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Selection of Rooftop for Home Load Calculation – Step by Step with Example (2025 Guide)

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Introduction

With rising electricity costs and the push toward clean energy, more homeowners are exploring rooftop solar. But before you install a solar system, the first step is to calculate your home load and determine how much rooftop area you’ll need. This guide walks you through a complete step-by-step example of rooftop selection and solar sizing, so you can make informed decisions for your home.


We’ll cover:

How to calculate your home’s connected and daily load.
Estimating peak demand.
Sizing a rooftop solar system with real-world formulas.
Finding out rooftop area required.
Checking structural strength.
Inverter and battery selection.
A practical homeowner’s checklist.
Let’s dive in.

Step 1: Calculate the House Electrical Load

First, make a list of your appliances, their power rating, and how many hours per day they run. Here’s an example of a 3–4 bedroom household.
👉 Daily energy requirement = ~22.4 kWh/day.

Step 2: Peak Demand Load

If all devices run at once, total connected load = 5.433 kW.
But in real life, not all loads run together. We apply a demand factor (0.5–0.8). Using 0.6:
Peak demand ≈ 5.433 × 0.6 = 3.26 kW
So, you need to size your rooftop system for average demand (~3.26 kW) and keep in mind worst-case peaks (~5.4 kW).

Step 3: Solar PV System Sizing
We want to offset daily usage of 22.4 kWh.

Formula:

PV (kW) = Daily load (kWh) ÷ (Peak Sun Hours × Efficiency)
Peak Sun Hours: 5 (India average)
System efficiency: 0.75
PV size = 22.4 ÷ (5 × 0.75) = 5.97 kW ≈ 6 kW

👉 For this example, a 6 kW rooftop solar system is ideal.

Step 4: Rooftop Area Requirement

Area depends on panel wattage. Assume 360 W panels (~1.95 m² each).
Panels required = 6000 ÷ 360 ≈ 17 panels
Area = 17 × 1.95 = 33.15 m²
Rule of thumb: 5.5–8 m² per kW.
For 6 kW → 33–48 m² rooftop needed.

👉 So, ensure you have at least 34 m² shadow-free rooftop area.

Step 5: Structural Load Check

Solar panels + mounting add 15–25 kg/m².
For 34 m², extra weight = 34 × 20 = ~680 kg.

👉 Always get your roof checked for strength, especially for wind loads.

Step 6: Inverter and Balance-of-System (BoS)

Inverter: 6 kW or 6.5 kW capacity.
Cables, isolators, earthing, surge protection: must be sized per design.
String configuration: match panel voltage/current to inverter MPPT input.

Step 7: Battery Backup (Optional)

If you want 1-day backup for 22.4 kWh:
Required usable battery = 22.4 ÷ (0.8 × 0.9) ≈ 31 kWhThis is large and costly. Most homes instead back up essential loads only (lights, fans, fridge, Wi-Fi). For that, a 5–10 kWh battery is often sufficient.

Step 8: Rooftop Solar Installation Checklist

1. ✅ List actual appliances and daily use.
2. ✅ Decide coverage: full offset or partial.
3. ✅ Check sun hours in your location.
4. ✅ Calculate PV size and number of panels.
5. ✅ Confirm rooftop area and shading.
6. ✅ Check roof structure strength.
7. ✅ Select inverter and BoS components.
8. ✅ Plan for optional battery backup.
9. ✅ Get 2–3 installer quotes.
10. ✅ Apply for net-metering approval.

Step 9: Rooftop Orientation & Tilt

Direction: South-facing (India/Northern Hemisphere).
Tilt angle: Equal to local latitude (e.g., Delhi ~28°).
Avoid shadows: Chimneys, water tanks, and nearby trees.
Good orientation ensures maximum energy output.

Step 10: Example Summary

Daily Load: 22.4 kWh
Peak Demand: 3.26 kW
Solar System Size: 6 kW
Panels Needed: 17 (360 W each)
Rooftop Area Required: ~34 m²
Extra Roof Load: ~680 kg
Inverter Size: 6–6.5 kW


This calculation shows how rooftop area, load demand, and solar system sizing all connect.

Conclusion

Choosing the right rooftop system starts with a proper home load calculation. With the example above, you can now estimate how many panels you’ll need, how much rooftop space is required, and what inverter/battery size suits your household. Always confirm final sizing with a professional installer, but this guide gives you a perfect starting point for your solar journey.

If you’re serious about cutting your electricity bill and moving to clean energy, start with your load calculation today – your rooftop is your power station!


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