10 March

## How Do You Measure the Power Produced by Solar Cells ?

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Excellent question from more than one of our readers:  How Do You Measure the Power Produced by Solar Cells ?

To set the stage for our following two film clips, please allow me to explain what a multimeter (or multitester) is:  it is an electronic measuring instrument that combines several measurement functions (measuring voltage, current, and resistance)  in one unit.  Multimeters are available in a wide range of features, precisions,  and prices, anywhere from less than US\$10 to more than US\$5,000.  To find out how much the power is produced by solar cells, we need to know the voltage and current produced and the fact that power equals to the product of voltage multiplied by current.

• voltage (unit of measurement is volt, V): electrical driving force, energy per unit charge, electrical potential difference between two points
• current (unit of measurement is ampere, A): rate of flow of electric charge ( carried by moving electrons in a conductor such as wire or in an electrolyte carried by ions, or in a plasma by both)
• resistance (unit of measurement is ohm, Ω): measure of the degree to which an object opposes an electric current through it
• power (unit of measurement is watt, W): power is the rate at which work is performed or energy is converted.  In direct current resistive circuits, electrical power is calculated using Joule’s law. In the case of resistive (Ohmic or linear)loads, Joule’s law is combined with Ohm’s law (I=V/R)
• such that R represents numerical value of ohm or resistance, I represents numerical value of ampere or current, V represents numerical value of volt or voltage, P represents numerical value of watt or power
• Joule’s law: P= VI, so solar cell or solar module measured at 2V and 1A would produce power at 2W, solar cell or solar module measured at 3V and 2A would produce power at 6W, solar cell or solar module measured at 2V and 1mA would produce power at 2mW (note: mA=0.001A  or mA means milliA)
• Joule’s law + Ohm’s law: P=(I2)R=(V2)/R
• series circuit:

the current through each of the components of the circuit is the same, voltage across the components is the sum of the voltages across each component

• parallel circuit:

the voltage across each of the components is the same and the total current is the sum of the currents through each component

• 1. Multimeter Tutorial-Solar Schoolhouse
• Posted by sunisthefuture-Susan Sun Nunamaker, sunisthefuture@gmail.com

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