The useful starting point
The best panel on a laboratory specification sheet may not produce the best installation on your roof. Compare the layout and complete system, then check the exact model.
Begin with the space available
A panel’s wattage tells you its rated output under standard test conditions. It does not tell you how many will fit around your roof’s edges, vents, windows or shading. A slightly lower-wattage model may allow a more useful layout if its dimensions fit better.
Ask for a drawing that identifies the exact panel count and dimensions. Compare predicted annual generation for the finished array, not just the biggest number on an individual module.
Use model documents instead of brand-wide claims
Manufacturers sell different ranges and generations. A warranty or efficiency figure for one model is not automatically true of everything carrying the same badge.
| Research example | What to inspect |
|---|---|
| REC Alpha Pure-RX | Exact wattage variant, physical dimensions, electrical characteristics and the conditions of the offered warranty |
| LONGi Hi-MO X10 | Which module format and variant is offered, its roof fit and the relevant regional documentation |
The manufacturer links below are starting points, not a tested ranking or a statement that either range is in stock with your installer. Confirm the model code and datasheet version on the quotation.
Compare these measurements fairly
- Rated power and area: compare how much roof space the proposed output requires.
- Temperature behaviour: check the power temperature coefficient using the same units.
- Mechanical loading: confirm the mounting design suits the site rather than treating a panel rating as a complete roof assessment.
- Electrical compatibility: the inverter designer needs string voltages and currents, not just total wattage.
- Appearance: ask to see the proposed frame and backsheet finish if visual consistency matters.
Read both warranties
The product warranty concerns defects in the equipment. A performance warranty concerns how much output is retained under defined conditions. They are not the same promise, and neither automatically covers all labour, scaffolding or removal costs.
Ask who you contact if the installer is unavailable, what registration is required and whether any enhanced cover depends on using an approved installation route. Keep the applicable documents with your handover pack.
Decide whether an upgrade earns its cost
Ask the installer to model the standard and upgraded panel on the same roof with the same assumptions. Compare the extra annual generation, the part you would use directly and the part exported. Then compare that value with the extra installed price.
A higher-efficiency module can be useful on a constrained roof. On another property, spending on a better layout, shading solution or necessary roof work may be more valuable. Use the solar tool for a first calculation and the cost guide to compare the complete proposal.
Published information supports your research. Your installer should confirm the exact product, suitability, scope and terms for your property.
Suggest a correction ↗Your next useful step
Put the information to work.
Take the questions that matter to your project, explore the numbers and decide what to ask next.