Module - 9Energy and Environment There have been some discussions on issues related to energy and environment earlier when we considered extraction of non-ferrous metals. Here we will discuss the subject in some detail.

Learning Objectives • To understand the importance of energy and environment

related cases in extraction processes• To understand the ‘cost of development’ • To understand the scope of energy reduction in extraction

processes• To understand the meaning and significance of the following

Waste, pollution, sustainable development, gross ecological product, Life cycle analysis, End use analysis, Subjective horizon, Carbon footprint, Carbon credit etc.

Why are we generating wastes ?Obviously because we are digging into earth’s crust. Earth – Radius 6371 km, of which about half consists of a core, presumably of an alloy of iron and nickel.There is an intermediate layer 2870 km thick which is thought to consist of silicates of magnesium, iron, chromium and also sulphides, tellurides and salenides. The crust of 30 km thick of which the ordinarily accessible portion comprises barely 3 km though boreholes put down for petroleum have reached a depth of 6000 m.When we talk about the abundance of elements forming earth’s crust we talk of only the top 10 km of the crust including the atmosphere and the oceans.

Abundance of elementsThe twelve most abundant elements account for 99.5 percent by weight of the crust, all other 86 elements together forming one-half of one per cent. Various geochemical factors have made distributions non-uniform.

Lower Limits of workable grade in deposits

Metal Percent

Aluminium 35

Iron 30*

Manganese 25

Chromium 25

Zinc 5

Lead 4

Nickel 1.5

Copper 1.0

Tin 1.0

Silver 0.05

Gold 0.001

Platinum 0.001

Percentage of metals from the lower limit of workable grade in deposits

* Carbonate Ore

Salient issues in computation of adjusted growth in GDP

• Health damage costs due to air pollution are based on population exposure, and morbidity and mortality figures that are attributed to respiratory ailments.

• Ecological damage costs due to air pollution includes vegetation loss, loss to ground water recharge, and soil erosion.

• Losses due to quantitative decline, and quality degradation due to excessive withdrawal of water and ground water contamination are estimated.

• Avoidance costs for surface water contamination from domestic and industrial wastewaters are estimated.

• Costs associated with land degradation are productivity losses of land mass under cultivation by assuming aggregate cropping patterns

• Loss of forest services / value is estimated based on charges in forest cover with recourse to the guidelines of the Ministry on benefit cost evaluation of projects involving diversion of forest land mass

• Biodiversity losses are not included in the estimation of total environmental and ecological losses

• Monetized value of natural resources used for growth in GDP not included in calculation.

What is development ?Development is availability of goods and services for all sections of the population.Not necessarily, highways, flyovers, tall buildings, gadgets and consumer items , clubs, disco joints, pubs, swimming pools, shopping malls, automobiles and aeroplanes. Yet these are also important.Progress/Development is demanded by the population. This needs more production, which needs more energy. Progress generally leads to more pollution.All P’s are related.The so called ‘Progress’, if not monitored, well can lead to problems, poverty from unbalanced growth, petty pressure politics , pessimism, prediction of dooms day.Progress with peace and prosperity demands plans, prioritization public participation, people’s power, pragmatism.

Example:

Replacing a 75 W incandescent lamp with an 18 W compat fluorescent lamp

: yields the same light for a duration nearly 13 times as long,

: keeps 1 tonne of CO2 and about 9 kg of SOX from being emitted by coal-fired station.

This also generates net wealth because the new lamp saves more in utility bills, replacement lamps, and the labour to install them than it costs. Saving electricity is cheaper than making it and pollution is avoided not at a cost but at a profit.

10t coal Transport 5 t coalThermal power 25% Eff

1.25 t coal

Transmit 25% loss0.7 t coal equivalent 0.9 t coal

Devices

80% Eff

An interesting example ( National Geographic March 2009)

• An incandescent bulb ( U S cost 65 cents) lasts 1000-2000 hr costing $ 72.55 in 15 years of electricity. With efficiency of 6% , 94 % of electricity is dissipated as heat.

• A CFL bulb with 25% efficiency costs $ 4 a bulb, lasts 6000-12000 hr and in 15 years the electricity bill will be $ 18.14

• The LED lamps being developed operate with 50 per cent efficiency, costs $120 a bulb and lasts 20,000-50000 hr . In 15 years the electricity bill will be $ 9.67

If we have long subjective horizon, we will invest in the last.

