*F.Y.I.*
"There were 5,135 inventions that were under secrecy orders at the end of Fiscal Year 2010. (Yes, it's a little dated, but that's not the point.)

The current list of technology areas that is used to screen patent applications for possible restriction under the Invention Secrecy Act is not publicly available and has been denied under the Freedom of Information Act. (*This* is the point.)

The 1971 list indicates that patents for solar photo-voltaic generators were subject to review and possible restriction if they were more than 20% efficient.  Energy conversion systems were likewise subject to review and possible restriction if they offered conversion efficiencies “in excess of 70-80%.”

D'ya think "There's Nothing New Under The Sun..."?

Well... you'd best think again.*

*Just don't let the U.S. Patent Office know what you're thinking about.

Oh... and read the rest of this fantastic yet brief article (by Steven Aftergood at the Federation of American Scientists), here: http://blogs.fas.org/secrecy/2010/10/invention_secrecy_2010/