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How to Test the Efficiency of a Photovoltaic Cell?

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Updated on May 07, 2013

Grade Level: 6th - 8th; Type: Physical Science/Mathematics

Objective

The performance of a photovoltaic cell (solar cell) is measured in terms of its efficiency at turning sunlight into electricity. Much of the light energy is reflected or absorbed by the material that makes up the cell. Because of this, a typical commercial photovoltaic cell has an efficiency of 15% or about one-sixth of the sunlight striking the cell generates electricity. The research aspect of this science fair project is to determine how much of the energy from the Sun that reaches a photovoltaic cell is converted into electric power.

A photovoltaic or solar cell will be exposed to sunlight at different angles to find which position will allow the greatest amount of sunlight to reach the cell. In the second part of the investigation a determination will be made of how much of the sunlight that has reached the cell is converted into electric power. Based on the results of these investigations data tables will be prepared and the efficiency of the photovoltaic cell calculated. A real world correlation of this project is to make aware to the investigator that low efficiencies mean that larger arrays of cells are needed in order to generate electricity, and that means higher cost. Improving photoelectric cell efficiencies while holding down the cost per cell is an important goal of the photovoltaic cell industry.

  • What is the project about?
  • What are the goals?

Research Questions:

  • How does changing the angle of the photovoltaic cell affect the speed of the fan?
  • At which angle is the fan’s speed the fastest?
  • Why does the angle of the photovoltaic cell affect the speed of the fan?
  • Why would the season of the year possibly affect the efficiency of the photovoltaic cell?
  • Besides angle, what other factors will affect the energy output of the photovoltaic cell?
  • Based on the results of this investigation would the power output of the photovoltaic cell be greater or less just beyond Earth’s atmosphere?

The sun produces 3.9 x 1026 watts of energy every second. Of that amount, 1,386 watts fall on a square meter of Earth’s atmosphere and is known as the solar constant. The amount of this energy that reaches the Earth’s surface on a sunny day varies according to the time of year, from about 1000 watts/meter2 on a sunny summer day to less than 700 watts/meter2 on a sunny winter day. A watt is a unit used to measure power. This energy can be used to generate electricity by a device called a photovoltaic cell.

Photovoltaic or solar cell convert sunlight directly into electricity. These cells are often used to power calculators and watches. They are made of semiconducting materials similar to those used in computer chips. When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the material to produce electricity. This process of converting light (photons) to electricity (voltage) is called the photovoltaic (PV) effect.

The performance of a photoelectric cell is measured in terms of its efficiency at turning sunlight into electricity. Much of the light energy is reflected or absorbed by the material that makes up the cell. Because of this, a typical commercial photovoltaic cell has efficiency between a low of 5% to a high of 20%. On average only about one-sixth of the sunlight striking a photovoltaic or solar cell generates electricity.

  • Any required diagrams/pictures (Pictures speak a thousand words!)

Digital photos can be taken during the investigation process also the following sites offer down loadable images that can be used on the display board.

http://www.esru.strath.ac.uk/Courseware/Class-16110/Images/pv1.jpg

http://www.pv.unsw.edu.au/images/future-students/solar-cell_p-n.jpg

Materials:

Photovoltaic cell, electric hobby motor with small plastic fan blade, wires, sheet of cardboard, multimeter, protractor, 5 ohm resistor, metric ruler, and masking tape

With the exception of the protractor, tape and metric ruler all the other items can be purchased from the local RadioShack retailer or from a hobby shop also, a Tri-fold cardboard display board can be purchased from an art & crafts supply store.

An inexpensive photovoltaic or solar cell can also be ordered online from Educational Innovations, and a multimeter is available from Science in a Bag or RadioShack.

  • What materials are required?
  • Where can the materials be found?

Experimental Procedure

Data Table 1

Photovoltaic cell area. Angle of fastest motor speed cm2
Voltage across the resistor
Current in the circuit

Voltage X current

= watts/cm

Area

Power Output Watts/cm2

Power Output Watts/meter2

Data Table

Photovoltaic cell efficiency %
  1. Gather the following materials: photovoltaic cell, electric motor with fan, wires, cardboard sheet, multimeter, protractor, 5 ohm resistor, tape, and metric ruler.
  2. Measure the length and width of the photovoltaic cell (do not include the base) and calculate the area using the following formula: Area = width x length. Record this value.
  3. Place the photovoltaic cell, electric motor with fan on the piece of cardboard and secure using tape as shown. Use the wire to make the connections.
  4. Bring the setup outside into direct sunlight.
  5. Set the board on level ground and hold it so that the Sun casts no shadow over it.
  6. Vary the angle of the electric circuit board by tipping one end of it up or down and observe what happens to the speed of the fan at different angles.
  7. Readjust the angle of the electric circuit board until the fan’s speed is the fastest. Record the angle using the protractor.
  8. Replace the motor-fan with a 5 ohm resistor and connect the circuit as shown.
  9. Use the multimeter to measure voltage across the resistor.
  10. Record the voltage.
  11. Disconnect the circuit at point A and connect the multimeter and measure current in the circuit.
  12. To determine how much of the energy that is reaching the photovoltaic cell is being converted into power use the following formula:
  13. Record the results.
  14. Then multiply the results by 10,000 to convert the value to watts/meter2
  15. The following values are estimates for how much energy reaches Earth surface on a sunny day, according to the time of year
    • 1000 watts/m2 on a sunny summer day
    • 900 watts/m2 on a sunny autumn or spring day
    • 700 watts/m2 on a sunny winter day
  16. Depending on the time of year, one of the values above is the power input from the sun that is converted into electrical energy by the photovoltaic cell.
  17. Use the formula to calculate the efficiency of photovoltaic cell.
  18. Record the results.

Terms/Concepts: Photovoltaic cell; solar cell; solar constant; area; voltage; current; electricity; power output; Earth’s atmosphere; “Watt”

References:

References to related books

Title: Practical Photovoltaics: Electricity from Solar Cells

Author: Richard J. Komp

Publisher: Aatec Publications ISBN-10: 093794811X and ISBN-13: 978-0937948118

This book presents in clear, concise, and understandable style comprehensive information about solar electricity. The book offers a unique combination of technical discussion and practical advice. A well-illustrated appendix offers step-by-step instructions for constructing a solar module. The young investigator and his or her parents (teachers) can use this book as a general reference resource.

Links to related sites on the web

Title: How do Photovoltaics Work?

URL: http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/

Title: Photovoltaic (solar cell) Systems

URL:http://www.renewableenergyworld.com/rea/tech/solarpv

Title:Future Students - What are Photovoltaic Devices

URL: http://www.pv.unsw.edu.au/future-students/pv-devices/how-they-work.asp

NOTE: The Internet is dynamic; websites cited are subject to change without warning or notice!

Mike Calhoun is a consultant for the National Science Teachers Association, a veteran science teacher, and hosts an online science website. Over the years Mike has studied trends in science, education, and finance, conducting research, developing programs, and writing articles on these topics.

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