Renewable Energy Resources Unit 2 Easy notes (EduShine Classes).pdf

Renewable Energy Resources(BOE074)
Unit – 2 Solar Thermal Energy
EduShine Classes – Arman Ali
Download Notes : https://rzp.io/rzp/FRkyPe16

🌞 Solar Thermal Energy
Solar thermal energy means using the Sun’s heat (radiation) to produce useful energy like
hot water, cooking, or electricity.
Instead of converting sunlight into electricity directly (like solar panels do), here we capture
the heat of sunlight using special devices called collectors.
🌞 Solar Radiation
Solar radiation is the energy we get from the Sun in the form of light and heat.
This energy travels through space as electromagnetic waves and reaches the Earth.
It is the primary source of energy for life on Earth. All renewable energies (wind, hydro,
biomass, etc.) directly or indirectly come from the Sun.
👉 Example: When you feel warm standing in sunlight – that’s solar radiation.
There are mainly three types of Solar Radiation let discuss it 

Initial State
Goal State
 Types of Solar Radiation :
1. Direct Radiation (Beam Radiation)(Shortwave Radiation)
Sunlight that comes directly in a straight line from the Sun to the Earth, without scattering.
It is strong and concentrated.
Can be focused using mirrors or lenses.
👉 Example: If you stand in open sunlight, the heat you feel directly from the Sun is direct
radiation.
👉 Used in: Solar cookers, concentrating collectors, solar power plants.
2. Diffuse Radiation
Sunlight that is scattered in the atmosphere by clouds, dust, and air molecules before reaching
the Earth.
It comes from all directions (not a straight beam).
It is weaker than direct sunlight.
👉 Example: On a cloudy day, you still see light even when the Sun is hidden – that’s diffuse
radiation.

👉 Used in: Flat plate collectors, solar water heaters (work even when cloudy).
3. Reflected Radiation
Sunlight that reaches the Earth’s surface after reflecting from surfaces like water, sand,
snow, or buildings.
Amount depends on how reflective the surface is.
👉 Example: If you stand near a white wall or on snow, you feel extra brightness – that’s
reflected radiation.
👉 Used in: Sometimes increases efficiency of solar panels if reflection falls on them.
🌍 Total Solar Radiation = Direct + Diffuse + Reflected
This is also called Global Solar Radiation (the total sunlight energy falling on a surface).

📖 Easy Story Example :
Imagine you are sitting in a park 🌳:
• The Sun is shining directly on your face → Direct Radiation.
• Some sunlight passes through clouds and spreads everywhere → Diffuse Radiation.
• Light bouncing from the pond nearby also reaches you → Reflected Radiation.
👉 Together, all three give you the warmth and brightness you feel.

☁️ What happens when solar radiation reaches Earth?

1. Atmospheric Reflection
Some sunlight bounces back into space because of clouds, dust, and gases.
This part never reaches Earth’s surface.
2. Reaching the Ground
The rest of the sunlight passes through the atmosphere and reaches the Earth’s surface
(ground, water, plants, etc.).
This is shown by yellow ashortwave radiation in the diagram.
3. Ground Radiation
The ground absorbs sunlight → becomes warm → and then sends the energy back into the
atmosphere.
But this energy is in the form of heat waves (longwave radiation), shown as red arrows.
4. Atmospheric Back Radiation
Some of the heat from the ground goes back into space,
but some gets trapped by gases (like CO₂, methane, water vapor, etc.) and comes back to
Earth’s surface again.This is called the Greenhouse Effect, which keeps Earth warm.

 What is Solar Constant?
• The solar constant is the amount of solar energy we get from the Sun per second on
1 square meter area, when measured just outside Earth’s atmosphere (before air
absorbs it).
• Value = ≈1361 W/m² (watts per square meter).
👉 Means: A 1 m² surface facing the Sun in space receives the energy of about 13
bulbs of 100W every second.
Where:
L = Sun’s total energy output
r = distance between Earth and
Sun (1 AU)
S= Solar Constant = 1361 W/m²
It tells us how much raw solar energy reaches Earth.

🌞 What is a Solar Collector?(V.IMP)
A solar collector is like a device that catches sunlight and changes it into heat.
This heat is then used to heat water, air, or any fluid for our daily use (like hot water in houses)
or for electricity in power plants.
👉 Think of it like a bucket that collects rainwater, but instead of water, it collects sunlight and
stores it as heat.
🔑 Types of Solar Collectors
1) Flat Plate Collector (FPC)
• Looks like a flat box with glass on top.
• Inside it has a black plate that absorbs sunlight and pipes that carry water.
• Sunlight → heats plate → heat goes into water in the pipes → hot water comes out.
Use: Solar water heaters in homes.
👉 Example: Like a black car getting very hot in the sun.

2) Evacuated Tube Collector (ETC)
• Made of many glass tubes, each with a vacuum (like a thermos flask).
• The vacuum keeps the heat inside (less heat loss).
• Works better than flat plate, even on cloudy or cold days.
Use: Hotels, hospitals, and homes for hot water.
👉 Example: Like a thermos bottle that keeps tea hot.
3) Integral Collector Storage (ICS)
• A simple tank painted black, covered with glass.
• Sun directly heats the water stored inside the tank.
Use: Small homes, low-cost systems.
👉 Example: Leaving a bucket of water in the sun — it becomes warm.

4) Concentrating Collectors
These use mirrors or lenses to focus sunlight onto a small receiver.
Because sunlight is concentrated, it makes very high heat.
Types:
1. Parabolic trough (curved mirror like a “U”).
2. Parabolic dish (satellite-dish shape).
3. Solar tower (many mirrors reflect sunlight to a tall tower).
Use: Power plants (to make electricity) and factories.
👉 Example: Using a magnifying glass to burn paper with sunlight.
5) Air Collectors
Instead of water, they heat air.
Use: Drying crops, space heating in cold regions.
👉 Example: Like drying clothes under the sun — the air gets hot and dries them.

In Short :
A solar collector is a device that absorbs sunlight and converts it into heat energy.
Flat Plate Collector → common for hot water.
Evacuated Tube Collector → works well in cold climates.
Integral Storage → simple, low-cost system.
Concentrating Collectors → use mirrors/lenses for very high heat, used in power plants.
Air Collectors → heat air for drying and heating.
👉 They help save electricity, reduce pollution, and use free energy from the Sun.

🌞 Solar Flat Plate Collector (FPC)(V.IMP)
• A Flat Plate Collector is a simple device that collects sunlight and converts it into heat
energy to warm water or air.
It looks like a flat box with glass on top.
• It is the simplest and most common solar thermal device.
Example: Solar water heaters at homes use FPC.
1. Solar Radiation (Sunlight ☀️)
Sunlight falls on the collector.
This is the main source of energy.
2. Transparent Screens (Glass Cover)
These are clear sheets at the top.
They allow sunlight to enter inside but stop the
heat from going out (like a greenhouse effect
🌿).
Helps in keeping more heat inside.

3. Black Absorber Plate
• Below the glass cover.
• Painted black → absorbs maximum sunlight.
• Converts sunlight into heat energy.
4. Fluid Tubes (Water/Air Pipes 💧💨)
• Attached under the absorber plate.
• Water or air flows inside these tubes.
• The heat from the black plate is transferred to the water/air.
• Now the water/air becomes hot.
5. Thermal Insulation (Bottom Layer)
• Material like glass wool is used.
• Stops heat from escaping downward.
• Ensures most heat goes into the water/air, not wasted.

📌 Applications
• Domestic solar water heaters (homes).
• Industrial hot water supply.
• Swimming pool heating.
• Space heating in cold regions.
 ⚖️ Advantages
• Simple & cheap.
• Easy to use.
• Eco-friendly (no pollution).
❌ Limitations
o Works only in sunlight.
o Cannot produce very high temperature.
o Needs large area.

🌞 How Does a Flat Plate Collector Work?
1. Sunlight Hits the Collector
• The collector has a black flat plate on top.
• Sunlight falls on it → black color absorbs maximum heat.
2. Heat Transfers to Pipes
• Small tubes/pipes are attached under the black plate.
• These tubes carry fluid (water, air, or water + glycol mixture).
• The heat from the hot black plate moves into the fluid inside the tubes.
3. Hot Fluid Moves to Storage Tank
• The fluid now becomes hot.
• It flows through insulated pipes to a storage tank or heat exchanger.
• Stored hot water can then be used for bathing, cooking, washing, etc.
4. Cool Fluid Returns for Reheating
After giving away its heat, the fluid cools down.
This cooler fluid is sent back into the collector.

• The cycle continues as long as the sun shines ☀️.
5. Glass Cover Traps Heat
• A transparent glass cover is placed above the plate.
• It lets sunlight enter but prevents heat from escaping → like a greenhouse effect.
6. Insulation Prevents Heat Loss
• The bottom and sides are covered with insulation material (like wool, foam, etc.).
• This stops heat from leaking out and keeps the system efficient.
7. Controlled Fluid Flow
• The fluid flow is controlled:
• If fluid moves too fast, it won’t get hot enough.
• If it moves too slow, heat may escape.
So, the flow is balanced for steady usable hot water.
Solar Water Heater in homes → You open the tap and get hot water heated by the sun
without electricity!

