Advances in binary-cycle power and submersible pump technologies over the past two decades have made electric power generation from geothermal fields in the moderate temperature range (100° to 180°C) convincingly commercial. For geothermal water in this temperature range, binary-cycle is more efficient for power conversion than flash-cycle and pumping of wells is more efficient than self flowing. The lower temperature limit of 100°C is imposed by the limits of binary-cycle technology and the upper limit of 180°C is imposed by the limits of pump technology commercially available today. This paper is a case study of optimization of net power generation from such a field at Raft River, in the State of Idaho, United States.

This paper investigates the practical range of net power capacity available from conventional and enhanced geothermal wells as a function of temperature and productivity index. For a temperature range of 100°C to 190°C, which is the operating temperature limit of presently available downhole pumps, wells are typically pumped and power is usually generated in a binary-cycle plant, and in rare cases in a flash-cycle or hybrid-cycle plant. In this temperature range, the net MW capacity of a well has an upper limit of about 7.3 MW, irrespective of how high the well’s productivity index is. This capacity limit cannot be improved unless technology can be improved to allow setting pumps deeper in the well than the current limit of 457m (1,500 feet) and pumping at a higher rate than the present limit of about 160 ℓ/s (2,500 gallons per minute). For resource temperatures greater than 190°C, wells must be self-flowed, and power is generated from such wells in a flash-cycle or hybrid-cycle plant. In the temperature range of 190°C to nearly 220°C a self-flowing well’s net power capacity (irrespective of its productivity index) is less than the maximum of 7.3 MW for a pumped well.