SOLAR ENERGY-2

Hi friends, now we will discuss on the topic
renewable energy that is solar energy production part 2. The content of this discussion is the techniques
for solar energy conversion to usable form, that is solar thermal and solar photovoltaic. So if you see the solar energy can be used
into different forms into different routes. So solar energy is converted to organic food,
organic materials through the plants, through photosynthesis. Solar energy can be used to produce hydrogen,
photocatalysis routes. Solar energy can be converted to electricity
through photovoltaic routes.

Solar energy can be converted to heating through
thermal route and then that heat can be used further for the production of electricity. So there are a number of ways or the routes
through which the solar energy can be converted to usable form. So this is a very complex process, still the
simulation of this process is not possible, this is under development, that is the hydrogen
production through photolysis, this is already developed, this photovoltaic is also developed. So, we will discuss this thermal route and
photovoltaic routes for the production of electricity by this solar energy. So we have thermal conversion and we have
PV conversion, basically we will be concentrating on these two routes.

Now see already passive design of building
helps us to get solar energy for heating applications, that is not actively or directly using some
liquid or something to capture the energy and then like this, that is that building
is designed in such a way that we are able to get some amount of energy automatically
by that way, but by using some heating device also, we can collect more energy for this
application. Here at the rooftop, we can use some heating
device that is collector that will collect the heat. Then we can send the liquid or that is water
here cold water, it will pass through it, the sunlight is coming here and the water
is heated and it is coming to this, and then there is some heat transfer, so then that
way we can get the energy collected at the top is available in the room and then we can
exchange this energy here also.

So, here we have used some external device
which is collecting the solar radiation and helping to heat the liquid pass through this
particularly designed device so that is called solar thermal technology and where the thermal
collectors for water heating, space heating and other uses we can use. So we can send here the water or we can send
here air also, if we send air, then also air will be heated and the room will also be heated,
and if we use the water, then also the water will be heated and then can be used for other
application, but this technology normally the temperature of water does not rise very
high, then the temperature of water maybe 60-70 like this, 70 degree centigrade like
this.

So, solar thermal collector, which we are
using at the top, that may be of different types. It may be flat plate collector, it may be
evacuated tube collectors, or it may be a concentrating collectors. So there are basically 3 types of collectors
so far has been reported that is a flat plate, evacuated tube, and then concentrating collectors. So, we will be discussing these one by one. The main uses are water heating and space
heating for homes and business establishment by this technology. But when we use concentrating collectors,
then we can get very high temperature water or even can produce high temperature steam
and that can be used for the production of electricity in steam turbine. Now, we will see the flat plate collectors. A flat plate collector consist basically an
insulated metal box with the glass or plastic cover and then a dark-colored absorber plates,
so this is the construction of different parts of a flat plate collectors.

Solar radiation is absorbed by the absorber
plate and transferred to the fluid that circulates through the collector in tubes and in air
dry collector the circulating fluid is air whereas water can be used also as a fluid,
and in some cases some anti-freezing agent is also used, otherwise if the temperature
is lower inside the room below say 0 degree centigrade, it will be frozen, so that anti-freezing
agent is also used to capture the sunlight when the temperature is very very less it
is say below 0 degrees centigrade.

Here we see the flat plate collectors, here
water is coming here, so we have your absorber plate, then sunlight is coming here and then
absorber plates will absorb it and it will be heated up and then through which the tubes
the water is going through so that will be heated and will be coming out. So, this is a very simple design of this,
primitive design we can say, that is it is a box type arrangement. Then from the top, the sun is coming, sunlight
is coming and then from this we are having the water flow or air flow and we are getting
here the heated water, but this method as I have mentioned that 30 to 70 degree centigrade
temperature rise can be available in this case, we cannot get very high pressures steam
that is the flat plate collectors, and basically these are used in home applications like residential
hot water heating. Then evacuated tube solar thermal design came
later. These collectors use a thermos bottle type
arrangement or collector.

So in this case, the vacuum is created so
that the vacuum due to the availability of vacuum it is able to give the high temperature
water, so the temperature of the outlet of this collector is more than that of the flat
plate collector and the vacuum acts as insulator and reducing any heat loss significantly to
the surrounding atmosphere either through convections or radiations making the collector
much more efficient than the initial insinuating that flat plate collectors have to offer.

So this is the features of this evacuated
tube solar thermal collectors. Then we are coming to concentrating collectors. So this is the latest development of this
collector, that is sunrays after incident those are directed in such a way that will
be focused on a certain point or in a central line. So the concentration of radiation will be
higher at the receiver. So here we have two things, one is your concentrators
and another is your receiver.

So concentrators or collectors, so those are
initially collecting the sunrays and then it is focusing these rays to a focal point,
on a certain point that is the receiver. So one is collectors and another is receivers. So depending upon the shapes of these collectors
and receivers, the extent of concentration also varies which is defined by the optical
concentration ratio that is average flux over the receiver divided by flux over the aperture
of the collectors, that is how much insolation is coming on the collector and then how much
insolation we are getting at the receiver.

