TPVs are capable of 30% and more -

http://www.appliancedesign.com/CDA/A...00f932a8c0____

Electric light bulb filaments are capable of 3,000K and more -
http://hypertextbook.com/facts/1999/AlexanderEng.shtml

Though not in the open literature, small self-heated nuclear filaments
that self regulate (neutron cross section changes with temperature)
and operate stably in a background - provide a means to create a tiny
very powerful very long lived very robust power plant - that with a
TPV stack turn into a very compact safe reliable etc., electrical
energy source with very high power to weight - to drive all manner of
electric engines.

http://en.wikipedia.org/wiki/File:Bo...trator_AB1.JPG