623 - RENEWABLE ENERGY SOURCES AND ENERGY CONSERVATION

ANSWER KEY

PART-A

1. Define Renewable energy?

Renewable energy is energy produced from sources that are renewed by nature again & again and

their supply is not affected by the rate of consumption. The most common examples include wind,

solar, geothermal, biomass, and hydropower.

2. Write any two classification of wind energy system

• Based on orientation of the axis of the motor

• Based on size as determined by their useful electrical power output.

3. What is a heliostat and what is its use?

A heliostat is a device that includes a mirror, usually a plane mirror, which turns so as to keep

reflecting sunlight toward a predetermined target, compensating for the sun's apparent motions in

the sky. Heliostats are used for daylighting or for the production of concentrated solar power, usually

to generate electricity.

4. List the types of solar cells.

• Amorphous Silicon solar cell (a-Si)

• Concentrated PV cell (CVP and HCVP)

• Crystalline silicon solar cell (c-Si)

• Hybrid solar cell

• Monocrystalline solar cell (mono-Si)

• Nanocrystal solar cell

• Organic solar cell (OPV)

• Photoelectrochemical cell (PEC)

• Polycrystalline solar cell (multi-Si)

• Solid-state solar cell

• Thin-film solar cell

5. Define flood tide and Ebb tide.

Flood the tidal phase during which the water level is rising and Ebb is the tidal phase during which the

water level is falling

Flood is the tidal phase during which the tidal current is flowing inland (flood current) and

Ebb is the tidal phase during which the tidal current is flowing seaward (ebb current).

6. State the applications of biogas plant.

• Gas production is cheap

• Less pollution.

• Waste material can be used as fertilizer.

• Gas is used for cooking, lighting, as fuel.

7. Define Critical thickness.

The thickness upto which heat flow increases and after which heat flow decreases is termed as critical

thickness. A critical thickness is typically defined as the limit of film thickness wherein the strain is still

elastically accommodated.

8. Define Cogeneration.

The production of electricity using waste heat (as in steam) from an industrial process or the use of

steam from electric power generation as a source of heat is called cogeneration.

PART B

9. Write about the importance of renewable energy sources.

Renewable energy sources are necessary and needed for the following reasons,

• The demand of energy is increasing due to rapid industrialization and population growth. So the

conventional energy sources will not be sufficient to meet the growing demand.

• Non renewable energy, such as coal and petroleum, require costly explorations an

potentially dangerous mining and drilling, and they will become more expensive as increases.

• Renewable energy is reliable and plentiful and will be cheap once technology and infrastructure

improves.

• Renewable energy includes solar, wind, geothermal, hydropower, tidal energy and bio fuels that

are grown and harvested without fossil fuels.

• Conventional sources cause pollution and degrade the environment whereas Renewable energy

produces only minute levels of carbon emissions and therefore helps combat climate change

caused by fossil fuel usage.

• The degree of civilization of any country is measured by the ability to utilize energy for human

advancements and needs.

10. Compare Horizontal and vertical axis windmill.

11. What is solar collector? Classify it.

A solar collector is a device that collects and/or concentrates solar radiation from the Sun.

These devices are primarily used for active solar heating and allow for the heating of water for

personal use. These collectors are generally mounted on the roof and must be very sturdy as they are

exposed to a variety of different weather conditions.

Classification:

• Flat plate collectors

• Evacuated collectors

• Solar ponds

• Stationary concentrators

• Linear focus collectors

• Point focus collectors

• Central receivers.

12. Explain a solar water heater with neat sketch.

Solar water heating (SWH) is the conversion of sunlight into heat for water heating using a solar

thermal collector. A variety of configurations is available at varying cost to provide solutions in different

climates and latitudes. SWHs are widely used for residential and some industrial applications.

A sun-facing collector heats a working fluid that passes into a storage system for later use. SWH are

active (pumped) and passive (convection-driven). They use water only, or both water and a working fluid.

They are heated directly or via light-concentrating mirrors. They operate independently or as hybrids with

electric or gas heaters.

13. Explain grid connected photovoltaic system.

14. Explain Environment impact and safety impact of solar system.

.

15. Draw a neat sketch of fixed dome type biogas plant.

16. List any four needs for energy audit.

PART-C

17. (A) (i) Write the classification of energy sources.

17. (B) (II) Name Five wind mills with its location In India.

