Dissertation

|1.4 Solar Energy Conversion|
needed in the petroleum and chemical industries. Therefore, its handling is possible on a multimegaton
scale.
Nowadays, industrial hydrogen production is mainly accomplished by steam reforming of natural
gas (48%). It is less often produced from more energy-intensive energy conversion methods like
the electrolysis of water (high overpotential) which accounts for 4% of the hydrogen production. [9]
In this context the investigation of light-driven water cleavage with formation of oxygen and
particular hydrogen provided very promising results.
[4, 12]
1.4 Solar Energy Conversion
The most desirable and seminal but almost untapped energy source appears to be the sun. Solar
average energy uptake of the earth surface (3.9⋅10 24 J) is almost four orders of magnitude higher
than the average energy consumption of mankind (4.7⋅10 20 J). [4, 11, 13] However, the energy density
of the sunlight is very low, compared to fossil fuels. This makes it unattractive because large
collector areas are necessary (the average flux density of the sunlight on earth, solar constant, is
1.37 kW/m 2 which would refer to 0.15 l of gasoline production in one hour at an energy conversion
efficiency of η = 100% whereat a car uses ∼7.0 l to drive 100 km in that time). Another fact is, that
sunlight, filtered through the earth atmosphere is still very polychromatic (compare figure 7).
Figure 7: Solar radiation spectrum at sea level with assigned atmospheric absorption bands. [13] |8|