Experiments with Solar Shingles
How long does it take to recharge a battery?
How to take measurements:
1. To measure voltage, turn the knob on the multimeter to 25 DCV, which means the multimeter can measure 0 to 25 DC volts. Touch test probes to the circuit. (This means touch the test probes to the wires of what you are measuring, like the shingle wires or the battery terminals). One probe should touch each wire or terminal. Read and record the voltage.
2. To measure the resistance on the circuit, turn the knob on the multimeter to RX1 Ohms. Touch the test probes to the circuit. Read and record the resistance.
3. Calculate current with Ohm's law.
How long does it take to recharge the battery?
1. First check to see if the battery needs to be charged by measuring the voltage. If a 12 volt battery is fully charged, the multimeter should read 12 volts. If your battery is already charged, try the How long will a battery hold a charge? activity first. If your battery has less than 12 volts, you can charge ahead!
2. Position the solar shingles in a sunny location. Measure the voltage and resistance of one shingle. Calculate the current.
3. Connect the two solar shingles in series. Measure the voltage and resistance and calculate the current. Did the voltage or current increase? What if the shingles are connected in parallel?
4. Electrical current flows from a higher voltage to a lower voltage. To charge a 12 volt battery, the shingles connected together need to produce more than 12 volts so the current flows into the battery. If the voltage is lower than 12 volts, current flows out of the battery. Using what you learned in step 2, should the shingles be connected in series or parallel to charge the battery?
5. If you guessed series, you are right! If the shingles are connected in series, the voltage is higher than 12 volts so the current will flow into the battery. Now, connect the shingles in series to the battery to start charging!
6. To see how the charging is going, disconnect the battery once every hour, measure the voltage and resistance of the battery and calculate the current. Don't forget to reconnect the battery to the solar shingles each time after measuring the voltage. When the sun goes down, what happens to the voltage and current the solar shingle produces?
Why should you disconnect the battery from the solar shingles when the sun isn't out? (Hint: Think about the direction the current will flow)
Can you think of a way to make sure the current only flows into the battery? (Hint: Check out the How does a photovoltaic panel work? activity and read about diodes)
How long did it take to recharge the battery?
This activity was created by Emily Wilson, Lemelson Center
All text and images © Smithsonian Institution. Updated 26 February 1999.