Advanced 25-year financial projection, NPV, and ROI modeling.
We calculate the true value of future savings in today's money.
See your cost of generation per unit vs grid prices.
Accounts for 0.5% annual efficiency loss over 25 years.
precise roof area estimation based on capacity.
Solar Investment Analyser : Logic & Methodology
This tool goes beyond simple estimation by running a full 25-year financial simulation. Instead of just looking at "Year 1," it models the entire lifespan of the solar system to provide a professional-grade investment analysis.
We convert the monthly bill into units (kWh) and divide by 30 to find the daily average.
We assume an average of 4.5 hours of usable peak sunlight per day (standard for India).
We apply a 1.3 safety margin (approx. 77% efficiency) to account for DC-to-AC conversion, heat loss, and wiring.
We estimate required roof space by multiplying the system capacity by 100 sq.ft per kW.
Panels lose 0.5% efficiency annually. Year 1 = 100%, Year 25 = ~88% efficiency.
We deduct 1% of the initial system cost annually for cleaning and inverter upkeep.
Calculated at a retail rate per watt.
Calculated at standard residential rates.
Calculated at lower commercial/bulk rates.
The exact moment your total electricity savings equal the amount you paid for the system.
The value of future savings in today's money (accounting for inflation). Calculated at 8% discount rate.
The total percentage profit made over 25 years relative to the initial cost.
The cost to produce one unit of electricity from your roof. Allows direct comparison with grid rates.
Frequently Asked Questions (FAQs):
What is a solar calculator?
A solar calculator is a digital tool designed to estimate the potential savings, costs, and return on investment (ROI) of installing a rooftop solar system. It uses data such as your location, average monthly electricity bill, and roof space to determine the optimal system size and projected payback period.
How do I calculate how much solar power I need?
To calculate your solar needs manually, look at your electricity bill to find your average monthly kilowatt-hour (kWh) usage. Divide that by 30 to get your daily usage. However, the easiest method is to input your monthly bill amount into the Solartyx Solar Investment Calculator, which automatically factors in your local sun-peak hours to recommend the perfect system size.
How to calculate kW for solar?
The formula to calculate the required system size in kilowatts (kW) is: (Daily kWh Usage ÷ Average Peak Sun Hours) × 1.15 (efficiency buffer). For example, if you use 30 kWh a day and get 5 peak sun hours, you need a 6.9 kW system. Our calculator handles this math instantly to give you a precise recommendation.
What is the solar 120% rule?
The “120% Rule” is an electrical safety standard (NEC 705.12) regarding your home’s main breaker panel. It states that the sum of the main breaker rating and the solar inverter’s backfeed breaker cannot exceed 120% of the panel’s busbar rating. This rule determines the maximum amount of solar power you can safely feed back into your home’s existing electrical panel without an expensive upgrade.
How do I calculate the ROI of a solar rooftop investment?
To calculate ROI, take your Total Lifetime Savings (electricity bill savings + incentives) minus the Net System Cost, then divide that by the Net System Cost. A good solar investment calculator will project this over 20–25 years, factoring in rising electricity inflation rates to show you the true financial picture.
What is the average payback period calculated for a rooftop solar system?
The average solar payback period typically ranges between 6 to 9 years, depending on your local electricity rates and available government incentives. Using a calculator is essential because homes with higher electricity bills usually see a much faster break-even point.
Does the solar investment calculator factor in tax credits and incentives?
Yes, a robust calculator (like the one on Solartyx) should estimate the Federal Solar Investment Tax Credit (ITC) and other local rebates. These incentives can reduce the upfront cost of solar by 30% or more, significantly altering your investment outlook.
Is a 5kW or 10kW solar system a better investment?
Bigger isn’t always better; it depends on your consumption. A system that is too large (producing far more than you use) offers diminishing returns if your utility company has poor “Net Metering” buy-back rates. Our tool calculates the “sweet spot” where your investment yields the highest return based on your specific energy habits.
How much roof space do I need for a 5kW solar system?
A typical 5kW system requires approximately 300 to 350 square feet (about 28-35 square meters) of shadow-free roof space. This assumes the use of standard 400-watt residential panels.
Can the calculator determine if my roof direction is suitable for solar?
While basic calculators assume a South-facing roof (in the Northern Hemisphere) for maximum efficiency, advanced assessments consider East or West orientations. You can still achieve a high ROI with East/West roofs, though you may need slightly more panels to offset the lower efficiency.