TOPCon or mono PERC? Do the payback sum before you pay the premium.

The quote says TOPCon. What are you paying for?

More Bengaluru quotes now list TOPCon panels, often at a higher price per kW than mono PERC. Both are silicon panels. TOPCon cells are built on n-type silicon with an extra passivation layer, and PERC cells are usually p-type. The technical details matter less to you than three numbers on the datasheet, and whether those numbers add up to more units from your roof.

This is not a verdict for either technology. It is a way to check any quote, from any installer, against your own roof.

Three datasheet numbers to compare.

• Temperature coefficient of power. Panels lose output as they heat up. Bengaluru is milder than many Indian cities, but a panel on a terrace in March can still run far hotter than the 25°C used for its rating. A lower (less negative) coefficient means less loss in the afternoon. Datasheets for TOPCon panels often list a smaller figure than PERC panels, but compare the two sheets you actually have.
• First-year degradation and yearly degradation after that. Datasheets state how much output the panel is guaranteed to lose in year one and each year after. Typical sheets show a lower first-year loss for TOPCon. Again, read the exact figures.
• Guaranteed output at year 25 or 30. This is the performance warranty, and it is the figure that turns the other two into rupees. Ask whether the warranty is backed by the manufacturer or only by the installer. Our guide to solar warranties explains the difference.

Efficiency in percent also appears on the sheet. A higher efficiency means more watts per square metre, which helps if your terrace is small. If you have space to spare, it matters less.

A simple payback test.

Every figure below is illustrative. Replace them with the numbers from your quote and your own BESCOM bill.

• System: 5 kW. Assumed yield: 1,350 units per kW per year, so 6,750 units a year.
• Value of a unit you generate: Rs 7 (a placeholder; use the rate on your bill).
• Yearly value: 6,750 × 7 = Rs 47,250.

Suppose the datasheets suggest the TOPCon option delivers about 3% more energy over its life. That is Rs 1,418 a year. If the premium on your quote is Rs 10,000, it pays back in about seven years. If it is Rs 40,000, it would take nearly 28 years, which is longer than the warranty. Change the 3% to 1.5% and the premium needs to be half as large to make sense. The test works in either direction.

Ask the installer to show you the 3% from the datasheets, not from the brochure.

Two checks that matter more than the cell type.

• Subsidy eligibility. If you want the PM Surya Ghar subsidy, the panels must meet the domestic content requirement, and the model has to be on the approved list. A cheaper or newer technology that fails this rule costs you the subsidy. See DCR panels under PM Surya Ghar.
• Who stands behind the warranty. A 30-year output guarantee from a manufacturer with no service presence in India is hard to claim. Ask how a claim works in practice.

Do not ignore shade and layout.

A panel upgrade will not rescue a poor layout. A few rows in the shadow of your water tank can cost more than any difference between cell types. Settle shading and terrace layout first, then compare panels.

The short version.

Get both options quoted on the same system size. Compare temperature coefficient, first-year and yearly degradation, and year-25 guaranteed output from the actual datasheets. Turn the difference into units and rupees, divide the premium by the yearly gain, and compare the answer with the warranty period. Check subsidy eligibility and who backs the warranty before you decide.