Name Location State Capacity (MW)

Muppandal windfarm Kanyakumari Tamil Nadu 1500

Jaisalmer Wind Park Jaisalmer Rajasthan 1064

Brahmanvel windfarm Dhule Maharashtra 528

Dhalgaon windfarm Sangli Maharashtra 278

Vankusawade Wind Park Satara District Maharashtra 259

Vaspet Vaspet Maharashtra 144

Mamatkheda Wind Park Mamatkheda Madhya Pradesh 100.5

Anantapur Wind Park Nimbagallu Andhra Pradesh 100

Damanjodi Wind Power Plant Damanjodi Odisha 99

Jath Jath Maharashtra 84

Welturi Welturi Maharashtra 75

Acciona Tuppadahalli Chitradurga District Karnataka 56.1

Dangiri Wind Farm Jaiselmer Rajasthan 54

Bercha Wind Park Ratlam Madhya Pradesh 50

17 (b) Explain with a neat sketch the working of a horizontal axis wind mill. Also, list the advantages and

disadvantages of wind energy.

Advantages:

• Wind energy is renewable & Sustainable

• It is good for the environment

• It reduces for fossil fuel consumption

• Wind Energy can provide power to remote locations.

• Wind energy has low maintenance & Low running costs.

Disadvantages:

• Wind energy fluctuates and not stable all the time.

• Installation of wind energy is costlier.

• Wind systems are noisy.

18 (a) Explain the principle of solar pond with a neat sketch. Also, give its advantages and

disadvantages

The sun is the largest source of renewable energy and this energy is abundantly available in all parts of

the earth. It is in fact one of the best alternatives to the non-renewable sources of energy.

One way to tap solar energy is through the use of solar ponds. Solar ponds are large-scale energy

collectors with integral heat storage for supplying thermal energy. It can be use for various applications, such

as process heating, water desalination, refrigeration, drying and power generation.

Working principle:

• The solar pond works on a very simple principle. It is well-known that water or air is heated they

become lighter and rise upward e.g. a hot air balloon.

• Similarly, in an ordinary pond, the sun’s rays heat the water and the heated water from within the

pond rises and reaches the top but loses the heat into the atmosphere. The net result is that the pond

water remains at the atmospheric temperature.

• The solar pond restricts this tendency by dissolving salt in the bottom layer of the pond making it too

heavy to rise. A solar pond has three zones. The top zone is the surface zone, or UCZ (Upper

Convective Zone), which is at atmospheric temperature and has little salt content. The bottom zone is

very hot, 70°– 85° C, and is very salty.

• It is this zone that collects and stores solar energy in the form of heat, and is, therefore, known as the

storage zone or LCZ (Lower Convective Zone).

• Separating these two zones is the important gradient zone or NCZ (Non-Convective Zone). Here the

salt content increases as depth increases, thereby creating a salinity or density gradient. If we consider

a particular layer in this zone, water of that layer cannot rise, as the layer of water above has less salt

content and is, therefore, lighter.

• Similarly, the water from this layer cannot fall as the water layer below has a higher salt content and

is, therefore, heavier. This gradient zone acts as a transparent insulator permitting sunlight to reach

the bottom zone but also entrapping it there.

• The trapped (solar) energy is then withdrawn from the pond in the form of hot brine from the storage

zone.

Advantages:

• The approach is particularly attractive for rural areas in developing countries. Very large area

collectors can be set up for just the cost of the clay or plastic pond liner.

• The accumulating salt crystals have to be removed and can be a valuable by-product and a

maintenance expense

• No need for a separate collector.

• The extremely-large thermal mass means power is generated night and day.

Disadvantages

• Relatively low-temperature operation means solar energy conversion is typically less than 2%.

• Due to evaporation, non-saline water is constantly required to maintain salinity gradients.

18 (b) (I) Compare flat plate and concentrating solar Collectors.

18 b) (ii) Write about Thermal Chemical Storage.

• Thermal energy from the sun can be stored as chemical energy in a process called solar

thermochemical energy storage (TCES).

• The thermal energy is used to drive a reversible endothermic chemical reaction, storing the energy as

chemical potential.

• During periods of high solar insolation, an energy-consuming reaction stores the thermal energy in

chemical bonds; when energy is needed, the reverse reaction recombines the chemical reactants and

releases energy.

19 (a) Write the step by step procedure involved in designing a solar Home Lighting system.

The step by step procedure for designing a solar home lighting system includes,

19 (b) With a neat sketch explain the closed cycle OTEC system.

• Ocean Thermal Energy Conversion or OTEC uses the principle of a heat engine. It works by

converting a temperature difference into energy. This means the difference in temperature

between the warmer water on the surface and the cooler water in the depths of the ocean can

be converted into electricity.

