The huge expansion of renewable energy in Europe will have a profound knock-on effect on the fossil fuel power plant portfolios of utilities in the region. Johannes Lambertz, CEO of RWE Power, outlines why older, inflexible coal plants will have to be shelved in favour of flexible plants, including coal, gas and nuclear.


Dr. Johannes Lambertz, RWE Power, Germany

Until recently, any look into the future of the European generation market focused on the threat of capacity constraints. This is indeed justified when looking, for instance, at the DENA study for Germany or the UCTE Generation Adequacy Forecast. However, this angle has to be widened today.

What are the consequences of energy-policy decisions and what is the impact of setting international climate protection targets? What are the new challenges we have to face, especially with respect to technical innovation? Electricity demand can in general be expected to grow all over Europe in the years ahead. There are obvious reasons for this: enhanced energy efficiency goes hand in hand, for instance, with rising living standards in Eastern and southeastern Europe, but above all with increasing electrification, too. Just think of the large number of modern devices such as computers or PDAs that nowadays are part and parcel of many private households. Or think of heat pumps operated by electricity; or the growing segment of electromobility.

It is obvious that this growing demand cannot be met by the development of renewable energies alone. Conventional power plants will still be required. However, they will also have to face enormous challenges resulting from the capacity growth, especially in the wind power segment. What is most important for the energy industry is the wise integration of renewable energies into the power generation market. Their continuous development will be reflected by an increasingly variable dispatch of power plants and more price volatility.

Against this backdrop, the existing and new conventional power generation capacities have to become much more flexible in response to growing volatility, in both technical and economic terms. These aspects will be at the centre of this article. Its focus falls on conventional power plants rather than storage technologies. The latter will continue to be developed and expanded by innovation and RWE is taking an active part in this process with several projects, such as the development of adiabatic compressed-air storage. The capacity of storage power plants in Germany currently totals about 7000 MW. However, due to the low storage volume, no more than just over two per cent of the average daily electricity consumption can be supplied with this capacity. This is nowhere near enough to meet the strong growth in demand for flexible generation resulting essentially from wind volatility.

Major fluctuations expected for electricity prices 

The targets for CO2 reduction and resource conservation are a crucial factor for the change in power generation at European level. The International Energy Agency expects the installed capacity for wind and solar power to grow from 57 GW and 5 GW respectively to 138 GW and 30 GW, in the 27 EU countries between 2007 and 2015. Capacities of 138 GW for wind and 48 GW for solar are then forecast for 2020. This has major economic implications. About 50 per cent of the expected capital expenditure will be accounted for by renewable energy.

Figure 1. Wind and solar together dramatically change the need for flexibility Source: RWE Power

The growth of installed capacity, however, does not automatically correlate with higher electricity output on the same scale. Quite simply, the wind blows whenever and wherever it likes, but not always exactly when the consumer needs it. The impact of these unpredictable fluctuations is felt in particular on extremely cold or hot days: electricity demand is high, but no wind is blowing because of stable high-pressure systems in the atmosphere. What is more, greater wind velocities do not automatically result in more power output. This is because more and more windmills have to be shut down as wind speed increases, in order to protect the systems.

Another example shows the particular challenges both system operators and power plants are confronted with: on the first weekend in October 2009, electricity demand was very low in Germany; at the same time, the wind turbines produced at full load and fed electricity into the grid. In this situation, gas fired power plants could reduce their output, and hard coal-fired and nuclear power plants cut their production. The remaining power surplus was still quite significant and was largely exported across borders, especially to the Netherlands, France and Poland.

In fact, an extra €500 ($660) had to be paid per megawatt-hour for the electricity to be taken off. Exactly the opposite then happened on 6 January 2010. Out of 25 800 MW of installed wind power capacity, only 300 MW were feeding into the system. This means that only 1.2 per cent of the wind power capacity could actually be used.

If it had not been for conventional power plants, 996 out of 1000 residential households, industrial companies and commercial establishments would have had to be shut down. Similar fluctuations also have to be taken into account for solar electricity. A capacity of just over 9.5 GW is currently installed in Germany. A look at the statistics from February to July 2009 shows that only 728 MW were generating power on a weekly average.

