Microturbines may offer one of the best short-term distributed power production options because of their simplicity and because no major technological breakthroughs are required for their deployment. Low emissions also characterize modern microturbines. This chapter describes three promising turbine technologies: single-shaft gas-fired turbines, dual-shaft gas-fired turbines, and Rankine cycle engines. The differentiators between combustion turbines, described in Chapter 3, and microturbines are four:
1. Size: less than 200 kW net shaft power output (this number is somewhat fuzzy, and various authors will include engines above 200 kW or restrict the size to less than 100 kW)
2. Simple cycle: single-stage compressor and single-stage turbine 3. Pressure ratio: 3:1 to 4:1 instead of 13:1 to 15:1 4. Rotor: short drive shaft with generator on one end with a bearing
in the middle
The classic open Brayton cycle described in Chapter 3 is also the basis of gasfired microturbine (MT) engines. The reader is referred to that chapter for cycle basics.