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Solar Home System

1. DIY SOLAR HOME SYSTEM

1.3. MODULE 3

Module 3:

 Solar Home System Sizing & Design

Key Concepts

1. Load Assessment (How Much Power Do You Need?)

Step 1: List all appliances + their power (Watts) and usage time (Hours).
Step 2: Calculate Daily Energy (Watt-hours, Wh) = Power (W) × Hours used.

📌 Example:

Appliance Power (W) Hours Used Daily Energy (Wh)
LED Bulb 10W 5 hours 10 × 5 = 50Wh
Fan 50W 8 hours 50 × 8 = 400Wh
Total     450Wh/day

2. Solar Irradiance (How Much Sun Do You Get?)

  • Measured in peak sun hours (average sunlight intensity per day).

  • Example: If your location gets 5 peak sun hours, a 100W panel produces:

    • 100W × 5h = 500Wh/day.

🌍 Check Your Sun Hours:

3. Solar Panel Sizing

Formula:

 
 
Total Daily Energy (Wh) ÷ Peak Sun Hours = Panel Size (W)

📌 Example:

  • Need 450Wh/day ÷ 5 sun hours = 90W panel (round up to 100W).

4. Battery Bank Sizing

Step 1: Decide Days of Autonomy (backup days, e.g., 2 days).
Step 2: Factor in Depth of Discharge (DoD) (e.g., 50% for lead-acid).
Formula:

 
(Total Daily Energy × Backup Days) ÷ DoD = Battery Size (Wh)

📌 Example:

  • 450Wh/day × 2 days = 900Wh

  • 900Wh ÷ 50% DoD = 1,800Wh (or 1.8kWh) battery needed.

  • If using 12V batteries: 1,800Wh ÷ 12V = 150Ah battery.

5. Cost Estimation

Component Example Specs Estimated Cost
100W Solar Panel Monocrystalline   1,000
150Ah Battery Lead-Acid Deep Cycle 10,000
20A Charge Controller PWM   3,500
300W Inverter Pure Sine Wave  5,000
Total   19,500

Activity 3: Step-by-Step Calculation (Excel/Google Sheets Tool)

📊 Downloadable Tool Includes:

  1. Load Calculator (Enter appliances → auto-sums energy needs).

  2. Solar Panel & Battery Sizing (Input sun hours → suggests system size).

  3. Cost Estimator (Compares budget vs. premium components).

Activity 4:

Case Study – Design a Rural Home System

  • A family in Khakhameka uses:

    • 3 LED bulbs (10W, 4 hours/day).

    • 1 Fan (50W, 6 hours/day).

    • 1 Phone Charger (5W, 2 hours/day).

  • Peak Sun Hours: 4.5.

  • Backup Needed: 2 days.

Task:

  1. Calculate daily energy needs. (Answer: 290Wh/day)

  2. Size the solar panel. (Answer: 65W → round to 100W)

  3. Size the battery (50% DoD). (Answer: 1,160Wh → 12V/100Ah battery)

  4. Estimate cost. 

Cheat Sheet: Solar Sizing Formulas

  • Daily Energy (Wh) = Power (W) × Hours Used

  • Panel Size (W) = Daily Energy ÷ Peak Sun Hours

  • Battery (Wh) = (Daily Energy × Backup Days) ÷ DoD

Common Mistakes to Avoid

❌ Forgetting inverter losses (add 20% extra panel power).
❌ Ignoring battery DoD (e.g., using 100% of lead-acid kills it fast!).
❌ Underestimating cloudy days (always add backup days).

Watch theStep by step video tutorial