Introduction and Structure - Renewable Energy: Technology, Economics and Environment - page 8

nature. In this respect, for instance, wind energy and hydropower, as well as,
ocean current energy (as energy flows) and solid or liquid biofuels (as energy car-
rier; i.e. stored solar energy) all represent more or less conversions of solar energy
(Fig. 1.5).
The energy flows available on earth that directly or indirectly result from these
renewable energy sources vary tremendously, for instance, in terms of energy
density or with regard to spatial and time variations. Since the following explana-
tions are limited to the most important utilisation methods of renewable energy
supply, only the energy flows and the corresponding conversion methods and
technologies will be discussed in detail. They mainly include
− solar radiation,
− wind energy,
− hydropower,
− photosynthetically fixed energy and
− geothermal energy.
The above options of using renewable energies are characterised by very different
properties. For this purpose, within the explanations throughout this topic, first the
corresponding physical and chemical principles of the formation of the respective
renewable energy flow are discussed in depth. Following an excursus on the given
possibilities of measuring the magnitudes relating to the respective energy flow on
site (e.g. measuring the wind speed with an anemometer or the solar radiation with
a radiation meter) spatial and time variations of the renewable energy supply are
addressed in detail.

Geothermal
power plant
Geothermal
heating plant

Geothermal heat

Thermal
energy

Solar energy Radiation Photovoltaic cells

Solarthermal collector
Solarth. power plant

Chemical

Heating of the
earth`s surface and
atmosphere

energy

Ocean thermal
power plant
Heat pump

Evaporation and
precipitation
Melting
Wind
Wave motion
Ocean current

Hydropower station
Glacial ice power plant
Wind energy converter
Wave power station
Ocean current
power plant

Mechanical
energy

Conversion plant

Production of biomass

Electrical
energy

Gravitation
and motion
of planets

Tid es Tidal power station

Fig. 1.5 Options of using renewable energies for the provision of useful energy (Solarth.
Solarthermal) (see /1-1/)