2. Energy Scenario of India
• India is world’s largest third energy consuming country. More than 80% of energy requirement is met
by coal, oil, solid biomass. Solar contributes less than 4% in energy requirement completion.
• India has target to produce 450GW by renewable resource till 2030.
• Present scenario of energy in India according to International Energy Agency report 2021
3. Energy Scenario w.e.f 30/09/2022
According to Ministry of Power of Indian govt. actual installed capacity of energy production is 407.797 GW.
In this production Solar is contributing about 14.9 % i.e. about 60.814 GW.
4. Key Points
• For every domestic and industrial operations we need energy, prominently required in form of
electricity and thermal
• Thermal energy requirement can be fulfilled by solar energy up to a large context.
• Solar radiations are generally converted to heat energy by using different type of collectors
• We will study about working principle, construction and components of collectors
• We are shifting towards renewable energy to reduce the carbon footprints or to lower the
carbon emission.
5. Modes of Heat Transfer
• Conduction:- The heat transfer takes place due to the vibration of atoms. This mode of heat transfer
mostly takes place in solid mediums. The first law of heat conduction, known as Fourier law,
states that the flux of heat in a homogeneous body is in the direction of, and proportional to,
the temperature gradient.
Qx = -k A dt/dx {Qx is heat gain in one dimension}
{k = thermal conductivity constant , SI Units = W/m k}
{A = Area of subject, dt/dx is temperature gradient}
• Convection:- The heat transfer takes place due to the movement of atoms generating convective
currents. This mode generally happens in fluids (liquids and gases). Newton Law of cooling
is also called as law of convection.
Qx = h A ∆T {h = convective heat transfer coefficient, S units = W/ m2 k}
{∆T = temperature difference}
6. Radiation:- In this mode we do not need any medium to transfer heat, it can happen in vacuum too,
generally infrared radiations are behind heat transfer. This law is also known as Stefan Boltzmann law of
radiation.
Qx = = σεA∆T4 { σ = Stefan Boltzmann Constant, value = 5.67 X 10-8 W/m2 k4 }
{ε = emissivity of a object}
Solar Collector
It is a device which is used to collect the solar radiation and covert radiations into heat and transfer this
heat to liquid or air which is in contact with it.
Types of Flat Plate Collectors:
• Liquid Heating Collector
• Air Heating Collector
7. Flat Plate Liquid Heating Collector
It is flat plate collector in which the water or any other liquid can be heated by using solar
radiations. Here the thermosiphon phenomenon takes place so no need of external pump for water
circulation. These can heat water up to 100 Celsius but the efficiency is about 20% to 50% only.
Components of Liquid Heating Collector:
• Glass cover: It is used to trap the radiations and minimize the losses.
• Absorber plate: This is plate is a heat exchanger painted black colour (as black colour absorb
most of the radiations) made up of good thermal conductive material (generally copper because
its affordable and highly conductive).
• Insulations: There are side and bottom insulations to minimize the heat transfer to atmosphere
and reduce the losses.
• Tubes: Tubes are attached to absorber plates where heat is transferred to liquid by convection.
Tubes are made up of copper or any other highly conductive and affordable material.
• Casing: The casing is made outside the whole collector to bind all the components together to
make it a single unit.
9. Evacuate Tubes Liquid Heating Collector
• ETCs are typically designed with parallel rows of twin glass tubes, with each
inner glass tube containing a metal heat pipe attached to an absorber fin. The
air between the two glass tubes is removed (or evacuated) to form a vacuum,
which reduces conductive and convective heat loss.
• They can extract heat more efficiently and much higher (up to 150 Celsius)
than flat plate collector .Its efficiency is about 50%. High efficiency and faster
than flat plate collector.
10. Air Heating Collector
These are also flat plate collectors in which air is flow between the collectors through a duct which
get the heat from absorber plate through convection. Generally at 0.02kg/s mass flow rate its
efficiency is some where 30% to 45%.
Components of Air heating collector:
• Absorber plate:- It is a black colour plate of highly thermal conductive material(usually copper).
• Duct:- It is a long passage of specific shape and dimension where air flow takes place and get
heated up from absorber plate.
• Glass cover:- There is glass cover to trap the heat and minimize the heat losses.
• Insulation:- All sides and bottoms are insulated so the heat loss must be minimum.
• Casing:- All units put together and a casing is made outside to make it a single unit.
12. Air heating collector
The experiment was conducted more than 2 hours for 630 Wm-2 and 730 Wm-2
solar radiation at mass flow rate of 0.02 kgs-1, 0.03 kgs-1 and 0.04 kgs-1
respectively. Generally, inlet and outlet temperatures increased constantly up
to 150 minutes and then tended to approach a constant and is it found that a
small increment of the inlet temperature compared outlet temperature.
Thermal efficiency of single -pass air solar collector is found increases with
increase of solar radiation intensity, but it reaches gradually to a constant.
For example at the mass flow rate 0.04 kgs-1, the efficiency increase from 70
% to 77% for radiation intensity 630Wm-2 and 730Wm-2 respectively.
13. Applications of Solar Thermal
• Water Heating
• Air Heating
• Space Heating
• Space cooling and Refrigeration
• Power Generation
• Solar Distillation or Desalination
• Solar Drying
• Solar Cooking
• Solar Pond
