Picking the Right Technology in an RPS Market

This article reports on a case study performed for a client in Southern California faced with Clean Water Act 316(b) regulation compliance on three once-through cooling facilities. The California-specific regulations will require, among other things, a minimum 93% reduction in intake flow rate for each unit. Compared to the unit’s design intake flow rate, enhanced intake structure redesign to minimize biological impacts may also be required. Alternative plant configurations being considered by the owner for compliance included wet cooling towers, air-cooled condensers (ACCs), hybrid cooling towers, and unit replacement.

The study also considered compliance with California Rule 1304 guidelines regarding Electric Utility Steam Boiler Replacement, which calls for existing capacity replacement to consist of combined cycle or advanced gas turbine technology (defined as those turbines that incorporate compressor intercooling) in order to qualify for an 1:1 air emissions credit.

This article concentrates on the selection process for the unit replacements only and the drivers that are imposed when operating as an independent power producer in a highly saturated renewable portfolio standard (RPS) market. It also includes a discussion of the salient features of the proposed facilities.

Figure 1 is the forecasted 2020 daily load profile of the California ISO (CAISO), in which the owner participates. The existing facilities operate in a peaking mode with low annual capacity factors that address the peaks of the load profile and as intermediate capacity when the large units of the investor-owned utilities are offline for maintenance or repairs.


1. Example of 2020 ramp rates under 20% RPS. Source: CAISO

Operating limitations of the existing equipment are attributable to their original design as steam electric plants, thus they have relatively long startup times and slow ramp rates, typical subcritical and supercritical heat rates, with high fixed and variable maintenance costs in comparison to their competition.

The owner has analyzed his position in the marketplace and recognizes that future participation in CAISO favors peaking and intermediate load range facilities capable of fast startup and shutdown, fast ramp rates, with the ability to perform dual-shift operation. This will result in multiple startups and shutdowns during a single operating day. To fit this mode, the ideal facility would have these characteristics:

Low capital costLow maintenance costOptimal part-load and good baseload heat rateCapable of fast startup/shutdownGood ramping characteristics

As previously stated, the allowable technology selections limited the owner to either advanced gas turbine or combined cycle technology. The advanced gas turbine offering is relatively new in the market; however, it offers several advantages, particularly a moderate-to-good heat rate coupled with good startup and ramp characteristics. However, with further analysis, the initial capital and forecasted maintenance costs for the advanced gas turbine cost proved to be prohibitive.

This led to the selection of combined cycle technology, requiring the development of a plant configuration meeting the criteria listed above.

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