Combined Cycle, Renewables

A Reliable Complement to Renewable Power

Issue 1 and Volume 118.

Richard Loose   By Richard Loose, director of marketing, siemens energy solutions

Renewable power is becoming a larger and larger part of the energy mix worldwide. California is a leader in this trend, adding significant amounts of wind and solar capacity to the grid. These renewable, green resources are environmentally friendly, but are intermittent due to their dependence on immediate local environmental conditions. Power today is primarily provided by power plants designed for base load and lacking the ability to quickly start up or quickly change load.

One plant designed to provide a solution is the Lodi Energy Center in California, which celebrated its one-year anniversary of commercial operation in November. The plant has an installed capacity of 300 MW and is located in Lodi, Calif.

The Lodi Energy Center in California celebrated its one-year anniversary in November.
The Lodi Energy Center in California celebrated its one-year anniversary in November.

Lodi Energy Center is a Siemens SCC6-5000F 1×1 Flex-Plant – a fast responding, clean, efficient combined cycle power plant to partner with California’s large non-dispatchable renewable generation. It is a highly efficient combined cycle plant with an operating efficiency of over 57 percent designed for intermediate to continuous duty and capable of daily cycling.

Since it began operation, the facility has more than 240 starts with a 99.7 percent reliability averaging 20 fired hours per start.

Wind and solar power plants are dependent on the weather so they can’t always operate. They are clean and efficient, and you want to use them when you can, but that means you have to have a plan in place so that you can still provide power when they aren’t producing. If you have one small wind turbine, this isn’t a problem, but when you have big blocks of wind and solar, it’s a big change when one of those locations stops producing. You need to replace that power.

The California grid operators, CAISO, publish information on generation, and they are looking at this issue. For example, on February 24 last year, they experienced 1,300 MW of solar and 800 MW of wind dropping off the grid in 2.5 hours. That’s about enough power for about 1700 homes that just went away in 2.5 hours. Something has to turn on.

That’s where Flex-Plants come in. At Siemens, we wanted to make clean, efficient flexible power plants to enable grids to use renewables and get real environmental benefit. Gas-fired combined cycle power plants have always been clean and efficient, but they used to be slow. It took several hours to get from off to base load, so you couldn’t really use them to back up fast moving wind and solar. They also produced more emissions when they were changing load. They were designed to turn on and stay on. Flex-Plants are still clean, high-efficiency power generation, but now that same plant can start fast, change load fast and maintain low emissions when it does. They are also available in a range of sizes going all the way to over 1,000 MW, so you can use a Flex-Plant combined cycle to back up a very large amount of renewable energy.

Plant start-up times are reduced by up to 50 percent due to the integration of fast-start features, including the three-pressure reheat heat recovery steam generator (HRSG) with Benson® once-through technology, high capacity steam attemperation, full capacity steam bypass systems, innovative piping warm-up strategies and Siemens’ steam turbine stress controller (TSC). Using the Siemens SGT6-5000F gas turbine as the prime mover, the plant will provide high power density while requiring a relatively small plant footprint. The Siemens SPPA-T3000 control system provides an easy-to-use control platform for the entire combined cycle power plant. Its fast start capability with 200 MW in 30 minutes or less can result in a carbon monoxide reduction of over 200 tons per year when compared to traditional F-class combined cycle plants.

Siemens partnered with NCPA for a successful project by delivering proven solutions and project execution know-how, including core execution competencies in plant engineering, procurement, transportation/logistics, construction management/TFA and commissioning.

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