Panel marketing sells efficiency percentages. What you are actually buying is watts per square metre of your roof, degradation over twenty-five years, and behaviour at high temperature. Those three, in that order.
When to pay for TOPCon
If your roof can physically hold the array you need, the extra efficiency changes nothing about your bill — you would have generated the same units with more modules. It matters when area is the binding constraint: a smaller roof that must reach 5 kW, or a roof with obstructions carving out usable space. There, higher efficiency per module is the only way to the target.
When bifacial is worth it
Bifacial modules collect reflected light on the rear face. On a dark roof with the module sitting close to the surface, there is very little to collect. On a white terrace, an elevated carport or a ground mount over light gravel, the rear-side gain is real and measurable. Ask what the mounting surface is before agreeing to the premium.
The right panel is the cheapest one that fits your roof, your climate and twenty-five years. Usually that is not the one on the front of the brochure.
Check the degradation warranty, not the peak rating
Two modules with identical day-one output can differ by several percent of retained capacity in year twenty-five. That difference is worth more than the rating gap you are comparing.
What to take away
Meera Iyer
Systems engineering
Specifies panels, inverters and battery blocks for RePrime systems, and tests what the datasheets do not mention.
Run these numbers against your own bill
The calculator uses state-wise generation data and the current subsidy slabs. Two inputs, one estimate, no call required.
