In the coming years, renewable energy resources are going to play a much bigger role in the energy mix – especially in Germany, but also in Europe and worldwide. However, when it comes to harvesting renewable sources, fluctuations in their availability pose some challenges. These can be overcome. There is no universal solution, because the power generation mix, demand for electric power, and the number and capacity of cross-border power lines differ from country to country. There are basically five key elements that will need to be involved, in various forms and to different degrees depending on the regions concerned, in any efforts aimed at increasing renewable power generation.
1. The first key element is renewable power generation itself. The most important consideration in connection with all renewable energy resources is that they must produce power at a competitive cost in the medium to long term and no longer be dependent upon subsidies. Apart from that, significant differences in the nature of renewable resources have an enormous influence on the importance of the other key elements. For example, a green power share of almost 100 percent in overall production in Norway poses no problems at all, as a share of over 50 percent in Switzerland or Austria. Why? All these countries have enough readily controllable hydropower. In Spain, by contrast, the grid operator Red Eléctrica, which has a green power contribution of 35 percent, has been reporting problems in coping with fluctuations in wind power, which accounts for around half of the renewable power generated nationwide.
2. Extending and expanding the power grid is one of the most important approaches to finding a solution. Red Eléctrica is already working on constructing an additional power line to France. Expanding the transmission network is indeed a very meaningful and worth-while option for balancing out local fluctuations. However, to achieve the targets set for growth in renewable power generation, grids will not only need to expand on a national scale but also extended across borders. In Germany, around 4,000 km of new power lines are needed, including a high-capacity north-south link. A solution that would result in low-loss, long-distance lines that could serve as the backbone of the grid. These are available and have a long history of being tried and tested.
3. In addition to expanding the transmission networks, controlling consumption in an intelligent distribution network, known as a smart grid, affords opportunities for cushioning generation peaks and troughs. As more than three quarters of a regular household’s power demand goes into space heating and hot water, the sluggishness of these thermal processes means that they can readily be brought backward or forward by an hour or two. This area of power usage particularly offers great potential. Specifically, a high-efficiency electric heater in the form of a heat pump, could be integrated and controlled in a smart grid. Adding this additional “intelligence” is needed to coordinate inputs from myriads of decentralized power generators in the distribution network so as to avoid perturbations in the grid.
4. High-efficiency, conventional power plants on standby to take over when the wind is not blowing and the sun is not shining are a further prerequisite for boosting renewable power generation. Combined-cycle power plants can ideally serve as the mainstay of a new energy system, because they are highly versatile in operation and their CO2 emissions are relatively low. But improving the efficiency and versatility of coal-fired plants can also be a module in a new energy policy, especially in conjunction with CO2 capture and segregation. These types of “back up” generation plants are especially important because most countries – including Germany – currently have no energy storage facilities with appreciable capacities that would be capable of absorbing excess power and releasing it again when it is needed.
5. Going forward, however, energy storage is going to play a crucial role. One technology that would be available quickly is conversion of excess electric power into hydrogen, which could be fed into the natural gas system already in place. It should be possible to achieve efficiencies of over 70 percent using this method. Germany has the highest natural gas storage capacity in Europe and can stockpile a quarter of its annual gas requirement. In slack wind periods, the natural gas together with the added hydrogen could be converted back to electric power with an efficiency of over 60 percent in high-efficiency power plants.
In the early phases of expansion of the renewable energy resources, most regions paid little attention to the key factors outlined above beyond renewable power generation. In countries with widely fluctuating renewable power contributions such as Denmark, Portugal or Spain, the energy systems are already coming up against their limits. In Germany, too, the grids are already overloaded in some regions at times, and on some days surplus power has to be “dumped” to other countries in return for cash. It is clear that, apart from the issue of grid construction, we need to address all five of the key elements as soon as possible if we are to achieve the objectives of promoting renewable generation. What is more, it is important to improve efficiency throughout the entire system. Some energy-saving measures pay off after only a few years, so that the investments made can be recovered via the savings achieved.