📌 Main Parts & Materials
1. Absorber Plate
• Material: Copper, Aluminium, or Steel.
• Why used?: These metals are good conductors of heat (they absorb heat from sunlight
quickly and transfer it to the water/air inside pipes).
• Extra coating: Black paint or selective coating (because black color absorbs more heat).
2. Tubes/Pipes
• Material: Copper or Aluminium.
• Why used?: They carry the water (or heat transfer fluid) and have good thermal
conductivity to transfer heat efficiently.
3. Transparent Cover (Glazing)
• Material: Toughened Glass or sometimes Plastic (like acrylic or polycarbonate).
• Why used?: Allows sunlight to enter but reduces heat loss (works like a greenhouse).

4. Insulation Layer
• Material: Fiberglass, Rockwool, or Polyurethane Foam.
• Why used?: Stops the heat from escaping from the bottom and sides of the collector.
5. Casing/Box (Enclosure)
• Material: Steel, Aluminium, or Wood.
• Why used?: Provides mechanical support and protection for all the parts.
🌞 Performance Analysis = How well the collector converts sunlight into useful heat
We usually check this by looking at Efficiency.
1. Useful Heat Gain (Qu)
The heat actually collected by the water/fluid.
Formula (don’t worry, just for understanding):

Where :
Ac: Area of collector (bigger area = more sunlight captured).
Fr: Collector heat removal factor (how well it transfers absorbed heat to fluid).
S: Solar energy absorbed.
UL: Heat loss factor (how much heat is escaping).
Ti: Inlet fluid temperature.
Ta: Outside air temperature.
2. Collector Efficiency (η)
Ratio of useful heat gained to the total solar energy received.
Formula:
Where:
It: Solar radiation intensity (W/m²).
Ac×It: Total solar energy falling on the collector.
Efficiency tells how much of the sun’s energy is
converted into heat.

🌞 Factors Affecting the Performance of Flat Plate Collector (FPC)
1. Absorber Plate Material
Better conductors like copper or aluminum → absorb and transfer heat faster.
Poor materials → low efficiency.
2. Absorber Surface Coating
Black, selective coating absorbs more heat and reduces reflection.
Shiny or light color → reflects sunlight → less heat.
3. Transparent Cover (Glazing)
Glass/plastic cover traps heat inside (like greenhouse effect).
If poor quality → more heat escapes.
4. Insulation
Good insulation on sides and bottom → reduces heat loss.
Weak insulation → heat escapes → low performance.
5. Flow Rate of Fluid
If too slow → fluid overheats, losses increase.

If too fast → not enough time to pick up heat.
Balance is important.
6. Tilt Angle & Orientation
Collector should face the sun directly (South in India).
Wrong tilt or direction → less sunlight captured.
7. Ambient Temperature & Wind
If outside air is very cold or windy → more heat loss.
Calm and warm weather → better performance.
8. Solar Radiation Intensity
More sunlight → higher heat gain.
Cloudy days → less efficiency.

🌞 What is Focusing of Collector?(Concentrating Solar Collector) : (V.IMP)
• Some solar collectors use mirrors or lenses to focus (concentrate) sunlight onto a small area.
• This increases the heat on that area much more than flat collectors.
• It works like a magnifying glass focusing sunlight on paper to burn it.

1. Parabolic Reflector (Curved Mirror)
The big curved surface is like a mirror.
It collects sunlight from a large area and reflects it to a single line (focus).
2. Absorber Tube (at the Focus Point)
A long black-colored tube is placed at the focus line of the reflector.
This tube absorbs the concentrated sunlight and becomes very hot.
Inside the tube, a fluid (like oil, water, or molten salt) flows and gets heated.
3. Glass Cover
The absorber tube is usually covered with glass.
The glass prevents heat loss and protects the absorber.
4. Working Principle
Sunlight → falls on reflector → reflector bends/focuses it → all rays concentrate on absorber
tube → fluid inside gets hot.
5. Output
The hot fluid can be used to produce steam → run turbines → generate electricity.

Also used for heating purposes (industrial or domestic).
A concentrated solar collector uses mirrors or lenses to focus a large area of sunlight onto a
small receiver (pipe or container).
Because sunlight is concentrated, the receiver becomes very hot (200 °C to 1,000 °C or more).
This high heat is used to make steam, run turbines, or provide industrial process heat.
🛠Main Parts
1. Reflector / Mirror
Curved or shaped to gather and direct sunlight.
Examples: parabolic trough (like a long half-pipe), parabolic dish (satellite-dish shape),
heliostat mirrors.
2. Receiver (Absorber Tube)
A metal pipe or plate placed at the focus point where sunlight meets.
Carries a fluid (water, oil, molten salt) that absorbs the concentrated heat.