EFFECTS ON ENVIRONMENT A. MINING ACTIVITIES• DEPLETION OF NATURAL RESOURCES• DEFORESTATION• DUST AND FINES• SPILLAGE DURING HANDLING & TRANSPORT

B. PROCESS• EMISSION OF POISONOUS GASES, FUMES• GENERATION OF DEBRIS, FLY ASH, SLUDGE, SLAG• SPILLAGE OF LUBRICANTS, HAZARDOUS CHEMICALS &

WASTES• NOISE, VIBRATION

EVERY ACTIVITY HAS AN EFFECT ON THE ENVIRONMENT

ENVIRONMENTAL POLICY

1. SET OBJECTIVES & TARGET REVIEW2. OPERATE TO COMPLY WITH LAWS, STATUTES

& REGULATIONS3. REDUCE CONSUMPTION & WASTAGES4. RECOVER & ERECYCLE MATERIAL WASTES5. PHASE OUT POLLUTION PRONE PROCESSES

AND UPGRADE TECHNOLOGY6. REHABILITATE WASTE DUMPS7. DEVELOP AWARENESS AMONG WORKFORCE

PROCEDURES 1. EVALUATION OF ENVIRONMENTAL ASPECTS AND

THEIR IMPACT2. ACCESS TO LEGAL REQUIREMENTS3. ORGANISATION STRUCTURE WITH RESPONSIBILITY &

AUTHORITY4. TRAINING – NEED & IMPART5. COMMUNICATION6. DOCUMENT CONTROL7. RESPONSE TO ACCIDENTS & EMERGENCY

SITUATIONS8. PROCESS CONTROL9. CORRECTIVE & PREVENTIVE ACTIONS10. RECORD KEEPING11. SYSTEM AUDIT12. SYSTEM REVIEW

ENVIRONMENTAL ASPECTS1. EMISSION TO ATMOSPHERE2. DISCHARGE OF WASTEWATER TO WATER

BODIES3. WASTE MANAGEMENT AND DISPOSAL4. MANAGEMENT OF HAZARDOUS SUBSTANCES5. CONTAMINATION OF LAND6. NOISE, ODOUR, DUST AND VIBRATION7. USE OF NATURAL RESOURCES, ENERGY8. LIKELY BREACH OF LEGISLATIVE

REQUIREMENTS9. EMERGENCY SITUATIONS

CRITERIA TO EVALUATE EFFECTS ON ENVIRONMENTCRITERIA DESCRIPTION POINT RATING

AREA (X) VERT KICAKUZED EFFECTDEPARTMEMT/AREA WISE EFFECTENTIRE WORKS IS AFFECTEDSURROUNDING COMMUNITY IS AFFECTEDGLOBAL EFFECT

12345

SEVERITY (y) INSIGNICANT EFFECTMOMENTARY SIGNIFICANT EFFECTINJURIS/EFFECT ON LESS THAN 10 PERSONS IN A MINOR WAYINJURIES TO MORE THAN 10 PERSONS IN A SIGNIFICANT WAYDEATH OF PERSONS OR FLORA/FAUNA AFFECTED SEVERELY

12345

DURATION (z) MOMENTARYIMPACT FOR LESS THAN 2 HOURSIMPACT FOR A DAYIMPACT LIKELY TO LAST FOR A PERIOD EXCEEDING ONE WEEKPERMANENT IMPACT ON THE ENVIRONMENT

12345

FREQUENCY (F) ONCE A MONTHONCE A WEEKONCE A DAYSEVERAL TIMES A DAYCONTINUOUSLY OCCURING

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TOTAL SCORE = X x Y x Z x F

WASTE MANAGEMENT

1. AVOIDANCE OF WASTES

2. RECYCLING & REUSE OF WASTES

3. MINIMISING ADVERSE IMPACT OF DISPOSAL OF THESE WASTES ON THE ENVIRONMENT

EMS AUDIT

EMS REVIEW

(EMS- ENVIRONMENT MANAGEMENT SYSTEM)

