A capacitor stores energy in its electric field. The energy is proportional to capacitance and the square of voltage. This quadratic relationship means small voltage increases dramatically boost stored energy. Capacitors can release energy much faster than batteries, making them ideal for high-power pulses.
⚠Capacitors store less energy than batteries of similar size, but can deliver it much faster (high power density). Supercapacitors bridge the gap between capacitors and batteries.
Capacitor vs Battery Energy Storage
While both store electrical energy, capacitors and batteries operate differently. Capacitors store energy electrostatically in an electric field and can charge/discharge nearly instantly. Batteries use electrochemical reactions, storing much more energy but charging/discharging slowly. Supercapacitors offer a middle ground.
Energy Density
Capacitors: 0.01-10 Wh/kg. Batteries: 100-300 Wh/kg. Supercapacitors: 5-10 Wh/kg. Batteries store more energy per weight.
Power Density
Capacitors: 10,000+ W/kg. Batteries: 100-1000 W/kg. Capacitors deliver power 10-100× faster. Ideal for camera flashes and regenerative braking.
Charge Storage Q
Q = C × V (coulombs). 1 coulomb = 6.24×10¹⁸ electrons. Charge is proportional to both capacitance and voltage.
Applications
Capacitors: flash, filters, decoupling, power conditioning. Supercaps: UPS backup, regenerative braking, peak power assist.
Teaching Example: C=1mF (0.001F), V=5V.
E = ½ × 0.001 × 5² = ½ × 0.001 × 25 = 0.0125 Joules.
Q = C×V = 0.001 × 5 = 0.005 Coulombs.
Compared: 100F supercap at 2.5V: E=½×100×6.25=312.5J. AA battery: ~10,000J.
Applications
Camera FlashPower FactorRegen BrakingUPS BackupDecoupling
Frequently Asked Questions
How much energy in a capacitor?▼
E = ½×C×V². A 1F capacitor at 5V stores 12.5J. A 100F supercapacitor at 2.5V stores 312.5J. Compare: AA battery ≈ 10,000J.
Can a capacitor replace a battery?▼
Not for long-term storage. Capacitors have 1/1000th the energy density of batteries. But they excel at rapid charge/discharge for high-power pulses and short-term backup.
Why is energy proportional to V²?▼
Derived from work = ∫V dq, where q=CV. Work = ∫V·C dV = ½CV². The V² relationship means higher voltages dramatically increase stored energy.
What is a supercapacitor?▼
Supercapacitors (EDLCs) use double-layer electrostatics for 100-1000× more capacitance than electrolytics. Low voltage (2.5-2.7V per cell). Used for backup power and energy harvesting.
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