Solar-Powered Electronics
Turning sunlight into electricity, and planning for cloudy days and short winter ones.
The question
A solar garden light glows all evening. Where does its energy come from, and why does it barely glow after a cloudy December day?
What you’ll discover: how solar cells work, how much power they really make, why storage is needed, and how to plan for weather and seasons.
In simple terms
BeginnerLight in, electricity out
A solar cell (photovoltaic cell) is made of specially treated silicon, like a big, flat diode (Lesson 9). When light hits it, the light’s energy knocks electrons loose, and the cell pushes them around a circuit: electricity straight from sunlight, with no moving parts.
One silicon cell makes only about 0.5 to 0.6 V, so a solar panel joins many cells in series (Lesson 14) to get a useful voltage. Small hobby panels are often labelled 5 V or 6 V.
Solar power only works while light is shining, so most solar devices store energy in a battery during the day to use at night.
Experiment: how much does light matter?
You need a small hobby solar panel (5 or 6 V), a multimeter, and a 100 Ω resistor rated 1 W (a common ¼ W resistor can get too hot to touch with this panel).
- Set the meter to DC volts. Connect it to the panel’s wires: red to +, black to −.
- Measure the voltage in direct sun, in shade, under cloud, and indoors under a lamp. Write each down.
- Now connect the 100 Ω resistor across the panel as a load and repeat the measurements. Use Ohm’s law (Lesson 15) to work out the current: I = V ÷ R.
Go deeper
IntermediatePlanning for real weather
A panel’s rated power (say, 1 watt) is measured in bright, direct sun, pointed straight at it. Real output is usually lower and changes all the time:
- Clouds can cut output by much more than half.
- The sun’s angle matters. In southern Alberta, the noon sun is high in June but low in December, so tilt panels steeply in winter and face them south.
- Day length: Lethbridge gets around 16 hours of daylight at the June solstice, but only about 8 in late December, the time when a solar weather sensor needs the most help.
- Snow on a panel can stop it completely until it slides off or is brushed clear.
- Cold actually raises a solar cell’s voltage a little, but makes batteries weaker.
AdvancedSizing a solar system
Engineers size solar systems for the worst realistic stretch, not the average day. Work out how much energy the device uses in a day (from its energy budget, Lesson 27), then size the battery to last through several cloudy days in a row, and the panel to refill it on the short, low-sun days of winter.
A solar device also needs a charge controller to stop the battery from being overcharged when it’s full, or drained too far. For Electronics School projects, buy ready-made solar charging products rather than building charging circuits yourself; that’s where battery safety risks are highest.
Quick check
About what voltage does one silicon solar cell make?
About 0.5 to 0.6 V.
Why do most solar devices need a battery?
To store energy during the day for use at night or when it’s cloudy.
Why might a solar weather sensor struggle in December in Lethbridge?
Short days (about 8 hours of daylight), a low sun angle, clouds and snow on the panel all cut its power, while cold weakens the battery.
Words to know
- Photovoltaic
- Turning light directly into electricity.
- Solar panel
- Many solar cells joined to give a useful voltage.
- Charge controller
- A circuit that protects a battery while charging it.
- Rated power
- A panel’s output in ideal, bright sun.
Electronics School is part of the Discovery Zone. Every activity here runs on small batteries or a USB cable: never wall outlets. The one plug-in tool is the optional soldering iron, set up by an adult.