The problem is that if you just pump the water into the ground and let direct action heat it it also picks up a lot of minerals and salts from the volcanic rock around it. It would be like sand blasting the inside of your turbine. Saying that turbines don't like hard water is something of an understatement. So you have to use a heat exchanger to transfer heat from the hard water coming out of the ground to “clean” water used for the turbine. But now you have another point of heat loss to the water coming out of the ground needs to be very hot or you end up with saturated steam in your turbine loop.
“The problem is that if you just pump the water into the ground and let direct action heat it it also picks up a lot of minerals and salts from the volcanic rock around it. It would be like sand blasting the inside of your turbine. Saying that turbines don't like hard water is something of an understatement. So you have to use a heat exchanger to transfer heat from the hard water coming out of the ground to “clean” water used for the turbine. But now you have another point of heat loss to the water coming out of the ground needs to be very hot or you end up with saturated steam in your turbine loop.”
Hence, that is why there is temperature and pressure control on both the geothermal and clean sides of the loops plus a honking big cooling tower, which probably is using condensed steam flash from the geothermal brine for the recirculating cooling water.
Geothermal plants have pretty exotic metalurgies for heat exchangers and other critical components compared to conventional steam turbine power plants, which makes geothermal more a greater capital cost and operating cost in the power generation section relative to a conventional plant of similar capacity. Competitive economics on the whole rest on the costs of the geothermal energy supply (hot brine or steam under pressure) versus using a conventional energy source.