For installed cost, retain the itemised quote showing modules, inverter, structure, protection, cabling, metering, civil work, taxes and excluded work. For generation, use the written design yield and loss assumptions, then compare them with shade and usable-roof evidence. For bill savings, separate energy consumed while the system generates from energy exported; apply the current tariff and DISCOM treatment to each rather than multiplying every unit by one retail rate.
Place financing on its own cash-flow line: down payment, interest, fees and payment dates. Add realistic inverter/service downtime and replacement reserves without pretending to know the exact future price. The result should show annual cash flows and cumulative balance, not only “system price divided by one year’s bill.”