Well, I found your word for you. It's "actinometry" - "the measurement of the heating power of electromagnetic radiation, especially that of solar radiation"
http://en.wiktionary.org/wiki/actinometry . See for example
http://dash.harvard.edu/bitstream/handle/1/3716614/Voskuhl_R... :
> Recreating Herschel's actinometry: An essay in the historiography of experimental practice
> In the course of a four-month period of research I worked with a replica of the so-called `actinometer', an instrument to measure the intensity of solar radiation, which was invented by John Herschel in 1824
The French word "actinométrie" has its own Wikipedia entry, which seems to be more focused on the sun than used in recent English. See http://fr.wikipedia.org/wiki/Actinom%C3%A9trie . Get your E.T.s to learn French and there's no problem.
Your insistence on "one word" is about equal to numerology in its usefulness.
Spaces are a question of orthography. In English we happen to use spaces to write "air raid shelter" instead of "airraidshelter". (Some even write 'air-raid shelters'.) In German they use "Luftschutzbunker" - "air protection bunker".
Had English gone a slightly different way some 1000 years ago, then we would write "solar radiometry" as "solarradiometry". There's no deep meaning to the space character on our psyche.
Indeed, the English compound expression "solar radiometry" is the single German word "Sonneradiometrie". Here's a paper which uses it to describe the focus of activities in the PTB laboratories - http://www.ptb.de/cms/fileadmin/internet/fachabteilungen/abt... .
It's also the Danish word "solradiometri", used in ftp://ftp.oami.europa.eu/bulletin/ctm/2012/2012_075_PDF/2012_075_DA.pdf .