Found on MAKEblog:
http://www.makezine.com/blog/archive/2007/04/hydrasolar_solar_tracker.html?CMP=OTC-0D6B48984890

2 axis passive tracker:
http://www.portasoltrackers.com.au/

http://www.abc.net.au/tv/newinventors/txt/s1881905.htm

"It is a new type of 'passive' solar tracker that uses a combination
of direct sunlight (radiant heat) and shade (ambient air temp) to
affect the thermal expansion and contraction of a liquid to make the
solar panel rotate. The expansion of the liquid causes the panel to
rotate toward the west during the day and the contraction causes the
panel to rotate back towards the east at night, ready for the morning
sunrise. The simple hydraulic system, ensures that the solar panel is
angled towards the sun from dawn through to dusk - all year round."
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