Renewable energy sources, solar collectors
The energetic crisis in 1973 caused the sudden increase in prices
of oil and than of all other fules. The environmental protection aspects and the
development of space explorations have resulted in the increased interest of new,
alternative sources of energy and techniques of electric energy production.
These new, alternative sources of electric energy can be divided into renewable
and non-renewable energy sources.
The renewable sources are: solar energy, wind, tidal, sea waves and sea thermal
(marethermal) energy and the non-renewable sources are: hydrogen,
magnetic-hydro-dynamic energy and fuel cells. Geothermal energy can be both
renewable and non-renawable source of energy: geysers are non-renewable source
but energy of hot rocks is a renewable one.
Because of the rising demand
for energy many dfferent alternative methods of energy gaining are being
considered. One of them is solar energy. The use of solar energy even in our
climatic conditions is economically justified as long as it is used for some
specified purposes. It is the result of the geographic location of our country
and the climate.
When the solar radiation crosses Earth atmosphere while the
sky is cloudless the infiltration degree of radiation amounts to 40-60%. During
winter (and also during summer mornings and evenings) when the Sun is low above
the horizon the way of radiation through the atmosphere layers is longer and
then a smaller stream of energy reaches the surface of a solar collector.
In 1969-1978 the National Institute of Meteorology and Water Management
conducted numerous researches about the amount of energy which reaches the
surface of Earth in our climatic conditions. The findings are presented on the
diagram. It is the average month radiation falling on the horizontal surface.
Solar collectors can be installed everywhere and in any configuration. They can
be installed on the roof or on the ground – even on the rack. But in order to
gain the best effects it is advisable to:
• Turn the glass side of the collector to the south
• Recline the collector (45 degree to the ground – it is the perfect angle for
the use of the collector from February to November)
• If the collector is supposed to be used only during summer (e.g. for heating
the water in a swimming pool or for heating a summer house) than it should be
installed at a 30 degree angle
• Collectors have to be installed in places unshaded by trees, bushes etc.
As an operating factor special liquids like
glycol or ergolit are used because they reduce the deposition of minerals on the
collector and eliminate freezing of liquids.
In low-temperature installations (e.g. heating the water in a swimming pool
during summer) the collectors without the frontal lid are used. They can operate
even more efficiently than standard collectors but only when the temperatures of
the surrounding are relatively high and when the required temperature of the
heating does not exceed 30°C. The collector’s efficiency is a function of its
structural (used materials, thermal insulations, pipeline’s layout) and
exploitative parameters (factor consumption, radiation, speed and direction of
the wind, thermal load).
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