The area under the curve describes the power that is produced by the 3000K carbon radiator. It looks to me that the power produced in the visible range is just 10% or less of the power available in the light spectrum produced by the SunCell. That visible range is subject to another percentage reduction based on the efficiency of the solar cells. As an estimate, 5% or less of the optical power produced by the SunCell is converted to electricity.
: Mills first idea was to directly convert XUV into current by high power PVC, which are able to convert (1000-1500 times) concentrated sun-light. But Mills lacks some knowledge. He was not aware, that concentrating sunlight will leave the spectrum intact!, whereas the SUN-CELL spectrum is at least 10 time more energetic compared to the suns (on earth!) spectrum.
The only solution would be to find a chemical with a reasonable UV break-up cascade, to down modulate the spectrum into SUN-like regions.
The second mistake he made, was to neglect that he needs a window between the radiation and the PVC and how he could keep this window open. Silver vapor will close down any surface.
This are reasons why products should be developped by engineers not by scientists.