The system use the refrigeration cycle principle working in reverse by the refrigerant absolving heat from sun panels and the refrigerant cooling from earth buried heat exchanger (liquidification). Under the refrigeration cycle principals the temperature difference is converted in pressure difference, then the pressure difference  is converted to motion (mechanical) energy then the motion is converted to electricity with an alternator.
All above technologies are existing technologies each of them widely known, widely available and easy to put together.
This system against the water steam system is much more energy efficient, it operates for A longer time, has lower investment cost, the technology to build up a system is widely available, and it can be deployed in small scale applications efficiently.