How SolarDecide Works

SolarDecide uses the same engineering methodology that professional solar installers use to size your system. Here's a step-by-step explanation of every calculation — in plain English.

Step 1: Calculate Daily Energy Load (kWh)

For each appliance you select, we multiply:

Daily Wh = Watts × Quantity × Hours per Day

We then sum all appliances to get your total daily energy consumption in kilowatt-hours (kWh).

Data source: Appliance wattages are based on manufacturer specifications and verified against Nigerian market products (2026).

Step 2: Size the Inverter (kVA)

The inverter must handle your peak instantaneous load, including motor startup surges:

Peak Surge Watts = Σ (Watts × Quantity × Surge Factor)
Inverter VA = Peak Surge Watts ÷ Power Factor (0.8)
→ Round up to nearest standard kVA: 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20

Motor-driven appliances (ACs, refrigerators, freezers, pumps) have surge factors of 2-3x their running wattage. Non-motor appliances have a surge factor of 1.0.

Step 3: Size the Battery Bank (Ah)

Batteries are sized to store enough energy for your specified backup duration:

Required Wh = (Daily kWh × Backup Days × 1000) ÷ (DoD × Efficiency)
Battery Ah = Required Wh ÷ System Voltage (48V)
→ Round up to nearest standard Ah: 100, 150, 200, 250, 300, 400, 500

We use:

• Depth of Discharge (DoD): 80% for lithium (LiFePO4), 50% for lead-acid
• System Efficiency: 85% (accounts for inverter and wiring losses)
• System Voltage: 48V (industry standard for systems above 1kVA)

Step 4: Size the Solar Panels (Watts)

Panels must generate enough energy daily to meet your consumption and charge batteries:

Panel Watts = (Daily kWh × 1000) ÷ (Peak Sun Hours × System Efficiency)
System Efficiency = 0.75 (accounts for temperature, dust, wiring losses)

Data source: Peak sun hours are sourced from the Nigerian Meteorological Agency (NiMet), covering all 37 Nigerian states and FCT. Values range from 4.5 hours (southern coast) to 6.5 hours (northern Sahel).

Step 5: Estimate System Cost (₦)

Total cost is calculated using average Nigerian market component prices:

Cost = (Inverter kVA × ₦150,000/kVA)
     + (Battery Ah × ₦1,200/Ah)
     + (Panel Watts × ₦350/W)
     + ₦150,000 (installation)

These per-unit prices are updated quarterly based on Lagos and Abuja dealer surveys.

Step 6: Calculate ROI and Payback

We calculate how quickly the solar system pays for itself by comparing it to your current spending:

Monthly Savings = Current monthly fuel/electricity spend
Payback Months = System Cost ÷ Monthly Savings
Annual ROI = (Monthly Savings × 12) ÷ System Cost × 100%
5-Year Savings = (Monthly Savings × 60) − System Cost

Edge Case Handling

• Commercial loads: Systems above 20kW are flagged as commercial and receive appropriate guidance.
• Extreme fuel spending: Monthly fuel spending above ₦5,000,000 is flagged for verification.
• Minimum backup: The minimum backup duration is 0.5 days (12 hours) to ensure practical battery sizing.
• Zero-fuel scenarios: When no fuel spending is entered, payback is calculated against grid electricity tariff savings.