How to Use Solar Panel Calculator
The Solar Panel Calculator sizes your solar system in seven simple inputs:
- Daily Energy Consumption (kWh/day) — Total electricity you use per day. Check your utility bill or add up your appliances. The Solar Panel Calculator uses this as the baseline load.
- Peak Sun Hours (h/day) — Average daily peak sunlight for your location. Look up your region's solar irradiance map or use 4–5 h as a global average.
- System Efficiency (%) — Combined efficiency of the inverter, wiring, and module soiling. The Solar Panel Calculator defaults to 80%.
- Panel Wattage (W) — The rated power of each individual solar panel (e.g., 400 W).
- Backup Days — How many cloudy days your battery should cover. Enter 0 if you are grid-tied and do not need storage.
- Depth of Discharge (%) — The usable fraction of battery capacity. The Solar Panel Calculator defaults to 80%, which is standard for lithium batteries.
- Electricity Rate (USD/kWh) — Your local electricity price for estimating annual bill savings.
The Solar Panel Calculator then shows recommended total panel capacity, number of panels, estimated daily generation, battery size, and annual savings — all updating instantly.
Formula & Theory — Solar Panel Calculator
The Solar Panel Calculator applies two core formulas from standard photovoltaic system design:
Required Panel Capacity (kW) = Daily Usage (kWh) ÷ Peak Sun Hours (h) ÷ System Efficiency
Required Battery Capacity (kWh) = Daily Usage × Backup Days ÷ Depth of Discharge
| Variable | Meaning |
|---|---|
| Daily Usage | Total kWh consumed per day |
| Peak Sun Hours | Hours/day with equivalent 1 kW/m² irradiance |
| System Efficiency | Fraction accounting for inverter and wiring losses |
| Backup Days | Days of autonomy without sun |
| Depth of Discharge | Fraction of battery usable without degradation |
The Solar Panel Calculator then divides total capacity by per-panel wattage and rounds up to give the integer number of panels needed.
Key Assumptions
The Solar Panel Calculator assumes panels are optimally oriented and unshaded. Temperature derating, ageing degradation, and local grid-feed regulations are not modelled here.
Use Cases for Solar Panel Calculator
The Solar Panel Calculator supports a wide range of renewable energy planning scenarios:
- Home rooftop solar sizing — Homeowners use the Solar Panel Calculator to estimate how many panels and what battery capacity they need before requesting installer quotes.
- Off-grid cabin or tiny house — The Solar Panel Calculator helps remote property owners plan a fully self-sufficient solar system, including the battery bank needed for multi-day autonomy.
- RV and van life — Travellers use the Solar Panel Calculator to size their mobile solar setup based on actual daily power consumption from appliances like refrigerators, lighting, and devices.
- Small business and farm microgrids — Agricultural businesses can use the Solar Panel Calculator to evaluate solar for irrigation pumps or cold-storage units and estimate payback through annual savings.
- Engineering and sustainability education — Students and teachers use the Solar Panel Calculator to explore how location (peak sun hours), system size, and efficiency trade-offs affect solar system economics in real time.
Whether you are planning a grid-tied rooftop system or a fully off-grid installation, the Solar Panel Calculator gives you a reliable, formula-based starting point for your renewable energy journey.