Stirling engine against solar panels

[Jarro]

Hello,
Since childhood, I have been wondering why it is not possible to make miniature electric motors with pistons and gas container covered with a very dark (meaning high absorption coefficient over a wide spectral width) material that would translate the energy of sunlight directly into electricity? In fact, only material and design features will significantly affect the converter efficiency when, as in the case of solar panels, expensive and complex photocells output η of only ~20%. I know that such engines are used on large solar parks (multiple mirrors concentrate solar energy at one point), but why not to simply replace each square meter of each solar panel (meaning literally everywhere it is used) with a such small converter? What did I miss in the concept?
P.S. English isn't my native language, sorry

 

[phyzguy]

Do you understand how to calculate the thermodynamic efficiency of a heat engine like a Stirling engine? It is dependent on the temperature difference between the hot reservoir and the cold reservoir. The best solar thermal generators, which (as you said) use concentrating mirror arrays to achieve high temperatures, only achieve an efficiency of about 30%. If you used small engines like you suggest, the temperature achieved would be much lower and the efficiency would be much less.

 

[Jarro]

It is dependent on the temperature difference between the hot reservoir and the cold reservoir.

Oh those are the basics I did not pay attention to, thanks.