Renewable energies are considered natural and environmentally friendly alternatives to fossil fuels. But with the use of wind, sun, etc., we also intervene in the earth’s natural energy flows. Researchers have now calculated how much energy we can “tap” from the earth system before planetary load limits are exceeded. They also determined which form of renewable energy is most effective in this regard.
Humanity consumes more resources than the earth can permanently supply. In addition, every year humans produce millions of tons of plastic that end up as garbage in the environment. As a result, we are already endangering a large part of the ecosystems, the climate and biodiversity. In order to relieve the earth, more and more researchers are calling for the concept of sustainable recycling management. Materials should be used, processed and reused for as long as possible in order not to be lost as waste. In a truly sustainable society, however, not only the material flows but also the energy flows have to stay within the limits set by our home planet.
How much energy can humanity “tap”?
A central question is therefore: Is there enough renewable energy available globally for our sustainable economy without exceeding the planetary boundaries? Scientists working with Harald Desing from the Federal Materials Testing and Research Institute Empa have investigated this. To do this, they first considered how large the share of renewable energies may be that people divert from the earth’s natural energy flows. Because the earth itself uses solar energy, for example, to “keep in operation” the oceans, the atmosphere and forests, but also reflecting ice surfaces. Most of these subsystems convert the energy, which is largely supplied by solar radiation, into other forms of energy, for example into wind and water currents or biomass production. Regardless of the use, whether in the natural earth system or the man-made technosphere, all of the energy is ultimately radiated back into space.
If humans now use the earth’s natural energy flows, the proportions available to the earth system are reduced. The earth system can only compensate for such disturbances to a certain extent. If they are too big, so-called tipping points can be exceeded. This leads to rapid and irreversible changes in the earth system, for example the polar ice caps are melting, which in turn accelerates climate change. To prevent this, the size of the land used for energy generation must not exceed the earth’s load limit. In addition, the way in which the area is used is decisive: for example, the construction of solar systems in former forest areas disrupts biodiversity, evaporation of water and the reflection of heat into space. The same upper limits as for solar use also apply to the use of chemical energy, for example from biomass.
In order to be able to examine these aspects and influencing factors, the research team converted the various potentials of renewable energy into electrical energy equivalents. In doing so, they based these calculations on the efficiencies of the power plant technology available today. In this way, they were able to determine how much energy mankind is allowed to withdraw from the earth system and use for itself and which renewable energies are the most “economical”.
We should use 0.04 percent
The result: The earth system itself needs a large part of the available energy. 99.96 percent of the energy reaching the earth from space is therefore required to drive the earth system and to produce food. If no planetary boundaries are to be exceeded, mankind can only use 0.04 percent of total energy technically – i.e. for power generation, heat generation and the like, as Desing and his team determined. However, this potential is still around ten times higher than today’s global energy demand.
The calculations also showed: The most effective way to generate energy would be by means of solar energy, because it results in the lowest conversion losses. Because almost all renewable energy resources – including wind and water power as well as biomass production – are ultimately powered by the sun. If you use solar energy directly, less energy is lost. All other energy potentials, for example from wind or biomass, are orders of magnitude smaller than the direct use of solar energy – and some of them are already overexploited, as the research team explains. Nevertheless, they can play an important role locally, in particular because they can reduce the need for storage capacity.
Solar energy: The problem lies in the implementation
According to the team, it would be cheapest and gentlest if all surfaces that have already been sealed, such as building roofs and facades, but also streets, rails and parking lots, are used for solar energy. These areas alone would be sufficient to supply a global society with medium to low electricity consumption, according to the researchers. If there is a higher demand, desert areas would have to be used. However, this is technically and logistically complex and therefore only makes sense if all other options have really been exhausted.
However, the use of solar energy also has its limits, as Desing and his colleagues point out. In theory, it offers great potential for generating energy in a sustainable circular economy. However, the actually available amount of energy will be smaller. Because there are numerous factors that limit the practical use of such systems. This includes the availability of raw materials, but also financial capital and manpower for the construction of the solar systems. In addition, raw material extraction and production, as well as the operation and disposal of the systems, sometimes have significant environmental impacts. Added to this are costs, effort and environmental interventions for the infrastructure, for example for energy distribution and storage.
Source: Empa, specialist article: Energies, doi: 10.3390 / en12244723