Content
1
2
2.1
2.2
2.3
2.4
3
4
4.1.1
4.1.2
4.1.3
4.2
4.3
4.4
1
Introduction
Function of a solar thermal installation
Circulation by gravitation
Circulation with speed-controlled pumps
Circulation with photovoltaic powered pumps
The liquid heat transformer medium
Faktors that should be considered for purchase
Flat collectors or collectors with vacuum tubes
Row or parallel connection of collectors with vacuum tubes
Compound Parabolic Concentrator(CPC)
Vacuum tube collectors with liquid or vaporised medium
High-flow- and Low-flow-systems
Positioning of the collectors
Versions of storage tanks
1
2
3
4
4
4
4
6
7
7
7
8
8
8
Introduction
The sun beams during three hours energy into the space which the earth
population consumes in one year (2002)
Because on the earth 95% of the solar energy is absorbed and transformed
into heat, theoretical it will be possible to cover 60% of the yearly energy
consumption by solar energy.
With solar thermal collectors it will be possible to gain 75% of the solar
radiation that touches the earth surface.1
Solar energy makes independent of the always rising oil prices.
In 2003 5% of all single family houses were equipped with a solar thermal
system. These installations saved 200 million litres of heating oil. So the
renewable energies are giving a lasting contribution for the climate
protection und the fulfilling of the German Kyoto obligations.
To reduce the arise of CO2, for electricity generation the German
Government intends to raise the rate of renewable energy till 2010 to 12,5%
and till 2020 to 20%. For the whole consumption of primary energy the rate
of renewable energy should cover 4,2% till 2010 and halve of the
consumption till 2050.2
Solar energy creates jobs – in 2004 in Germany roughly 30.000 jobs in the
branch for solar energy were existing. In 2010 the entrepreneur association
1
2
Vgl http://www.rankweil.at/zwischenwasser/documents/2005/zwischenwasser20050706000024.pdf
Vgl http://www.solarthermie2000plus.de/
of the solar business (Unternehmensvereinigung Solarwirtschaft e.V.)
expects nearly 90.000 jobs.
2
Function of a solar thermal installation
Kollektorfeld
Trinkwasser
Regler
Kaltwasser
Heizkessel
Speicher
Kollektor
Pumpe
Wärmetauscher
Speicher
Zufluss
Heizkessel
collector
array
drinking
water
controller
cold water
boiler
storage
Collector
Pump
Heat exchanger
storage
inlet
boiler
A solar thermal installation will be used to heat up water in a big tank by
solar energy. The heated water will be used for consumption in the
household (Kitchen, washing, shower a. s. o.)
A solar thermal installation consists of
 Heat collector
 Piping system with pump
 Heat exchanger in a tank (storage)
The collector must be installed at a place where it is intensively exposed to
the sun radiation. Such a place is the roof of a building as example.
The collector is connected to the piping system. A pump carries a liquid heat
transformer medium through the collector. Depending on the sun radiation
and the construction of the collector the heat transformer medium can reach
temperatures up to 80°C.
From the collector the liquid flows to the heat exchanger. The piping system
has a strong isolation so that during the transport (as an example from the
roof to the cellar) the lost of heat is as low as possible.
The heat exchanger is situated inside the storage tank where the water will
be heated up.
The heat of the liquid heat transformer medium will be given to the water
inside the storage tank. At the outlet of the heat exchanger the exchanger
liquid has nearly the same temperature as the water in the tank.
The more exchanger liquid runs through the tank and the warmer the liquid
is the faster the water inside the tank heats up. Like the piping system as
well the storage tank is specially isolated and keeps the heat for long time.
Is the solar radiation not strong enough, the water inside the storage tank
can be additionally heated up with a second heat exchanger that is
connected to a heat oil boiler to keep the storage water on the right
temperature.
An overpressure valve protects the storage tank and the whole piping
system against the expansion of the hot water. 3
After the heat exchanger the cooled down exchange liquid must flow back to
the collector. For this circulation different solutions are available:
Gravitation system
Installation with a speed controlled pump
Installation with a photovoltaic driven pump
2.1
Circulation by gravitation
Installations working by gravitation always have the heat exchanger on a
higher point than the collectors.
The heated liquid (low density - light) ascends in the pipes toward the heat
exchanger. Inside the exchanger the liquid cools down (high density heavy) and flows back to the collector through the reflow pipe. In the
collector the cycle starts again.4
3
Vgl http://www.solaranlagen-portal.de/solarthermie/technik/enfuehrung-solarwaerme/einfuehrungsolarthermie.htm
4
Vgl http://www.solaranlagen-portal.de/solarthermie/technik/systemvarianten-solarthermie/solarsystem.htm
2.2
Circulation with speed-controlled pumps
The higher the temperature difference of the liquid heat transformer medium
is between inlet and outlet of the storage tank, so the more heat energy is
exchanged, the faster the liquid can circulate through collector and tank.
With a pump that automatically adapts its speed and capacity to the
temperature-difference it is possible to control the circulation. In the most
simple case the pump will run with the electric current of the in-house
power-supply.
2.3
Circulation with photovoltaic powered pumps
Solar cells give the electric power for the circulation pump. The advantage is
that such an installation can work without mains current. The disadvantage
are the higher purchase costs for because additionally the solar cells must
be acquired.