• Ocean thermal energy conversion (OTEC) uses the temperature difference between cooler deep

and warmer shallow or surface seawaters to run a heat engine and produce useful work, usually

in the form of electricity. OTEC can operate with a very high capacity factor and so can operate

in base load mode.

• OTEC Systems may be either closed-cycle or open-cycle. Closed-cycle OTEC uses working fluids

that are typically thought of as refrigerants such as ammonia. These fluids have low boiling

points, and are therefore suitable for powering the system’s generator to generate electricity.

• The most commonly used heat cycle for OTEC is the Rankine cycle, using a low-pressure turbine.

• Open-cycle engines use vapor from the seawater itself as the working fluid.

• OTEC can also supply quantities of cold water as a by-product. This can be used for air

conditioning and refrigeration and the nutrient-rich deep ocean water can feed biological

technologies.

Closed cycle system:

• In Closed cycle system, The warmth of the sea water from the surface causes a liquid with a

lower boiling point than water, for example ammonia (having a boiling point around -33 °C at

atmospheric pressure), , to boil and turn to vapour. This vapour then drives a turbine which turns

a generator, creating electricity.

• Warm surface seawater is pumped through a heat exchanger to vaporize the fluid.

• The expanding vapor turns the turbo-generator. Cold water, pumped through a second heat

exchanger, condenses the vapor into a liquid, which is then recycled through the system.

Closed cycle OTEC System

Advantages:

• Fluid evaporates at around 25°C and does not require vacuum pumps.

• The pressure at the turbine will be of the order of 9 to 6 bar resulting in compact turbine

Limitations:

• The overall efficiency of the plant is very low.

20 (a) What is a biodiesel? Explain base – catalyzed method of preparing bio diesel with a block diagram.

Biodiesel production is the process of producing the biofuel, biodiesel, through the chemical

reactions of transesterification and esterification. This involves vegetable or animal fats and oils being reacted

with short-chain alcohols (typically methanol or ethanol). The alcohols used should be of low molecular

weight. Ethanol is the most used because of its low cost, however, greater conversions into biodiesel can be

reached using methanol.

The transesterification reaction can be catalysed by either acids or bases, the base-catalysed reaction

is more common. This path has lower reaction times and catalyst cost than those acid catalysis. However,

alkaline catalysis has the disadvantage of high sensitivity to both water and free fatty acids present in the oils.

Base-catalysed transesterification mechanism

The transesterification reaction is base catalyzed. Any strong base capable of deprotonating the

alcohol will do (e.g. NaOH, KOH, sodium methoxide, etc.), but the sodium and potassium hydroxides are often

chosen for their cost. The presence of water causes undesirable base hydrolysis, so the reaction must be kept

dry.

In the transesterification mechanism, the carbonyl carbon of the starting ester (RCOOR1) undergoes

nucleophilic attack by the incoming alkoxide (R2O

−) to give a tetrahedral intermediate, which either reverts to

the starting material, or proceeds to the transesterified product (RCOOR2). The various species exist in

equilibrium, and the product distribution depends on the relative energies of the reactant and product.

20 (b) Explain the preparation of ethanol from various types of biomass with a line diagram.

Ethanol (CH3CH2OH) is a renewable fuel that can be made from various plant materials, collectively

known as “biomass.” Ethanol is an alcohol used as a blending agent with gasoline to increase octane and cut

down carbon monoxide and other smog-causing emissions.

The most common blend of ethanol is E10 (10% ethanol, 90% gasoline). Some vehicles, called flexible

fuel vehicles, are designed to run on E85 (a gasoline-ethanol blend containing 51%–83% ethanol, depending on

geography and season), an alternative fuel with much higher ethanol content than regular gasoline. Roughly

97% of gasoline in the United States contains some ethanol.

Most ethanol is made from plant starches and sugars, but scientists are continuing to develop

technologies that would allow for the use of cellulose and hemicellulose, the non-edible fibrous material that

constitutes the bulk of plant matter. In fact, several commercial-scale cellulosic ethanol bio refineries are

currently operational in the United States.

The common method for converting biomass into ethanol is called fermentation. During fermentation,

microorganisms (e.g., bacteria and yeast) metabolize plant sugars and produce ethanol.

CELLULOSIC ETHANOL

Cellulosic ethanol is a large potential source of fuel ethanol. Ethanol can also be produced by breaking

down cellulose in plant fibers. This cellulosic ethanol is considered an advanced biofuel and involves a more

complicated production process than fermentation. While large potential sources of cellulosic feedstocks exist,

commercial production of cellulosic fuel ethanol is relatively small.

