Systems and methods for harvesting geothermal energy use temperature-based flow control to optimize the extraction of thermal energy from a geothermal reservoir. In one example, a thermal transport fluid is flowed into a wellbore traversing a thermal reservoir of a formation. Flow of the thermal transport fluid into and out of the thermal reservoir is dynamically controlled at each of a plurality of injection and/or return locations in response to a downhole parameter such as temperature. For example, flow may be controlled so that the flow into the thermal reservoir is greater at the injection locations where the temperature is hotter and that the flow out of the thermal reservoir is greater at the return locations where the temperature is hotter. The thermal transport fluid produced from the return locations is then conveyed to surface to extra the thermal energy.