2.4
The liquid heat transformer medium
The liquid heat transformer medium is a mixture of antifreeze and water.
The anti freeze is necessary to prevent the medium from freezing under low
temparatures5.
Such anti freeze consists of as an example 25% 1,2 Propylenglycol and 5 %
Inhibitors. The recommended dosing therefore is 40% anti freeze and 60%
water. This keeps the mixed liquid fluid down to -27°C
3
Faktors that should be considered for purchase
Number of persons in the household
Average water consumption
Alignment of the house
(perfect: 10° south-west, inclination of the roof 30° - 45°)
An alignment of the collectors in direction to the sun is necessary for a
maximum utilisation. The wave angle of the sun rays is changing during the
day. Additionally the altitude of the sun varies of 47° between summer and
winter.6
Influences of shadows
Surface that should be heated (if additional heating is required)
The general formula
Surface of collectors = number of persons x factor for water-consumption x
surface-correction factor x pipe lengt x location
For the different factors the following tables are valid:
Water-consumption factor:
Hot water consumption Factor
5
6
Vgl http://www.ufesolar.de/fileadmin/doc/preisliste.pdf
Vgl http://www.rankweil.at/zwischenwasser/documents/2005/zwischenwasser20050706000024.pdf
regular (40l.)
1,2
Boosted (50l.)
1,5
high (60l.)
1,8
Surface-correction factor:
south < alignement > east / west
Roof pitch
0°
22,5° 45° 67,5° 90°
15°
1,2
1,3
1,3 1,5
1,7
30°
1,0
1,1
1,2 1,4
1,7
45°
1,0
1,0
1,1 1,4
1,8
60°
1,1
1,1
1,2 1,5
2,0
75°
1,3
1,3
1,4 1,8
2,7
90°
1,8
1,9
2,0 2,5
3,7
Pipe length:
Distance between collector and storage tank
Meter
5
10
15
20
Factor
1,00
1,02
1,04
1,08
Location: (See following map)
Specific local global radiation
Zone I
1,15
Zone II
1,00
Zone III
0,90
4
Flat collectors or collectors with vacuum tubes
Flat collectors are cheaper than collectors with vacuum tubes. But flat
collectors only can gather energy when they are perfectly aligned in south
direction and with a optimal roof pitch.
With vacuum tubes the maximum energy absorption can be reached by
turning the tubes. But such tubes need more roof surface than flat collectors
with a comparable surface.
4.1.1 Row or parallel connection of collectors with vacuum tubes
Basically it is the best to connect several collectors in a row.
Only when larger surfaces should be covered with collectors it is reasonable
to build several parallel lines with identical surfaces.
4.1.2 Compound Parabolic Concentrator (CPC)
CPC-mirrors are semicircular shaped reflectors, that concentrate the solar
radiation at the absorber and thus maximise the energy intake.
Maximum utilisation also with
diffuse radiation
High surface radiation also with
direct, right angle radiation
4.1.3 Vacuum tube collectors with liquid or vaporised medium
Vacuum tube collectors can be operated with liquid or vaporised heat
transformer medium. If it is liquid or vaporised depends on the evaporating
temperature of the medium and the pressure in the piping system.
The advantage of liquid heat transfer medium is a more effective heat
transfer. But if one of the tubes must be replaced the liquid medium
must be partially drained.
The advantage of vaporised heat transfer medium is the better replaceability
because the medium must not be drained in the case that a tube must be replaced.
The disadvantage is the worse heat transfer.
4.2
High-flow- and Low-flow-systems
Low-Flow-Systems are working with a low volume of heat transfer medium.
The volume is less than 25 Litres per m² of the collectors surface.
High-Flow-Systems are working with a high volume of heat transfer medium.
The volume is mostly 50 Litres to 60 Litres per m² of the collectors surface.
The Low-Flow-System reacts faster on changes in the solar radiation be
less medium is in circulation. A piping-system with smaller pipe-diameters
can be used. But to use the high temperature level the storage tank must be
a stratified storage tank.
The High-Flow-System works on a lower temperature level so that the
isolation of the piping system is more simple and cheaper. As well the
efficiency of the collector is better because of less lost of temperature. But
the heat transfer medium must be circulated very often to reach higher
temperatures. The storage tank heats up quite slowly.
Today most of the heating systems are working with the high-flow
technology.
4.3
Positioning of the collectors
There are four different possibilities to mount the collectors.
On roof - collectors on the roof of a building
In roof - collectors are integrates in the roof of a building
Flat roof – the collectors are mounted on special frames to put the collectors
in the best position
Cladding – the collectors are mounted on the wall of a building
4.4
Versions of storage tanks
The simple storage tank suites for simple systems without additional heating
support of a heat oil system.
Trinkwasser
Nachheizung
Solarkreis
drinking water
solar circel
Tank-in-tank-system fits for systems with additional heating support of a
heat oil system.
Trinkwasser
Nachheizung
Solarkreis
Heiszung
drinking water
supplementary
heating
system
solar circle
heater
Stratified storage tanks can be used for both: with or without additional
heating.
Trinkwasser
Nachheizung
Heizung
Solarkreis
drinking water
supplementary
heating system
heater
solar circle
The double storage tank is suitable for multi-consumer systems with
additional heat oil-support
Trinkwasser
Solarkreis
Nachheizung/Heizkreis
drinking water
solar circle
supplementary
heating
system/heating
circle