Converting sunlight to electricity with solar cells has an efficiency of 15%. It
ID: 1775407 • Letter: C
Question
Converting sunlight to electricity with solar cells has an efficiency of 15%. It's possible to achieve a higher efficiency (though currently at higher cost) by using concentrated sunlight as the hot reservoir of a heat engine. Each dish in (Figure 1) concentrates sunlight on one side of a heat engine, producing a hot-reservoir temperature of 600 C . The cold reservoir, ambient air, is approximately 24 C. The actual working efficiency of this device is 30%.
Part A
What is the theoretical maximum efficiency?
Explanation / Answer
The maximum theoretical efficiency of a heat engine (which no engine ever attains) is equal to the temperature difference between the hot and cold ends divided by the temperature at the hot end, all expressed as absolute temperatures (in kelvins)
To convert from degrees Celsius to Kelvin, add 273.15.
The cold temperature:
T_C = 24 degC = 297.15 K
The hot temperature:
T_H = 600 degC = 873.15 K
The Carnot efficiency:
eff = 1 - (T_C / T_H) = 1 - (297.15 K / 873.15 K) = 0.6596
So the theoretical maximum efficiency is 65.96 %. or 66%