AGENDA OF MANAGEMENT REVIEW

1. LAST MINUTES2. RESULT OF EMS AUDIT3. PROGRESS OF ENVIRONMENTAL MANAGEMENT

PROGRAMMES4. PERFORMANCE AGAINST OBJECTIVES & TARGETS5. RESULTS w.r.t. LEGAL REQUIREMENTS6. RESOURCE REQUIREMENT7. TRAINING AND AWARENESS8. POSSIBLE NEEDS FOR CHANGES9. ANY OTHER RELEVANT ISSUES

POLLUTION AND THE ALUMINIUM INDUSTRY

Local, regional and global effect of emissions

Local – release of fluorides cause bronchitis, dental and skeletal fluorisis

Regional – CO2, SO2 released can be transported to long distances, washed away by rain and then falling on ground. Reduces growth of vegetation due to acidification of soil. pH of rivers and lakes goes down. Fish cease breeding and eventually leave the area. Aggravates corrosion.

Global – Increased CO2 in the air contributes to greenhouse effect and global warming.

Air pollutants – C ( shoot), Al2O3 , cryolite, other Al-Na compounds, AlF3, CaF3

Gases – HF, CF4, C2F6, SiF4, SO2, H2S, CS2, COS, CO2, CO, H2O, Hydrocarbons

Solid residues – Red mud from Al2O3 plant, flyash from thermal power plants

CO2 emissions from carbonaneous fuels have become a critical subject now. It is increasing at a rate of .028% per year.

Carbon emission reduction targets for different countries are as of now the following.

The U.S. – 17 per cent of 2005 levels by 2020, 30 per percent by 2030 and 80 per cent by 2050.

European Union – 20-30 percent of 2005 levels by 2020.

Brazil – 36-38 percent by 2020

South Africa – 15-20 percent by 2020

Indonesia – 26 per cent by 2020

India – No target has been set as yet.

Present annual growth rate of carbon emissions – ( In percent)

U.S- 25, Canada – 54, Japan – 17, Germany -18, India -97, China – 109

U.K – only 1 and in Russia it is negative( See National Geographic March 2009)

Two new words that are important today

Carbon footprint - Carbon consumption by an individual required to maintain his lifestyle.

Carbon Credit – This is acquired by minimizing carbon consumption (1 ton of CO2 saved is on CER) and this can be traded with somebody not doing so in exchange of financial gains.

This is one way of rewarding cleaner operation and punishing the polluter. Yet it does not solve the problem.

The U.S is emitting about 6 billion metric tons of CO2 per year which is a fifth of the total world emissions. The main culprit is not the industry. The shares are as follows :

• Buildings ( with lighting, heating and appliances) – 38 per cent of the total energy

• Transportation – 34 percent of the total energy• Industrial sector ( refineries, paper plants, manufacturing industry) – 28 per

cent

The metal industry is not that big a culprit – even the steel sector is responsible for only 4-6 percent of the global CO2 emission. Yet we cannot be complacent.The commercial aviation sector releases 2% of total CO2 , that too high above earth (more damaging) but it is committed to keep it at that level.The subject of CO2 sequestration is very important but we will not discuss it here.

Development needs electricity but one can use electricity more efficiently

Process Fuel equivalent

Table : Process Fuel Equivalent(PFE) for Metal Production from Concentrate

Metal Process/Route Product PEE GJ/t

Fe Blast furnace, oxygen Steelmaking, Pyro

Steel Ingot 22

Pb Blast furnace,dross,Fire-refine , Pyro

refined Pb 23

Al Bayer leach, Hall Electrolysis , Hydro

Al ingot 280

Cu Flash smelt(O2), Convert,Eletrofine, PyroLeach sulphideConcentrate, eletrowin,Hydro Roast, leach,

Cu cathode

Special high

100

51

Zn Roast, leach,Electrowin

Special high grade ZnSpecial high Grade Zn

5155

Source : H H Kellog, Energy Efficiency in the age of scarcity , J Metals, Vol 26, June 1974, p.25

RECYCLING OF ENERGY

Energy considerations have led to many technological and resources management innovations including recycling. In this section, we will briefly discuss some issues regarding potential energy savings through recycling and reuse. Many producers are not simply interested in a product that saves most the energy if recycled but, rather, a product that has the lowest overall environmental impact. In some situations, product reuse or material substitution may be more desirable than recycling. From an environmental perspective, energy savings are only one of several important considerations. In many cases, there is a trade off between reduction in energy consumption and that of water and air pollution as well as in generation of solid hazardous wastes. The actual impacts on the environment will vary greatly with population density, available fuel sources, transportation infrastructure and other factors.

