#Solar Spectrum and PV Performance: Wavelength Effects

The AM1.5G standard spectrum (ASTM G173-03) is the international reference against which every commercial solar panel is rated. It describes the distribution of solar energy arriving at Earth's surface at a specific air mass, tilt angle, and atmospheric condition - and it matters because silicon responds very differently to different wavelengths of light.

UV (280 - 400 nm) contributes about 5% of total AM1.5G irradiance but drives only 3 - 4% of silicon PV output. Visible light (400 - 700 nm) contributes roughly 42% of irradiance and the bulk of useful current. Near-infrared (700 - 1,100 nm) accounts for nearly half of total irradiance and represents silicon's peak efficiency zone, where external quantum efficiency reaches 80 - 90%.

This spectral mismatch is why tools like EC JRC PVGIS apply spectral correction factors to yield predictions. A system in northern Norway sees a different spectral distribution than one in southern Spain - richer in red and NIR in high-latitude winter conditions - and silicon responds differently to those differences. For perovskite-silicon tandem cells, spectral management becomes even more critical: the two stacked bandgaps compete for different wavelength windows, and getting that allocation right is partly why the architecture has reached 34.85% certified efficiency (LONGi, NREL, 2025).

These articles explain the spectral physics and their practical consequences for real-world system performance.

Seasonal spectrum shifts add a layer most yield models undervalue. Winter sun travels through more atmosphere, shifting the spectrum redward and boosting NIR-rich diffuse light - conditions where bifacial panels gain a measurable edge. Bifacial modules capture reflected albedo from ground and snow on the rear face, and that rear-side gain averages 5 - 15% in high-albedo environments (IEA PVPS Task 13, 2021), partially compensating for lower winter irradiance totals.