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Solar Roof Top Calculator

Find out what size solar panel system you need to zero out your electricity bill, how much roof space it takes, and the estimated cost.

By Monthly Bill (₹)
By Monthly Units (kWh)

Electricity Usage

Solar Assumptions

Excludes govt. subsidies. Premium systems (mono PERC) may cost more.

Solar Expert Tips

1
The 4-Unit Rule

In most parts of India, a 1 Kilowatt (1 kW) solar system generates an average of 4 units (kWh) of electricity per day over the course of a year.

2
Space Requirements

Modern polycrystalline or mono PERC panels require roughly 100 square feet of shadow-free rooftop space per 1 kW of installed capacity.

3
Net Metering

With an On-Grid system, you export excess power to the grid during the day and import at night. You only need to generate enough to match your total 24-hour usage to get a zero bill.

Enter your electricity bill to get your solar sizing.

The Ultimate Solar Rooftop Calculator for India (2026-2027)

Transitioning to solar energy is one of the smartest financial and environmental decisions a homeowner or business can make today. With electricity tariffs constantly rising across India and lucrative government subsidies available under schemes like PM Surya Ghar Muft Bijli Yojana, adopting rooftop solar has never been more accessible. However, determining exactly how many solar panels you need to eliminate your electricity bill can be confusing. Our advanced solar rooftop calculator simplifies this process by analyzing your monthly consumption, local solar irradiation levels, and available roof space to provide a highly accurate system size, cost estimate, and physical layout requirement.

How to Calculate Your Solar Rooftop Requirement (Step-by-Step)

Finding the perfect solar system size takes less than a minute. Follow these steps:

  • Step 1: Choose Your Input Method: Select whether you want to calculate based on your monthly electricity bill amount (in ₹) or your exact monthly consumption in units (kWh).
  • Step 2: Enter Usage Data: If using the bill method, input your average monthly bill and the per-unit tariff. If using units, simply enter your monthly kWh consumption.
  • Step 3: Select Solar Generation Rate: Choose the solar generation capacity based on your region. The Indian standard is 4 units per kW per day, but high-sun states like Rajasthan may hit 4.5 units.
  • Step 4: Confirm System Cost: We've pre-filled a standard cost per kW (around ₹50,000 to ₹60,000 depending on panel technology). Adjust this if you have a local quote.
  • Step 5: Get Your Estimate: Click calculate to see the exact kilowatt (kW) size you need, the roof area required in square feet, and the estimated total installation cost!

Engineering Formulas & Thumb Rules for Solar Sizing

The core of solar calculation relies on the "4-Unit Rule". In most parts of India, 1 kW of installed solar capacity will generate roughly 4 units (kWh) of electricity daily, totaling about 120 units a month. Therefore, if your monthly consumption is 600 units, you divide 600 by 120 to find you need a 5 kW system. For physical space, the thumb rule dictates that modern polycrystalline or Mono PERC panels require approximately 100 square feet of shadow-free roof space per 1 kW of capacity. This means a 5 kW system requires 500 square feet of clear, unshaded rooftop facing South.

Current Market Rates in India & 2027 Projections

Solar technology costs have decreased significantly over the last decade, though local installation and mounting structure costs remain stable. Here are the expected rates for 2026-2027:

  • Standard Polycrystalline System: ₹45,000 - ₹50,000 per kW. (Slightly older technology, requires more space).
  • Mono PERC Half-Cut Panels: ₹55,000 - ₹62,000 per kW. (Highly efficient, works better in low light and high temperatures, becoming the new standard by 2027).
  • TopCon / N-Type Bifacial Panels: ₹65,000+ per kW. (Premium technology capturing light from both sides, ideal for commercial flat roofs).
  • Government Subsidies: Central subsidies for residential rooftops currently cover a significant portion of the cost for systems up to 3kW, drastically reducing the payback period to 3-4 years.

Frequently Asked Questions (FAQ)

What is an On-Grid vs. Off-Grid solar system?

An On-Grid system is connected to the state electricity grid. You use solar power during the day, export the excess to the grid via net-metering, and import from the grid at night. An Off-Grid system uses expensive batteries to store power for night use and is independent of the state electricity grid.

Does the system produce electricity during monsoons?

Yes, solar panels still generate electricity on cloudy or rainy days, but the efficiency drops by 40% to 60%. However, our calculation of "4 units per kW per day" is an annualized average that already accounts for the lower generation during the monsoon and winter months.

Do I need a battery with my rooftop solar system?

If you live in an urban area with minimal power cuts, you do not need a battery. An On-Grid system with net-metering is the most cost-effective solution. Batteries (Hybrid or Off-Grid systems) double the initial cost and are only recommended for areas with frequent and prolonged power outages.

Which direction should solar panels face in India?

Because India is located in the Northern Hemisphere, solar panels should ideally face True South to capture maximum sunlight throughout the day. If South is not possible, South-East or South-West are the next best alternatives, though there will be a slight drop in total generation efficiency.