Fraunhofer magazine 1.18 ENERGY - 51 The energy transition is well underway in Ger- many, but the climate targets defined under the Paris Agreement are becoming increasingly un- attainable. After all, Germany has not succeeded in reducing its CO2 emissions since 2009. To help turn this situation around, more than 100 experts from the scientific academies involved in the Future Energy Systems ESYS initiative have joined forces to identify solutions. In November, they presented their results in a report entitled “A cross-sectoral approach – Options for the next phase of the transition to a sustainable en- ergy economy.” In line with the climate targets, the aim is to have a flexible and future-proof energy system in place by 2050 that is compati- ble with new technologies. “Germany is entering a new phase of the energy transition. In the last 25 to 30 years, wind pow- er, photovoltaics and also biomass technologies have been developed, expanded and their costs reduced significantly. Now, the basic technol- ogies are available for comprehensive system integration. From now on, the aim is to support and implement cross-sectoral technologies,” explained Prof. Hans-Martin Henning from the Fraunhofer Institute for Solar Energy Systems ISE at the presentation of the study. Alongside acatech Executive Board member Prof. Eberhard Umbach, Prof. Henning chaired the working group that determined key aspects of the future energy supply on the basis of expert discussions, a comparison of relevant energy scenarios and his own model calculations. They then used this information to establish the options available to Germany to optimize its energy system. The calculations were made using Fraunhofer ISE’s REMoD-D simulation and optimization model. This model determines – on the basis of binding CO2 reduction targets – the cost-optimized path Germany must follow between now and 2050 to transform its energy system, taking all sectors and energy sources into account. The energy transition is not just about electricity According to Hans-Martin Henning, the exten- sive model calculations and analyses show that only a holistic, cross-sectoral approach will open up the avenues necessary to gradually convert the whole energy system to predominantly renewable energy, and thus achieve a drastic reduction in the use of fossil fuels. The transition must not focus solely on electricity generation but rather incorporate all three sectors, he says. Eberhard Umbach adds: “Although wind power and photovoltaics have grown considerably in recent years, 80 percent of Germany’s energy is still generated from fossil energy sources. In the building and mobility sectors in particular, fossil fuels still dominate.” In the long term, the researchers expect elec- tricity from renewable sources to become the leading source of energy. The new applications in the mobility and heating sectors, however, may cause electricity consumption to almost double by 2050. Wind power and photovoltaic systems would have to increase their capacity five- to sevenfold as a result – a highly am- bitious task. Efficiency technologies and the targeted use of bioenergy, solar thermal power and geothermal energy could limit the need for additional wind parks and photovoltaic power and thus ensure society’s acceptance of the energy transition. Electricity generated from renewable sources is also the key to reducing CO2 emissions in the mobility and building sectors. “Technologies that use electricity directly and efficiently, such as electric vehicles and heat pumps, are set to play an increasingly important role in the future. It’s important that we start giving these technolo- gies a stronger market presence today. We need to counterbalance the fluctuations in wind and solar energy generation with short- and long- term storage solutions and flexible energy usage models,” says Hans-Martin Henning. Batteries and pump storage units alone are not enough. For this reason, flexible electrolysis sys- tems will be required to generate hydropower for use in industry, in mobility or as large-scale storage solutions. “To ensure the supply remains sustainable, additional energy sources such as hydrogen and synfuels should also be available for sea and air transport, for instance, or to cover seasonal, weather-related bottlenecks,” says Hans-Martin Henning, describing the tasks that researchers must address in the future. A great deal of research is still required to find solutions. Synfuels set to become indispensable Synthetic fuels are set to become a cornerstone of the energy system thanks to their suitability for storage and use in applications for which purely electric solutions can be used only with difficulty or not at all, i.e. air, sea and heavy-duty transport. According to the study, hydrogen will play a decisive role in third phase of the energy transition due its versatility. It can be used, for example, for heating buildings and as fuel for transport, or stored for energy generation at a later time. Converting hydrogen into methane or liquid fuel allows it to be easily stored and transported. The natural gas grid provides an ideal long-term storage solution. Whether in the form of natural gas, biogas or synthetic gas, gas will play an increasingly important role in gener- al thanks to its low emissions and versatility. Reserve capacities, however, will be required to secure the supply in all weather conditions and at all times of the year. Suitable candidates for the purpose include cogeneration plants, low-emission gas-fired power stations or fuel cells powered by hydrogen, natural gas or syn- thetic methane. Restructuring the energy system will be an extremely expensive process. ESYS experts estimate that the supplemental annual costs involved will amount to one to two percent of Germany’s gross domestic profit. As a funda- mental control mechanism, the experts advocate a standard, effective CO2 price. Only this way will renewable energies be able to compete with fossil fuels in the market. Another important consideration the experts highlight is certainty in planning, which is a key factor for investment in environmentally friendly technologies. For this reason, policy makers must commit to meeting binding climate protection targets. According to the experts, an integrated energy system will be in place by 2050. This system will have zero CO2 emissions, yet will remain affordable and ensure a stable and reliable power supply.