renewables – Made in Germany

g Technology and
market overview
The use of solar energy to generate heat is a tried and
tested technology already in use for decades. Solar
thermal energy can be used to heat water and to heat
and cool buildings. German solar thermal energy
companies have many years of comprehensive experience
in producing, planning and building solar heating
systems and their components. The German solar
thermal industry is a global leader.
Technologies and applications
There are two types of solar thermal energy systems for
residential buildings: those used solely to heat water
and those that also provide heating, the latter are
so-called ‘combi-systems’. Around half of all newly
installed solar thermal energy systems in Germany are
used exclusively to heat water �p 125. They are typically
designed to meet all hot water needs during the
warmer half of the year. During the colder half of the
year, a boiler fired by gas, oil or wood, or a heat pump,
supported by the solar thermal energy system on sunny
days, provides water heating. This means that around
60 % of water heating requirements can be met by solar
thermal energy over the entire year.
In 2009, solar combi-systems, which also provide
heating, had a market share of more than 60 % of newly
installed systems in Germany. These have larger solar
collector surface areas and help to heat the building
in the spring and autumn months. Detached houses
usually have installed systems with collector surfaces
of 10 to 18 m 2 . Solar energy typically supplies 10 – 30 %
of a building’s total heating needs, depending on
how well insulated the house is and on the extent of
its heating requirements. There are also special solar
houses that obtain more than 50 % and up to 100 % of
their total heating requirements from solar thermal
energy.
Solar collectors
There are different types of solar collectors. The simplest
form of collector is the unglazed plastic absorber;
these black plastic mats, through which water is
pumped, are typically used to heat swimming pools,
reaching temperatures of 30 – 50 °C. About three
quarters of the collectors used in Germany are flat
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g Solar thermal energy systems for domestic water heating in
a detached house: 1) Collector 2) Solar storage tank 3) Boiler
4) Solar station 5) Hot water consumer (e.g. shower)
f Installations thermiques solaires pour la production
d’eau chaude domestique dans une maison individuelle :
1) Capteur thermique solaire 2) Ballon de stockage solaire
3) Chaudière 4) Station solaire 5) Consommateur d’eau
chaude (par exemple la douche)
e Instalaciones termosolares para el calentamiento de
agua potable en viviendas unifamiliares: 1) Captador
2) Acumulador 3) Caldera 4) Central solar 5) Consumidor
de agua caliente (por ejemplo, la ducha)
plate collectors, the rest are evacuated tube collectors.
In flat plate collectors the solar absorber, which converts
solar radiation into heat, is installed in an insulated
glazed box to reduce heat loss. Flat plate collectors
usually operate at temperatures ranging from
60 °C to 90 °C. Air collectors are a special type of flat
collector, which heat air and are usually used to heat
buildings directly, without intermediate storage.
The heated air can also be used to dry agricultural
produce. Integrating an air-water-heat exchanger can
also enable these systems to heat water for domestic
use. Evacuated tube collectors achieve even higher
temperatures and efficiency factors, because the
strong negative pressure in the glass tubes further
reduces heat loss. A collector is comprised of several
glass tubes. The rotatable mounting of the individual
tubes enables the flat absorber in the glass receiver to
be optimally positioned towards the sun. For this reason,
evacuated tube collectors can also be installed
nearly horizontally on flat roofs. The individual tubes
form a closed system that transfers the heat to the
water via a frost-resistant thermal circuit.
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www.solarpraxis.de / M.Römer
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