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Companies to conventional hot-water heating systems, solar
water heaters (swh) can represent an alternative with moderate
costs in countries with high energy costs and sufficient irradiation.
While having significance for the supply of energy in these
countries, the introduction of these new but simple techniques
also opens up possibilities for sustainable socio-economic
development. The circulation of the heat carrying fluid in
the swh described here is effected by the difference of density
between the warmer liquid in the solar panel and the colder
liquid in the storage tank. There fore, no electrical pumps
or control equipment are needed. Due to their simple nature,
these swh can be produced by local craftsmen because of this
investment costs for the set-up of a swh can be reduced and
a swh can become a cost-effective alternative to conventional
hot-water tanks. SWH are used mainly in hospitals and hotels
in developing countries. However there are also market opportunities
in urban surroundings with increasing standard of living.
Projects on SWH carried out in Zimbabwe (1) and Puerto Rico
(3) have already shown successful implementation and stable
market conditions for SWH. At present the Okezentrum langenbruck
accompanies partners in Eritrea in setting up the local production
of SWH. |
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Feasibility
study on SWH: |
Planning
the introduction of SWH in the corresponding partner countries
requires a thorough feasibility study for economical and technical
clarification. The most important technical parameters are
the meteorological conditions which are available as weather
data.
For the thermal use of solar energy such as in SWH, mainly
direct radiation (being part of global radiation can be used
for energy production. Therefore the ration between diffuse
and direct radiation in the area in question has to be checked
care4fully. Diffuse radiation resulting from dust, mist and
cloudily conditions can despite high values of global radiation
in tropical and subtropical regions and has to be taken into
account. Another important considerations the occurrence of
frost do occur, the SWH has to he operated with a mixture
of antifreeze to water at a ratio of 1.3. in this case the
hot water storage tank must be put inside the building which
will raise costs. In regions which experience frosts, the
use of a pump driven collector circulation and placing the
storage tank in the boiler room may be petered. High wind
speeds and low ambient air temperatures usually require the
collectors to be covered with glass, especially if high demands
with regard to hot-water availability and temperature exist.
The use of hardened glazing for solar collection with high
transmission and low emission of radiation, is preferable
for SWH but costs more than conventional glass Conventional
glass can only be used if no hailstorms which can destroy
the glass are known in the region Alternatively, a protective
barrier made of metal grating can be used to protect the glass
be reducing the impact speed of hailstones, but this also
increases the investment costs of the SWH. The ph value of
the water must be taken into account when constructing a SWH
ground water with a strong deviation from neutral jpg 7 can
influence the corrosion of various components heavily and
lead to the early destruction of the SWH. In these regions
the direct flow of drinking water through the collector (open
system) should be avoided.
Using meteorological data the gross solar heat gain of the
SWH can be calculated. The economical efficiency of a SWH
can be estimated from the energy savings made possible in
comparison to a conventional system. Two factors are considered
to analyze the economic efficiency and market potential of
the SWH. First, the amount of energy saved and corresponding
financial savings. Have to be calculated, Second the repayment
time for the investment costs has to be calculated from the
savings made possible through the use of solar energy instead
of conventional energy. |
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Techniques
of constructions |
The
solar collector consists of a copper absorber which transports
the energy of the solar radiation from an absorbing lacquer
to the water. The absorber is insulated against energy losses
by glass on the front and an insulation layer in the soldering
back. If warm climatic conditions prevail, the glassing and
insulation may be unnecessary. As shown in Fig 5 no bends
which will allow siphoning should be present in the absorber
of a gravity circulating system.
Securely connecting the absorber pipes with the collecting
pipes at each side of the absorber is achieved using a special
enlargement tool and hard soldering. The absorber pipes are
soldered to the absorber sheet metal using a custom made soldering
table which allows pressing the pipes downs on the sheet metal
for subsequent soldering.
When doing so, care has to be taken to heat up the absorber
in a regular fashion. Otherwise, thermal stress swill makes
the sheet metal bend and corrugate. For insulating the collector,
a material has to be used which does not release any of its
constituents when heated up. These vapors can precipitate
on the inner side of the glazing and greatly reduce the efficiency
of the collector. The suitability of an insulating material
can be instead quite simply by heating a sample of the material
in a cooking pot and watching if any precipitation occurs
on a piece of glass which covers the pot. The choice of the
proper glazing was already discussed in chapter2.
The collector can be assembled using a simple construction
of metal sheet. For reinforcement of the frame, wood can also
be used.
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