3. Tracking System
Motors or gears that follow the sun during the day so mirrors stay pointed at it.
4. Heat Transfer Fluid
Fluid (oil, molten salt, pressurized water) that carries heat to a boiler or storage.
⚙️ Step-by-Step Working
1. Sunlight Collection
The mirror or lens captures sunlight across a wide area.
2. Concentration
The mirror’s curve or the lens’s shape bends the light, focusing it onto the receiver line or
point.
3. Heat Absorption
The receiver pipe, coated black for good absorption, gets very hot.
The fluid inside the pipe heats up quickly.
4. Heat Transfer / Steam Generation
Hot fluid moves to a heat exchanger or boiler.

Water turns into steam.
5. Power Generation or Direct Use
Steam drives a turbine to produce electricity OR hot fluid is used directly for industrial
heating.
Types of Concentrated Collector (V.IMP)
Parabolic Trough Mirror Strip reflector Fresnel Reflector Compound Parabolic

1.Parabolic Trough Collector?
• It is a long, curved mirror shaped like a U (parabola).
• The mirror focuses sunlight onto a receiver tube that runs along the center (focus line).
• Inside the tube flows a special fluid (like oil or molten salt) that gets very hot.
• The hot fluid is then used to produce steam for electricity or for industrial heating.

⚙️ Step-by-Step Working
Sunlight falls on the curved mirror.
2. Concentration
The parabolic shape reflects and concentrates the sunlight onto the receiver tube at the focus.
3. Heat Absorption
The fluid inside the tube absorbs the intense heat (up to ~400 °C).
4. Heat Transfer
Hot fluid is pumped to a heat exchanger or boiler.
5. Power Generation or Direct Use
Heat makes steam → steam drives a turbine → electricity.
Or heat is used directly for industrial processes.

✅ Advantages
• High temperatures and efficiency compared to flat-plate collectors.
• Suitable for large solar power plants.
• Can store heat (e.g., molten salt) for evening or night use.
❌ Disadvantages
• Needs clear sky and direct sunlight.
• Mirrors and tracking systems require regular cleaning and maintenance.
• High initial installation cost.

2. Mirror Strip Reflector :
A Mirror Strip Reflector is a solar collector made of many small, flat mirrors arranged side
by side.
Each mirror strip reflects sunlight toward one single point (focus) where a receiver (like a
pipe or small container) is placed.

🔹 How It Works
 Sunlight hits each mirror strip.
 Each strip reflects the sunlight toward the same focus point.
 At the focus, there is a tube or vessel containing a fluid (like water or oil).
 The fluid gets heated by the concentrated sunlight and can create steam or provide heat for
different uses.
✅ Advantages
• Cheaper than building one large curved mirror.
• Easy to make and replace if a strip breaks.
• Lighter and simpler to install.
❌ Disadvantages
• All strips must be carefully aligned; small errors reduce efficiency.
• Needs strong, direct sunlight.
• Regular cleaning of each strip is important.

3. Fresnel Lens Collector?
• A Fresnel lens collector is a solar device that uses a special flat lens to focus sunlight onto a
small receiver (like a tube or a container).
• It works like a big magnifying glass but is lighter and thinner.
• A normal magnifying glass is thick and heavy.
• A Fresnel lens is made of many small, thin circular or rectangular sections (called grooves)
that bend light like a big, thick lens would.
• Because of these grooves, the lens is flat and
light but still focuses sunlight to a strong point.
Think of using a magnifying glass to burn paper
with sunlight.
Fresnel lens does the same thing, but on a bigger
scale to heat pipes.

 How It Works (Step by Step):
• Sunlight comes down in straight parallel rays.
• The Fresnel lens bends these rays inward.
• All the bent rays meet at a focus point.
• At that point, an absorber pipe is placed.
• The pipe gets heated very strongly because all sunlight energy is concentrated there.
• This heat is then used to heat water, make steam, or produce energy.
✅ Advantages
 Lightweight & Thin: Easier to mount than a thick glass lens.
 High Concentration: Can create very high temperatures (up to 200–1000 °C).
 Cost Effective: Uses less material than a thick curved lens.
❌ Disadvantages
 Needs direct sunlight—not good on cloudy days.
 Must be kept clean for clear focusing.
 Accurate alignment of the receiver is important.

4. Compound Parabolic Collector?
A Compound Parabolic Collector is a solar collector shaped like two smooth parabolas joined
together.
It is designed to catch sunlight from many directions and reflect it onto a small receiver tube in
the center.
Think of it like a wide open funnel of
mirrors that guides sunlight to a narrow
tube.

