Flex-Power Services™

State-of-the-art features for your power plant to remain competitive

The global energy markets are changing, which may lead to new operating profiles with higher flexibility requirements for many fossil power plants. To help address a wide range of changing operational requirements, Siemens Energy has developed and continues to evolve Flex-Power Services™.

Four aspects of Flex-Power Services™ for your power plant

The Flex-Power Services™ portfolio includes products and solutions as well as studies and assessments to help adapt to changing operational requirements. Siemens Energy develops solutions to help enhance operational flexibility of power plants and its key components.

Flex-Power Services™ can be provided as a retrofit for the Siemens Energy service fleet and often be combined with other modernizations. Implementing these state-of-the-art features can help to increase power plant flexibility and retain or improve plant competitiveness in the changing energy market.

Start & Stop Performance

Products and solutions supporting Power on Demand are intended to enhance Start & Stop Performance and can include upgrades designed to:

  • decrease waiting times for water-steam cycle warm up
  • decrease or even eliminate holding times
  • increase ramp rates of ST and/or GT

A shortened start-up or shutdown time may not only increase flexibility, but also support a reduction of fuel consumption and associated emissions in these operating conditions.


Some combined cycle power plants which were originally built as base load plants are now operating as peak load plants or as cycling plants with frequent start-ups. Hot starts after an overnight shutdown may need to be performed fast, using predictable and reliable measures to provide a high dispatch ability and in-market availability.

Hot Start on the Fly is an innovative upgrade for combined cycle power plants designed to significantly reduce the plant’s hot start times down to a plant specific value of - in many cases - approx. 30 minutes.

Improved start-up concept with Hot Start on the Fly (schematic illustration only)

Potential benefits

Depending on the operational limitations and requirements of your power plant, the benefits of the improved Hot Start on the Fly may include: 

  • Increased start-up efficiency
  • Significantly reduced combined cycle start-up time
  • Higher plant load transients due to combination of GT & ST load output, resulting in reduced specific start-up costs
  • Minimized fuel consumption for hot start-up
  • Reduced CO2-emissions during start-up

** Example for illustration. Actual results may vary depending on plant conditions and other factors.

Potential benefits of improved plant start-up concept**


Siemens Energy Flex-Power Services™ supplies an integral solution tailored to the specific situation and configuration of the power plant.

  • Engineering evaluation of relevant components as needed
  • Logic modifications within unit master control and major component subsystems
  • Implementation of logic changes into the plant’s digital control system

Intended Benefits

A start-up from warm conditions may take considerable time for a power plant originally built for less volatile operating profiles.

In competitive markets, the ability to start up your plant faster can help reduce time spent in transient conditions with non-optimal efficiency and make a difference in dispatch.

Warm Start on the Fly has been designed to support

Combined Cycle Start Performance - Warm Start on the Fly

Increased start-up efficiency

  • Significantly reduced combined cycle warm start-up time, in some cases to less than 45 min*
  • Reduced start-up fuel consumption and reduced associated emissions from reduced start-up time
  • Increased responsiveness to the transmission system operator (TSO)

*50Hz F-class 1x1 reference case - example only -actual results may vary


Applicable for many combined cycle power plants with Siemens Energy Design steam turbines and control system

  • Engineering of enhanced control philosophy and component evaluation as needed
  • Automation and logic modifications within unit master control and major component subsystems
  • Implementation of logic changes into the plant control system; typically no hardware required

Enhanced warm start-up (schematic illustration only)

Intended Benefits

A plant shutdown may consume considerable time and fuel for the unloading processes.

In competitive markets, the ability to shutdown your plant faster can help reduce time spent in transient conditions with non-optimal efficiencies and enhance responsiveness.

Enhanced Plant Shutdown (schematic illustration only)

Fast Plant Shutdown has been designed to support


  • Significantly reduced combined cycle shutdown time, in some cases down to below 15 min*
  • Reduced shutdown fuel consumption and reduced associated emissions, from reduced shutdown time

*50Hz F-class 1x1 reference case - example only -actual results may vary



Applicable for combined cycle power plants with Siemens Energy Design turbines and control system

  • Engineering of enhanced shutdown control concept and component evaluation as needed
  • Automation and logic modifications within unit master control and major component subsystems
  • Implementation of logic changes into the plant control system; typically no hardware required

Combined Cycle Stop Performance - Fast Plant Shutdown


A start-up from a condition where the water-steam cycle has already cooled down significantly may require long holding and waiting times where the gas turbine is running in lower part load for the water-steam cycle to warm up and achieve start release.

The Steam Turbine FlexStart upgrades comprise a range of features focused on the steam turbine designed to shorten the start-up time and enhance start-up flexibibility. Many of the features mainly address enhancements of start-ups from more cooled down conditions, while some of them can also help enhance warm or hot start-ups for combined cycles.

