Solar panel buying guide for businesses: mono PERC, TOPCon and bifacial compared

Rooftop and ground-mounted solar is now one of the fastest paybacks available to factories, warehouses, schools and hospitals. The panels are the biggest single item in the project, and they have to perform for 25 years or more. Choosing them on price per watt alone is a common mistake.

This guide explains the main panel technologies, how to read a datasheet, and what paperwork to insist on.

The main panel technologies

Monocrystalline PERC

PERC (passivated emitter and rear cell) panels have been the workhorse of commercial solar for years. They are mature, widely available and well understood by installers. Newer technologies have begun to replace them in many markets, but PERC panels remain a valid budget choice.

TOPCon

TOPCon (tunnel oxide passivated contact) is an n-type cell technology that has become mainstream. Compared with PERC, TOPCon panels generally offer higher efficiency, a lower temperature coefficient (they lose less output in hot weather) and lower degradation over time. For hot climates such as most of India, the temperature behaviour is a real advantage.

Heterojunction (HJT)

HJT panels combine crystalline and thin-film silicon layers. They offer very good efficiency and temperature performance but are typically more expensive and produced by fewer manufacturers.

Bifacial panels

Bifacial is a design feature rather than a cell type: the panel collects light from both front and back, usually with a glass back sheet. The extra rear-side gain depends on what is under the panels. Over white roofs, light-coloured ground or elevated structures, it can be meaningful. On a dark roof with panels mounted close to the surface, the gain is small. Many TOPCon panels are now sold as bifacial.

The datasheet numbers that matter

• Rated power (Wp): output under standard test conditions. Compare panels of similar power class.
• Efficiency (%): output per unit area. Higher efficiency matters most when roof space is limited.
• Power tolerance: a positive-only tolerance (for example 0 to +5 W) means you never receive less than the rated power.
• Temperature coefficient of Pmax (%/°C): how much output falls for each degree above 25 °C cell temperature. A smaller number is better, especially in hot regions.
• Degradation: first-year degradation and annual degradation after that. This drives how much energy the panel delivers over its life.
• Dimensions and weight: matter for structure design and roof loading.
• Mechanical load rating: wind and snow load capacity in pascals.

Warranties

Panels carry two separate warranties:

• Product warranty, covering defects in materials and workmanship, often 10 to 15 years or more.
• Performance warranty, guaranteeing a minimum percentage of rated power after a set number of years, often 25 to 30.

A warranty is only as strong as the company behind it. Check how long the manufacturer has been in business, whether it has a local presence to handle claims, and whether the warranty is backed by insurance.

Certifications and approvals

• IEC 61215 (design qualification) and IEC 61730 (safety) are the basic international certifications.
• In India, solar modules fall under BIS compulsory registration, and many government-linked and subsidised projects require modules from the ALMM (Approved List of Models and Manufacturers) published by MNRE. If your project needs subsidy, net metering approval or a government tender, confirm the ALMM requirement before you choose a panel.
• For export markets, buyers may ask for additional certifications or factory audits.

Matching panels to the rest of the system

Panels have to work with the inverter and structure:

• Check the panel's voltage and current against the inverter's input range when designing strings.
• Bifacial panels need appropriate mounting height and back-side clearance.
• Larger, heavier modules may need stronger structures and more handling care on site.

Our guide to on-grid, off-grid and hybrid inverters explains the inverter side.

Questions to ask suppliers

1. Which cell technology and which power class?
2. Are these panels BIS registered and, if needed, ALMM listed?
3. Can you share the datasheet, IEC certificates and the warranty document?
4. What is the flash test report for this lot?
5. What are the packing, palletisation and freight terms?
6. Who handles warranty claims locally?

Checks on delivery

• Match serial numbers on the panels with the flash test report.
• Inspect for cracked glass, damaged frames and bent junction box cables.
• For large orders, consider electroluminescence (EL) testing on a sample to detect micro-cracks from transport.

Frequently asked questions

Is TOPCon worth the extra cost over PERC?

In hot climates and where roof space is limited, TOPCon's higher efficiency, better temperature coefficient and lower degradation usually produce more energy over the panel's life. Compare the cost per kWh generated over 25 years, not just the price per watt.

Do bifacial panels help on a rooftop?

Only if light reaches the back of the panels. On white or reflective roofs with raised mounting, the gain can be useful. On dark roofs with low mounting, it is small.

What is ALMM and do I need it?

ALMM is MNRE's Approved List of Models and Manufacturers. Many government schemes, subsidised projects and net-metering programmes require ALMM-listed modules. Check your project's requirements before you choose.

How long do solar panels last?

Good panels typically carry 25 to 30-year performance warranties and continue producing beyond that at reduced output. Actual life depends on quality, installation and climate.

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