Return on investment (ROI) is the single most useful number for deciding whether solar makes financial sense for your property. Here's how it's calculated and what factors influence it.
The Basic ROI Formula
At its simplest, solar ROI compares your net investment (system cost minus subsidy) against the cumulative savings generated over the system's lifetime, typically calculated over 25 years to match panel warranty periods. Payback period is the point at which cumulative savings equal your net investment.
Key Factors That Affect ROI
System cost and subsidy: A lower net cost after subsidy directly improves ROI. Electricity tariff: Higher tariffs mean each unit of solar generation is worth more in avoided grid cost. Tariff escalation: Since grid tariffs tend to rise over time, future savings are typically worth more than year-one savings, which compounds your ROI over the system's lifetime. Generation losses: Shading, soiling, inverter efficiency and panel degradation all reduce actual generation compared to theoretical maximum, so accurate assumptions matter for a realistic ROI estimate.
Why Rough Estimates Can Mislead
Many online calculators use a single flat "performance ratio" assumption that doesn't account for your specific roof's shading, local weather patterns, or realistic degradation over 25 years. This can produce ROI estimates that look better on paper than what actually happens once the system is installed.
Our Calculator Uses Granular, Real-World Assumptions
Rather than one flat efficiency number, our solar savings calculator factors in inverter efficiency, shading loss, soiling loss, wiring loss and temperature derating separately, along with your state's actual peak sun hours, current subsidy slabs, and net metering export limits. This gives a more realistic estimate of system size, cost, savings and payback period specific to your situation.
Try It With Your Own Numbers
Enter your monthly electricity bill or units consumed, and the calculator will show you an estimated system size, 25-year generation and savings projection, and payback period, all in a few seconds. For a proposal based on an actual site survey rather than an estimate, contact our team.