Impact areas for ST FlexStart Upgrades (schematic illustration only)

Potential benefits can include:

  • Reduced waiting and warm-up times as well as optimized speed and load gradients
  • Increased responsiveness to the transmission system operator (TSO)
  • More efficient start-up process
  • Potential for reduced fuel consumption and emissions during start-up



  • Unit-specific engineering evaluation of boundaries and applicable features
  • Engineering of necessary adaptations & logic changes
  • Implementation of control logic upgrades
  • Typically no or only minor hardware required

Select potential Features

Steam Turbine FlexStart Upgrades can comprise a number of potential features. For a specific unit, the best applicable and matching features are selected based on configuration and detail customer needs. Some of the potential features are: 

Advanced Fast Loading

Implementation of Siemens Energy´s advanced speed ramp and load gradient optimization features to the steam turbine controller, adapted to site specific capabilities and conditions. Includes mechanical analysis of steam turbines for enhanced transient capabilities. May also include changes to the unit master control system.

Benefits from Advanced Fast Loading (schematic, for illustration only)

Early Pre-Warming and Modified Pre-Warming Concepts

Designed to help significantly shorten the start-up of H-IL type steam turbines for cold starts through advanced pre-warming concepts for HP (Early Pre-Warming) or IP/LP section (Modified Pre-Warming)

Benefit from Enhanced Pre-Warming Concepts (conceptual illustration only)

Degassed Conductivity for faster starts of combined cycle power plants 

Degassed Conductivity is a method used to analyze steam purity and determine whether the steam can be delivered to the steam turbine. Degassed Conductivity makes it possible to eliminate the contribution of carbon dioxide to the Acid Conductivity (AC).

It has been designed to support

  • reduced waiting time to release ST for start-up and
  • reduced ST operating hours in respective steam purity action levels

Degassed Conductivity – potential benefit chart*


In combined cycle mode, start-up times are greatly influenced by the configuration and requirements of the water-steam cycle. However, an increase of the gas turbine gradient capabilities may also help with start-up times and start-up efficiency. For the SGT5-4000F, Siemens Energy has developed a start gradient optimization which is designed to

  • Increase gas turbine start-load gradient to a maximum value of up to 30 MW/min*
  • Reduce gas consumption per start resulting from reduced start-up time
  • Help further reduce combined cycle start times when combined with relevant start optimization products for water-steam cycle (e. g. Hot Start on the Fly, Warm Start on the Fly, Fast Plant Shutdown, Advanced Fast Loading)

* achievable values may vary by site

SGT5-4000F Gradient Optimization


Engineering of solution & applicable logic updates

  • Implementation & GT tuning if needed to promote stable combustion with the increased load gradients
  • Implementation requires certain configuration minimum standards which can be offered as retrofit in case not yet fulfilled

Wet Compression Modernization for SGT-2000E series

Wet Compression Modernization for SGT-4000F series

Grid Services & Peak Power

While on load, upgrades to enhance flexibility can include:

  • Grid code studies (e.g. ENTSO-E)
  • Load following capabilities (e. g. enhanced ramp rates)
  • Grid Services, e. g. Primary and Secondary Frequency Response
  • Peak Power Capabilities

Wet Compression Modernization for SGT-2000E series

Wet Compression Modernization for SGT-4000F series

Turn Up Upgrade for SGT-4000F series

Fast Wet Compression for SGT-4000F series

Minimum Part Load & Emissions

In energy markets with a volatile infeed from various generation sources, combined cycle power plants may find themselves in part load situations for higher shares of their uptime than originally intended.

Enhanced part load capabilities may make a difference in the ability to successfully participate in such generation environment.

Upgrades to enhance part load capabilities can include:

  • Reduction of Minimum Load for GT and/or plant
  • Measures to enhance part load efficiency
  • Measures to address / enhance part load emissions


The Modified ST Valve Staggering upgrade is designed to support lower load operation and to reduce loss of efficiency in this operating condition.

Amongst other criteria, minimum load is typically restricted by logic to avoid high HP exhaust temperatures, and may lead to opening of bypass stations or even shutdown for protection.

The Modified ST Valve Staggering introduces an upgraded logic which has been designed to facilitate modified operations to support lower minimum part load with same or improved margins.

Modified Valve Staggering effect (schematic only)

Intended Benefits & Scope

The Modified Valve Staggering upgrade modifies the valve staggering logic for part load operation to help:

  • Avoid losses from opening of the IP bypass station
  • More efficient operation in part load
  • Lower potential for tripping on high HP exhaust temperature
  • Lessen throttling of reheat control valve


  • Assessment of current part load operation
  • Engineering and implementation of the recommended process logic changes
  • Typically no hardware changes required

Part Load Efficiency

Intended Benefits

Many Gas Turbines have been designed to operate most efficiently at maximum load conditions. With today´s changing market, the need to efficiently operate at part load is becoming more important as well. Siemens Energy has developed a range of solutions to enhance part load capabilities, which can help to:

  • increase operational flexibility
  • reduce part load fuel consumption
  • reduce minimum emission compliant part load
  • enhance part load efficiency

Part Load Optimization

Cool Down & Start Readiness

Advanced preservation concepts and the ability to maintain a plant in a status which allows fast re-start even after multiple days of shutdown may greatly enhance flexibility and support better dispatch success.

