How to Choose Solar PV Modules?

Start With the System Not the Module

A module is only correct in the context of the inverter and battery it feeds. Fix the system voltage and the inverter input range first, then choose a module whose open-circuit voltage and string length fit inside that range. Choosing a panel because it has the highest wattage on the datasheet is how arrays end up outside the MPPT window.

Mono and Poly Are a Space Decision

Monocrystalline modules give more watts per square metre, so they win where roof area is the binding constraint. Polycrystalline modules cost less per watt and make sense on ground mounts where there is room to spread the array. Both are supplied in blue or black, and the electrical behaviour of the system does not change with the choice.

Read the Degradation Clause Not the Warranty Length

A twenty-five year warranty is only meaningful together with the output it guarantees at the end of that term. Check the guaranteed percentage of rated power, because that number is what determines the array size you need in year twenty, not the number on the box today.

PID Salt and Ammonia Resistance Matter By Site

PID resistance protects output where modules sit at high system voltage in humid conditions. Salt and ammonia resistance matters on coastal installations and near livestock buildings. On an inland domestic roof neither will change much, so do not pay for a specification the site does not need.

Match the Module to the Mounting

Module weight and frame dimensions decide the rail spacing and the clamp positions on the mounting structure. Confirm the module before the bracket is drawn, otherwise the structure has to be adapted on site with holes that were not in the design.

Check the Cable and Connector Side

Every module choice implies a string current, and the string current sets the PV cable cross section. Single-core 4mm2 and 6mm2 cable covers most residential arrays, and MC4 connectors rated for the array voltage should be specified in the same order rather than sourced locally.

What to Send a Supplier

Give the supplier the roof or ground area, the inverter model or the system voltage you intend, the daily kWh you need and the site conditions. That is enough for a module choice and a string layout to be proposed, and it avoids two rounds of revisions.