Solar & Off-Grid Energy Calculators
Plan a solar or off-grid setup end to end — estimate how much energy your panels will make, total your daily power use, size the battery bank and inverter, check a wire run for voltage drop, work out charge times, and see what an appliance costs to run or how long a system takes to pay back. Industry-standard formulas with cited reference values, running entirely in your browser.
- Solar Panel Output Calculator Enter your panel wattage, how many panels, your peak sun hours and a system-efficiency factor to estimate daily, monthly and yearly production.
- Off-Grid Load Calculator List your appliances with their watts, quantity and daily run-time to get your total daily energy use in watt-hours.
- Solar Battery Bank Calculator Enter your daily load, how many days of backup you want, your battery type and system voltage to size the bank in Amp-hours.
- Inverter Size Calculator Enter the total watts of everything running at once and your largest startup surge to size the inverter's continuous and surge ratings.
- Appliance Energy Cost Calculator Enter an appliance's power, how many hours a day it runs and your electricity rate to see the running cost.
- Solar Payback Calculator Enter the net system cost, its annual production and your electricity rate to estimate the simple payback period and long-term savings.
- DC Voltage Drop Calculator Enter the run length, current, wire gauge and system voltage to get the voltage drop, the voltage at the load and whether it's within limits.
- Battery Charge Time Calculator Enter the battery capacity, the charge current and a losses allowance to estimate the charge time and the C-rate.
- Solar Panel Tilt Angle Calculator Enter your latitude to get the optimal panel tilt angle for year-round output, and separate summer and winter angles.
- Solar Array Wiring Calculator Enter your panel specs and wiring layout to get the whole array's voltage, current and power.
Size an off-grid system, step by step
Every off-grid or solar-plus-battery design is built from a handful of numbers that flow into each other. Start by totalling your daily energy use — watts times hours for every appliance. That figure sizes two things: the battery bank (enough usable storage for the cloudy days you want to ride out) and the solar array (enough daily production to replace what you use, plus losses). Then the inverter is sized for your peak simultaneous load and the surge when a motor kicks in.
The rest is getting the details right so the system actually delivers. The voltage-drop calculator keeps your wiring losses in check — low-voltage DC is unforgiving over distance — and the charge-time calculator checks you're charging at a rate your batteries can handle. For grid-tied decisions, the appliance cost and payback tools turn kilowatt-hours into money. The formulas are the industry-standard ones and the reference values are cited (NREL/PVWatts, battery manufacturers); the site-specific figures — your peak sun hours, your electricity rate — are yours to enter. For the underlying electrical maths, see the Electronics and Physics categories.
Frequently asked questions
Are these solar calculators accurate?
The formulas are the standard ones used across the solar industry — production from peak sun hours, battery Amp-hours from load and depth of discharge, inverter sizing, DC voltage drop, and charge time. The reference values (peak sun hours, system derate, depth of discharge, voltage-drop limits) were verified against NREL/PVWatts and battery-manufacturer references and are cited on each tool, with the site-specific ones left for you to enter.
Do I need my exact location or an account?
No. Every tool runs entirely in your browser — no location access, no accounts, nothing uploaded. Where a figure depends on where you live (like peak sun hours or your electricity rate), you enter it, and the tools do the maths. They work offline.
How do I size a whole off-grid system?
Work through the tools in order: total your daily energy use (load calculator), size the battery bank for the days of backup you want, size the solar array to replace that energy plus losses, then size the inverter for your peak simultaneous load. Each tool produces the input the next one needs.
Is the payback calculator financial advice?
No — it's a simplified estimate for comparing options. It ignores electricity-price inflation, panel degradation, maintenance and the time-value of money. Use it to get a feel for the numbers, then get real quotes and check local incentives and net-metering rules.