The Economic Competitiveness of Renewable Energy: Pathways to 100% Global Coverage

Chapter 6

PV Value Chain and Technology

6.1 Basics of Solar Radiation and Conversion in PV Cells

The solar spectrum outside the earth’s atmosphere has a power density of 1,300 W/m²; this is called the “solar constant”. The energy distribution for the photons (energy per wavelength and area) is shown in Fig 6-1 and resembles the radiation of a black body radiator with a temperature of 6,000 Kelvin – the temperature at the surface of our sun. The visible part of the spectrum from about 400 nm (ultraviolet) up to about 700 nm (red) is only a small part of the complete spectrum. The relationship between energy, frequency and wavelength for a photon is described by

with E the energy of the photon, h Planck’s constant, v the frequency, c the light velocity and λ the wavelength.

Figure 6.1 The solar spectrum above the earth’s atmosphere and at sea level.

Entering the atmosphere, some absorption of light takes place due to water vapor and other molecules and aerosols in the air. The absorption bands at the various wavelengths of H₂O (900, 1,100, 1,400, 1,900 and 2,500nm), O₂ (750nm), O₃ (250nm), and CO₂ (2,050nm) are indicated and result in the decrease of the yellow area down to the red one. This decreases the power of the sunlight which is coming from the outside of the atmosphere. If ...