So receiver insolation divided by the collector
insolation that is we can say optical concentration ratio. As you see here for this, we need some mechanical
help, that mechanical design will play a role, we may we may need to change the orientation
of the collector or we have to equip it in such a way that maximum concentration is possible. So here we see the plane reflector plane receiver
if we use, then the concentration ratio can be 1 to 4, but if we use the conical reflector
and then cylindrical receiver, then you can get 4 to 10, if we use parabolic cylindrical
reflector and cylindrical receiver, then you can get 10 to 100.

When it is paraboloidal reflector and spherical
receiver that will give us 10,000 up to. So that is the maximum capacity or the maximum
concentration we can get by this type of arrangement. So we see here the different types of concentrating
collectors, one is your parabolic trough system, so this is trough systems, like this type
of structure it is the trough. So it will be if we have a tube here so water,
rays will be coming here and these after reflection it is going and concentrating on this, so
this is our receiver, so this is a parabolic trough. So it may be a parabolic dish, so here the
parabolic surface, rays are coming, then incident, after its reflection it is going and then
it is it is focusing on a point.

So there are some mirrors, here also some
mirrors are there. So rays are coming and it is being reflected
and it is being concentrated. So here it is, this rod is there, here the
point is there for the concentration, and a receiver for the collecting of the concentrated
rays. Here, we may have the power tower, so power
tower, so we have mirror at the bottom, so ray will come and it will be reflected and
will be focused on the point at the top, so this is called power tower. So these are 3 major important designs for
the collection of the sunrays by these concentrating collectors. Apart from these, we have stationary concentrating
collector. So stationary concentrating collectors use
compound parabolic reflectors and flat reflectors are used for directing solar energy to an
accompanying absorber or aperture through a wide acceptance angle.

So as the wide acceptance angle means due
to the use of wide acceptance angle, these reflectors eliminates the need for a sun tracker,
so sun tracker is not needed for this type of the stationery concentrating collectors. These are some photographs how it looks like,
so parabolic disc and parabolic trough, so how it looks like it is shown here. So you see here, it is a disc that is after
reflections it concentrates to this one point and then here it is a tube, so it is concentrated
on a tube, that is the parabolic trough. Now, we will see how can we calculate the
performance of a flat plate collector, the primitive one say, how can we determine the
collector efficiency, we will discuss now.

So in a flat plate, as you have seen that
one flat surface is there, so where we have here one surface and then sunray will come
and it will be taken up by the plate and some amount of energy will go out. So energy in is your Ein and energy out is
Eout. So Ein–Eout, so that is the energy taken
up by the water or we can say that energy gained by the system. So useful energy gain we can say that is equal
to, Qu = Ein-Eout, that is energy which is coming inside this that will be absorbed first,
that will be collected by the collector, then it is absorbed from the top and the transmitted
towards the bottom where the liquid is flowing.

So we have two terms here say collector efficiency
that will influence the overall efficiency of the process, then absorptivity of collector,
how the collector is able to absorb the solar radiation that will also influence the overall
performance. Then transmissivity of glass cover, so one
glass cover at the top, so how it is transmitting the light so that will also influence the
overall performance and here we have insulation, here through which the water is passing through
the tube we have some insulation, so there will be some losses of heat energy through
this if insulation is not proper, so that insulation loss is there, so overall loss
coefficient is also considered which is important and will influence on the overall performance
of the system.

This Tf and To, temperature of the fluid in
the tubes and the ambient temperature that will also influence the performance. Another is important incident solar radiations
on collectors, what is the radiation it is coming on the collector that will also influence
the process performance. So if we want to get the collector efficiency
here, this equal to obviously how much energy we are getting that is Ein-Eout /how much
energy was available in the incident rays. So if the surface area is Ac and It is incident
solar radiation, so this is our total solar radiation in kilowatt per meter squared unit
and this is our energy we are getting amount of heat we are getting from the system, so
this by this, Qu/(Ac x It ) is our collector efficiency. Now efficiency is equal to Qu/AcIt, but now
what is our Qu, Qu is also this one that Fa, FR that is equal to collector efficiency x
Ac x α τ IT – UL (Tf,o-Ta). So this is the expression for the Qu. So if we put this expression in place of Qu,
so efficiency will be like this.

So efficiency
is equal to Qu/AcIT x (FR (τα) – FRUL x (Tfo-Ta)/IT). So now this equal to y = mx+c type of expression,
y = a+b type of expression. So if we plot efficiency versus this, we can
measure the Tf, we can measure Tm Me and we can measure the intensity of the light which
is coming that IT. So then we can plot and we can get the value
of this A and B and A and B we can get the value of FR we can get the UL like this. So now we can get the value of A and B. Now, solar thermal power plant. So how the solar technique, thermal technique
can be used for the electricity production that part will discuss now. So we have some say some collector here, so
we have collector, so that is a parabolic trough collector here, so these are the tubes
so we are sending cold water, so it is going through these tubes and it is heated up and
ultimately we are getting steam. So this steam is going and this can be used
for different applications. It can be used in hot tank and it can be going
for the super heater and this can be used in a turbine for the electricity production.

