Not Just More Megawatts, Better Megawatts: The Case for Combined Cycle Output Augmentation in a Low Power Price Environment

Currently, the fragmented U.S. wholesale power markets do not face a scarcity of megawatts, as evidenced by the North American Electric Reliability Corporation’s (NERC) recent Summer Reliability Assessment and reported by Public Power Daily here.

However, this does not suggest turbine inlet air chilling (TIAC) is not a valuable resource for U.S. power generators.  TIAC quickly elevates a combined cycle unit’s productive capacity during challenging ambient conditions. The benefits of the additional megawatts produced from low-heat rate/low-cost generation resources may be evaluated on a relative (better) or absolute (more) basis.

Frontera Final ProductThe relative benefits of TIAC are readily apparent as the U.S. power mix continues to evolve.   The swift growth of intermittent renewables on the grid increases the need for other power supplies to react quickly to system fluctuations in real-time.  Grid operators and other stakeholders in these markets need better incentives to ensure all resources are compensated at a price reflecting real-time market conditions and consistent availability.  The ability to start, stop and ramp at the lowest cost will continue to evolve as a critical and valuable element of the thermal power fleet in the U.S.

Furthermore, TIAC equipped with a thermal energy storage (TES) tank provides a generation resource with the potential to take advantage of the relative difference between peak and off-peak power prices. TES enables the chilling capacity of TIAC (and associated parasitic load) to be created with low priced off-peak power and then used to provide additional output during high priced periods.  This “pump-storage” type arbitrage may also be applicable to regions with excessive off-peak renewable resource supplies and resulting low off-peak pricing in the wholesale markets.   The recent introduction of a bill in the U.S. Congress to provide for an energy investment tax credit for energy storage capabilities further accelerates the industry’s growing interest in this additional aspect of the power supply chain.

More Megawatts: The Absolute Advantage of TIAC

On an absolute basis, TIAC’s restoration of capacity is necessary to satisfy minimum run-times and/or an overall power output threshold to achieve annual or seasonal production targets and associated performance payments.  Stellar Energy specializes in the creation of customized solutions for independent power producers globally to meet contracted availability and annual output performance targets.  The enhancement in a combined cycle unit’s production to nameplate capacity on a consistent basis enables the full payment of tariff payments based on net output for a merchant generator.  The evaluation of TIAC on an absolute basis currently is applicable to areas of the world that face an overall scarcity of power generation capacity and MW availability.

Better Megawatts: The Relative Advantage of TIAC

On a relative basis, Turbine Inlet Air Chilling is a cost-effective method to lower the average heat rate of a utility’s overall generation stack by supplementing the production capability of efficient gas-fired resources.  TIAC mitigates the need of a utility or independent system operator (ISO) to follow system load increases with less nimble and more costly units during periods of high peaking demand and/or low renewable generation availability.  This system planning consistency becomes more relevant given the increased presence of intermittent resources and the declining reliance on coal fired and nuclear units in generation stacks.  With more renewable power sources coming on line, there is an enhanced need for quick-start, efficient units and associated spinning reserves to provide grid reliability at the lowest possible cost.  This relative benefit is especially important for smaller sized utilities that may have less natural gas fired generation in their stacks as larger, competing utilities.

In addition, power augmentation for maximum summer power should not be an “either / or” choice between chillers and duct firing, but rather should be the combination of the two, due to the design parameters for the heat recovery steam generator and steam turbine.   Built into every nominal combined cycle plant, there is the ability to tap this extra capacity on a peaking basis, on an intermediate basis, or even as base load in warm climates.  For maximum power output, power plant owners may rely on the consistent power augmentation provided by TIAC, and balance system requirements with duct firing.  This scenario allows a unit to produce the required power at the lowest possible heat rate.  Furthermore, a TIAC solution costs less than half of an aero-derivative peaking turbine and has a more consistent heat rate at any ambient temperature.  The chilling capability of TIAC may be started or ramped much more quickly than a fast-acting peaking unit and will not require expensive LTSAs, maintenance intervals, or hot-gas-path parts.


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