Annual value = self-used kWh × avoided import price + exported kWh × export compensation. Simple payback = upfront cost ÷ annual value.
Self-consumption and export are different values
Solar generation can offset purchased electricity when it is used at the same time it is produced. Surplus generation may be exported, stored, curtailed, or compensated at a rate that differs from the retail price. This calculator separates those two portions so you do not automatically value every generated kilowatt-hour at the full import price.
Choose the right generation estimate
Annual production depends on location, roof direction and tilt, shading, weather, system size, inverter performance, and maintenance. Use a proposal based on your site and an explicitly stated system size. A generic annual kWh figure is useful for a scenario but not for a purchase decision.
What simple payback leaves out
The calculator divides the assumed upfront price by estimated annual energy value. It does not include panel degradation, inverter replacement, financing cost, maintenance, insurance, export-rule changes, tariff escalation, taxes, or the time value of money. It also assumes the entered self-consumption share and tariffs remain stable. For a detailed investment decision, compare a full cash-flow estimate and the exact local contract.
How to use this as a scenario tool
Calculate a conservative, central, and optimistic case using different generation and self-consumption assumptions. If the payback result changes sharply when self-consumption changes, a load-shifting plan or appropriately sized battery may deserve further analysis—but any battery should be modeled with its installed cost and round-trip losses. Do not assume storage is automatically financially beneficial.
Related tools and guides
For the basic relationship between watts and kWh, read Watts vs. kilowatt-hours. You can also use the Home Energy Planner to combine several devices in one estimate.