Solar & Off-Grid Calculator

Comprehensive calculators for planning your off-grid life and solar power system

SolarRatio is a free, comprehensive calculator hub for solar and off-grid system design. From panel sizing and battery bank to inverter selection, wire gauge, charge time, solar ROI, and optimal tilt angle — covering everything from grid-tied savings to fully off-grid system design. Built for real-world conditions including local PSH, LiFePO4 and AGM battery characteristics, and regional solar irradiance variation. In the US, the federal Investment Tax Credit (ITC) currently covers 30% of installed system cost through 2032, and peak sun hours range from 3.7 h/day in Seattle to 6.5 h/day in Phoenix — factors that dramatically shift both your panel wattage requirement and your payback period. Whether you're sizing a rooftop grid-tie system in California, a Texas hill country off-grid cabin, or a Colorado mountain van build, every calculator here accounts for the geographic and regulatory variables that generic tools ignore.

Daily Power Consumption Calculator — Calculate daily energy needs by listing appliances with wattage and usage hours
Solar Panel Sizing Calculator — Find required panel capacity based on daily consumption and peak sun hours
Battery Bank Sizing Calculator — Calculate battery capacity needed for your autonomy days and depth of discharge
Inverter Sizing Guide — Determine the right inverter VA rating for your total load and usage patterns
Wire Gauge Calculator — Find the correct AWG wire size based on current, length, and voltage drop
Charge Time Calculator — Estimate time to fully charge your battery based on capacity and charging current
Solar ROI Calculator — Calculate payback period, annual savings, and 25-year ROI for your solar system
Solar Panel Tilt Angle Calculator — Find the optimal tilt angle for your solar panels based on your latitude
RV & Van Life Solar Calculator — Calculate battery bank and panel sizing for RV, van, and camper van solar builds

SolarRatio is a free, independent set of solar and off-grid sizing tools built around transparent methodology over marketing claims. We are not an installer, a panel brand, or a lead-generation funnel — every calculator here exists to give you the same engineering math a professional uses, so you can sanity-check a quote, plan a DIY build, or simply understand what a solar system actually demands before you spend money. The sections below explain how the tools work, who they are for, the public standards they rely on, and the honest limits of any online estimate.

How these calculators actually work

Every tool on SolarRatio starts from one number — your daily energy demand in watt-hours (Wh/day) — and threads it through the same chain a system designer follows. Panel sizing divides that demand by your local peak sun hours and a real-world system-efficiency factor, because peak sun hours dictate every downstream number: the identical 1,000 Wh/day load needs roughly 280 W of panel in sunny Phoenix but closer to 480 W in cloudy Seattle. Battery-bank sizing multiplies daily demand by your desired days of autonomy, then divides by system voltage and usable depth of discharge (50% for lead-acid and AGM, 80–90% for LiFePO4) to return the amp-hours you must install. Inverter sizing sums your simultaneous running loads and adds headroom for inductive surge; wire-gauge sizing solves for acceptable voltage drop over distance; charge-time estimates divide remaining battery capacity by charge current. Each calculator is a small, auditable formula rather than a black box, so you can see exactly why a result changed when you adjust an input.

Who these tools are for

SolarRatio is built for people making real decisions about real systems. Off-grid cabin and homestead owners use it to confirm an array and battery bank will carry a fridge, lights, water pump, and laptop through a string of cloudy days without a generator. RV, van-life, and overlanding builders size a 12 V system around a compressor fridge, roof fan, and DC-DC charger. Homeowners weighing a grid-tied install use the ROI tool to translate an installer's quote into a payback period they can defend. DIYers planning a permitted build use the wire-gauge and inverter results as a starting point for the load calculations their local inspector will review. If you are comparing a contractor bid, the calculators give you an independent second opinion grounded in the same numbers — not a sales pitch.

The standards and data behind the numbers

Our deeper calculator pages reference the public engineering standards that govern real installations so you can trace any figure back to its source. Battery-bank guidance draws on NEC Article 480 (storage battery installations) and the depth-of-discharge limits published by battery manufacturers. Energy-storage safety references UL 9540, the standard for energy storage systems and equipment. Panel-sizing relies on peak-sun-hours irradiance data of the kind published by NREL and the EU's PVGIS database, which is why our examples span the 3.7 h/day of the Pacific Northwest to the 6.5 h/day of the desert Southwest. Wire-gauge results follow voltage-drop and ampacity practice from the National Electrical Code. We cite these openly because transparent methodology over marketing claims means showing our work, not asking you to trust a brand name.

Using the calculators together

The tools are designed to hand off to one another in the order a system is actually planned. Start with the Daily Power Consumption calculator to establish your Wh/day baseline from a real appliance list. Feed that number into Panel Sizing to find required array wattage, and into Battery Bank to find required storage capacity — peak sun hours dictate every downstream number, so set yours accurately first. Pass your battery voltage and panel open-circuit voltage to the Charge Controller calculator, and your peak simultaneous load to Inverter Sizing. Use Wire Gauge to keep voltage drop in check across your run lengths, and Charge Time to confirm your array can recharge the bank between cloudy stretches. Finally, Solar ROI turns the whole design into a payback estimate. Worked end to end, these tools produce a coherent, internally consistent system plan rather than seven disconnected guesses.

Honest limits of any online estimate

These calculators produce engineering estimates to validate with a licensed installer, electrician, or your local authority having jurisdiction — they are not a substitute for a professional design, a permit, or a code inspection. Real installations are shaped by roof orientation and shading, temperature derating, conductor and conduit specifics, local code amendments, utility interconnection rules, and the exact equipment you buy, none of which a general-purpose tool can fully model. Treat every result as a well-grounded starting point: use it to understand the trade-offs, ask sharper questions, and catch a quote that looks wrong, then confirm the final numbers with a qualified professional before you purchase equipment or energize a system. Always follow your local electrical code and manufacturer instructions.

SolarRatio is a free, independent reference tool. Results are estimates for planning and education only — verify your final system design with a licensed solar installer or electrician and your local code.