Understanding the calculation
First-year production declines annually by the entered degradation. On-site use is production times its share, capped at annual consumption; the rest is exported. Savings equal avoided purchases plus exports at the manual price, minus maintenance. The balance starts at negative net investment and accumulates savings. Recovery is the first zero crossing, interpolated within the year; simple payback uses year-one savings and is shown only if recovery occurs within the horizon.
Annual net savings = on-site use × avoided price + exports × export price − maintenance. Net investment = installation − incentives.
Worked example
Fictional EUR example: installation 6,000, zero incentives, production 5,000 kWh/year, consumption 4,000, self-use 60%. On-site use is 3,000 kWh and exports 2,000. At 0.20 avoided price and 0.05 export price, minus 100 maintenance, net annual savings are 600. With no degradation, recovery is ten years and the year-15 balance is 3,000.
Assumptions and limits
No country-based irradiation estimate or production guarantee. Self-use is an annual assumption, not an hourly demand-match model. Prices and maintenance stay constant. Discounting, financing, taxes, replacements and batteries are excluded. Incentives and export prices are manual; no universal policy is assumed.
Questions about this tool
Is all production assumed self-consumed?
No. Only the entered share, capped at annual consumption. The remainder is exported at the manual price, possibly zero.