 How it Works (Step by Step):
 Sunlight enters the collector.
 Some rays directly fall on the absorber plate.
 Other rays strike parabolic mirrors A & B.
 These mirrors reflect and bend the rays downward.
 All the rays finally meet at the flat absorber at the
bottom.
 The absorber heats up → this heat is used to warm
water, air, or to generate steam for energy.
✅ Advantages
 Collects Sunlight from Many Angles – works well all day.
 Simple Design – no need for expensive moving parts.
 High Efficiency – concentrates sunlight 3–5 times more
than flat collectors.
❌ Disadvantages
 Bigger Size – takes more space.
 Cleaning Needed – dust on
mirrors reduces reflection.

 Material Used in Concentrating Collector :
1. Reflector / Mirror Surface
This is the part that catches sunlight and reflects it to the focus.
 Materials Used
• Glass mirrors (highly polished) – most common.
• Polished aluminum sheets – light and cheaper.
• Silver-coated glass – very high reflectivity.
Why: Needs to be very shiny, smooth, and long-lasting.
2. Receiver / Absorber Tube
This is the pipe or plate where sunlight is concentrated and heat is collected.
Materials Used
• Copper – great heat conductor.
• Stainless steel – strong and resists corrosion.
• Aluminum (with coating) – light and conducts heat.

Surface Coating:
• Black chrome or selective black paint to absorb maximum heat and lose less to the air.
3️. Transparent Cover (Glass Envelope)
A glass tube or cover often surrounds the absorber.
Material: Borosilicate glass (heat-resistant).
Purpose:
• Prevents heat loss by trapping air.
• Protects the absorber from wind and dirt.
4️. Heat-Transfer Fluid (Inside the Receiver)
The liquid that carries the heat away.
Materials
• Synthetic oil (thermal oil).
• Molten salt.
• Pressurized water or steam.
Why: Must withstand very high temperatures without breaking down.

5️. Support Frame / Structure
The skeleton that holds mirrors and receiver.
Materials
• Steel (galvanized or stainless) – strong and weather-resistant.
• Aluminum – lighter but strong.
Purpose: Must be stable, resist wind, and hold heavy mirrors.
6️. Tracking System (for Sun-Following Collectors)
Motors, gears, and electronics to keep the mirrors aimed at the sun.
Materials:
• Steel for gears and shafts.
• Electric motors and sensors.
7️. Insulation
Used around pipes or storage tanks to keep the heat.
Materials: Mineral wool or glass wool, High-temperature ceramic insulation.

 Recap Table

🌞 Applications (Where We Use It)
1. Electric Power Generation
Big solar thermal power plants make steam to run turbines and produce electricity.
2. Industrial Process Heat
Provides high-temperature heat for factories (food processing, chemicals, textiles).
3. Desalination of Water
Heat is used to turn seawater into fresh water.
4. Solar Cooking
High-temperature cookers for community kitchens or large canteens.
5. Air Conditioning (Solar Cooling)
Runs absorption chillers for cooling buildings.
6. Water & Space Heating
Supplies hot water or space heating for hotels, hospitals, or large buildings.

✅ Advantages
1. High Temperature & Efficiency
Focused sunlight can reach very high
temperatures (200 °C–1000 °C), good for
making steam and power.
2. Clean & Renewable
Uses free sunlight; no air pollution or
greenhouse gases.
3. Saves Fuel
Reduces use of fossil fuels in industries.
4. Scalable
Works for small cooking units or large
power stations.
❌ Disadvantages
1.Needs Direct Sunlight
Works best in clear-sky areas (deserts). Not
effective on cloudy or rainy days.
2.High Initial Cost
Mirrors, tracking systems, and installation are
expensive.
3.Regular Maintenance
Mirrors must be cleaned and aligned to stay
efficient.
4.Large Space Requirement
Big collectors need wide, open land.
5.Sun-Tracking Needed
Most designs need motors or systems to follow
the sun, adding complexity.

 Performance Analysis (Concentrating Collector):
Performance analysis is simply checking how well the collector converts sunlight into useful
heat or power.
We look at how much solar energy goes in and how much useful heat comes out.
 Key Factors Affecting Performance
a) Solar Radiation (Input Energy)
The stronger the sunlight, the more energy is available.
Measured in W/m² (watts per square meter).
b) Optical Efficiency (ηopt)
How well mirrors/lenses capture and focus sunlight onto the receiver.
Depends on:
• Reflectivity of mirrors.
• Cleanliness and alignment.
• Accuracy of tracking the sun.

c) Thermal Efficiency (ηth)
How well the receiver absorbs heat and transfers it to the fluid.
Influenced by:
• Absorber coating (black coatings absorb more).
• Heat loss through convection and radiation.
• Insulation around the receiver.
d) Heat Losses
Heat escapes from the receiver to the air by:
• Conduction (through metal parts).
• Convection (air movement).
• Radiation (infrared emission).
e) Operating Conditions
Flow rate of heat-transfer fluid.
Ambient temperature and wind speed.

