Energy flow is the process of transferring physical energy between different technical or natural systems. In energy technology, one also speaks of energy transmission . The strength of an energy flow is an achievement .
Ecological and technical energy flow
In ecology , energy flow denotes the energy transfer and the energy conversion of radiated solar energy (or of existing chemical energy) in the ecosystem via the biomass of the primary producers and the subsequent food chain (consumer and destructive chain ). The energy flow, like the physical power, is measured as energy per time period . It therefore has, for example, one of the following units , the unit symbols of which are not to be written in square brackets ( DIN 1313 ):
- W (= watt ),
- J / s (= joules per second, 1 J / s = 1 W),
- J / d (= joules per day),
- HP (traditional engineering unit: horsepower , 1 HP = 735.5 W)
In the energy sector, other units are used, e.g. B.
- kWh / d (= kilowatt hours per day) or
- tSKE / a (= tons of hard coal units per year)
If the energy flow is not given for an individual, a population or a technical installation, but for a distributed energy source (e.g. in the primary production of a maize field, in technology in the energy conversion of a solar collector), one gives an area-related one Power on, e.g. B.
- J / (m 2 × d) (= joules per square meter and day) or
- W / m 2 (= watt per square meter).
In technology , energy flow can be described in the same units as in ecology (see energy flow diagram ), e.g. B. the energy flow of the water force ( primary energy as potential energy of the accumulated water) over the obtained therefrom electrical energy ( secondary energy or energy ) and the supply to the traction network for converting the kinetic energy of the trains ( final energy and usable ). With this energy transfer , a large part of the energy is often released as waste heat , for example due to network losses .
Both energy flow systems, the ecological and the technical, are based on the principle of multiple energy conversion , which operates with a certain degree of efficiency with each conversion . With every transition from one form of energy to another, thermal energy is released. In the transition from one trophic level to the next (e.g. in the transition from herbivores to predators) in the course of a food chain, ecological systems often show efficiencies of around 10% or less. The efficiency when changing along technical energy flows can be very different.
In the real world, the ecological and technical energy flows are partially networked with one another, e.g. B. when using water power or biomass as primary energy, or - in the opposite direction - when using the pulling power of a donkey to drive a water pumping system.
Importance of the ecological energy flow
Ecological energy flows can be created for individuals, for populations, for ecosystems or as an energy cycle for the whole earth and allow the calculation of complete energy balances . As a result of the flow of energy through the various trophic levels of the ecosystems, all of the radiated light energy that can be assimilated by the green plant is ultimately released back into the environment in the form of heat in a time-delayed form. By means of the complex equipment of living beings with compartments and enzyme chains , the activity of which can be controlled by the organism, energetic cascades are realized that make the diverse earthly life processes and also the principle of the food chain possible through gradual and step-by-step conversion, storage or release of energy .
Magnitude of the energy flow
The flow of energy through a Central European forest ecosystem is approx. 1 W / m 2 as so-called gross primary production (i.e. biomass production without taking into account the proportion inhaled by the metabolism of the plants) .
The energy flow of an adult human is in the order of 100–150 W. This corresponds to around 3 kWh per day or 10 MJ per day or 4 GJ per year. Man uses this energy for the sum of all his metabolic activities, for his tissue production, his movements and physical work, for his communication and heat production. The total energy consumption per person in Central Europe today is, however, significantly (approx. 20-30 times) higher, since energy in the form of crude oil, wood, electricity etc. is also used for transport, heating, industrial production and other things.
Energy flow and material cycle
The primary energy in ecosystems does not necessarily have to come from the radiant energy of light, but can also come from biochemical reactions (e.g. oxidation of sulfides ). This has v. a. a meaning in oxygen-free regions of the earth (e.g. hydrothermal vents in the ocean). A functioning flow of energy in ecosystems is the energetic basis for ensuring that they can exist with their organism world in the long term and that an ecological material cycle is possible.