Energy Lab

Educational off-grid solar system estimator

Estimate your solar & battery system.

Pick your appliances, set your sun hours, and choose your equipment. This tool estimates battery bank size, PV array size, charge controller rating, and inverter rating with a live system diagram. Not a substitute for professional design.

Start with your appliances Back to portfolio
Educational sizing estimate — not installation-ready. This tool helps you explore off-grid solar system sizing concepts. Do not buy, wire, or install equipment based solely on these results. Actual system design requires professional assessment of local codes, cable sizing, overcurrent protection, equipment specifications, and site conditions.

Step 1: Your appliances.

Toggle the loads you plan to power and set how many hours per day each runs.

Total daily energy: 0 Wh/day Peak simultaneous: 0 W

Step 2: Site & sun.

Your location and backup requirements.

5.0 h/day

How many full-sun-equivalent hours your location gets per day. Most regions average 3–7 peak sun hours. Check a solar map for your city's average.

What are peak sun hours?Peak sun hours measure the amount of usable solar energy at your location — 5 peak sun hours means the sun delivers about the same energy as 5 hours of full midday sun, even if daylight lasts longer. Higher numbers mean more solar power available.
25°C Max DoD: 0.80   Capacity factor: 1.00

Cold batteries deliver less usable capacity. At -20°C only 63% depth-of-discharge is safe, and capacity drops to 90%. Above 25°C full capacity is available.

3 days

How many days your system should run without sun. The tool also computes a PSH-based storage days formula and uses whichever is larger.

System voltage

Auto picks the lowest standard voltage (12V, 24V, or 48V) that keeps battery current under 100A. Manual sets it directly.

What is system voltage?The voltage your battery bank runs at (12V, 24V, or 48V). Higher voltages allow more power to flow through smaller wires. Most small cabins use 12V or 24V; larger homes typically use 48V.

Step 3: Your equipment.

Choose the batteries and solar panels you plan to use.

Pick a battery you have or plan to buy. For custom batteries, common lithium values like 12.8V, 25.6V, and 51.2V are compatible with 12V, 24V, and 48V systems.

What do battery specs mean?Battery voltage (V) and amp-hour capacity (Ah) determine how much energy the battery stores. Multiply V × Ah to get watt-hours (Wh). For example, a 12V 100Ah battery stores 1,200 Wh (1.2 kWh).

Choose a panel wattage. Higher-wattage panels reduce the number of strings needed and simplify array wiring.

What do panel specs mean?Solar panels are rated by maximum power (Pmax in watts), voltage at max power (Vmp), and current at max power (Imp). Higher wattage panels generate more energy per panel.

Typical inverter efficiency. Most good inverters run 85–96%. Lower efficiency means more battery capacity is needed.

Your system.

Every component sized from your inputs.

Enable at least one load and set your equipment to see an estimate.

Daily AC energy

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System voltage

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Battery load

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Storage days

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Battery bank

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PV array

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Charge controller

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Inverter

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Reading your results: The numbers above estimate your system size based on the loads, site conditions, and equipment you selected. The battery bank and PV array show series/parallel configuration — e.g. 2S11P means batteries arranged in strings of 2 (for higher voltage), with 11 such strings wired in parallel (for more capacity). All values are rough estimates for educational use.

System schematic

Conceptual wiring diagram — not installation-ready. This tool provides educational sizing estimates. The schematic above shows a structural arrangement of components; actual system design must consider cable sizing, overcurrent protection, voltage drop, temperature derating, manufacturer specifications, and local electrical codes. Always have your final design reviewed by a qualified solar installer.
Positive wire Negative wire Busbar Series jumper Solar panel Battery Charge controller Inverter Loads

How it works.

Three steps that determine your whole system.

Loads → battery need

Your daily energy use divided by inverter efficiency and system voltage gives the battery amp-hours you need to supply each day. Backup days and temperature derating scale it up.

Battery → PV array

The daily battery requirement is divided by each panel string’s daily amp-hour production (panel current × peak sun hours × derating) to find how many strings needed.

Controller + inverter

The charge controller is sized for the total array current with a cold-temperature safety factor. The inverter is sized for peak simultaneous load with a 25% surge margin.

Technical details.

Formulas and assumptions behind the sizing.

How to use these results

  • Daily AC energy is the sum of your appliance watt-hours. This is what your inverter must supply each day.
  • Battery load is the daily amp-hour requirement at your system voltage, accounting for inverter losses.
  • Storage days is the larger of your manual backup setting and the PSH-based formula: 9.43 − 1.9×PSH + 0.11×PSH².
  • Battery bank shows series/parallel configuration: e.g. 2S11P means 2 in series per string and 11 parallel strings.
  • PV array shows series/parallel panel configuration with total rated watts.
  • Charge controller minimum rating uses a 1.25× cold-temperature safety factor on short-circuit current.
  • Inverter continuous rating = peak simultaneous load × 1.25 surge margin.

A note on real-world conditions

This tool provides a conservative estimate using standard derating factors (combined PV derating of 0.85 for wiring, dust, and mismatch; additional 0.90 for temperature). Real-world performance depends on exact equipment specifications, site conditions, wiring losses, and equipment quality. Always consult manufacturer datasheets for final design.