Power and the Solar Cell:
Measuring the Best Angle for Your Solar Panel
by Tony Romanello
Murray High School
5440 South State
Murray, UT
Purpose
As a prelude to building your solar car, this lab will help you to find the angle at which the power output of your photovoltaic cell is maximized under race conditions.
Equipment
Solar Panel, protractor, ring stand, board, CBL,
TI85 graphing calculator
with SOLAR program, A Vernier voltage
probe, 10 ohm resistor or resistor board, multimeter, and lead wires with
alligator clips.
Procedure
 Before leaving the classroom, make sure that your calculator has the program SOLAR loaded.
 Take all equipment [except multimeter] outside with you. I will have one multimeter station outside.
 Set up the ring stand with one end of the board clamped to it. The other end of the board should be resting on the ground.
 Lay the solar panel on the board and then wire the circuit, starting at one of the solar panel leads, to the resistor, and from the resistor back to the other solar panel lead.
 Link the CBL to the calculator and insert the voltage probe in channel one.
 Connect the voltage probe at each lead of the solar panel. You are now ready to collect data.
 Run the program SOLAR and follow the screen prompts to complete the table below.
 When finished, bring your solar panel to the multimeter station and measure the internal resistance of the solar panel and record it in the table.
Data Table
Angle q
[degrees]

Voltage [v] 
Power [Joules] 



0 
. 
. 
5 
. 
. 
10 
. 
. 
15 
. 
. 
20 
. 
. 
25 
. 
. 
30 
. 
. 
35 
. 
. 
40 
. 
. 
45 
. 
. 
50 
. 
. 
55 
. 
. 
60 
. 
. 
65 
. 
. 
70 
. 
. 
75 
. 
. 
80 
. 
. 
85 
. 
. 
90 
. 
. 
Resistor: ___________ohms
Internal Resistance: _____________ohms
Total Resistance: _________________ohms
Calculations:

Calculate the total resistance of the panel and the
resistor.

Calculate the power of each trial using the equation:
. This can be done on your calculator simply by entering the formula and
storing it in a list variable in the following manner:
[2^{nd}][list][L4][^][2][/][Resistor
Value][Enter][sto>][L5]

at this point your data is stored in Lists 2,4,and 5
and you can either copy it into the data table or upload it to the computer
via graphlink.
Analysis:

Using your data, what is the best angle to mount your
solar panel?
In complete, coherent sentences, discuss factors that
could influence your results and determine a way to counter this factor
in the design of your solar car.
Extension Activity:
Since a motor has a resistance that varies with speed,
you could set up an additional experiment which uses a set of different
resistors to simulate the change in resistance of the motor with speed.
Then, using a second voltage probe [or a current probe], you could measure
the actual power output using the equation: .
Notes to the Teacher:

This activity was designed for students who are participating
in the Junior Solar Sprint, a model solar car race, to help them to decide
at what angle to mount their solar panel. It uses CBLs so that they can
do the activity outside under actual race conditions.

It uses the CBL program SOLAR, which was written
for the TI85.

A preparation note: you need to try some different
resistors with this lab in order to keep the voltage between 5 volts, which
is the range of the voltage probe that comes with the CBL. Different solar
panels have different outputs, so I can't tell you what to use.
PROGRAM : SOLAR.85P
:FnOff
:AxesOn
:{6,0}L1
:Outpt("CBLSEND",L1)
:{1,0}L1
:Outpt("CBLSEND",L1)
:ClLCD
:{1,1,1}L1
:Outpt("CBLSEND",L1)
:ClLCD
:1dimL L2
:1dimL L4
:ClLCD
:Disp " MURRAY HIGH SCHOOL"
:Disp ""
:Disp " SOLAR PANEL"
:Disp " TESTING PROGRAM"
:Disp ""
:Disp ""
:Disp " [PRESS ENTER]"
:Pause
:ClLCD
:Disp "INPUT THE NUMBER"
:Input "OF DATA POINTS? ",N
:For(X,1,N,1)
:ClLCD
:Disp X
:Input "ANGLE (DEGREES?)",D
:DL2(X)
:Disp "PRESS ENTER TO"
:Disp "READ VOLTAGE.":Pause
:{3,.01,5,0}L1
:Outpt("CBLSEND",L1)
:5dimL L6
:Input "CBLGET",L6
:(sum L6max(L6)min(L6))/3L4(X)
:End
:10xScl:2yScl
:max(L2)min(L2)A
:min(L2).2AxMin
:max(L2)+.2AxMax
:max(L4)min(L4)B
:min(L4).3BüyMin
:max(L4)+.3ByMax
:xyline L2,L4
:DispG
:Stop