About the Energy: Solar vs Grid Calculator

Installing solar panels is a long-term investment that can significantly reduce electricity bills and provide energy independence — but whether it makes financial sense depends on your location, system size, local electricity prices, available incentives, and how you handle excess generation. This calculator models the complete financial picture of solar adoption versus continuing to rely on grid electricity, so you can determine your break-even point and long-term savings with confidence.

How the calculation works

The calculator compares two scenarios over a 25-year period (the typical warranty life of solar panels). In the solar scenario, it accounts for the upfront system cost, reduced by any government tax credits or utility rebates, then models annual electricity generation based on your system size and local peak sun hours, reduced by the panel degradation rate over time. It also factors in any income from feed-in tariffs or net metering credits for excess generation. In the grid scenario, it models your current electricity bill growing at the annual rate increase you specify. The net present value calculation uses your chosen discount rate to express future savings in today's money.

Understanding peak sun hours

Peak sun hours are not the same as daylight hours. They represent the number of hours per day when solar irradiance averages 1,000 watts per square metre — the standard condition used to rate panel output. A location receiving 5 peak sun hours will generate twice the electricity from the same panel as a location receiving 2.5 peak sun hours. Globally, values range from around 2 hours per day in northern European locations like the UK to 6–7 hours in desert regions like the Middle East, Australia's interior, or the US Southwest.

Key factors that affect solar ROI

• System cost per watt: Prices have fallen dramatically over the past decade and continue to decline. Getting multiple installer quotes is important as prices vary significantly.
• Government incentives: Many governments offer tax credits, grants, or accelerated depreciation for solar installations. These can cover 20–50% of system cost in some markets.
• Grid electricity price: The higher your current electricity rate, the faster solar pays back. Markets with expensive electricity (Germany, Australia, UK) typically see faster payback than those with cheap grid power.
• Grid price escalation: Electricity prices have risen faster than inflation in most markets over the past 20 years. Locking in solar generation costs now provides a hedge against future price increases.
• Feed-in / net metering rate: If you generate more than you consume, the rate you receive for exported electricity significantly affects the economics, particularly for larger systems.
• Panel degradation: Quality panels degrade at about 0.5% per year, meaning a panel producing 400W today will produce around 390W in 5 years. Budget panels may degrade faster.

Common mistakes when evaluating solar

• Using manufacturer peak output ratings without accounting for real-world efficiency losses from temperature, shading, inverter losses, and wiring.
• Ignoring the replacement cost of the inverter, which typically needs replacing after 10–15 years at a cost of several hundred to a few thousand.
• Assuming your consumption patterns won't change — adding an EV or heat pump after installation significantly improves solar economics by absorbing more self-generated power.
• Not considering roof orientation and shading — south-facing roofs (in the northern hemisphere) with no shading can generate 20–30% more than east/west-facing installations.

Is solar right for you?

Solar typically makes strong financial sense if you have a suitable roof, pay above-average electricity rates, live in a reasonably sunny location, and plan to stay in your home for 7+ years. The combination of falling installation costs, rising electricity prices, and improved panel efficiency means that payback periods of 5–10 years are now common in many global markets, followed by 15+ years of near-free electricity.