How would you translate
The US National Renewable Energy Laboratory
I would say
Das amerikanische Erneuerbareenergielabor
It is correct to write "Erneuerbareenergielabor" as one word? If not, how should it be?
As it is an administrative body that exists solely in the US, it would just keep the name (examples). We don't translate Federal Bureau of Investigation (FBI) either. Or NSA or CIA or Fed. If there is a need for a translation so as to have the text be understandable for people who know no English at all, then I would keep the name and add a rather free translation.
Das NREL (das nationale Institut für erneuerbare Energien)
The comound you suggested is understandable but hard to read and it sounds quite clunky. Compounding nouns generally works fine. With all other things (adjectives) it doesn't work all that often.
Wikipedia ist bei solchen Übersetzungen oft hilfreich, und in diesem Fall übersetzten sie es auch nicht. https://de.wikipedia.org/wiki/National_Renewable_Energy_Laboratory