3.1.2. Step 2. Conventional Units Commitment

Lignite power plants are used today as a base load units. They are not flexible to switch on and switch off, and their operation should be scheduled in medium term. The number of lignite power plants to be committed is estimated with respect to the expected demand of next days, taking into consideration their non-flexible features and their high technical minimums of the order of 50%. The criterion is that the technical minimums of lignite units to be committed should not exceed the minimum expected residual load of the following seven days. Initially, there are set to operate at their technical minimums or more in case of power deficit. Given this simulation approach, the operation of lignite power units in the Greek power system will be gradually reduced as far as the PV capacity increases. It should be noted that lignite power plants are considered only for reference year 2019, since by 2028 according to national targets the lignite units shall have been decommissioned.

Natural gas units are more flexible than the lignite units, and as a result, they are dispatched in order to support the balance between supply and demand in the short term. The number of natural gas units operating is defined in order to be able to cover the mean residual load of the next twenty-four hours. Initially, they are set to operate at their technical minimums (30% of the nominal output) or more in case of power deficit. The flexibility of natural gas units allows the efficient and rapid response to the fluctuations of power supply.

The combined heat and power (CHP) plants and the biomass units are dispatched hereafter. The total nominal power of these units is relatively small, and their contribution is limited. The produced energy of both is defined using an average capacity factor of 70%.
