Sterling Energy Systems made the news by setting a new solar-to-grid efficiency record of 31.25 percent for commercially available solar thermal systems. Its notable that the sterling engine approach is closed, so it doesnt require large amounts of water as some other solar thermal systems.
From the sources I have that compares to other solar technology as follows:
Multijunction (multi band gap) concentrator PV: 40.7%
SES Sterling engine concentrator: 31.3%
Multijunction (multi band gap) concentrator PV(expensive): ~30%
Traditional Monocystalline Si PV: 11-16%
Thin Film a-Si, CdTe, CIS, CIGS PV (lowest cost): 5-8%