 Performance Parameters to Calculate
Engineers use these main values:
1. Useful Heat Output (Qu)
The actual heat energy collected.
Where :
m = mass flow rate of fluid
cₚ = specific heat of fluid
T_out / T_in = outlet and inlet fluid temperatures.
2. Collector Efficiency (ηc)
The fraction of sunlight turned into useful heat. Where :
A = aperture area (mirror area)
I = solar radiation intensity.

3. Concentration Ratio (CR)
How much the collector focuses sunlight.
Higher CR = higher temperatures.
 Tips to Improve Performance
 Clean mirrors regularly to maintain reflectivity.
 Precise tracking of the sun.
 Use selective black coatings on the receiver to absorb more heat.
 Add good insulation around the receiver to reduce heat loss.
 Optimize flow rate so the fluid absorbs maximum heat without
overheating.

 Solar Thermal Power Plant?
It is a big power station that uses sunlight to make steam, and that steam drives a turbine to
generate electricity.
Instead of burning coal or gas, it uses concentrated solar heat.
It can be classified as low, medium and high temperature cycle.
Types of Solar Thermal Power Plant
Low Temperature
Solar Power Plant
Medium Temperature
Solar Power Plant
High Temperature
Solar Power Plant

1. Low Temperature Solar Power Plant :
A low-temperature solar power plant is a solar system that works with moderate heat (below
about 100 °C) to produce usable energy—mainly hot water, warm air, or very small amounts
of electricity.
It does not need extreme
high heat like big solar
thermal power stations.
👉 This is called a
Low-Temperature Solar
Power Plant because it
doesn’t need very high
temperatures (like
traditional steam plants).
It works even at lower
temperatures,

🔹 Components in the Diagram:
1. Flat Plate Collector – absorbs heat from the sun.
2. Pump – circulates water through the system.
3. Hot Water Line – carries heated water.
4. Heat Exchanger (Butane Boiler) – transfers heat from
hot water to butane gas.
5. Turbine (Gas) – rotates using butane vapor and produces
mechanical power.
6. Generator – converts turbine’s mechanical power into
electricity.
7. Condenser – cools butane vapor back into liquid.
8. Butane Gas Feed Pump – pushes liquid butane back into
the boiler.
✅ Advantages
 Clean & Renewable – No
greenhouse gases while
running.
 Large-Scale Electricity – Can
power entire cities.
 Heat Storage Possible –
Works even after sunset if
storage is included.
 Saves Fossil Fuels – Reduces
need for coal or gas.
 ❌ Disadvantages

 Working of Low Temperature Solar Power Plant :
• Sunlight (solar radiation) falls on the flat plate collector.
• This collector absorbs heat from the sun and transfers it to water.
• So, water becomes hot.
💧 2. Hot Water Flow
• The hot water from the collector flows through pipes to a heat exchanger.
• The heat exchanger works like a boiler.
🔥 3. Heat Exchange (Butane Boiler)
• Inside the heat exchanger, the hot water gives its heat to a working fluid (here Butane gas).
• Butane is chosen because it boils at a much lower temperature compared to water.
• So even with low-temperature hot water, butane can easily turn into vapor (gas).
💨 4. Expansion in Turbine
• The butane vapor (high-pressure gas) goes to the turbine.
• As it expands through the turbine, it makes the turbine blades rotate.

• The turbine is connected to a generator, which produces electricity.
❄️ 5. Condensation
• After doing work in the turbine, the butane vapor becomes low-pressure.
• It is then sent to a condenser, where it cools down and turns back into liquid butane.
🔁 6. Recirculation with Pump
• A butane gas feed pump pushes this liquid butane back into the heat exchanger.
• At the same time, a water pump recirculates water from the flat plate collector.
• This creates a continuous cycle.
⚡ Overall Working in Simple Words:
 Sun heats water in the flat plate collector.
 Hot water transfers heat to butane in the heat exchanger.
 Butane turns into vapor and drives the turbine.
 Turbine rotates generator → electricity is produced.
 Butane is cooled in condenser, pumped back, and reused.
 Water is also pumped back to the collector for reheating.

2. Medium Temperature Solar Power Plant :
• A medium-temperature solar power plant is a solar thermal system that heats a fluid to
about 100 °C to 400 °C.
• This heat is stronger than a low-temperature plant (water heating) but lower than big high-
temperature power towers.
• It is mostly used for industrial process heat or to make steam for small-scale electricity
generation.
✅ Advantages
1. Higher Temperature = Better Efficiency
Generates steam for power and industrial processes more efficiently than low-temperature
systems.
2. Good for Industry
Provides steady heat for drying, food processing, textiles, and small power plants.
3. Clean & Renewable
Uses free sunlight, no greenhouse gases while operating.

