIVIDUAL COLLECTOR EFFICIENCY

   THERMAL EFFICIENCY

   VARIATIONS

   80

   EFFICIENCY OF COLLECTOR

   60

   WITH

   OUT PANEL

   PV PANEL

   IS ON

   BOTTOM PV PANEL

   IS ON TOP

   60

   40

   EFFICIENCY

   20

   0

   80

   40

   20

   COLLECTOR

   8:00

   9:00

   10:00

   11:00

   12:00

   1:00

   2:00

   3:00

   4:00

   5:00

   0

   8:00

   9:00

   10:00

   11:00

   12:00

   1:00

   2:00

   3:00

   4:00

   5:00

   TIME IN HOURS

   EFFICIENCY

   TIME IN HOURS

   TEMPERATURE VARIATIONS OF SOLAR

   COLLECTOR

   80

   60

   TEMP,0C40

2. RESULTS

INLET

OUTLET

20

0

8:00

9:00

10:00

11:00

12:00

1:00

2:00

3:00

4:00

5:00

Our proposed flat-box cu-alloy solar PV/T collector has may merits, as compared to the flat-box collectors, such as the large contact area to facilitate heat exchange between the absorber plate and the fluid, the uniform transverse temperature distribution across the collector width, and the flat metallic surface as a high-quality lamination between the PV cells and the absorber plate.

TIME IN HOURS

The PV/T water heating system was designed with natural circulation and experiments were conducted As the hot-water load per unit heat-collecting area exceeded 80 kg/ m2, the daily electrical efficiency was about 10.15%, the characteristic daily thermal efficiency exceeded 45%, the characteristic daily total efficiency was above 52% and the characteristic daily primary energy saving was up to 65%, for this system with a PV cell covering factor of 0.63 and front-glazing transmissivity of 0.83.

Because of the shared front glazing, back cover and fixed frame, this flat-box collector is able to achieve more energy yield and needs less investment per unit surface area than the conventional PV and solar thermal systems in parallel. When more and more solar systems are required to be installed in buildings, the PV/T application can be the solution for it maximizes the solar energy outputs from the very limited facade areas.

REFERENCES

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