LAB 52: CONVERTING LIGHT ENERGY INTO ELECTRICAL ENERGY 8/1/2017
OVERVIEW:
Photovoltaic cells are used to convert light ("photonic" energy) energy into electrical
energy ("voltaic" energy). Each cell consists of a semi-conductor circuit that will produce
a voltage and current flow when the electrons on its surface are energized by light. Light
comes in chunks of energy called photons, and their energy is proportional to their
frequency. The photons striking the surface of the photovoltaic cell must be in the right
energy range for the type of semi-conductor in the circuit. For most applications, the
optimum energy range is somewhere in the visible range, since that is the most abundant
form of sunlight received at the Earth's surface. That's why photovoltaic cells are often
called solar cells. The price of this energy converter is becoming increasingly competitive
worldwide, especially in areas far from a centralized electrical grid. In 1982, a kilowatthour of photovoltaic energy would set you back about a dollar. Twenty years later a
kilowatt-hour cost 25 cents, and the trend continues downward. At the same time, the
efficiency of solar cells has steadily increased. Solar cells are connected in series to form
solar panels. Solar panels are generally connected in series to increase the voltage of the
electrical system. Panels connected in parallel would have roughly the same voltage as an
individual panel, but with a more stable current and a longer lifetime.
In this lab, you will calculate the efficiency of a single solar panel, a pair of solar panels
in series, and a pair of solar panels in parallel.
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LAB 52: CONVERTING LIGHT ENERGY INTO ELECTRICAL ENERGY 8/1/2017
OBJECTIVES
1) Measure the conversion efficiency of a photovoltaic panel.
2) Determine the effect of connecting panels in series and in parallel.
3) Measure the sun's irradiance.
EQUIPMENT
A solar panel
small motor
2 digital multimeters (DMM)
one photometer for the entire class
lead set
circuit board
small light bulb
wire strips
centimeter ruler
PROCEDURE
1) Prepare the circuit as shown below. "M" is for motor, "V" is for voltmeter, "A" is
for ammeter. If there is not enough sunlight, you may wish to substitute a small
light bulb for the motor.
SOLAR PANEL
-
+
M
A
v
Note that the DMM measuring voltage must be connected in parallel to the load
and the DMM measuring current must be connected in series. Set them both on
their highest range, and then move down the scale according to the size of the
measurement.
Take the panel and the circuit outside. Orient the panel so it is receiving as much
sunlight as possible, though it may be meager on a cloudy, rainy day. Record the
voltage and current in the data Table. Check the values with your instructor to
ensure your numbers are reasonable.
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LAB 52: CONVERTING LIGHT ENERGY INTO ELECTRICAL ENERGY 8/1/2017
2) Re-set the DMM's to their highest scales. Partner up with another group and
connect two panels in series, as shown below. Adjust the DMM's to the
appropriate scales and record the values in the Table.
SOLAR PANEL # 1
+
-
-
+
A
M
v
SOLAR PANEL # 2
3) Re-set the DMM's to their highest scales. Connect the two panels in parallel, as
shown below. Adjust the DMM's to the appropriate scales and record the values
in the Table.
SOLAR PANEL # 1
+
-
v
SOLAR PANEL # 2
M
-
+
A
4) Measure the photovoltaic receiving area of the panels as accurately as possible.
Note that the solar cells do not cover the entire surface of the panel. Record the
area of your single panel in units of cm2. Add the areas of the two panels and
record this value as well.
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LAB 52: CONVERTING LIGHT ENERGY INTO ELECTRICAL ENERGY 8/1/2017
CALCULATIONS
1) Measuring the Input Solar Power
The solar irradiance (that's power per unit area) will be measured by a photometer. You
can make the measurement yourself or watch somebody else. The photometer must be
pointed where the daylight is strongest, directly at the sun if it is visible. There is a high
and low scale setting. The photometer measures the light intensity in milliwatts (mW).
The measured photonic power must be divided by the area of the photometer's sensor
(0.0246 cm2 with the cap on, or 0.50 cm2 with the cap off - when it's not very light
outside) to obtain the irradiance (s), where
𝑷
 = 𝑨𝒎𝒆𝒕𝒆𝒓
𝒎𝒆𝒕𝒆𝒓

Record the meter reading and the solar irradiance ( ) in W/cm2.
The power received by the single panel is calculated by multiplying the irradiance by the
total area of the solar cells on your panel:
Pin = Acells
Record the value for your single panel and for the two panel configurations in the Table.
2) Measuring the Output Electrical Power Electrical power in a DC circuit is the product
of the output voltage and current:
Pout = Vout•Iout
Use this formula to calculate the output electrical power for the single panel, the panels in
series and the panels in parallel. The current must be converted from mA to A for the
power to be in units of watts. Record the values for output power in the table.
3) Calculating the Efficiency of the Solar Cells The efficiency () of each of the solar
panel configurations is given by the formula
=
𝑃𝑜𝑢𝑡
𝑃𝑖𝑛
• 100%
Record the efficiency of each of the three panel configurations in the table.
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LAB 52: CONVERTING LIGHT ENERGY INTO ELECTRICAL ENERGY 8/1/2017
___________________
__________________
SUPERVISOR
RECORDER
LAB 52: SOLAR PANELS
________________________
OPERATOR(S)
DATE_________
OBJECTIVES
SKETCH
CIRCUIT
TYPE
VOUT
(V)
IOUT
(mA)
POUT
(W)
IN
(W/cm2)
PIN
(W)
(%)
SINGLE
PANEL
SERIES
PANELS
PARALLEL
PANELS
PHOTOMETER READING: _______________ mW
AREA OF SINGLE PANEL: _______________ cm2
AREA OF BOTH PANELS: _______________ cm2
CALCULATIONS:
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LAB 52: CONVERTING LIGHT ENERGY INTO ELECTRICAL ENERGY 8/1/2017
Analysis
1. Which circuit would you expect to have the highest voltage, and why? Which circuit
actually had the highest voltage?
2. Describe the possible sources of error in your measurements.
3. Which circuit had the highest efficiency? Why do you think this circuit was more
efficient than the other two?
4. Five-Step Problem. A solar panel consists of 64 solar cells connected in series, each
with an area of 4 cm2. The solar irradiance is 950 W/m2. The efficiency of the cells
is 0.18. The output voltage is 6 V.
a)
What is the output power, Pout?
b)
What is the output current, Iout?
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