Reduced cool-down times may support faster access to components for inspections and repairs, thus supporting shorter outages.

Advanced inspection and interval concepts can help to safeguard and enhance availability.

Intended Benefits

With natural cooling, it may take multiple days for a steam turbine to be sufficiently cooled down to access for inspection or outage work.

Through extensive analysis, Siemens Energy is able to offer Fast Cooling of Steam Turbines which has been designed to significantly accelerate cool-down time and thus help get access to components sooner after shutdown.

Longitudinal section through an SST5-5000 (exemplary illustration only)

Fast Cooling is designed to save up to 3.5 days of cool down time (site specific; actual values may vary) compared to natural cooling,

which may support

  • reduced overall total outage duration
  • increased availability

Cool down temperature curves (exemplary, actual results may vary)


  • Engineering & Process optimization - Detailed analyses of the cool down process taking into account material strength limits, plant specific operating variables and usage factors. Site specific check of the existing cool down procedure and engineering of optimized process
  • Hardware modifications - improvements for accessibility, ease of activation can be proposed and implemented
  • Automation - degree of automation of the cool down process can be increased and optimized.

For turbines already equipped with the forced cooling system, Fast Cooling may offer incremental optimization, e. g. improved handling and automation, improved process, etc.

Temperature distribution at the beginning and end of fast cooling procedure (exemplary illustration only)

Intended Benefits

Steam Turbine standstills can lead to increased exposure to air moisture which can result in parts corrosion. Preservation measures are recommended to remove and control residual moisture to below recommended thresholds.

Siemens Energy has developed an enhanced preservation system for steam turbines and its auxiliaries to support more flexible shutdowns and longer standstills.

Flexible Preservation concept schematic (illustration only; actual configuration may vary)

This enhanced dry air system has been designed to help

  • Reduce the potential for corrosion and resulting damage during shutdowns, contributing to improved reliability
  • Reduce time and effort for installing and disconnecting the preservation system after shutdown and during start preparations
  • Support better responsiveness and availability through reduced time for connecting / disconnecting to the dry air supply
  • Enhance installation ease through redesigned and relocated access points.
  • Better control of preservation operation through automation and measuring points (optional) 


  • Engineering, documentation and hardware (as needed). Reuse existing dryer(s) as possible
  • Optional: Installation of required components and initial start-up of system
  • Optional: automation & integration into control system 

Intended Benefits

After a shutdown, the steam turbine and other plant components increasingly cool down the longer the shutdown lasts. Consequently, startup times can correspondingly increase with the duration of the preceding shutdown. Siemens Energy has developed a trace heating system which can keep the relevant steam turbine sections warm or heat them up, and enable a startup from a warmer condition.

Hot Standby operating principle (schematic for illustration only)


Steam Turbine Hot Standby can help

  • Increased responsiveness and operational flexibility based on enabling usage of a shorter warm startup process
  • Reduced startup life consumption for steam turbine by avoiding cold condition starts
  • More efficient startup operation & reduced startup fuel consumption by enabling a shorter warm startup process even after longer shutdown periods


  • Site specific engineering, procurement, implementation of a trace heating system for the HP / IP turbine(s) including valves to keep the steam turbine in a warm condition
  • Automation, integration into control system
  • Active heating from ambient condition (optional, site specific evaluation needed) 


Our reference projects

Hamm-Uentrop power plant, Germany

  • Start and Stop optimization solutions
  • Boosted capabilities for warm-start, hot-start and fast shutdown 
  • Reduced emissions with upgrades
  • Supporting adaptation to ever more volatile market environment


Mainz-Wiesbaden power plant, Germany

  • Enhanced operational flexibility for the combined cycle power plant
  • Reduction of start-up time with Hot Start on the Fly to 27 minutes
  • Optimal adaption to new requirements of the German energy market

Is your plant operation optimized for changing market demands?

To help you determine the right solution from the Flex-Power Services™ portfolio ideal for your operational requirements, we conduct a Technical Plant Assessment. It provides detailed insights into the improvement potential for 

  • Operational flexibility
  • Thermal performance recovery
  • Availability and reliability improvements
  • Plant upgrade capability

Download our technical paper

Four aspects of Flex-Power Services

From Base to Cycling Operation

The paper uses the Mainz Wiesbaden Combined Cycle Power Plant as an example of a plant that has switched from base load to cycling mode as a result of renewable energy input into the grid. The content includes successfully implemented enhancements to improve the plant's operational flexibility. It also includes test results for possible future upgrades. 

How can we help you?

Contact us to learn more about Flex-Power Services™.