Solar heating efficiency ?

[Externet]

Hi all.  

Photovoltaic solar panels are around 18% efficient.  That means a 1m²  panel should yield about 180 Watts to heat something electrically at full sun.

What is the typical efficiency extracting heat directly from sun radiation, assuming also 1KW/m²  irradiance as in a 1m²  uncovered coil like :

http://getgotechnology.com/wp-content/uploads/2014/12/Sun-Coil-heating.jpg

Would it be around 60% ?  Wind and thermal losses should be taking a good chunk, right ?

Edited March 20, 2022 by Externet
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[swansont]

It depends. If you are just making hot water it’s 60-70%. If you are generating electricity it’s significantly lower.