By Dr. Michael Ladwig, Director Marketing & Product Management, Alstom Power

Less than 10 percent of our Alstom GT24/GT26 based power plants are running today as the owner originally thought they would operate. There are several factors contributing to why the world of energy production has changed. Many countries have seen a drastic change in their energy mix. Today, some regions of the world get more than 30 percent of their electricity production by wind and solar photovoltaics, which can experience periods of unexpected production loss caused by environmental factors associated with wind speed and sun exposure. In fact, losses of up to 18 GW within 12 hours have been witnessed in cases when the wind suddenly stops and the sun does not produce electricity in PV units.

A plant manager of an 850 MW combined cycle power plant (CCPP) told me recently, "The first thing I do when I leave the house in the morning, is test the wind speed. Then I know how much we will likely produce that day."

Our customer survey shows that the cost of electricity is still the No. 1 criteria for selecting CCPP equipment. When I started in 1990 in heavy-duty gas turbine development, the No. 2 criteria was emissions. Nobody spoke about CO₂ at that time. Since then, the heavy-duty gas turbine industry has shifted to dry low NO_X combustion – dropping emissions from over 50 vppm for NO_X to single digits.

Today, operational flexibility has become the No. 2 criteria for CCPP equipment. Some of the key areas of focus for our customers include: start-up and shutdown times, loading gradients, primary and secondary frequency support, emission compliant turn-down capability, spinning and non-spinning reserve capability. We develop techniques to park the entire combined cycle at loads below 20 percent to be able to produce a significant number of megawatts in minutes. We see markets where operators start the entire combined cycle power plant twice a day to cover peaks. It is well understood that such flexibility can have economic as well as reliability benefits for operators in competitive markets.

And that is not all: Gas is no longer gas! In a time when plant operators get their fuel from all over the world, equipment manufacturers must be prepared to handle natural gas with a changing mix of components and characteristics. Gas turbines must be robust enough to handle high amounts of various hydrocarbons. We see markets where the portion of butane, ethane, etc. can go above 20 percent volume. In addition, the fuel gas energy density (Wobbe Index in MJ/kg) is changing to ranges well above ±5 percent, a value that was for a long time the industry standard. Current technology can now handle fluctuations above ±15 percent without any changes in the combustion control – and of course be fully compliant with emissions standards – just by the robustness of the burner/combustor system.

Operators are also inquiring about our equipment's ability to handle hydrogen in the gas the units burn – hydrogen that has formed from the excess energy produced by renewables and mix with the natural gas. Therefore, we have validated our equipment for up to 5 percent hydrogen.

You may think that combined cycle equipment does not need these operational flexibility features today. But is it possible for you to predict what features you will need in the next 25 years? Our analysis shows that this is very unlikely. We believe part load efficiency will influence the economics of CCPPs more and more – and by the way, it will influence CO₂ emissions as well. We have developed sequential combustion to achieve highest part load efficiencies. We go a step further and can keep the efficiency virtually constant between 80 and 100 percent plant load. Operational flexibility is likely to become ever more important in our industry. For example, 20 years ago nobody asked us for the ability to run up a 1,000 MW combined cycle power plant in less than 30 minutes to above 95 percent load. Today, it's nearly the norm.

Plant managers understand such challenges very well. Like my colleague who looks to the sky every morning to gauge how much his plant will need to run, they are practical and flexible in responding to such challenges. The industry will continue to do its part by providing technology that maximizes the operational flexibility of CCPPs.