TOP 5 methods to increase efficiency of a solar collector

This video will not describe traditional and
well-known methods. For example, I will not describe this Danish
solar collector with this additional polymer film which significantly increases the collector
efficiency if it must produce heat of high temperatures. This type of solar collector forms the world's
largest solar thermal station which produces heat for the district heating of the Danish
city of Silkeborg. Or for example, we understand that reducing
the distance between these pipes of the absorber of a solar collector increases its efficiency Therefore we can come up with the idea of
this solar collector with this absorber, which was made in Finland from two thin sheets of
stainless steel.

Or we can come up with the idea of this homemade
absorber which should be placed under a glass sheet, and now I show how that absorber was
made of steel sheets. So, I will not talk about traditional methods,
for example, about radical increase in efficiency of a collector due to selective coating of
its absorber, or about increasing the thickness of the thermal insulation of the north wall
of a collector.

However this video will describe a ranking
of the following 5 non-traditional methods, from the least effective to the simplest and
most effective method. We know about these solar panel rotation systems
according to the movement of the sun across the sky from morning to evening. A similar system is called a “tracker”,
and it increases the electricity production from its solar panels by 20-40 %. These percentages can be noticeably greater
for cases where a solar collector is installed on such a tracker, especially for cases of
a large temperature difference between the liquid inside solar collector pipes and the
ambient air. It is interesting that trackers of such large
solar stations cost several tens of dollars per sq. m, and this is only 10-20 % of the
cost of a traditional solar collector, although small trackers can cost more than 100 $ / sq.
m.

So, it may seem to us that installing solar
collectors on such trackers makes good economic sense for cases of a cheap tracker and if
the cost of our solar collectors is more than 100 $ / sq. m. But we must understand that traditional trackers
are designed for lightweight panels, and not for heavier solar collectors, and their summer
effect is noticeably greater than in winter. We know about such air solar heaters where
solar radiation can heat air to almost 100 ºC. We also remember this solar collector from
Finland, and it has this absorber for heating liquid In addition, the Finnish collector has this
fan for circulating ambient air through the space between the absorber and the glass sheet,
and may be also through the space under the absorber.

So, we have the opportunity to connect the
Finnish collector with an air solar heater which will heat air for its circulation through
the Finnish collector. Obviously, the hot air will increase the efficiency
of the Finnish collector because it will reduce heat losses from the collector through its
glass sheet. In addition, the hot air can transfer heat
from the air solar heater to the absorber of the Finnish collector. The economic sense of this idea is based on
the fact that our solar collector is many times more expensive than the air solar heater
which increases the efficiency of our collector by several tens of percent.

Now I will show four of my experiments which
measure the efficiency of this simpler version of our idea, but without the fan. This part is our solar air heater, and this
part is our solar collector which uses this polymer absorber to heat water. My first experiment measured the efficiency
of this homemade solar collector where that absorber was covered with a transparent polyethylene
film. This is the first experiment when the collector
heated 26 liters of water of this tank from 22 ºC to 69 ºC for 2 hours. One hour later, the temperature of those 26
liters increased to almost 79 ºC. This is the idea of the second experiment
when this black film should heat air which rises here to give its heat to that black
absorber for water.

It turned out that now the black absorber
produces 14 % more heat compared to the first experiment. Unfortunately, the thickness of the air gap
under the transparent film was only 5 cm, and therefore the air transferred its heat
to the absorber very poorly. This is my third experiment when I added this
wooden stick with a length of 25 cm, and therefore now the hot air better goes up to the absorber. This fact noticeably increased the efficiency
of the absorber, and now it produces 24 % more heat than it was in the first experiment. This is my fourth experiment where the thickness
of the air gap under the transparent film is 15 cm, and this is 3 times more than it
was in the case of the second experiment. This graph shows how the thermal capacity
of my solar collector decreased due to an increase in this temperature difference between
its water and the ambient air during the first experiment, the second experiment, the third
experiment and the fourth experiment. Experts may be interested in these results
of my measurements of the energy parameters of my solar collector for the cases of those
four experiments. We know that a solar collector can produce
heat during cloudy weather, but this heat has a low temperature which is several degrees
or several tens of degrees higher than the ambient temperature.

Thus, we can add a cheap plastic tank for
cold water which will be heated by our solar collectors during cloudy hours. In addition, the cold water can be heated
during sunny mornings and evenings when our collectors are not able to produce heat of
the high temperature we need, but they are able to heat the cold water. The heat of the water can be taken by a small
heat pump which will increase its temperature to the level we need. This idea may be interesting for large solar
stations where that plastic tank and that heat pump can increase their heat production
by several tens of percent. In addition, this idea can radically improve
solar space heating of a European house due to the fact that European December and January
have only several sunny days per month.

Therefore the increase in heat production
of European solar collectors during December and January may be several times, but this
effect in America or Asia will be noticeably less due to sunny winters The Internet can help us find such graph which
shows this heat production per one day from this flat plate solar collector, depending
on this temperature difference between the liquid inside the collector pipes and the
ambient air. We can notice that if the temperature difference
decreases from 50 ºC to a level of 30 ºC, the heat production increases 5 times for
a cloudy day, 2 times for a partly cloudy day, and 1.5 times for a sunny day.

So, we should try to reduce the temperature
of the liquid inside our solar collector as much as possible, and usually we can find
some traditional and non-traditional opportunities to achieve this. For example, sometimes we can refuse antifreeze
inside collector pipes, or we can increase the performance of the heat exchanger which
transfers heat from the antifreeze to water of our heat storage. Very often, we can achieve a noticeable decrease
in the temperature of the collector liquid if we increase the volume of our heat storage. Sometimes we need to increase the performance
of our pump for circulating the liquid through our solar collectors. A large solar station can use a variety of
complex schemes, and for example, one of my old videos analyzed this scheme with these
3 heat storages for different temperatures. This is my neighbor’s solar hot water system,
and these mirrors give additional solar radiation to these simple solar water heaters.

Obviously, the additional radiation significantly
increases the efficiency of the solar heaters and the temperature of heating their water,
and here we see the edge of the zone where the solar radiation from the mirrors falls. These are my two experiments when these mirrors
significantly increased the heat production of these solar water heaters. The mirror of the left video is located on
the south side of the solar heater, and the mirror of the right video is installed north
of the heater.

But it is obvious that we will achieve the
maximum positive effect if we place the mirrors on both the north and south sides of our solar
heater. The mirrors can increase the heat production
of our solar heater several times, especially if they are not flat, but curved, as we see
now. It is important to note that I did not pay
anything for these mirrors because they were made from similar mirror strips which are
garbage from glass workshops. This is another type of mirror for our solar
heaters, and the price of these stainless steel sheets is only 12 $ / sq.

M. I bought this mirror mylar film from one of
the Ukrainian manufacturers at a price of 20 American cents per sq. m. This is one example of the use of that mirror
film on the south side of a fence or building where the film provides additional solar radiation
to this solar heater. Obviously, a similar effect will be under
such walls with sheets of mirror stainless steel or under such mirror windows. But we must understand that stagnation can
destroy our solar collector if it is not ready for very high stagnation temperatures due
to additional solar radiation from the mirrors.

That is why similar experiments with mirrors
are recommended only for a cheap homemade solar heater, for example, for this..

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