Energy Storage
Science FactRobots and gadgets need energy on the go. Storing energy safely and lightly is one of engineering's biggest challenges.
How a battery works
A battery has two ends (the anode and cathode) separated by a material called an electrolyte. A chemical reaction pushes electrons out one end, through your device, and back into the other end. Recharging pushes them back to the start.
Capacity and energy density
Battery capacity is how much energy it stores, often in watt-hours. Energy density is how much energy fits in each kilogram. Lithium-ion batteries have high energy density, which is why phones, laptops and electric cars use them.
Solar power
Solar cells turn sunlight directly into electricity using silicon. They don't store energy themselves, so solar robots usually charge a battery during the day. NASA's Opportunity rover ran on solar power for almost 15 years on Mars.
The power budget
Every part uses energy: motors use the most, then computers and sensors. Engineers add up each part's power use to predict battery life. To run longer, you either store more energy or use less.
- Battery capacity
- − Motors
- − Brain + sensors
- = Leftover energy
- Run time
COOL REAL FACTS
- An electric car battery can weigh over 400 kg.
- Batteries work slower in the cold, which is why phones die faster in winter.
- Gasoline stores about 50 times more energy per kilogram than lithium-ion batteries, which is why electric planes are hard.
SCIENCE FACT vs SCI-FI
Dark Matter Cells and Star Cores are fiction. Real devices store energy in batteries, capacitors, fuel or springs.
TRY IT (SAFELY!)
Wind up a toy car, or stretch a rubber band, to store energy, then let it go. That's mechanical energy storage!
REAL ENGINEER TIP
Engineers always protect batteries from overheating, overcharging and physical damage.
PARTS THAT USE THIS IDEA
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