It’s the paradox of Germany’s energy transition— even though renewable energy sources such as wind and photovoltaics are being expanded on a massive scale, carbon dioxide emissions aren’t declining as planned. On the one hand, this is due to the fact that coal-fired power plants are still needed for much of the base load, because the amount of energy generated by wind and solar sources is unpredictable. Another factor is that market mechanisms benefit old, long-amortized coal-fired power plants. Given these factors, state-of-the-art combined cycle power plants have often turned out to be uncompetitive, even though they produce very low emissions and generate electricity reliably and flexibly.
The Future of Energy
A Gas-Fired Plant for the Energy Transition
By providing base load electricity, fossil fuel power plants are expected to ease the transition to a renewable energy economy. But as they do so, they will have to minimize their emissions and maximize their flexibility. An example of this is the Lausward Power Plant in Düsseldorf, which has set several benchmarks.
A significant departure from this trend is represented by Stadtwerke Düsseldorf AG, an energy utility, which has benefited from Siemens technology. The Fortuna unit of the utility company’s Lausward Power Plant demonstrates that generating electricity from natural gas can make economic and environmental sense. Fortuna is the most efficient combined cycle power plant in the world. The facility’s cutting-edge H-Class Siemens gas turbine has set three world records. A few months ago, the plant achieved the highest energy conversion efficiency recorded in power generation: 61.5 percent. As a result, it emits just 230 grams of carbon dioxide per kilowatt-hour when its district heating is used at the same time.
In its first year of operation, the gas-fired power plant and the Düsseldorf district heating system together saved 600,000 tons of CO2 emissions. That corresponds to the amount of carbon dioxide produced by approximately 265,000 new passenger cars, each driving 15,000 kilometers a year. A forest covering 160,000 hectares (the size of London) would have been needed to offset this amount of CO2. By 2025, the power plant will have saved more than one million tons of CO2 emissions.
Fortuna’s second feat is that its generating capacity has reached record levels of up to 603.8 megawatts. Moreover, the unit can supply around 300 megawatts of thermal energy for Düsseldorf’s district-heating distribution system — another world record for a power plant consisting of only one gas and one steam turbine.
All told, Fortuna’s environmental performance is outstanding. But does the unit also make economic sense in view of Germany’s adverse market mechanisms? The answer is yes because Fortuna is operated as a combined heat and power plant. This means that it not only produces electricity, but also channels its waste heat into the utility company’s extensive district-heating distribution system. The waste heat that the gas turbine produces — with combustion temperatures of up to 1,500 °C— is recovered for power generation by a downstream heat recovery steam generator in the steam turbine. The steam turbine uses the same shaft as the gas turbine and the generator. Steam is extracted from the steam turbine and channeled through three pipes to the heat exchangers in the neighboring building, where the steam heats up water for district heating. Depending on the outside temperature, this water can be at 95 degrees Celsius, for example, when it flows through an insulated pipe underneath the Rhine River and on to the Region.
Fortuna is operated in a heat-controlled mode on days when sufficient electricity is available from wind and solar power. This means that the power plant maximizes the utilization of waste heat for district heating purposes. By the end of 2016, the utility company also started the operation of a 54-meter-high water tank with a volume of 35,000 cubic meters. The tank will store hot water for several days, giving the utility company added flexibility in terms of deciding what mix of electricity and heat Fortuna should supply.
The combined cycle facility’s start-up behavior greatly increases its flexibility. Thanks to its “co-start” function, the power unit can achieve maximum output just 25 minutes after it’s turned on. This is twice as fast as other combined cycle power plants. Moreover, Fortuna consumes less fuel and emits less CO2 during start-up. This is because the steam turbine starts up at the same time as the gas turbine instead of with a delay. In addition, the steam turbine ramps up its output as quickly as possible until it reaches full capacity. “It’s a world premiere,” says Siemens Head of Project Engineering Willibald Fischer, who used to be Siemens’ program director for the SGT5-8000H gas turbine in the Fortuna unit. The co-start function makes the entire power plant significantly more flexible, as does new Flex-Ramp technology, which enables the unit’s output to be quickly ramped up by up to 55 megawatts per minute.
Combined cycle power plants are in demand worldwide. One example is South Korea, where Siemens already has eight H-Class gas turbines in operation and seven more being assembled. The biggest order for these turbines has come from Egypt, which is building three large power plants with eight gas turbines each. These turbines are the same size as the one in Lausward, giving each power plant a capacity of 4.8 gigawatts. Egypt is building the new power plants to ease its shortage of electricity and reduce emissions. In May 2016 the first four gas turbines were sent to Beni Suef, where the facilities will gradually increase their output until they reach their full capacity of 14.4 gigawatts in mid-2018.
The Egyptian megaproject demonstrates that simultaneous power generation from fossil fuels and renewable sources isn’t a contradiction. On the contrary, the two types of energy sources perfectly complement one another. In addition to its three big gas-fired power plants, Egypt plans to build several wind farms with a total output of two gigawatts. The project will therefore have a combined capacity of 16.4 gigawatts and increase Egypt’s power generation capacity by 50 percent.