In some ways, tuning up a power plant is a similar endeavor. Even if it doesn't move like a Formula One car, it often has to be run at full load, just like Felipe Massa's Ferrari at the Nürburgring race circuit. When operating in this mode, a power plant generates a lot of energy, usually in the form of electricity. At other times, when the grid's hunger for power is lower, the plant is operated at partial load.

But unlike racing cars, power plants do best when operated at a relatively uniform pace. No gas turbine or coal-fired boiler, for instance, can reach full power in seconds. In fact, depending on the type of plant, reaching full output may require anything between ten minutes and several hours.

Increasingly, however, electricity companies need to be able to ramp up generation on short notice, not least because the growing use of renewable sources of energy leads to greater fluctuations in capacity. Since the wind and sun are variable factors, solar and wind farms feed power into the grid on an irregular basis. For this reason, the hours of darkness or periods of calm at sea must be bridged by conventional base load power plants. This, in turn, means that such plants need to operate more flexibly than before in order to compensate for load variations and prevent blackouts.

Older plants in particular have problems cushioning such rapid changes in load. Given the growing trend toward renewable energy sources, a lot of base-load plants now need to be upgraded. And there's another, equally pressing reason to modernize existing turbines, boilers, and generators: With the cost of fuels such as gas and oil set to become more and more expensive in the long term, operators are looking for optimal efficiency from their power plants. What's more, as they invest in efficiency improvements, they and their customers stand to benefit from reduced carbon dioxide emissions per kilowatt of energy produced.

At the same time, the International Energy Agency calculates that the colossal sum of $16 trillion will be needed by 2030 to expand and modernize the world's energy infrastructure. Around $10 trillion of this is earmarked for power supply systems..

The modernization and upgrading of power plants has developed into an important line of business at Siemens. In the German town of Mülheim an der Ruhr, for instance, it's the job of Ralf Hendricks and his colleagues from the Siemens Energy Sector's Lifetime Management Unit to turn base-load power plants into racing machines.

On behalf of a client in the United Kingdom, for example, the unit recently upgraded a combined cycle power plant without having to replace any components. A team traveled from Mülheim to England for a couple of days in order to analyze the 400-MW plant and check parameters such as pump flow rates, feedwater temperatures, steam cation conductivity, and boiler temperatures. As a result of the fine-tuning of these factors, the plant's control system was able to operate more efficiently, thus shortening the time it takes for the plant to reach full load.

"Adjustments to the plant's instrumentation and control technology helped us get the best out of its equipment," Hendricks confirms. As a result, it now takes only 30 minutes, rather than an hour, for the turbine to rev up to full load and for the plant to start feeding power into the grid—and all without the need for any new hardware such as pumps or valves.

Such improvements can provide a quick return on investment. Assuming 50 start-ups a year and a price of 80 €/MWh, the operator will recoup the upgrade costs of around €80,000 within 12 months.

Siemens engineers were also able to reduce the cooling time for the combined cycle power plant by means of a technique known as force cooling. This involves extracting air from the machine room—something that only requires minimal installation of extra ducting, valves, and filters—in order to provide additional cooling for the steam turbine. "Instead of having to wait 160 hours for the turbine to cool before the plant can be shut down, it now takes only 60 hours," says Hendricks. That means a time difference of four days, which is a valuable savings when operators are waiting to start routine inspection and maintenance. For large plants, such as nuclear generation facilities, it can reduce the cost of an overhaul by millions of euros.

There is often also scope to extract more performance from the turbines without the need for extra fuel consumption, thereby increasing generating capacity without additionally burdening the environment. The effectiveness of a turbine depends very much on its blades and flow area. In this connection, major advances in the field of 3D computer simulation over the last 20 years have given rise to the development of turbine blades that exhibit very low flow resistance. Moreover, when additional improvements are made to the blade path, this reduces losses even further, thus resulting in very high efficiency. This means that as much thermal energy as possible is transferred from the gas or steam to the turbine blades.

All of this, in turn, allows efficiency to be increased without having to increase the volume of gas swept by the blades and therefore the size of the turbine. That's important, since turbine enlargements are usually not an option in an existing plant. "This is a huge benefit for customers," explains Dr. Norbert Henkel, who is responsible for upgrading steam turbines at Siemens in Erlangen, Germany. "We fit between 20 to 25 power plants a year with upgraded turbines."

Last but not least, there is also the generator, which converts the rotary motion of the turbine into electrical energy. In itself, a generator has an efficiency of almost 100 %. However, it has to be tailored to other components, which as a rule age faster. In older plants, for example, the turbine blades have to be replaced either because the material has become brittle and there is a danger of failure or in order to make the turbine more efficient. "It's like a champion cyclist getting onto a normal bike," says Anastassios Dimitriadis from Siemens Energy in Mülheim. "Obviously we then have to check whether the existing generator is up to handling the increased performance." If necessary, a new rotor has to be installed or the coils rewound.

"Inevitably, the state of technology in the energy industry tends to lag behind the latest technological developments," points out Thomas Sattelmayer, Professor of Thermodynamics at the Technical University in Munich. For this reason, every new power plant that goes online is already to a certain extent out of date. "It therefore makes good sense to upgrade efficiency when conducting routine maintenance," says Sattelmayer, who is spokesman of "Kraftwerk 21," a Bavarian energy research alliance. Sattelmayer sees huge business opportunities in the optimization of power plants.

Whatever the outcome of that prediction, government interest in reducing carbon dioxide emissions from power plants certainly coincides with the goals of utility companies, which want to operate the most efficient plants possible. Considering this, we can expect to see a major increase in the number of projects introduced to upgrade the efficiency and start-up speeds of power plants in the years to come.

                                                                                                            Jeanne Rubner