Solar quotes are usually compared on two numbers: system size and price. Both are easy to read and neither tells you what the system will produce in year fifteen.
A rooftop system is a twenty-five year purchase. The panel that looks like a bargain on installation day can quietly hand back a good deal of that saving over its life, and the mechanism is not obvious unless you know where to look.
Degradation is the number nobody quotes
Every panel loses a little output each year. The rate is what separates the tiers. Panels from established tier-one manufacturers typically degrade in the region of 0.3 to 0.5 per cent a year, while cheap imports commonly run at 0.8 to 1.5 per cent — sometimes worse.
Compounded across a couple of decades that gap is large. It is the difference between a panel still producing close to nine-tenths of its original output late in life, and one that has lost a fifth of its capacity before its warranty even expires. You paid for the same nameplate wattage; you did not buy the same electricity.
There are two warranties, and people conflate them
A product warranty covers the panel as an object — manufacturing defects, delamination, junction box failures, frame corrosion, glass. It typically runs ten to fifteen years.
A performance warranty is a separate promise about output: that the panel will still produce at least a stated percentage of its rating after twenty-five or thirty years. When a salesperson says twenty-five year warranty, it is worth asking which of the two they mean, because they are very different commitments.
- Product warranty: defects, typically 10-15 years
- Performance warranty: guaranteed output, typically 25-30 years
- Ask which one the quoted figure refers to
- Compare the guaranteed output at year 25, not just the headline
A warranty is only as good as the company behind it
A thirty-year promise from a manufacturer unlikely to exist in ten is not worth much. This is the strongest argument for sticking with established names, and it is a practical rather than a snobbish point — you want a company you can still claim from.
The Indian market is fortunate here. Manufacturers like Waaree, Adani, Vikram and Tata Power Solar have long track records domestically and meet the standards you would want, so choosing well-supported panels does not mean paying for imports. We stock Waaree and Adani among others for exactly this reason.
What to check before signing
The specification sheet answers most of this if you know which lines to read. Alongside efficiency, look at the annual degradation figure, the guaranteed output at year twenty-five, and the temperature coefficient — that last one matters in Kerala, because panels lose output as they heat up and a better coefficient holds performance through the hottest part of the day.
Certification is the floor, not the ceiling: panels should meet the relevant BIS and IEC standards. Ask for the actual datasheet rather than a brochure, and check that the model quoted is the model delivered.
- Annual degradation rate
- Guaranteed output at year 25
- Temperature coefficient
- Product and performance warranty terms, separately
- BIS and IEC certification for the exact model quoted
Where the saving is real
Cheaper panels are not always the wrong answer. If roof space is plentiful and the installation is a modest one, mid-tier panels can be perfectly sensible — you simply fit a couple more to reach the same output.
It is where roof space is limited that the premium earns itself, because you need every panel to work harder and keep working. And with rooftop subsidy tiered by capacity, the sums shift again — which is why we would rather show you the numbers for your roof and your bill than issue a blanket rule.
The short version
Compare degradation rates and the guaranteed year-twenty-five output, not just price per watt. Know which warranty you are being quoted. Prefer manufacturers likely to honour it. And remember that on a constrained roof, the cheaper panel is often the more expensive electricity.