Table : Energy for production of metals from their respective ores and secondary sources ( in 106 kJ/t of metal)

Metal Primary(from Ore)

Secondary (from scrap)

energy savingsfrom recycling

Magnesium 358 10 348

Aluminium 244 12 232

Nickel 144 15 129

Copper 112 18 94

Zinc 65 18 47

Steel 32 13 19

Lead 27 10 17

Source: H S Ray and S C Panigrahi, Energy and the Metallurgical Lecture Notes ( Dept of Metallurgical Engg, IIT, Kharagpur, India),1987

Obviously recycling not only saves energy but also solves an environmental problem. This has become an integral part of many industries in the advanced countries where huge amounts of scrap are readily available.

Recycling : Definitions and TerminologyThere is no widely accepted definition for the term ‘recycling’. Different people have adopted different definitions to suit their needs, for example, incineration to recover energy, is considered to be a form of recycling by some people. From an environmental point of view, the recycling of material displaces the need for extraction of virgin or primary resources. In practice, however, any secondary use of material is often considered recycling. Significant amounts of scrap that accumulate in the initial production process of smelting or milling, is known as industrial or home scrap. Such materials are generally sent to a separate facility to cleaned, cut, shaped, rolled and finished. More scrap generated in this stage is referred to as prompt, industrial scrap.

Such materials are generally sent to a separate facility to be cleaned, cut, shaped, rolled and finished. More scrap generated in this stage is referred to as prompt industrial scrap. Being clean, these two types of scrap are usually reincorporated into furnaces in most industries. Products sold to consumers invariably become unusable after a lifetime and are discarded. These, when collected for the purpose of remanufacturing of new products, are called post consumer or old or obsolete scrap. Since this scrap lies scattered, it generally presents difficulties in way of collection and reuse. However, with improved collection systems, more and more old scraps are being recycled. It is estimated that by the year 2010. 75% of the 400-500 mt total scrap consumed will consist of obsolete scrap.

Recycling : Definitions and Terminology…

In the Table , the third column represents the best possible industrial energy consumption data considering only reduction steps. In the case of Cu and Pb, different process routes have different energy values, classical processes being the most energy intensive. For these energy consumption data, theoretical conversion factor of 3.6 is assumed.

It can be stated that of all the metallurgical reduction processes for the ‘big four’ non-ferrous metals, ( Al,Zn,Cu and Pb), the Pb metallurgy is the least energy consuming process followed by Zn pyrometallurgy. The most energy wasting processes are the classical pyro, hydro and electrowinning of Cu. Hence there is ample scope to narrow the gap between the gap between the theoretical and the practical energy need.

Energy Requirement for Production of Metals from their concentrate

Metal Process Energy Free Energy Process ( 103 kWh/tonne) (103 kWh/tonne) Efficiency(%)

Titanium Sponge 105.8 4.7 4.4Magnesium Ingot 99.9 6.0 5.9Aluminium Ingot 58.0 7.5 12.9Ferrochrome low carbon 36.9 2.6 7.0Sodium Metal 26.8 2.1 7.8Nickel Chloride 26.2 0.9 3.5Ferrochrome High carbon 16.3 2.6 15.8Ferromanganese(arc furnace) 14.2 2.1 14.8Copper refined 14.2 0.5 3.7Zinc(electrolyte) 14.2 1.3 9.0Ferromanganese(blast furnace) 12.0 2.1 17.0Steel slab 6.4 1.6 26.6

Tin ingot 5.6 1.2 20.0Lead Ingot 5.3 0.2 4.4

Source : H S Ray , R.Sridhar and K.P.Abraham, Extraction of Non-ferrous metals( Affiliated East-West Press, Pvt Ltd, New Delhi), 1985

Considerable gap exists between the theoretical energy required for extracting a metal from its mineral and the actual energy requirement for winning it for its available ores. This is because ores and minerals, contain a lot of gangue, which consumes considerable energy during processing. With the many unit operations involved in minerals and metal processing industries, several of which require significant inputs of energy, this industry has experienced substantial increase in percentage of total cost for energy alone.

