Solar, Battery & Power Station Calculators
Plan solar power, off-grid batteries, and portable power for your home or RV. Calculate capacity, runtime, charging, and electricity cost.
Built by a software engineer for U.S. households, RVs, and small off-grid systems. Every calculator publishes its formula, assumptions, and sources, and runs in your browser — no account needed. About JouleCalc
Solar & Battery
- Solar Battery Bank CalculatorSize an off-grid battery bank from your daily load and days of autonomy — capacity in kWh and Ah, plus a series/parallel layout for the cells you choose.
- Solar Panels Needed CalculatorFind how many solar panels cover a target daily energy use, using peak sun hours and a system derate factor.
- Inverter Size CalculatorFind what size inverter you need from the appliances you will run — continuous watts, startup surge, and the DC current your battery bank must supply.
- DC Wire Size CalculatorSize copper DC wire or cable for 12V, 24V and 48V systems. Enter amps and one-way length to check AWG, voltage drop and NEC ampacity.
- Off-Grid Solar System CalculatorSize panels for average daily AC energy, batteries for autonomy, and an inverter for running and startup power.
Portable Power
- Power Station Runtime CalculatorEstimate how long a portable power station runs a given load, after inverter and battery-reserve losses.
- Appliance Wattage CalculatorAdd up running watts, daily watt-hours, and surge watts for the appliances you plan to power.
- Power Station Size CalculatorPick the appliances you need to run and get a recommended power station capacity plus matching models.
- Solar Charge Time CalculatorEstimate how long solar panels take to charge a portable power station, in full sun, partly cloudy, or overcast skies.
Home Backup
- Home Battery Backup CalculatorEstimate how many hours a home battery will cover a chosen average load during an outage. AC-rated usable energy is used as-is; DC battery energy is reduced by inverter loss.
- Generator Size CalculatorSize a portable generator from the loads you actually plan to run — with the NEC continuous-load rule and the power your engine loses to elevation both on the page.
- Battery Usable Capacity CalculatorEstimate usable DC energy and delivered AC energy from your battery's SOC, health and temperature factors.
EV
- EV Charging Cost CalculatorWork out what one charging session costs, with the conversion loss counted on the side of the meter that actually bills you for it.
- EV Charging Time CalculatorEstimate how long a charging session takes from the pack size, the state-of-charge window, and the charger you are plugged into.
Cost
- Appliance Electricity Cost CalculatorEstimate what one appliance costs to run per day, month, and year from its watts, daily hours, and your kWh rate.
- Solar Payback CalculatorWork out how long a rooftop solar system takes to pay for itself — with the federal residential tax credit shown as what it now is, expired, rather than baked in at 30%.
- Battery Arbitrage CalculatorEstimate time-of-use battery savings with annual capacity fade, maintenance, cash flows, payback, NPV and IRR.