Traditionally the solar energy has used in southern
countries, but it has used also in northern ones. Most popular
kind of use of the solar energy in Latvia is solar collector for
water heating. Traditionally flat-plate solar collectors are used
because of simplicity of manufacturing. However, some
peculiarities in use of solar energy in northern countries must
be taken into account. In northern countries there is lower
irradiance, but longer day and longer path of the sun during
summer. Therefore, traditional flat-plate solar collectors are not
appropriate enough in northern countries and new forms have
to be developed.
There are two forms of solar collectors - cylindrical and
semi-spherical – proposed in this work. Such collectors can be
made for both water and air heating.
Theoretical calculations and measurements of energy gain
from those two collectors were carried out.
Results show that daily energy sum received by the semispherical
collector from the sun at the middle of summer is 1.43
times more than that of the flat one, but for the cylindrical
collector it is 1.74 times more than that of the flat one, or equal
to that of the tracking the sun flat-plate collector. Resulting
difference in energy gain from collector will be not so large
because of the difference in heat loses. Heat loses can be
decreased by switching off the water circulation pump when the
sun is covered by clouds. For these purpose circulation pump
powered by solar batteries can be used instead of complicated
and expensive automatics. Even more important than overall
energy gain is the fact that semi-spherical and cylindrical
collectors work all the day (17 hours in the middle of summer
at 57 northern latitude), while flat-plate collector only about 11
hours. Yearly energy sum received by the collector from the sun
is 1.5 and 1.9 times larger for the semi-spherical and cylindrical
collector respectively as for the flat one.
The cylindrical solar collector is easier to manufacture, but
semi-spherical one is more aesthetical and durable against
impact of the wind. Although solar collectors for water and air
heating are studied in this article, main ideas are applicable also
for solar batteries.
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .