In recent years, renewable energies have undergone rapid technological and economic development. In Germany, this process is characterized by the accelerated nuclear power phase-out following the reactor disasters at Fukushima and a strong increase in renewable electricity generation capacities. Renewable energies - in particular photovoltaics and wind power - already cover a quarter of the annual electricity demand. The question of the market introduction of renewable energy technologies has long since given way to the question of market integration of growing PV and wind power volumes. The development in the heating and mobility sector is quite different. A lack of incentive structures and pending technological decisions lead to stagnation at a low level. The heating sector plays a decisive role in achieving the climate targets.
The first phase of the conversion of our energy system was characterized by the broad promotion of various concepts in the electricity, heat and fuel sectors. In the course of technological development and because of political influence, this phase showed quite abrupt changes. Examples are the promotion of pure biogenic fuels or offshore wind power. In the second phase, energy policy must now ensure that energy concepts that are both cost-effective and environmentally and climate-friendly are enforced. This can be achieved through appropriate market mechanisms as well as through a concentration of research funding. The following theses attempt to evaluate the upcoming energy policy decisions regarding energy technology options and their costs from the perspective of an engineering efficiency concept.
Different forms of energy have different proportions of exergy. Exergy is the amount of energy that can be converted into another form of energy without restrictions. The higher the proportion of exergy, the more energy can be used. Electrical and mechanical energy consist entirely, fuels predominantly of exergy. The exergy content of heat energy depends on its temperature and is less than 15 percent at a temperature level of 60°C, for example.
In every energy conversion, according to the Second Law of Thermodynamics, exergy is destroyed, i.e. the energy is thermodynamically devalued. The exergy losses are particularly significant when using electrical energy for direct heating (around 85 percent loss for “PV heat”) or for storage via complex conversion processes (more than 60 percent loss for “power-to-gas”). To put it simply, in the first case a valuable energy source was used below its potential and in the second case a little more than one was made from three units of electrical energy.
The use and storage of energy must therefore be exergy-efficient. In concrete terms, this means that where low-exergy energy in the form of room, service water or process heat is required, low-exergy energy sources such as solar thermal energy, geothermal energy or environmental heat must first be used. High-exergy energy sources should only be used in addition (biomass) or by means of a heat pump (electrical energy).
More than half of Germany's final energy requirements - and thus also CO2 emissions - are in the heating sector. The success of energy and climate policy in Germany will therefore depend to a large extent on progress in the heating sector. This applies equally to the reduction of space heating requirements, the efficient use of process heat and the expansion of renewable energies in the heating sector.
Building refurbishment is only to be promoted to the extent that it makes more sense in terms of CO2 avoidance and economic efficiency than the use of renewable energies. Their potential - in particular that of solar thermal energy as well as geothermal and ambient heat - has not yet been sufficiently exploited in Germany.
“Prizes must tell the ecological truth.” This postulation by Ernst Ulrich von Weizsäcker applies on the one hand to different technologies operating on the same market. The existing mechanisms for integrating the global warming potential through a CO2 certificate trade have not proved to be effective, so that a direct CO2 tax should be discussed again. On the other hand, the previous tariff structure provides incentives for an even demand for energy, especially among medium-sized and large customers, by dividing it into work and performance prices. It is therefore well adapted to a base-load-based generation structure. In an energy system that is predominantly based on volatile energy sources, the tariff structure must create new incentives to shift energy demand in times of high energy supply.
The future electricity supply in Germany will mainly be determined by wind power and photovoltaics. Both energy sources have a good seasonal passability, so that the storage horizon resulting from the volatile supply will be in the daily or weekly range. In addition, there are numerous flexibility options that can reduce storage requirements. Part of these can be tapped through energy supply related tariffs.
The connection between the transport and electricity sectors represents a flexibility option that has hardly been developed to date. It enables the mobilisation of large, decentralised storage capacities. These can decouple generation and consumption over a period of up to several days. They are based either on direct storage of electrical energy in batteries or on indirect storage processes such as hydrogen generation or methanisation. The exergetic quality of energy should also be largely maintained for storage processes in the transport sector.
Although the time window for a reconstruction of our energy system is limited, not all questions of an energy supply in 2050 need to be answered today. This applies in particular to major infrastructure investments in networks and storage facilities. However, as long as the electricity market design has not changed, the feed-in of renewable energies will continue to require a fixed feed-in tariff. In future, however, all cost efficiency potentials must be exploited, i.e. increased support for comparatively expensive small plants or poor locations must be avoided.
The approaches taken so far to restructuring the energy system have mobilised large amounts of private capital and integrated a rapidly growing proportion of renewable energies into the electricity grid. In the future, greater attention should be paid in particular to aspects of cost efficiency and energy efficiency. The lack of a detailed and technologically underpinned roadmap for the further expansion of renewable energies in Germany is currently leading to investment uncertainty and local optimisation strategies with ultimately higher economic costs. A climate-neutral, affordable and thus social energy supply is part of public services of general interest. However, public institutions must ensure optimum cost efficiency through central planning and control.