# 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, TI-85 graphing calculator with SOLAR program, A Vernier voltage probe, 10 ohm resistor or resistor board, multimeter, and lead wires with alligator clips.

Procedure

1. Before leaving the classroom, make sure that your calculator has the program SOLAR loaded.
2. Take all equipment [except multimeter] outside with you. I will have one multimeter station outside.
3. 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.
4. 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.
5. Link the CBL to the calculator and insert the voltage probe in channel one.
6. Connect the voltage probe at each lead of the solar panel. You are now ready to collect data.
7. Run the program SOLAR and follow the screen prompts to complete the table below.
8. 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:

1. Calculate the total resistance of the panel and the resistor.
2. 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:
[2nd][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:
1. 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 TI-85.
• 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"
:{3,.01,5,0}L1
:Outpt("CBLSEND",L1)
:5dimL L6
:Input "CBLGET",L6
:(sum L6-max(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