Panels, efficiency and quality tiers

More watts can mean more efficiency, more area, or both

Panel ratings are in watts: 300 W is 0.300 kW and 645 W is 0.645 kW. Comparing those numbers alone does not prove that the newer panel occupies the same roof area. Compare length, width and efficiency for the actual models.

Illustrative calculation: a 2 m2 panel at 20% efficiency under 1,000 W/m2 test irradiance rates about 400 W. At 23% efficiency, the same area rates about 460 W. Better efficiency helps where roof space is scarce, but mounting gaps and access routes also use space.

Same area, test conditions
2 m2 x 1,000 W/m2 x 20% = 400 W
2 m2 x 1,000 W/m2 x 23% = 460 W

Do newer panels start earlier and stop later?

Some modules convert weak morning, late-afternoon and cloudy light more effectively, so they can add usable energy at the edges of the day. But panels do not have one universal activation switch, and high nameplate wattage alone does not guarantee a longer generating day.

Usable AC output also depends on the inverter's start voltage and MPPT operating range, string or microinverter design, module temperature, shading and roof direction. Ask for a modeled annual yield using the actual panel and inverter combination. Compare low-irradiance curves and temperature coefficients rather than relying only on an 'earlier activation' claim.

• See how system size and net yield become total production

Tier 1, Tier 2 and Tier 3

BloombergNEF's Tier 1 classification concerns manufacturer acceptance in financed projects; it is not a certification of an individual panel's quality. BNEF explicitly does not publish Tier 2 or Tier 3 lists. A seller using those labels should explain its own definition.

A whole solar installation cannot be meaningfully graded by a panel manufacturer's tier alone. Ask about exact equipment, certifications, installation workmanship, local support and the enforceable warranty.

• Compare module dimensions, temperature coefficient and degradation terms.
• Distinguish a product-defect warranty from a long-term power-performance warranty.
• Confirm authorized supply, serial numbers and who will handle a claim.