Combined Cycle, Renewables

Gas: Paving the Way for Renewables

Issue 9 and Volume 117.

alt   Timothy Effio, Regional Marketing Manager, Alstom Power

As America’s energy landscape continues shifting towards cleaner and renewable sources, the industry is looking for ways to compliment this conversion with minimal impact on the price and availability of electricity. Due to the somewhat unpredictable variations in wind and other renewables, operators must have an alternative generation source, a substitute. Natural gas has proven to be a reliable, fast ramping, flexible, safe, cost effective and sustainable power source to fill in the generation gaps inherent to the realities of renewable energy.

GT24 MXL2 implementation at Bayside Power Station, Canada
GT24 MXL2 implementation at Bayside Power Station, Canada

Addressing the Changing Energy Market

Renewable energy, once a punch line for American environmental policies, has now become an integral part of our power generation mix. Seeking to increase America’s world standing as a leader in renewable energy production, thirty U.S. states and Washington, D.C. had established mandatory renewable energy targets by mid-2010. The contribution from wind energy has significantly increased over the past ten years, becoming the largest renewables contributor in Regional Transmission Organization (RTO) markets such as ERCOT and PJM. The energy generation capacity for wind will continue to increase over the coming decades, growing approximately 14 GW by 2020, according to the U.S. Energy Information Administration’s Annual Energy Outlook 2013 report. Solar energy generation capacity is also growing, by a faster percentage than wind, with its total capacity at approximately 22 GW by 2020.

Integrating Renewables: Wind Chasing with Flexible Gas Plants

The increasing contribution of renewables brings certain challenges. While advances are being made, wind energy generation remains a difficult thing to forecast accurately. In the wind-heavy Electric Reliability Council of Texas market, wind energy generation can fluctuate over 2 GW in less than four hours on a typical day. RTO’s depend on renewable forecasts to determine the amount of power needed from traditional power sources such as coal, gas and nuclear. Variations in forecasts need to be accounted for by these traditional plants. The need for predictable, flexible, clean and efficient forms of energy that can “wind chase” to balance unpredictable variations in renewables arises.

Natural gas-fired combined cycle power plants (CCPP) have become increasingly flexible, able to react to variations in renewable generation, and are substantially cleaner burning than traditional coal-fired plants. Many CCPP’s have a relatively wide operating range, safely between 70 percent to 100 percent plant capacity and maintaining low emissions. Once online, CCPP’s can vary load faster than other traditional fossil plants, allowing them to respond minute-to-minute to the micro variations of wind energy. Furthermore, the ability to operate at part loads provides the benefits of grid frequency response, the ancillary service of maintaining the critical 60 Hz grid frequency should energy supply dip below demand.

Flexibility in a Renewable market

Recently, Alstom, a world leader in energy solutions, has reinforced its gas offering to the 60 Hz market with the latest GT24 gas turbine and associated 2×1 CCPP, the KA24-2. The latest GT24 incorporates features designed to meet the flexibility needs of a renewables integrated energy market in a sustainable way. With its unique sequential combustion, the KA24-2 can maintain 100 percent relative CCPP efficiency down to 80 percent load, which helps operators respond to micro variations in wind production while maintaining high plant profitability. The GT24 offers industry leading turndown capabilities with its Low Load Operation (LLO) feature. LLO allows both GT’s to operate at a lower load when demand is low, maintaining close to base load emissions. During plant turndown both GT’s and the steam turbine are kept completely online. With fast ramp rates, the KA24-2 can ramp from LLO to full plant load in just 10 minutes, providing a spinning reserve capacity of 500 MW.

As America moves forward in its pursuit of cleaner energy and power generation, natural gas fired combined cycle power plants are critically important to the integration of renewable energy sources.

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