Whoever carelessly puts the blame for this development on the conventional power plants, holding them responsible for network congestion at the expense of renewable energies, is not telling the whole story. These power plants, especially nuclear power plants, are very responsive when their power output has to be increased or reduced as quickly as possible. They are able to ensure supply security in situations where renewable energy sources tail off, such as the wind suddenly calming down or the sun becoming obscured by clouds. Power generation from renewable energies can already fluctuate by 20 GW within a single day. This order of magnitude will keep increasing in the next few years as the development of renewables continues in Germany.

What do these developments mean for an electricity generator? As far as our current and future plans for power plants are concerned, we must keep our sights firmly set on the intended massive growth of renewable energies. This is because every single megawatt of new capacity for wind and solar power requires about 0.9 MW of baseload power plants as back-up.

However, what could this back-up look like? Other renewable energies such as biomass, geothermal and hydroelectric power are not yet available in sufficient quantities and their potential is limited. This is why gas was primarily in focus as the fuel for flexible power generation until recently.

RWE Power responded by adjusting its power plant portfolio. In fact, in 2006 we built topping gas turbines in two units of our lignite-fired power plant at Weisweiler near Aachen to be better able to meet the load requirements. Our strategic approach of operating this baseload power plant also in mid-merit and peak load by way of topping gas turbines proved its worth already in the first few weeks of operation.

Figure 2. RWE power plant portfolio – 2008 vs. 2013/14: strong investments in “smarter” and “greener” megawatts Source: RWE Power

Even today, four years later, this assessment has not changed at all. However, the market environment has become even tougher: flexibility is of the essence more than ever before. The answer consists in technical innovation and cutting-edge power plant technology. Intelligent control and flexible dispatch of all energy sources is therefore required for a viable energy mix that is fit for the future. This is why RWE has developed a three-pillar strategy for our conventional power plant portfolio.

1. Gas fired power plants 

Fast start-up and shut-down, steep load ramps – these are the key attributes of gas when it comes to balancing out fluctuations in the power grid. Apart from the topping gas turbines at Weisweiler, RWE Power is growing its gas expertise with two projects at the Lingen site. Last year, we started a €200 million project there, by which we are replacing four old turbines in the existing gas fired power plant with new powerful models from Rolls-Royce. The project is due to be completed in 2011; our state-of-the-art combined cycle gas turbines power plant is already coming on stream in the spring of this year. It comes with 887 MW, an efficiency of over 59 per cent and with a total investment volume of €500 million.

These are two more examples of how we secure efficient energy supplies fit for the future with new technologies. In partial load operation, however, the efficiency of this power plant type is significantly lower, which is why this mode of operation is relatively expensive, and, what is more, gas has to be imported. A realistic assessment has to reflect both these aspects. 

2. Hard coal fired power plants 

Reducing output from 800 MW to about 200 MW in less then 30 minutes and going back up to full load, this is what the two hard coal fired units that we are currently erecting at Hamm/Westfalen will be able to do. With their state-of-the-art technology, they can temporarily also be operated at 25 per cent of rated power, which is a significant advantage over older hard coal fired power plants. When electricity is in plentiful supply, this will enable us to respond better to the load requirements and price signals in the market. And hard coal gives us another advantage: Global reserves will last for around 140 years and thus four times longer than the world’s oil reserves. Hard coal is mined in many countries and therefore reliably available irrespective of the political development in individual regions. Our new power plants reach an efficiency of 46 per cent and emit 30 per cent less CO2 compared with older plants. What is more, they will be capture-ready, which means that once the option of carbon capture and storage (CCS) is commercially mature and available after 2020, we can retrofit the power plants with this technology to further reduce our carbon footprint. 

3. Nuclear energy and lignite 

Lignite fired and nuclear power plants have a much greater potential for flexible dispatch than is commonly known. By using sophisticated instrumentation and control systems, for instance, the plants are able, just like hard coal and gas fired power plants, to balance out fluctuations in the power grid so as to contribute to stability in the system. Slow power plants? The prejudice has long since been overtaken by the reality of technology! 

