This article walks through the formulas and steps for sizing the PV array, battery bank, and matching inverter. ShopSolar.com

It may not cover every nuance (e.g. local climate, temperature effects, wiring losses), but it gives a solid framework. Use it as a reference while applying the principles below.

📐 How to Calculate Solar Panel, Battery & Inverter Requirements — Step by Step

Below is a structured methodology you can follow. At the end, there’s a worked example.

1. Estimate Your Energy Demand (Load Analysis)

• List all your appliances / loads (AC or DC) you intend to power.
• For each, note its power rating in watts (W) and the number of hours per day you expect to run it.
• Multiply to get energy usage (in watt-hours, Wh):

Energy per device (Wh)=Power (W)×Hours used

• Sum across all devices to get total daily energy demand in Wh (or kWh).

Remember: for AC loads via inverter, you must also account for inverter inefficiencies (e.g. 85–95% efficiency) when converting DC ➝ AC.
Also, allow additional margin for system losses (wiring, temperature, shading, dust, etc.). Many guides suggest adding 10–30% overhead. GoGreenSolar.com+2SolarTown+2

2. Determine Peak Sun Hours (Insolation) for Your Location

• Peak Sun Hours (PSH) is the equivalent number of hours per day when solar irradiance is at 1,000 W/m² (i.e. “full sun” equivalent).
• You need local solar data or insolation maps (e.g. from meteorological sources or solar databases).
• This factor is critical: more sun hours means fewer watts of panels needed.

3. Size the Solar Panel Array

You want enough solar generation so that:

Total solar energy generated (Wh)≥Your daily demand (Wh)+losses / buffer

A typical calculation:

1. Divide your daily demand by peak sun hours (to get required wattage).
2. Add margin for losses (e.g. 1.2 ×, i.e. 20% extra).
3. Then divide by watt-rating of an individual module to find number of panels.

Formula:

Required PV (W)=Daily energy demand (Wh)Peak Sun Hours×Safety factor (e.g. 1.2)
Number of panels=Required PV (W)Module rating (W)

This approach is described in guides like GoGreenSolar’s sizing method. GoGreenSolar.com

4. Size the Inverter

The inverter must be able to handle:

• The peak load in watts (i.e. sum of power of devices you may run simultaneously).
• Surge / startup currents (some appliances like motors, fridges, pumps draw much more momentarily).
• A safety margin (often 25–30% more than the anticipated load).

Also, consider the voltage of the system (12 V, 24 V, 48 V, etc.) and ensure inverter compatibility.

Leonics provides a worked example: sum of loads = 153 W, safety margin → ~190 W inverter. leonics.com

5. Size the Battery Bank (for Off-Grid or Hybrid with Storage)

Key points:

• Decide how many days of autonomy you need (i.e. how many days you want the system to run without sun).
• Determine acceptable Depth of Discharge (DoD) (for lead-acid you may use only 50%, for Li-ion maybe 80%+).
• Consider system inefficiencies (charging/discharging losses) and temperature derating.

A standard formula:

Battery Capacity (Wh)=Daily energy demand (Wh)×Days of autonomyDoD fraction×system efficiency

Then convert to amp-hours (Ah) based on battery nominal voltage:

Ah=WhVoltage (V)

An example from a PDF guide: for 3 days autonomy, daily 1.8 kWh, system losses, 50% DoD, 48 V nominal → ~225 Ah capacity. CRS Emergency Field Operations Manual

🧩 Worked Example (Hypothetical)

Let’s go through a simplified example:

• Suppose you have the following loads:

• Step 1: Energy demand

E=50×5+150×8+100×4+200×3=250+1200+400+600=2,450 Wh/day
Back to Blog Listing