This brings up a somewhat more scary discussion: It's more efficient to be a cybernetic organism than a gene-modified human with genes from plants.

If I get this correct, this (cited) Wikipedia-article says that solar cells with a 0.01 m^2 surface area would produce approximately 1.4 watt. Multiplying 1.4 watt by 20, to get a 0.2 m^2 surface area, gives us 28 watts.

http://en.wikipedia.org/wiki/Solar_cells#Energy_conversion_e...