Table : Energy Consumption Distribution for Processing of Copper Sulphide Ore

Unit Operation Energy Distribution(%)

Crushing, grinding 73.5 Floatation 7.8Filtration 1.6Water recycle & new water

17.1

Total 100.0Source: C H Pitt and M.E. Wardsworth. An assessment of energy requirements in new copper process . US Dept of Energy Divn of Industrial Energy Conservation, Final Report, Dec 31, Contact No – EM-78-S-071743

There are several approaches to energy saving. The potential of some of these are as follows : control 10-15%, optimization , 20%, and grinding aids, 10% Similarly, flotation energy requirements can be reduced by employing the larger volume floatation cells that are presently available. It has been shown that 10% energy savings can be achieved by increasing cell volume by 50% to 80%.

When wet solids are to be thermally dried or subjected to an endothermic reaction such as calcinations or disposed for land filling where a transportable and handleable material is essential, then mechanical dewatering should be considered. Generally, one will employ a device such as a filter, belt press or a centrifuge to remove moisture. There are now many new solid-liquid separation methods that offer potential energy savings as well as other cost reduction elsewhere. Some of these are listed as follows

• Steam drying• Use of surfactants or speciality chemicals• High-pressure flitration• Improved thickening methods• Electrophoresis

High Pressure Grinding Rolls( HPGR)

Size reduction accounts for about 3% of the total world electrical energy consumption and it is estimated that energy consumption in commination constitutes over 50% of that used in raw material processing. It has also been estimated that grinding process efficiency is generally around 1.5-12% and the majority of commination tasks being carried out at less than 5% efficiency. Sustained research carried out over the last three decades indicate that scope for improving energy efficiency of traditional grinding machines, such as ball mills, is limited. It has been assessed that the potential energy saving with existing technology is about 13% compared with 29% energy saving through improved or new technology such as high pressure grinding, ultrasonic grinding mills, stirred mills. Comparison with conventional ball milling for grinding of limestone, cement clinker and coal indicates that , in all cases, the new grinding devices gives lower specific energy consumption with possible energy saving of 15-40%. Depending on the grinding unit selected and the type of material being ground.

Energy savings potential using HPCR

Material EnergyEsc*(k Wh/t)

Consumption Esb**(kWh/t)

Energy Saving (%)

Copper Ore 1 5.2 6.1 15

Nickel Ore 7.1 13.0 45

Copper Ore 2 6.7 9.2 26

Granite 4.0 5.2 23

Bauxite 4.4 7.4 41

Clinker 19.6 28.8 32

Gold Oxide Ore 2.4 5.9 59

Gold Sulphide Ore 2.4 9.4 73

Limestone 4.6 10.6 57

*Energy consumption recorded using HPGR** Energy consumption predicted using Bond formulaSource: Chu Yong Cheng and Vibhuti N Misra, CSIRO DMR-987,year

SOME PROBLEMES

The following are the specifications of two motors A and B

Motor A Motor B

Output rating 7.5 kW 7.5 kW

Conversion efficiency 80% 90%

Initial Cost Rs 3000 Rs 6000

Replacement Life 5 years 20 years

Salvage Value Rs 1000 Rs 2000

Annual Maintenance Rs 100 Rs 100

Electricity Cost Rs 3/kWh Rs 3/kWh

Operating schedule of both the motors is 8h/day and 22 days/month. Based on life cycle costing analysis for an assumed desired life of 20 years, determine which motor is the better option?

Solution

Life cycle costing is based on a consideration of all the costs associated with an alternative during its entire lifetime. The following Table lists the relevant cost for motors A and B for the calculation of life cycle costing.

Item Description Motor A Motor B

Per year (Rs.) Total(Rs.) Per Year(Rs.) Total(Rs.)

Annual Maintenance 100 2000 100 2000

Operating Cost 59,000 11,88,000 52,800 10,56,000

Replacement Cost 600 12,000 300 6000

Salvage Value 200 -4,000 100 -2000

Total Life cycle Cost 11,98,000 10,62,000

The life cycle costing analysis shows that motor B will cost less than the motor A over the entire useful lifetime of the investment, while if one were to make a decision on motor A versus motor B based on initial cost only, then motor A will be selected. However, life cycle costing is said to be a first approximation since no consideration is given to the cost of money.

