Integrated off-grid system planning

Off-Grid Solar System Planner

Add the loads you actually need to run, then size battery storage, panels, and controller current in one transparent planning scenario.

Build your off-grid system plan

Start with an editable scenario

Apply one visible planning starting point. It fills the fields below and calculates a first estimate; every value remains editable.

Home load starters Editable examples for a first pass

Always-on / standby powerOptional · 24-hour loads

Always-on / standby power W · optional Use for routers, controls, and other loads that run close to 24 hours.

Appliance Watts Qty Hours Surge W

Load previewincludes optional standby power

Daily energy: --
Running power: --
Listed surge total: --
Standby power: --

These are editable examples, not fixed appliance ratings. Replace them with measured or nameplate data.

Battery and solar planning inputs

Add the load first, then enter the site and equipment values you want this scenario to cover.

Days of autonomy days How long the battery should cover without charging. System voltage V Use the battery-bank voltage, not a single module voltage. Peak sun hours hours/day Use a local long-term planning value, not daylight length. Solar coverage % Share of the listed daily load the array should offset. Panel rating W Enter the nameplate rating of one planned panel.

Battery chemistry preset

Editable starting point. Check the battery maker's operating limits.

Battery module for an integer layoutOptional

Enter both module values to include a whole-battery layout, or leave them blank for a capacity-only result.

Module voltage V Module capacity Ah

Use matching modules from the same documented system. The layout is rounded up and its installed capacity is recalculated.

Advanced assumptionsEditable planning values

Depth of discharge % Usable share of rated battery capacity. Battery efficiency % Energy retained after battery-side losses. Inverter efficiency % Used for AC conversion. DC runtime ignores it. Reserve margin % Extra nominal capacity above the loss-adjusted result.

Solar and controller assumptionsEditable planning values

Solar system efficiency % Combined planning factor for temperature, wiring, controller, and conversion losses. Controller planning factor Applied only to the current baseline; it does not replace Voc/Isc checks.

The visible values are editable planning starting points, not manufacturer specifications.

Integrated system planning estimate

Local calculation

Enter your values, then calculate. Results will show the formula inputs and rounding used.

Formula used

daily Wh = Σ(appliance W × quantity × hours) + standby W × 24; battery Wh = daily Wh × autonomy ÷ (DoD × inverter efficiency × battery efficiency) × (1 + reserve); array W = daily Wh × coverage ÷ (peak sun hours × solar efficiency)

The system planner composes the shared load, battery, and panel calculation modules. Battery capacity is sized for the entered autonomy and losses; solar production is sized for the selected coverage target; whole units are rounded upward and installed capacity is recalculated. The controller figure is a current baseline, not a product selection.

See the full assumptions and rounding policy.

Maintenance and verification

Maintained by: SolarMathKit Formula version: 1.3.0 Last reviewed: July 27, 2026

The calculator calls the shared, tested TypeScript calculation modules documented in the methodology. Automated tests cover published examples, invalid inputs, rounding, and result invariants.

SolarMathKit maintains this implementation. The review is an internal technical check, not an independent engineering certification.

Worked example: a small off-grid load

A 120W refrigerator runs for 8 hours, four 10W lights run for 5 hours, and 8W of standby load runs continuously. Use 2 days of autonomy, 24V, 5 peak sun hours, 80% solar efficiency, and 400W panels.

Daily load: 120 × 1 × 8 + 10 × 4 × 5 + 8 × 24 = 1,352 Wh/day.
Battery design energy: 1,352 × 2 ÷ (0.90 × 0.92 × 0.95) × 1.10 ≈ 3,781 Wh nominal.
Solar array need: 1,352 ÷ (5 × 0.80) = 338W; one 400W panel is the upward-rounded installed array.
Controller baseline: 400W ÷ 24V × 1.25 ≈ 20.8A before datasheet checks.

Result: The planning scenario is one 400W panel, about 3.78kWh nominal battery capacity, and a 20.8A controller-current baseline before equipment-limit checks.

Common mistakes to avoid

Sizing from running watts instead of daily watt-hours.
Leaving standby, router, controls, or ghost loads out of the daily total.
Treating peak sun hours as daylight duration.
Rounding a fractional panel or battery count down.
Treating the controller baseline as a complete Voc, Isc, charge-profile, wiring, or protection check.

Questions people ask

What does an off-grid solar system calculator need?

Start with appliance watts, quantity, and hours per day. Then enter battery autonomy, system voltage, peak sun hours, panel rating, and editable loss assumptions. The load list is the bridge between the energy you need and the battery and solar capacity you plan.

Is this different from a solar panel sizing calculator?

Yes. The panel sizing calculator starts with an energy target and focuses on array watts and panel count. This page keeps the load list, battery autonomy, battery assumptions, solar coverage, and controller-current baseline in one scenario so the inputs stay connected.

Can I plan a home, cabin, shed, or van system?

Yes, as a first-pass planning estimate. Use measured or documented load data, and replace the editable starter examples. RV-specific seasonal and travel workflows remain on the RV solar calculator.

Why does the result show both battery Wh and panel count?

Battery storage covers the selected autonomy after depth-of-discharge and conversion losses. Panels cover the selected share of daily load after peak-sun and solar-efficiency assumptions. They answer different parts of the same system plan.

What is the controller current baseline?

It is installed array watts divided by the entered battery-system voltage, multiplied by the visible planning factor. Verify cold Voc, Isc, controller input limits, charge voltage, battery charge current, wiring, and protection with the equipment documentation.

Does this choose an inverter, cable, fuse, or breaker?

No. It reports running and listed surge power to make the next checks visible, but it does not make equipment, cable, protection, or installation decisions.

What happens when I enter battery module values?

The calculator checks whether the module voltage divides evenly into the system voltage, rounds the parallel module count upward, and reports the installed whole-module capacity. Leave both fields blank when you only need a capacity estimate.

Before you build: Check voltage, current, temperature, protection, cable sizing and installation rules with the equipment manuals and a qualified professional.