Abstract
With rising electricity costs and increasing interest in renewable energy, rooftop solar installations are becoming more common in urban households. This analysis evaluates whether installing a small residential solar system in Bangalore is financially viable by estimating electricity generation, consumption offset, and earnings from feeding excess power back to the grid.
Motivation
Return on Investment (ROI) is the most important factor when deciding whether to install rooftop solar. One major concern in Bangalore is that the city experiences approximately three months of reduced sunlight during the monsoon season. Therefore, understanding real-world solar generation and financial returns is essential before making the investment.
Electricity Consumption
My monthly electricity bill usually ranges between ₹2,500 and ₹3,000. Taking an average bill of ₹2,750 and assuming a higher tariff rate of ₹7.50 per unit:
Units consumed per month = ₹2,750 / ₹7.50 ≈ 367 units
This represents the approximate monthly energy consumption of the household.
Solar Generation Estimate
According to installers, a 1 kW solar system can generate a minimum of 4 units per day. To account for better sunny days and occasional absence from home, I assumed an average generation of 6 units per day.
For a 3 kW solar system:
Daily generation = 3 kW × 6 units = 18 units
Monthly generation = 18 × 30 = 540 units
Excess Solar Power
Since the household consumption is approximately 367 units per month, the remaining electricity becomes surplus and can be exported to the grid.
Excess units = 540 − 367 = 173 units (approximately 180 units)
Earnings from Grid Export
Under the net metering policy, BESCOM pays approximately ₹3 per unit for excess electricity exported to the grid.
Monthly earnings = 180 units × ₹3 = ₹540
Total Monthly Savings
Savings come from two components:
- Electricity bill reduction
- Earnings from excess power exported to the grid
Electricity savings ≈ ₹2,700 Grid export earnings ≈ ₹540
Total monthly savings = ₹3,240
Total yearly savings = ₹3,240 × 12 = ₹38,880
ROI Calculation
Assuming the installation cost of a 3 kW rooftop solar system is approximately ₹2.5 lakhs:
Payback period = ₹2,50,000 / ₹38,880 ≈ 6.4 years
Therefore, the estimated ROI period is around 5–6 years, depending on sunlight availability, electricity tariff changes, and system efficiency.
Conclusion
Installing a rooftop solar system in Bangalore can be financially viable even with seasonal sunlight variations. With consistent electricity savings and additional income from grid export, a household solar system can recover its installation cost in approximately six years. After the payback period, the electricity generated essentially becomes free energy for the remainder of the system's lifespan.