How Outdoor Solar Lighting Works
Solar lights gather energy while the sun is out and store that energy in a battery. When the light sensor indicates that night has come, the solar lights use the battery's energy to power their lamps. Here's a brief nuts and bolts explanation of what's involved.
A basic solar light will have the following components:
- Several solar cells for collecting the sunlight
- A Nicad battery for storing that energy
- An LED lamp for producing light at night
- A photosensor to detect darkness
- A compact controller board
All of this will be contained in a plastic or metal casing.
Solar cells are manufactured from silicon crystals and require clean room conditions. A single solar cell produces a maximum of 0.45 volts. The current will vary depending on the size of the cell and the amount of light it receives. To produce a useable voltage, typically, your lamp will need four cells wired in series.
These solar cells connect to the battery through a diode. This prevents the current from running the other way when the cells stop gathering energy at night. The battery, a standard 1.2 volt AA Nicad, can store about 700 milliamp-hours. During the day, the battery charges up off the energy collected by the solar cell. Except on overcast days and perhaps the shortest days of winter, the battery will reach its maximum charge by dusk.
When dusk comes, the photosensor sends a message to the controller board that it's time to turn on the lamp. The controller board handles power from the solar cell and the battery and sends that power to the lamp via a three-transistor circuit.
A typical LED lamp draws about 45 milliamps from the Nicad battery. This produces about half the light of a standard candle. More powerful lamps may also include a halogen flashlight bulb. If the Nicad battery is fully charged, it can operate the lamp for about 15 hours. If daylight comes before the 15 hours are over, the battery gets a head start on that day's job of storing energy up for the night.