Due to the increasing renewable penetration in the grid, not only the flexibility in fuels is essential for the future success of operating a reliable power plant. Offering operational flexibility to the power market increase the revenue streams from selling power also into ancillary services.
In the classic power markets mainly the increase of power output has been the focus of the generators. Providing increased power on demand became a key business which was also considered as mandatory reserve within the grid codes. The intermittency of renewable power and the capability of highest possible ramp rates to be utilized with the shortest possible response time became a key aspect for frequency stability which can only be achieved with rotating equipment when online.
To keep the emissions as low as possible and simultaneously with low operating costs, a low, emission compliant turn down with a high part load efficiency (see Efficiency) becomes more and more important. In case the generation units are offline, a fast and reliable start-up becomes essential for a successful operation. These operating properties are in many countries payed services and so, additional revenue stream can be created to increase profitability of the power plant.
As there are different technologies with different unique properties, we recommend you identify the best technology and solution for your operating profile. As an example for decision criteria, we discuss the start-up capability more in detail.
Fast-start capability is valued by customers because they can realize additional revenue streams. In markets with capacity mechanisms, merit order rankings, for secondary and tertiary frequency response, plant operators can offer power in five or 15 minutes at high prices.
Gas engine and gas turbine start-up time depends on the initial conditions. Gas turbines require only the lube oil to be at or above 20° Celsius. Gas engines require the cylinder heads to be at or above 60° Celsius, and the lube oil to be at the correct operating temperature. This is achieved by heating and circulating cooling water, which can take several hours starting from the ambient temperature. That’s why gas engines are often maintained at fast-start conditions, and the standby power consumption is factored into the overall operating cost.
In general, the starting and loading phases from warm standby are similar for gas turbines and gas engines, usually five to 10 minutes. Both fast-start gas engines and gas turbines are available with the ability to achieve full load within one to two minutes. Both engines and turbines can run both at part-load and full load to adapt to specific duties. Both technologies can be used for emergency power/ standby power applications, backup-peaking applications with low annual operating hours (<2,000 h) or run for 8,500 hours per year for baseload applications.
A combined cycle plant’s start-up time is much longer than that of simple cycle plants. A state-of the-art gas turbine in a combined cycle plant needs less than 30 minutes to full power for a hot start. With a bypass stack, operators can first fast start the gas turbine and later synchronize the steam turbine.
