The relationship between power, voltage and current is especially important to the function of a light bulb. The solar power needed to light one light bulb depends on the specific power ratings of the bulb. To power a light bulb when the sun might not be shining, batteries will be needed to store the energy collected by your solar power system. Otherwise, the light bulb would light up only when the solar panels receive energy from the sun.
Power Requirements of a Light Bulb
Light bulbs are rated for the amount of power they consume at a specific voltage. Power, measured in watts, is the product of current and voltage. Most light bulbs are designed to function with 120 volts of alternating current (AC) power. If a bulb is rated at 60 watts and 120 volts, it will draw a current of 0.5 amps.
Power Output of Solar Panels
Solar panels come in a variety of sizes; the bigger they are, the more power they produce. A typical solar cell puts out about 0.5 to 0.6 volts of energy with a current between 30 to 36 milliamps per square centimeter. Therefore, if a cell is 100 square centimeters in area, it will produce between 3 and 3.6 amps of current in ideal conditions. A standard panel of 36 solar cells may therefore generate 50 to 75 watts of power, depending on its wiring and construction quality.
Intermediate Devices Between the Panel and the Bulb
The intensity of a light bulb depends on the voltage it receives. If the solar panel puts out 17 volts of energy, a light bulb rated at 120 volts will probably not light. A light bulb that receives too much current may heat up and burn out too fast. Intermediate devices between your solar panels and the bulb can address these problems. A charge controller regulates the power between the solar panels and the battery. If your light bulb uses AC power, you should also use a power inverter to convert the panel's direct current (DC) output to AC.
Battery Output and Light Bulb Ratings
Your solar power batteries should have a voltage rating equal to that of the light bulb. For a 120 volt light bulb, you need 120 volts of energy in the batteries. Many solar power batteries are rated at 12 volts, so you would need to connect 10 batteries in series to obtain 120 volts. Batteries store their power according to an amp-hour rating. This refers to the number of amps a battery can supply over the course of an hour on a single charge. If your battery is rated at 100 amp-hours, a light bulb that draws 1 amp could be powered for 100 hours on a single battery charge. A light bulb that draws 0.5 amps could be powered for 200 hours on the same battery.
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