How to choose solar panels without getting lost in the brochure.

There is no single best solar panel for every roof

A compact high-efficiency panel can be valuable where usable roof space is tight. A larger, lower-cost module may work just as well on an open roof. A coastal home may place more weight on corrosion testing and local warranty support. A shaded or split roof can make array layout and inverter design more important than a small efficiency difference.

The useful question is: which exact panel model produces the best complete design for this roof, household and budget? Compare the finished system rather than ranking logos.

Use EECA’s approved list as a starting filter

EECA now maintains a voluntary approved list for residential solar panels, inverters and batteries. Products on the list have been assessed against its technical specification for efficiency and demand flexibility. For panels, the broader specification covers durability tests for wind, hail, exposure and temperature as well as safety. [1]

The programme is voluntary and the list continues to grow, so absence is not automatically proof of a poor panel. Presence is useful independent evidence that the submitted model met EECA's published requirements at assessment. Always match the exact model number; a brand may sell many different ranges.

Panel watts and panel efficiency are related, but not interchangeable

Watts describe a panel's rated output under standard test conditions. Efficiency describes how much of the light falling on its area is converted into electrical output under those conditions. A 500 W panel is not automatically more efficient than a 450 W panel; it may simply be larger.

EECA's example of 13 × 400 W panels totals 5,200 W, or 5.2 kW. The multiplication is simple; deciding whether 5.2 kW suits the home requires the power-use and roof analysis covered in our solar system sizing guide. [2]

Dimensions can matter more than a small efficiency gain

Obtain the proposed layout with each panel drawn to scale. Roof edges, ridges, valleys, vents, skylights, aerials, plumbing penetrations and access paths can prevent a neat rectangle from fitting. Two models with similar power may have different length, width and weight, changing how many fit on the useful roof plane.

Higher efficiency is most valuable when roof area is the constraint. Where space is abundant, compare the extra energy and price of the entire array. Do not pay a premium for an efficiency percentage without seeing what it changes in total kW and annual kWh.

Temperature coefficient explains what heat does to output

Panel power is rated under laboratory conditions. As cell temperature rises above the test reference, output falls. The datasheet's power temperature coefficient states the approximate percentage change per degree Celsius. A value closer to zero indicates less loss as the panel gets hotter.

This coefficient is useful for comparing otherwise similar models, but it is not an annual yield prediction. Roof clearance, airflow, local weather, array orientation, inverter behaviour and shade all affect real production. Ask the installer to use the quoted model in the generation software rather than applying one generic panel profile.

Claims about “better low-light performance” also need context. Every array generates less in weak light. Compare an installer’s annual or monthly kWh model and assumptions instead of accepting an isolated brochure phrase.

Cell technology labels are not a shortcut to the right panel

Residential quotes may mention monocrystalline silicon, P-type or N-type cells, TOPCon, heterojunction, back-contact cells, half-cut cells, shingled cells or bifacial modules. These describe aspects of cell design and module construction. They can influence efficiency, degradation, shade behaviour, appearance and price, but the label alone does not establish whole-system value.

Bifacial panels can collect light from the rear as well as the front. The extra yield depends on rear exposure, surface reflectivity, mounting height and shading behind the module. A panel mounted close to an opaque residential roof may not receive the same rear-side benefit shown for an elevated or ground-mounted array. Require any bifacial gain included in a savings model to be stated.

Construction, weight and mechanical ratings belong in the roof decision

Panels may use a glass-and-backsheet or dual-glass construction, different frame depths and different mounting zones. These choices affect weight, handling, stiffness and how the module is fixed. The roof structure, racking and fasteners must be designed as a system.

EECA's approved-list criteria include panel durability for wind, hail, exposure and temperature. WorkSafe points to AS/NZS 5033 for PV-panel installations. MBIE's consent exemptions also distinguish large arrays and higher wind speeds; arrays over 40 m² or where design wind speeds exceed 44 m/s need engineering conditions met to use the relevant exemption. [1] [3] [4]

For Canterbury long-run roofs, the fixing method and roof condition deserve their own review. See our Colorsteel and metal-roof guide.

Product and performance warranties cover different promises

EECA says well-maintained panels can be expected to last 25–30 years, with output declining around 0.5% per year. The exact quoted model may promise a different first-year loss and annual degradation schedule. Check the model-specific warranty document rather than a general website claim. [2] [5]

Degradation changes output slowly, not all at once

A linear performance warranty often permits a larger reduction in year one and smaller annual reductions after that. Compare the guaranteed percentage at a common year, not simply the warranty length. A 30-year term with a lower end guarantee is not automatically stronger than a shorter term with a higher guaranteed output.

The warranted curve is a minimum contractual threshold, not a prediction that every panel will follow exactly. To compare financial forecasts, ask whether the generation model includes degradation and what annual percentage it uses.

“Tier 1” does not replace a model-specific check

Tier language is widely used as shorthand for manufacturer scale or financeability. It is not a complete test of the panel on your quote, the factory batch, local support, installer workmanship or roof design. A panel does not become suitable for a Canterbury roof because a salesperson calls its manufacturer Tier 1.

Use the label as one piece of background at most. Give more weight to the exact model's EECA status, datasheet, certifications, warranty terms, New Zealand supplier, installer track record and the site-specific design.

A bankability label describes a manufacturer from one angle. You are buying a particular model installed on a particular roof.

The panel and inverter must be designed together

The installer must check array voltage and current across expected temperatures, string arrangement, inverter input limits and the total DC-to-AC ratio. A high-watt panel is not useful if the proposed string exceeds equipment limits or creates a poor roof layout.

EECA says having around 20% more panel capacity than inverter capacity tends to give good value for many New Zealand homes. This deliberate overpaneling can increase generation in weaker conditions while clipping some peak output. The actual combination must remain within manufacturer and network requirements. [2]

If shade affects part of the roof, ask the installer to model it and explain the proposed string layout, optimiser or microinverter approach. Equipment should solve a measured design issue, not be added as a generic upgrade.

Installation quality can outweigh small panel differences

WorkSafe recommends a registered electrician for PV work and points to AS/NZS 5033 for panels. EECA's installer criteria call for a site-specific design, shading and orientation assessment, compatible equipment, roof-condition check, reasonable performance claims, compliant mounting, preserved weathertightness, commissioning and after-sales support. [3] [6]

Ask who designs the system, who performs the electrical work, who installs the roof fixings and who remains responsible if water enters later. A premium panel fitted badly is still a poor purchase.

Solar panel quote comparison checklist

Compare installed system price and forecast output alongside these specifications. A cheaper panel can be good value in a sound design. A more expensive panel needs to earn its premium through additional usable generation, better roof fit, stronger support or lower risk.