A. Lignite 

Lignite requires a more variable range of operation to secure its role in the energy mix. This requirement is met with the BoA technology (lignite-fired power plant with optimized plant engineering). It comes with modern power plant control performance so that temporary part-load operation is possible without major efficiency losses. The electronic control system knows all parameters of the plant and can change much faster from the actual condition to the required status.

Moreover, the design boundaries of materials (e.g. pipework) can be better exploited. The I&C technology can control individual components much more precisely and thereby adjust steam and water temperatures with a high degree of precision. The same applies to the air supply for combustion. This leads to reduced emissions.

How flexible today’s lignite fired power plants already are is demonstrated by the following comparison: 300 MW units can be reduced in part-load operation to up to two thirds of their rated output. Our BoA 1 plant that came on stream in 2003 and the second and third units currently under construction can even be reduced to half the rated output.

Although the BoA units are significantly larger plants with capacities of over 1000 MW, their control performance is much superior to the 300 MW units. This factor is also noteworthy in comparison with the aforementioned gas fired power plant at Lingen whose output can be reduced or increased by some 38 MW per minute. The BoA technology (lignite fired power plant with optimized engineering) reaches a value of about 30 MW per minute.

Figure 3. RWE’s strategy is threefold: sprinting; lurking; and gliding, diving and rising Source: RWE Power

However, the control performance is only half the story. Equally important is the economic efficiency of part-load operation. In this respect, we have also made significant progress with the BoA technology that already achieves the characteristics of modern hard coal-fired units. At the same time, it comes with a significantly enhanced efficiency of 43 per cent. The 1000 MW plant emits about 3 million tons less CO2 than older power plants with the same input of coal.

But we will not stop here. In our coal innovation centre, where we are advancing processes to improve the climate friendliness of the domestic energy source, we are developing a process to pre-dry the coal (fluidized bed drying with internal reject heat utilization). Before combustion, the lignite is processed and pulverized in a fluidised bed dryer using process heat so that its water concentration is lowered by some 80 per cent and the combustion process becomes much more efficient.

The results produced with this technology developed in-house by our engineers are so promising that we plan to build the next generation of power plants as dry lignite fired power facilities. This will enable to us to reach the level of modern hard coal fired units and to be even partly competitive with gas fired power plants, for instance, in the event of load changes. These are bright prospects for the future of lignite. 

B. Nuclear energy 

It is widely known that nuclear power plants are an established option to produce electricity on a continuous basis. It is less known, however, how flexible their operation is. Even modern gas turbine power plants cannot get close to the steep load ramps of nuclear power plants, which can cut their output by half from 1260 to 630 MW within just a few minutes. In France, the electricity system has long since been stabilized by nuclear energy when solar and wind power fluctuate.

In Germany, too, this advantage is used more and more. Look at what happened over Christmas in 2009: low consumption coinciding with high wind power input led to a situation where our nuclear power plants at Gundremmingen, Biblis and Lingen reduced their output by some 1500 MW in 100 minutes, which is equivalent to about 30 per cent of the capacity installed (excluding the currently shut-down Biblis A unit), thus making a significant contribution to system stability.

Overall, some 9600 MW of output can be cut within 15 minutes in Germany’s nuclear power plants. This control performance clearly shows that nuclear power plants can support renewable energies quite substantially.

So there is no contradiction at all, both energies are rather pillars of the same bridge. What is more, the nuclear power plants avoid about 150 million tons of CO2 every year. If we wanted to achieve a similar effect in road traffic, all the cars in Germany would have to stay in the garage. The need for extended lifetimes of our plants in Germany becomes quite clear against this backdrop, too. 

Broad-based energy mix secures reliable electricity supplies 

There can only be one conclusion from the assessment of the various energy sources: the mix is important. We need a broad-based energy mix of renewable energies combined with gas, hard coal, lignite fired and nuclear power plants that can be dispatched flexibly and balance out the fluctuations of renewable energies. It is the best guarantee for secure and reliable energy supplies in the long run.

This is why RWE invests systematically in the construction of new power plants and is currently erecting about 12 GW of these ‘smart’ generation capacities. We are also modernising our existing fleet and extending our research and development projects. This is because we intend to demonstrate the energy to lead with smart megawatt capacities. 

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