The concept of concentrating small temperature differentials in the environment for power generation is often considered impractical or inefficient due to fundamental thermodynamic principles.
According to the second law of thermodynamics, heat naturally flows from a region of higher temperature to a region of lower temperature until thermal equilibrium is reached. In order to extract useful work from heat, a temperature difference or gradient is required. The greater the temperature difference, the more efficient the conversion of heat into work. This principle is known as the Carnot efficiency, and it sets the theoretical limit for heat engine efficiency.
When dealing with small temperature differentials in the environment, the available energy is extremely low, leading to low efficiency and limited power output. The efficiency of converting heat into work decreases as the temperature difference decreases, making it challenging to extract a significant amount of useful work from these small differentials.
While it's true that some energy conversion technologies can utilize low-grade heat sources or waste heat, such as geothermal or industrial processes, these sources typically have higher temperature differentials compared to the ambient environment. They can provide enough energy to drive power generation systems with reasonable efficiency.
The concern about perpetual motion arises because perpetual motion machines violate the laws of thermodynamics, particularly the conservation of energy and the second law. These machines claim to produce more energy or work than is inputted, which is not possible according to our current understanding of physics.
In summary, while it's theoretically possible to extract some amount of useful work from small temperature differentials, the efficiency and power output would be extremely low. Practical power generation methods typically rely on larger temperature differences to achieve reasonable efficiency and significant power output.