Assume you are the energy manager of the XYZ company. You have recently completed energy audits of several projects and have identified some for immediate action. Preliminary engineering analysis have confirmed the technical feasibility and economic viability of the projects. The following four projects are identified

Project Initial Cost($) Energy Savings(Units/

year)

$ Saved/year

Modify lighting control 1000 25,000 kWh 1250

Install heat recovery system 2000 1,250 GJ 5000

Temperature set back at night 0 200 GJ 800

Insulate building attics 5000 150 GJ 600

Now how should you proceed to prioritize the above projects

Solution :

To select the priority the above four projects should be ranked based on some criteria. They can be ranked in several different ways but we have selected the following criteria.

Ranking Criterion Project Ranking Worst Best

Least capital Cost 2 4 1 3Greatest energy savings 1 4 3 2Greatest money savings 4 3 1 2Shortest simple payback 4 2 1 3Greatest Energy savings/dollar invested

4 2 1 3

Project which reduces electricity

4 3 2 1

If money for new projects is limited, the strategy might be to implement that project which requires little or no capital cost. Hence Project 3 will be the highest priority. On the other hand, if energy supplies were short, the project 2 might be selected first. If electricity was in short supply or subject to curtailment project 1 might be implemented first. So far only economic criteria have been considered. Completely different answers will be obtained if the criterion will be changed. For example, if the building considered for the project 4 is occupied under terms of a 4-year lease then project 4 might be totally eliminated because money invested will not be recovered during the lease .

In the XYZ plant project 1, modify light controls , saved 25,000 kWh/year . However during the second year, right after the project was implemented, a new wing was added to the building. This wing caused additional lighting electricity use of 20,000 kWh. What are the cumulative project savings that are avoided after three years compared to the base year ? Assume base year lighting energy is 250,000 kWh and escalation of price is constant at 10% per year.

Solution :

The following Table shows the project cost if the project I is not implemented

Year Energy Energy Net Energy cost Annual Annual Used Saved kWh/yr ($/kWh) Cost($) Saving($)1 250,000 0 225,000 0.05 12,500 02 270,000 0 270,000 0.055 14,850 03 270,000 0 270,000 0.061 16,700 0

In three years net kWh used is 790,000 and total cost is $43,820. If now the project I is implemented the above Table will be modified and the following Table shows the result of the implementation

Year Energy Energy Net Energy cost Annual Annual Used Saved Wh/yr ($/kWh) Cost($) Saving($)

Base 250,000 0 250,000 0.05 12,500 01 250,000 25,000 225,000 0.05 11,250 1,2502 270,000 25,000 245,000 0.055 13,475 -9753 270,000 25,000 245,000 0.061 14,945 -2,445Total 75,000 715,000 39,670 -2,170

In three years total energy saved is 75,00 kWh and total cost is $39,670. Hence total cost avoidance will be 43,820 -39,670 = $ 4,150

In this example, implementation of project I is saved money for the first year. During the second and third year , the escalation of electricity price and increased production causing more electricity to be used, resulted in an increase in the electricity bill relative to the base year. However, without the energy management project, costs would have been $ 4,150 higher than they actually were.

Nuclear Reactors

Currently, world over, 436 nuclear power plants are in operation with an installed capacity of 372 GWe supplying 16 per cent of electricity and 35 reactors are under construction. Further about 220 new reactor plans are planned across the world by 2030. India plans to increase the present nuclear capacity of 4120 MWe to 20000 MWe by 2020 and 63000 by 2032.

[ S. K Jain IIM Metal News Vol 12 No 5 Oct 2009, p 6]

Indian nuclear plants have witnesses over 300 reactor – years of accident free safe operation with high availability factors ( above 80% during the last decade)

World wide there are three main industrial fuels – Petroleum (43%), Coal (36%) and natural gas (20.3%). The main emissions come from electricity and heat generation (24.6%). The figures for others are : land use change (18.2%), agriculture (13.5%), transportation (13.5%), industry(13%).Nuclear power plants do not emit CO2. However, the electricity consumed does imply CO2 generation elsewhere to a smaller extent.

A recent issue of National Geographic (March 2009) gives the number of nuclear reactors operating in different countries as follows. The percent of country’s energy need met is given in brackets.

France -59 (77) , S Korea 20 (55) Japan -55(28), The U.S -104 (19), Russia -31(16), The UK -19 (15), India – 17(3), China 11(2)

The number of reactors in India is actually more as mentioned earlier and they are meeting more than 4 per cent of country’s energy needs.