Bill savings over time with a yearly price rise and panel degradation. Every preset value is invented. A design aid, not a forecast or financial advice. Decimal commas are accepted; write 1000, not 1.000.
Model: saving in year t = output x (1 - degradation)^(t - 1) x price x (1 + escalation)^(t - 1). All output is valued at one price; exports, fixed charges and tariff structure are ignored. Year-end flows, nominal money, no tax. The yearly change is (1 + escalation) x (1 - degradation) - 1.
Compound yearly rate between two prices, for example two annual averages from a regulator table. Past rates are not a forecast.