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Solar Water Heater Sizing & Savings Calculator

Determine LPD sizing requirements and electric geyser cost offsets.

Live 2026 Data
System Capacity 100 - 500 LPD
Collector Type ETC vs FPC Tube
Temperature Rise Up to 60°C - 80°C
Annual Savings ~₹4,000 - ₹12,000

1. Enter Configuration Parameters

Frequently Asked Questions (FAQ)

Are there monthly subsidies for solar water heaters on my power bill?

Yes. Many DISCOMs (like BESCOM in Karnataka) provide a direct rebate of Rs. 50/month on your electricity bill if a solar water heater is installed.

What is the cash subsidy for rooftop solar under PM Surya Ghar Yojana?

The central government provides a direct subsidy of Rs. 30,000 per kW for the first 2 kW of solar capacity, and Rs. 18,000 for the 3rd kW. The maximum subsidy is capped at Rs. 78,000 for any residential installation of 3 kW or higher.

How much roof space is required to install a 3 kW solar system?

A 3 kW residential solar system requires approximately 250 to 300 square feet of shadow-free rooftop space. Each solar panel is roughly 20 square feet, and a 3 kW setup typically uses 6 to 8 high-efficiency monocrystalline panels.

How many units of electricity does a 1 kW solar panel generate daily?

In India, a 1 kW solar plant generates an average of 4 to 4.5 kWh (units) of electricity per day in standard sunny conditions. This translates to roughly 120 to 135 units per month, or 1,500 units annually per kW of installed capacity.

What is solar net-metering, and how does it work?

Net-metering uses a bidirectional meter to record both the power you import from the grid and the excess solar power you export to the grid. At the end of the billing cycle, your DISCOM bills you only for the net units consumed (Import minus Export).

What is the typical ROI payback period for residential solar in India?

With the PM Surya Ghar subsidy, the net out-of-pocket cost for a 3 kW solar system is roughly Rs. 70,000 to Rs. 90,000. Generating Rs. 30,000 worth of free power annually, the system pays for itself in 2.5 to 3 years, followed by 22+ years of free power.

Does a grid-tied solar system work during power outages?

No. Standard grid-tied solar systems automatically shut down during a power cut for safety reasons (anti-islanding) to protect utility workers repairing the lines. To run appliances during power outages, you need a hybrid solar system with battery backup.

About This Calculator

Target Audience: Property owners exploring solar ROI, panel sizing & government subsidy benefits

What Does This Calculator Do?

This calculator estimates the required capacity (LPD - Liters Per Day) and monthly/yearly electricity bill savings after installing a domestic solar water heater.

How to Use It

  1. Family Size: Enter the number of people.
  2. Geyser Capacity: Select typical electric geyser power rating (kW) and usage time (hours).
  3. Grid Tariff: Enter your domestic tariff rate per unit.

The Logic Explained Simply

  • The Concept: Water heating accounts for 15-20% of domestic power bills. Solar water heaters use thermal collectors to heat water, entirely replacing electric geysers. Many states also offer a flat rebate on electricity bills for installing them.
  • The Formula:
  • Recomended LPD = Family Members * 30 to 40 Liters/person
  • Geyser Units Saved = Geyser kW * Run Hours * 30 days
  • Financial Savings = Units Saved * Tariff + DISCOM Monthly Rebate (typically Rs. 50)

Real-World Calculation Breakdown

For a family of 4 using a 3 kW geyser for 1.5 hours daily with a Rs. 7/unit tariff:

  1. Recomended Sizing: 4 * 35L = 140 LPD -> Recomended 150 LPD system.
  2. Energy Saved Monthly: 3 kW * 1.5 hours * 30 days = 135 units.
  3. Tariff Savings: 135 units * Rs. 7 = Rs. 945.
  4. Total Monthly Benefit: Rs. 945 savings + Rs. 50 BESCOM rebate = Rs. 995.

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