This guide is based on public sources and stated assumptions, not a claim of hands-on product testing. Specifications, prices, incentives and energy tariffs can change by country and date.
Start with your actual electricity bill
Whether rooftop solar makes financial sense depends on your current tariff, the amount of electricity you use, your roof, your location, the price of installation and the rules that apply to exporting electricity. A general answer such as “solar always pays for itself in seven years” is not reliable.
Use twelve months of electricity consumption if you have it. Consider seasonal changes, future electric vehicle charging and whether your utility offers different peak and off-peak prices.
Estimate generation before looking at products
A useful first estimate requires your location, system size, roof orientation, roof tilt and losses from shading or equipment. The U.S. National Renewable Energy Laboratory provides the PVWatts calculator for estimating the electricity production of grid-connected photovoltaic systems.
Annual generation and household self-consumption are not the same thing. Solar generation can peak when no one is home, while evening demand may still require purchased power.
Evaluate full project cost and risks
Compare itemized quotes on the same assumptions. Include inverter replacement, monitoring, maintenance, financing terms, insurance considerations and any local fees.
Treat tax credits, rebates and export payments as location- and date-specific variables. Never assume an incentive described in an older article still exists.
- Annual bill before solar
- Estimated yearly generation
- Share used on site rather than exported
- Upfront installed cost and financing
- Maintenance and possible equipment replacement
- Savings under conservative, base and optimistic assumptions
The practical next step
Run an independent generation estimate, calculate savings using your own tariff and request several comparable installation quotes. If the quote assumes unusually high production or uninterrupted tariff increases, ask for the underlying evidence.