Sample interview questions: Can you explain the concept of thermodynamic limits in solar energy conversion?
Sample answer:
The thermodynamic limits of solar energy conversion define the maximum efficiency for converting sunlight into usable energy. These limits are set by the fundamental laws of thermodynamics and cannot be overcome with any technology.
Carnot Limit:
The Carnot limit is the theoretical maximum efficiency for converting heat into work. It states that the maximum possible efficiency of a heat engine is equal to:
η_Carnot = 1 – T_C / T_H
where:
T_C is the temperature of the cold reservoir
T_H is the temperature of the hot reservoir
For solar energy conversion, the cold reservoir is the ambient temperature, which is typically around 25°C. The hot reservoir is the temperature of the solar absorber, which can vary depending on the technology being used. However, even the most efficient solar absorbers can only reach temperatures of around 150°C.
This means that the Carnot limit for solar energy conversion is:
η_Carnot = 1 – 25°C / 150°C = 0.83
Shockley-Queisser Limit:
The Shockley-Queisser limit is a more specific limit for solar energy conversion that takes into account the bandgap of the semiconductor material being used. The bandgap is the energy difference between the valence band and the conduction band, and it determines the wavelength of light that can be absorbed by the semiconductor.
The Shockley-Queisser limit states that the maximum possible efficiency of a single-junction solar cell is:
η_SQ = 1 – (Eg / qV_OC)
where:
Eg is the bandgap of the semiconductor material
q is the elementary ch… Read full answer