As electricity usage continues to grow, there is a trend away from centralised power plant towards Distributed Power Generation, locating smaller power plant closer to the consumers. However, a distributed generation plant has the same issues in today’s electricity network as a centralised plant: the need for improved efficiency, reduced emissions and the flexibility to compensate for large power fluctuations caused by power generation from intermittent renewable energy sources. Traditionally gas turbine power plant have focussed on combined cycle configurations to maximise efficiency using large gas turbines between 100MW and 300MW in output, with heat recovery to drive steam turbines . This configuration is relatively slow to react to changes in grid power demand, and the efficiency falls as load falls. The large size of the turbines also leads to long construction times and maintenance downtime, particularly when forced to cycle daily due to intermittency. This paper examines the use of multiple small gas turbines in various combined cycle configurations with outputs up to 60MW in place of larger units, to provide distributed power plant between 25MW and 300MW in output for mid merit and peaking applications, and using either steam turbines or Organic Rankine Cycle (ORC) technology depending on the availability of water. These configurations allow cost efficient low emission power plant to be built in discrete modules, reduces construction times, improves efficiencies under part-load operating conditions and offers faster start-up and response times due to the characteristics of small industrial and aero-derivative turbines. Such plant also offer lower maintenance downtimes due to the ‘core swap’ capability of these gas turbine designs, and require fewer operating staff. By connecting to the distribution grids there is also a significant benefit from reduced system losses and better network asset utilisation.
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