☀️ Solar Panel Calculator

Solar Panel Calculator - System Size, Cost & ROI Explained

Going solar is one of the smartest financial decisions a homeowner can make right now - but only if you size the system correctly and know the numbers before you talk to any vendor. This calculator works through the complete picture: how big a system your home actually needs, what it costs after government subsidies, how much you save every year as electricity rates rise, and exactly when the system crosses from being a cost to generating pure profit.

How the System Size Calculation Works

The calculator converts your monthly consumption into the minimum solar capacity needed to cover it, accounting for real-world losses:

• Daily kWh needed = Monthly kWh ÷ 30
• Raw system size (kW) = Daily kWh ÷ (Peak sun hours × (1 – System loss %))
• Recommended size = Raw size rounded up to the nearest 0.5 kW
• Panels required = System kW × 1000 ÷ 400W per panel (rounded up)

System losses (typically 15–25%) account for wiring resistance, inverter inefficiency, dust, and temperature. Peak sun hours vary by location - Rajasthan gets 6–6.5 hours daily while northeast India averages 4–4.5 hours. Using the right sun hours figure for your city makes the size estimate significantly more accurate.

Understanding the Cost & Subsidy Figures

Reading the 25-Year Projection

The projection models two real-world effects that dramatically impact long-term returns:

• Panel degradation (~0.5%/year): Solar panels slowly lose output over time. A panel generating 400W today produces roughly 390W in year 5 and 350W by year 25. Most premium panels carry a 25-year performance warranty guaranteeing at least 80% output at end of life.
• Electricity price inflation (~5%/year in India): Every year your electricity tariff rises, the value of each unit your solar system generates also rises. This compounding effect is why the annual savings numbers accelerate over time - your solar system is essentially a hedge against electricity price inflation.

The payback year (marked with ★ in the table) is when cumulative savings equal your net installation cost. Every year after that is pure return on investment - with no risk, no market volatility, and a government-backed net metering framework protecting your earnings.

On-Grid vs Off-Grid vs Hybrid - Which One Should You Choose?

This calculator focuses on on-grid (grid-tied) systems, which are the right choice for the vast majority of urban and semi-urban Indian homes. Here's a quick comparison to help you decide:

• On-grid: Connected to the DISCOM grid. Net metering credits excess generation. No battery required - lowest cost. Power cuts off during grid outages (safety requirement). Best ROI for areas with reliable grid supply.
• Off-grid: Completely independent with battery storage. Ideal for remote areas or locations with frequent long outages. Higher upfront cost due to battery bank. No net metering benefit.
• Hybrid: Grid-connected with battery backup. Best of both worlds - net metering when grid is up, backup power during outages. Highest upfront cost but maximum flexibility. Increasingly popular as battery prices fall.

Is Solar the Right Decision for You Right Now?

Solar makes strong financial sense if most of these apply to your situation:

• Monthly electricity bill above ₹1,500 (India) / $80 (US) / £60 (UK)
• You own the property and the roof is in good condition
• South-facing roof (India/US) with no major shading from trees or buildings
• Your DISCOM offers net metering - most urban DISCOMs do as of 2025
• You plan to stay in the property for at least 5 years
• Your current tariff is ₹6/unit or higher - and electricity costs only go one direction

If fewer than three of these apply, the calculator still gives you an honest payback figure so you can decide with real numbers rather than a vendor's sales pitch.