Trees, grasses, and agricultural residues are potential feedstocks for cellulosic ethanol production.

Trees and grasses require less energy, fertilizers, and water to grow than grains do, and they can be grown on

lands that are not suitable for growing food crops. Scientists have developed fast-growing trees that grow to

full size in 10 years. Many grasses can produce two harvests a year for many years without annual replanting.

A company in the United States is using the corncobs and stocks of corn plants to make cellulosic fuel ethanol.

21 (a)Expalin Reuse and Recycling with suitabe examples.

Reuse:

Reuse is the action or practice of using an item, whether for its original purpose (conventional reuse)

or to fulfil a different function (creative reuse or repurposing). It should be distinguished from recycling, which

is the breaking down of used items to make raw materials for the manufacture of new products. Reuse – by

taking, but not reprocessing, previously used items – helps save time, money, energy and resources. In

broader economic terms, it can make quality products available to people and organizations with limited

means, while generating jobs and business activity that contribute to the economy

Historically, financial motivation was one of the main drivers of reuse. In the developing world, this

driver can lead to very high levels of reuse, however rising wages and consequent consumer demand for the

convenience of disposable products has made the reuse of low value items such as packaging.

Current environmental awareness is gradually changing attitudes and regulations, such as the new

packaging regulations, are gradually beginning to reverse the situation.

One example of conventional reuse is the doorstep delivery of milk in glass bottles; other examples

include the retreading of tires and the use of returnable/reusable plastic boxes, shipping containers, instead of

single-use corrugated fiberboard boxes.

Advantages:

• Energy and raw materials savings as replacing many single use products with one reusable one reduces the

number that need to be manufactured.

• Reduced disposal needs and costs.

• Refurbishment can bring sophisticated, sustainable, well paid jobs to underdeveloped economies.

• Cost savings for business and consumers as a reusable product is often cheaper than the many single use

products it replaces.

Disadvantages:

• Reuse often requires cleaning or transport, which have environmental costs.

• Some items, such as freon appliances, infant auto seats, older tube TVs and secondhand automobiles could

be hazardous or less energy efficient as they continue to be used.

• Sorting and preparing items for reuse takes time, which is inconvenient for consumers and costs money for

businesses.

• Special skills are required to tweak the functional throughput of items when devoting them to new uses

outside of their original purpose.

Recycling

Recycling is the process of converting waste materials into new materials and objects. It is an

alternative to "conventional" waste disposal that can save material and help lower greenhouse gas emissions.

Recycling can prevent the waste of potentially useful materials and reduce the consumption of fresh

raw materials, thereby reducing energy usage, air pollution (from incineration), and water pollution

(from landfilling).

Recycling is a key component of modern waste reduction and is the third component of the

"Reduce, Reuse, and Recycle" waste hierarchy.[1][2] Thus, recycling aims at environmental sustainability by

substituting raw material inputs into and redirecting waste outputs out of the economic system.[3]

There are some ISO standards related to recycling such as ISO 15270:2008 for plastics waste and ISO

14001:2015 for environmental management control of recycling practice.

Recyclable materials include many kinds of glass, paper, cardboard, metal, plastic, tires, textiles,

batteries, and electronics. The composting or other reuse of biodegradable waste—such as food or garden

waste—is also a form of recycling.[4] Materials to be recycled are either delivered to a household recycling

center or picked up from curbside bins, then sorted, cleaned, and reprocessed into new materials destined for

manufacturing new products.

Recycling of a material would produce a fresh supply of the same material—for example, used office

paper would be converted into new office paper or used polystyrene foam into new polystyrene. This is

accomplished when recycling certain types of materials, such as metal cans, which can become a can

repeatedly, infinitely, without losing purity in the product.[5] However, this is often difficult or too expensive

(compared with producing the same product from raw materials or other sources), so "recycling" of many

products or materials involves their reuse in producing different materials (for example, paperboard) instead.

Another form of recycling is the salvage of certain materials from complex products, either due to their

intrinsic value (such as lead from car batteries, or gold from printed circuit boards), or due to their hazardous

nature (e.g., removal and reuse of mercury from thermometers and thermostats).

21 (b) List the ways by which you will conserve energy in (i) Compressors (ii) Pumps and fans.

Compressors:

Pumps and Fans:

Prepared by

Mr. K Saravanakumar

ID - 32092019

Lecturer

Automobile Engineering

PSG Polytechnic College

Coimbatore - 641 004