 Working of Medium Temperature Solar Power Plant :

🌞 Step 1: Solar Energy Collection
• The system uses Focusing Parabolic Collectors (mirror-like reflectors).
• These collectors focus sunlight onto an absorber tube.
• The absorber tube carries synthetic oil (heat transfer fluid).
• As sunlight is concentrated, the oil becomes very hot (around 300–400°C).
🛢Step 2: Hot Oil Flow
• The hot synthetic oil flows to a Heat Exchanger.
• The job of this exchanger is to transfer the heat from oil to water/steam.
• Oil never mixes with water – it only gives heat.
💨 Step 3: Steam Generation
• In the heat exchanger, water absorbs heat from the hot oil.
• Water converts into high-pressure steam.
⚙️ Step 4: Power Generation (High Pressure Turbine)
• This high-pressure steam is directed into a High-Pressure (HP) Turbine.
• As steam expands, it rotates the turbine.

• The turbine shaft is connected to a generator, producing electricity.
⚡ Step 5: Reheating & Expansion
• After passing through the HP turbine, steam pressure drops.
• This low-pressure steam is sent to a Re-heater (again heated by hot oil).
• Then the reheated steam is expanded in a Low-Pressure (LP) Turbine.
• More electricity is produced here.
❄️ Step 6: Condensation
• After leaving the turbines, steam enters the condenser.
• In the condenser, cold water cools the steam back into liquid water.
💧 Step 7: Pumping & Recirculation
• The condensed water is pumped back to a storage tank (store water).
• From there, the pump sends it again to the heat exchanger for heating.
• The synthetic oil also keeps circulating between the collector and heat exchanger.
🔁 Continuous Cycle
Sun heats oil → oil heats water → water turns into steam → steam drives turbines → electricity is produced → steam
condenses → water is reused.

3. High Temperature Solar Power Plant :
A high-temperature solar power plant is a type of solar thermal plant that heats a fluid to 300
°C or more (sometimes over 1000 °C!).
It uses strongly concentrating mirrors to focus sunlight and make very hot steam or gas, which
runs a turbine to produce large amounts of electricity.
 Key Components
1. Large Concentrating Mirrors – heliostats (power tower) or giant parabolic dishes.
2. Receiver – absorbs focused sunlight.
3. Heat Transfer Fluid / Molten Salt Tank – carries and stores heat.
4. Boiler, Turbine, Generator – create and convert steam into electricity.
5. Sun-Tracking System – keeps mirrors pointed at the sun.

⚙️ How It Works (Step by Step)
1️. Collect & Focus Sunlight
Big mirrors (like solar power towers, parabolic dishes, or very large parabolic troughs) track
the sun all day and concentrate sunlight onto a small receiver point.
2️. Heat Transfer Fluid (HTF)
Inside the receiver, a fluid such as molten salt, pressurized water/steam, or synthetic oil
absorbs the intense heat.
3️. Make Steam
The hot fluid boils water into superheated steam.
4️. Power Generation
The steam drives a steam turbine, which spins a generator to produce electricity—similar to a
conventional power plant, but the heat comes from the sun instead of burning fuel.
5️. Thermal Storage (Optional)
Many plants store extra heat in tanks of molten salt so they can continue to make electricity at
night or during clouds.

🌞 What is a Solar Air Heater?
A solar air heater is a device that heats air using sunlight.
Instead of water or oil, it directly warms up air, which can then be used for drying crops,
heating rooms, or industrial purposes.
✅ Advantages
 Simple & Low Cost – Easy to build and maintain.
 No Fuel Needed – Free heat from the sun.
 Good for Drying – Crops, fruits, timber, clothes.
 Clean Energy – No smoke or pollution.
❌ Disadvantages
 Depends on Sunlight – Less effective on cloudy days or at night.
 Large Area Needed – To heat big volumes of air, you need a bigger collector.
 Moderate Temperature – Usually heats air to about 30–80 °C only.

 Step-by-Step Working
1. Sunlight Entry – Solar radiation passes through the transparent cover.
2. Heat Absorption – The absorber plate absorbs this solar heat and becomes hot.
3. Air Heating – Air enters from the Air In side and flows through the air passage.
While moving, the air touches the hot absorber plate.
The air gradually gets heated.
4. Hot Air Outlet – The warmed air comes out
from the Air Out side.
5. Insulation Role – The insulation at the
bottom makes sure that heat does not
escape downward, so maximum heat goes
into the air.
6. Radiation Loss – A little heat is lost
through the transparent cover, but most
heat is captured.

🌡What is Thermal Energy Storage (TES)?
It is a method to store cold (cooling energy) during off-peak hours (night) and use it during
peak hours (daytime) when cooling demand is high.
Instead of running chillers or ACs at high power all day, we store cooling energy first and then
use it later.
 Main Components
1. Solar Collector (1 – Sun Ammonia)
Uses heat from the sun.
Heats up the ammonia–water solution.
2. Generator (2)
The heated solution enters here.
Ammonia (NH₃) separates from water because of solar heat.
Produces ammonia vapour (strong NH₃) and leaves behind a weak solution (mostly water).
3. Rectifier (3 & 4)
Cleans the ammonia vapour.

Removes any water particles, so that only pure ammonia goes forward.
4. Condenser (5)
The pure ammonia vapour is cooled here.
Changes into liquid ammonia.
5. Receiver (6)
Stores liquid ammonia.
Controls flow towards the evaporator.
6. Throttle Valve (7)
Reduces pressure of liquid ammonia.
Now ammonia becomes low-pressure liquid.
7. Evaporator (8)
This is the cooling part.
Low-pressure liquid ammonia absorbs heat from the space (like a fridge room).
It evaporates and provides cooling.

8. Absorber (9)
The evaporated ammonia gas is absorbed back into weak water solution.
This forms a strong ammonia–water solution again.
9. Heat Exchanger (10)
Transfers heat between weak and strong solutions.
Improves efficiency by saving heat.
10. Pressure Reducing Valve (11)
Maintains proper pressure difference in the system.
11. Storage Tanks (12, 13, 14)
Store solutions (weak and strong).
Pump (13 & 14) circulate solutions back to generator with the help of solar heat.

 Working Cycle in Simple Steps
• Solar heat → heats ammonia–water solution in
generator.
• Ammonia vapour separates → purified in
rectifier.
• Ammonia vapour → cooled in condenser →
liquid.
• Stored in receiver, passes through throttle valve
→ low pressure.
• In evaporator, ammonia absorbs heat → gives
cooling effect.
• Ammonia vapour absorbed again in absorber by
weak solution.
• Strong solution pumped → through heat
exchanger → back to generator.

• Cycle repeats using solar energy as main power source.
🌞 What is Solar Air Conditioning?
It is an air conditioning system that uses solar energy (instead of only electricity from the grid).
The main idea is: Sunlight → Solar Energy → Cooling effect for rooms/buildings.
⚙️ How it Works (Two Main Methods)
1. Solar PV Air Conditioning (Mechanical Type)
• Solar Panels generate electricity.
• This electricity runs the compressor of a normal AC.
• Cooling cycle is same as a normal AC:
• Compressor compresses refrigerant.
• Refrigerant passes through condenser → expansion valve → evaporator.
• In evaporator, refrigerant absorbs heat from room air → room gets cooled.

2. Solar Thermal Air Conditioning (Absorption/Adsorption Type)
• Instead of electricity, solar collectors (flat plate/parabolic) produce heat.
• This heat runs an Absorption Refrigeration System (using Lithium Bromide–Water or
Ammonia–Water).
Steps:
• Solar heat drives the generator (separates refrigerant).
• Refrigerant vapor goes to condenser (cools into liquid).
• Liquid refrigerant passes through expansion valve → enters evaporator.
• In evaporator, refrigerant absorbs heat from indoor air → gives cooling.
• Absorber reabsorbs refrigerant and cycle repeats.
A solar-powered AC in a house:
In the daytime, when sunlight is strong, solar energy powers the AC.
The system cools the house without depending much on grid electricity.

⚡ Limitations of Solar Power Plant :
1. Depends on Sunlight
Works only when the sun is shining.
At night or cloudy/rainy days, power generation drops.
2. High Initial Cost
Solar panels, collectors, batteries, inverters, and installation cost is high.
3. Large Land Requirement
Needs a lot of open space/land for installing panels or collectors.
4. Energy Storage Problem
Extra electricity must be stored in batteries or thermal storage for night use.
Batteries are expensive and need maintenance.
5. Low Efficiency
Efficiency of solar panels/collectors is limited (15–25% for PV panels).
A lot of sunlight energy is wasted.

6. Weather Dependent
Dust, pollution, shade, snow, or rain can reduce performance.
7. Maintenance Requirement
Panels need regular cleaning and maintenance for proper working.
8. Limited Locations for Some Types
Solar thermal plants need high direct sunlight (desert-like areas).
Not suitable for regions with less sunshine.

Download Notes : https://rzp.io/rzp/FRkyPe16
Thank You….

Renewable Energy Resources Unit 2 Easy notes (EduShine Classes).pdf

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