I think the 300C target is to support the article's assertion that geothermal could replace e.g. nuclear plants. Geothermal for heating can work well with a lower approach temp, but industrial processes/power generation needs a higher differential.
Could I get your help understanding your statement "industrial processes/power generation needs a higher differential"? Why does geothermal need a higher differential for power generation?
Power generation is already accomplished with lower heat cycles (e.g., binary plants mentioned earlier would probably use a rankine cycle to deal with the low heat), though we'd expect those power plants to have less nameplate capacity than something like a double flash-steam plant.
I think you're correct you'd get more efficiency with higher gradients, but I don't understand what's limiting about the lower temperatures. Is it economics?
The higher the differential the higher the efficiency of heat to electricity transformation. If I remember correctly it's a big efficiency gain between 200C and 300C. From economic side of things, more bang for the buck.
