CALCULATORS / BATTERIES AND ENERGY STORAGE

Capacitor and supercapacitor energy storage calculator

Ideal capacitor energy over a voltage interval.

batteries-capacitor-storage.napkin / editable

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

Scenario	energyJ
	400
	320

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

stored energy target400.00 J✓ passes

BASELINE INPUTS

capacitance10 FhighVoltage12 VlowVoltage8 V

CALCULATED

energy400 J

Edits change the baseline source.

THE SOURCE

Edits below update the same model.

# Capacitor and supercapacitor energy storage
# Scope: Ideal capacitor energy over a voltage interval.
# Status: illustrative worked example; engineering review pending.
# Inputs are example values. Checks are editable example requirements, not standards.

capacitance = 10 F
highVoltage = 12 V
lowVoltage = 8 V

energy := capacitance*(highVoltage^2-lowVoltage^2)/2 [J]

check stored energy target: energy >= 300 J

scenario alternative: capacitance = 8 F

Calculated from your source · not saved

Baseline · Baseline

stored energy target400.00 J ✓ passes

alternative · alternative

stored energy target320.00 J ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

energy: energy = capacitance*(highVoltage^2-lowVoltage^2)/2 [J]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

capacitance: 10 F
high voltage: 12 V
low voltage: 8 V

Calculated

energy: 400 J

Assumptions and limits

Ideal capacitor energy over a voltage interval.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Capacitor and supercapacitor energy storage. Inputs: capacitance; voltage bounds; load; ESR. Outputs: usable energy; droop; approximate runtime. Model scope: Cell/pack data and stated electrical and thermal conditions. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

Inputs: capacitance, voltage bounds, load, ESR
Outputs: usable energy, droop, approximate runtime
Modes: calculate, compare, sweep
Drawing: Pack and energy-budget plot

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS