So in theory they could heat up the air with geothermal too?

The hybrid model is much more practical than any stored energy system.

re; Carlos Grados
There are more efficient ways of converting geothermal energy into mechanical energy than through a heat exchanger into air that is running through a gas turbine. Stirling cycle springs to mind. Also tappable geothermal usually is not nearly that hot.

Basically this is a jet engine with an extended turbine shaft between the compressor and the expandor stages, using a solar concentrated air heater, instead of a combuster.
I have been designing this kind of gear for years...
Kudos - simple and if you use a closed loop cycle on the air, you can use all that heat energy for other purposes.

re; Mr Stiffy
If you use a closed loop you loose efficiency in the generation of electricity.

Apparently, NIMBY doesn't exist in these other countries. Good for them! I am curious as to why a brine solution or even some hypertutechtic salt isn't used, only because of the btu/volume. Even a Rankine cycle would seem better by definition. I defer to you, Mr. Stiffy, as you design these, I hope you could shed light on this curiosity.

Slowburn, If one were to use the high(er) temp exhaust to preheat the medium prior entering the target receiver, wouldn't that INCREASE the overall efficiency?

@Slowburn......
NO - you extract the heat out of the working fluid for other purposes......

re; Burnerjack
Yes. It is a fairly common design feature on large ground based gas turbines but it is still on open system.

System efficiency is in 'how much energy you can take out in a cycle'. If air is heated to 1000 degrees, and cooled to 200 during the power stroke, then reheated, 800 degrees of power is taken out every cycle. Very efficient.
The re-heating is the problem. Energy transfers to liquid (coefficient of conductivity) at an rate of '1' and to air at an rate of '.5'. very inefficient.
If your energy is free, however, it works.