system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When we say that solar power is not (yet) efficient, what exactly do we mean?

Does this imply that the amount of energy used to produce a single panel is greater than the total amount of energy that panel will be able to generate in its lifetime? This is the only way I can see it being inefficient.
gpt
Typically when using the word "efficiency" in a comparative fashion for energy production the measurement refers to the source-energy relative to the converted usable energy.  E.G. if gasoline has X amount of energy in it, the combustion engine can only create about X*.3 of that to its usable energy (movement, in this case).  

A solar panel converts about 20ish percent of the suns energy.  If we compare that to other forms of _electricity_ production (the most reasonable analogue for your not-well-defined statement) then we'd be saying that "compared to the efficiency of capture of energy from coal and conversion to electricity, solar panels are significantly less efficient".

The REASON we might emphasize this statement however is that increasing efficiency of the panel in this dimension is correlated with requiring less physical space, likely high return on investment of actual purchase of the panels and so on.  Its perceived that improved efficiency - amongst other things - is the path towards more economic viability for widespread solar.