How to Calculate the Ideal Rooftop Solar System Size for Your Home (2025 Guide)
Are you planning to install solar panels on your rooftop but unsure how much capacity you need? You’re not alone. One of the most common questions people ask is:
👉 “How much solar power does my home really need?”
In this guide, we’ll break down how to calculate the right solar system size for your home, so you can save money, get the best return on investment, and reduce your electricity bill — all in simple terms.
☀️ Why System Size Matters?
Choosing the correct size of your rooftop solar system ensures:
- You generate enough power for your daily needs.
- You avoid overspending on extra panels.
- You maximize your return on investment (ROI).
- You make the most of government subsidies and net metering benefits.
📊 Step-by-Step Guide to Calculate Your Ideal Solar System Size
✅ Step 1: Know Your Monthly Electricity Usage
Look at your last 6–12 months’ electricity bills and note down the average units (kWh) consumed per month.
For example:
If your average is 400 units/month, that’s your consumption target.
✅ Step 2: Calculate Your Daily Energy Requirement
Divide your monthly usage by 30.
Example:
400 units/month ÷ 30 = 13.3 units/day
✅ Step 3: Estimate Solar Power Generation per kW
In India, 1kW of solar panels generates around 4 units per day under ideal conditions.
So, to meet your daily need of 13.3 units:
13.3 ÷ 4 = 3.33 kW
Round it up slightly to ensure a buffer.
📦 Final size = 3.5kW system
🏠 How to Match Solar Size with Your Roof Space?
Roof Space Requirement (Approx.)
| System Size | Roof Area Needed |
|---|---|
| 1kW | 100 sq. ft. |
| 2kW | 200 sq. ft. |
| 3kW | 300 sq. ft. |
| 5kW | 500 sq. ft. |
| 10kW | 900–1000 sq. ft. |
If your rooftop is shaded, use high-efficiency panels (Mono PERC) to get more output from less space.-to-end services, including net metering and government documentation.
🧠 Quick Formula to Calculate Solar Size
Solar Size (kW) = (Monthly Power Consumption in kWh) ÷ 120
📌 Why divide by 120?
Because 1kW = 4 units/day → 4 x 30 = 120 units/month
⚡ Common Household Examples
| Monthly Bill | Avg. Units | Recommended Size |
|---|---|---|
| ₹800–₹1200 | 100–150 | 1–1.5 kW |
| ₹1500–₹2500 | 200–300 | 2–3 kW |
| ₹3000–₹4000 | 350–450 | 3.5–4.5 kW |
| ₹5000+ | 500+ | 5–6 kW or more |
🏡 Residential Solar System Types
🔌 On-Grid (Grid-Tied)
- Works with electricity grid
- Net metering available
- Best for homes with low power cuts
🔋 Off-Grid (With Battery)
- Works without the grid
- Battery backup included
- Ideal for remote areas with frequent outages
🔄 Hybrid
- Grid + battery
- Costlier, but offers best of both worlds
💡 Tips for Choosing the Right System Size
- Consider future expansion (EV charging, AC usage).
- Account for seasonal variation in power use.
- Ask for a free site visit from a certified solar company.
- Opt for high-efficiency panels if space is limited.
- Use BEE-rated appliances to reduce load.
🧾 Documents Needed for Rooftop Solar in India
- Recent electricity bill
- Property proof or NOC (for tenants)
- Government ID proof
- Net metering application (via installer)
🔧 How Bhandari Solar Helps You
At Bhandari Solar, we:
- Provide free site survey
- Analyze your electricity usage
- Offer tailor-made system sizing
- Take care of net metering & subsidies
- Provide AMC and real-time monitoring
📍 Active in Indore, Bhopal, Khargone & all across Madhya Pradesh
🙋 Frequently Asked Questions (FAQs)
Q1. What if I install a bigger system than needed?
👉 Extra energy is exported to the grid (if on-grid), and you get credit. But ROI reduces if system is too large.
Q2. Can I add more panels later?
👉 Yes, if your inverter supports more capacity or is upgradeable.
Q3. How many hours of sunlight are required per day?
👉 Ideally, 4–5 hours of good sunlight is enough for optimal output.
Q4. Does net metering reduce the size I need?
👉 Yes. You can size your system slightly smaller if you rely on grid at night and export extra during the day.
Q5. What size solar system is eligible for subsidy?
👉 For residential users, systems up to 10kW are eligible under the PM Surya Ghar Yojana in 2025.
✅ Final Thoughts
Calculating the right rooftop solar system size is the most important step in your solar journey. Don’t guess — plan it right.
Use your power bills, roof space, and sunlight exposure to decide your ideal system size.
For a free evaluation, contact a trusted installer like Bhandari Solar, and let the savings begin! 🌞