So this is the method through which the electricity
is produced. The steam is generated here, it goes through
this and it is after super heating, it goes there to the turbines, which is coupled with
the generator, which gives us electricity and the exhaust steam is condensed and again
used here or it can be sent here for the heat recovery or like this So this is the arrangement
for the use of heat captured by the steam in this plant. (Refer Slide Time: 18:03 So one example of this power tower in Barstow,
California. This figure shows that how the solar energy
is produced by the capturing of solar lights. So this is 10 megawatt solar power plant in
Barstow, California, that is 1900 heliostats, each 20 feet by 20 feet is used and a central
295 five feet tower. So all are focused in this tower and then
it gives us that amount of electricity. Now we are coming to solar photovoltaic.

So solar photovoltaic, it is another type
of technology and which is the latest development of the solar technology and most important
one, which can give us electricity directly without the production of steam, unlike solar
thermal route. So here what happens, solar energy comes on
some surface which is having an N and P type semiconductors and then when the solar cell
is P type semiconductor and N type semiconductor. The solar light hitting the cell produces
negatively charged electrons and positively charged holes, so negatively charged electrons
and positively charged holes. So sunlight is falling on it and these holes
and electrons and generated and then electrons are moving towards this N-type semiconductor
and P-type semiconductor, those are the positive holes are moving towards it and they are collecting
these things, and when we will add external load, then we will get electricity through
it. So we are getting the electricity now. So this method is the most important method
for the conversion of electricity from the solar rays. Now we will see different types of materials
for the PV cells and their efficiency. So solar cell, it may be silicon semiconductor,
it may be compound semiconductor, it may be organic semiconductor.

So silicon semiconductor, it may be crystalline
or amorphous and crystalline maybe single crystal maybe poly crystalline, and their
conversion efficiency for the single crystalline 10 to 17%, for poly crystalline 10 to 13%,
it may be non-crystalline that is 7 to 10%. Compound semiconductor that is gallium arsenide,
it is 18 to 30% conversion efficiency. Organic semiconductor that is dye-sensitized
type, it is 7 to 8% and organic thin layer type 2 to 3%. So these are the different types of materials
have been investigated for the production of electricity in a PV photovoltaic mode. Then conversion efficiency, obviously electricity
output by energy of insolation on cell into 100 that will be in the percentage. Now we will see the volt and current which
can be achieved in this PV cell.

So this is for low insolation, this is the
graph people have reported and for high insolation. So 0.5 volt for silicon photovoltaic cell
is available for a single cell and intensity of insolation and size of cell will also influence
the amount of voltage generated. Now this is one photograph for PV cell which
can give some details on this. So here, we have these are aluminum electrode
and this blue colored film that is anti reflection film and then black surface, this black surface
is P-type conductor semiconductor and all black surface is aluminum electrode with full
reflection and this is front surface N-type side, so N-type side and P-type side is backside,
that is black side.

This is your PV module, one module single
crystal, and this is your polycrystalline, so this is poly crystalline, this is single
crystalline. So single crystals which has more capacity
128 watt, this is 120 watt, same size both are having, but single crystal will give some
more capacity as it is evident from this. Then there is the hierarchy of the PV cells,
so a single cell we see here, 2-3 watt, so this is black and blue, so alumina and N and
P type that we were talking about the N type and P type semiconductor, so we are using
it and 2-3 watt is generated, so you have 0.5 volt and 5-6 amps and 2-3 watt, so about
10 cm size. Then gradually the improvement came and then
module structure came, so this is our module, so this module is able to give 20-30 volt,
5-6 amps and then 100-200 watt and 1 meter its size. The number of modules was put in arrays and
then we get array that is say 200-300 volt it is possible, 50 amps to 200 amps is possible,
10-50 kilowatt capacity was developed, and the size is around 30 meter.

So gradually the PV cells developed. This is the roughly size of PV power station. If we need to get say 20 kilowatt power through
PV techniques, then it requires 10 meter by 20 meter roof area. So 1 kilowatt PV need 10 meter square area
for its production. Now the temperature also influences the performance
of this process. The temperature increases, efficiency of the
process decreases. As shown here say a typical 25 degree centigrade
we are having, if it is an amorphous silicon PV cell, then this will be having around 8%
percent efficiency. If we go to say 65 degrees centigrade which
is available in some places during summer at the rooftop, then there it is slightly
less than this. In this case for crystalline cell if it is
around say 13% percent, so here it is coming to say 11%, so 2% down due to the increase
in temperature from 25 to 65 degrees centigrade. So that way we have come to know that the
efficiency of PV cell can also be changed with increasing the temperature.

So up to this in this class. Thank you very much for your patience..

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