1kw/m^2 is the "standard" rule of thumb for heat energy from solar irradiation. I'm unsure whether OP has done the calculation (in which case, credit to a well built system) or simply cited the standard rule.
There are some large Stirling engines out there that operate on hot oil. With a large diameter piston, quite a bit of torque can be generated with even small ∆T. Oil can be heated as with traditional solar water heaters (i.e., with no concentration), though concentration doesn't hurt.
There are some large Stirling engines out there that operate on hot oil. With a large diameter piston, quite a bit of torque can be generated with even small ∆T. Oil can be heated as with traditional solar water heaters (i.e., with no concentration), though concentration doesn't hurt.