Work is manifestation of energy. Energy is a basic need for any activity. There is no change in the status of any object without the application of force produced by energy. Everything is at a standstill without energy due to inertia. Even if all the creatures on the earth are alive till all their essential organs like mind, lungs, kidneys, intestines, gland etc. are regularly functioning. And energy is required for the functioning of these organs. Therefore, the creator has provided energy sources within the body. Carbon is taken as food in the form of carbohydrate and oxygen in air while breathing. Energy required by each organ is produced locally by metabolic process. This is example of natural distributed generation of energy. This biological energy is primarily used for internal functions as above. This energy is also useful for external essential activity like movement for water, food and shelter for protection and peaceful rest.
Spare energy is used for play and pleasure. This is almost common for all living people on earth. But humans have an additional gift of a fully developed mind. So, they apply their intelligence to use spare energy for other purposes in their favor. They developed various tricks for ease in their essential activities. Such tricks made their task easy and fast. So, they developed more and more devices for such convenience. So, they were eager for such facilities. Also, some of the devices made life comfortable. So, they liked such a luxurious life. This followed endless efforts for more and more facility and luxury.
All such tricks-devices-machines require energy to operate it. In some cases, human capacity is found insufficient for the purpose. So, they resorted to joint efforts and succeeded in achieving the goal. Their intelligence suggested the use of animal power. So, they employed horses, bullock, camel etc. depending on the requirement of power and availability of animal. Later on observed power of solar radiation useful for heat and light. Solar heat proved protective against cold. This may be the first lifeless energy source introduced to humans. Accidental fire in the forest introduced other sources of light and heat. Fire found useful for making the prey soft for eating with better test. Fire was also protective from cold, darkness and wild animals. They understood wood (dry tree) as source of fire and also found out how to get fire.
Natural sources
As discussed earlier, there is provision for energy within the body for essential functions to be alive. Similarly, there is the provision of energy sources on earth itself. Energy packs in various forms are available in nature at sub-terrain, sea and sky. We just identify and develop tricks to get the energy.
Never ending chase for energy continued and is still ON. Numbers of energy sources in different forms were identified at different times at different places. Primary adoption of such energy source was to utilize it in the raw form where and when available. Energy in solar radiation is available in open space during the daytime as heat and light. So, it was utilized for that purpose only. Hence, there were limitations for utilization of natural energy.
Raw energy available in sources deviates in the following three aspects that impose restriction on utilization.
- Energy may be available in a form other than usable.
- Energy may be available at places other than where needed.
- Energy may be available at any time other than when required.
Therefore, raw energy requires processing as under to match the needs.
Transform
Available energy is transformed to usable form. So, some device is used to change the form of energy. Requirement may be single or multiple conversions to get usable form. Each conversion requires an appropriate device. Energy in chemical form of fossil fuel cannot be used as it is but useful when transformed to heat by burning.
Transport
Energy is required to transfer from the place of availability to the place where it can be utilized. Appropriate device has to be used for transfer of energy. Transfer of energy may be feasible and convenient in specific forms. When the original form of energy is not suitable for transport, it may require transforming to a suitable form for transport. In such case devices are required for transformation as well as transport. Natural gas is taken to the place of utilization.
Time shift
Time shift is required when energy is available but cannot be used at that time. So, it requires temporary storage of energy till the time when it can be used. Again, the feasibility of storing depends on the form of energy. In case the energy form is not suitable for storing, it requires to transform in convenient form to store. In this case the device is required for transformation in addition to the device for temporary storing and retrieval when required. In the case of pumped storage system, spare electrical energy is stored as potential energy and again converted to electrical energy when needed.
All together possibility is need of multiple devices to transform raw energy in the suitable form for use, transfer and storage. Devices are also required for storage, retrieval and transfer when so required. Sometimes, transforming from particular form to desired form is not feasible. So, that needs first to first transform to intermediate form and then to desired form.
Net energy is reduced through devices due to anyone or more of the following:
Rejection
Rejection is part of the energy fed to the device is not converted as desired. It remains as if and leaves as waste. Heat in condensate of condenser.
Leakage
Leakage is the part of energy diverting from the process to waste. Liquid and gas leaking from joints and control devices, heat lost to atmosphere from steam and hot water line, electricity lost as dielectric loss.
Device use
Energy required for functioning of device. Energy consumed in motor for forcing magnetic field through core, current through conductor and mechanical force to overcome friction in movement.
Ultimately results are poor gain from available energy sources. Therefore, it is desirable to manage with minimum devices for conversion, transportation and storing.
The following measures may be useful:
- Use natural (raw) forms of energy where possible: Lighting requirements during daytime can be accomplished by using daylight.
The heat of the sunray can be used for heating and drying purposes as in solar water heaters, solar cookers, and solar steam generators for industrial and large kitchens.
Natural breeze is a better option instead of fan and air conditioner. Cross ventilation facilitates fresh air flow. This is more evident in the upper floors of multi-storey buildings where the air is clean and cool.
- Preference to local source: Transportation and probable conversion to suit transportation is avoided while using local energy source. Distributed generation is the right approach in the matter. In addition to wind and solar, use of agricultural and domestic waste has dual advantages.
- Matching available and utilization time: Formation of energy grid facilitates the purpose. Energy sources available at different times of the day, week, year, season feeds to users at different times. Only net surplus / deficit is required to store, retrieve or transport.
- Cascade utilization: Energy should not go to waste till there is scope to utilize residue energy. Heating element is provided in air conditioning system of the car. On the other side heat of the engine is wasted in the radiator. Coolant from the engine may pass through the AC system before going to radiator. Coolant can have a bypass system when heating is not required.
- Minimize steps for linking source to use: There may be many devices linking energy source to use, each wasting part of energy. So, energy systems should have minimum intermediates for best utilization of the source.
Review of multiple conversions while using natural gas for industrial heating via electricity.
- Heat produced by burning gas in boiler is transferred to water, but part of the heat is wasted in flue gas.
- Energy gained by water in the form of heat and pressure is transferred to turbine but only part is converted speed and major part is wasted in condenser.
- Generators produce electricity but part of it is wasted as auxiliary consumption.
- Voltage is boosted in GT wherein energy is wasted as loss.
- Power is transmitted online to near the user area wherein transmission loss occurs.
- Distribution loss occurs while supplying electricity to consumers.
- All above steps are avoided while using natural gas direct for producing heat for industrial purpose.
So, using electricity to produce bulk heat is most uneconomical. Similar multiple conversion to be avoided.
Better alternative / efficient device
Most of the devices used now are traditional. With technological development, now it may be feasible to have innovative simple, short and efficient methods or improvement in performance / efficiency in traditional methods. Adoption of these may improve overall gain.
All above tools of multiple conversion for matching energy form, time and place do away with adoption of common intermediate versatile form of energy pool for supply and use.
Electricity is an appropriate intermediate form of energy due to the following:
- Most versatile form of energy.
- Feasible to convert raw energy to electricity by befitting option.
- Feasible to convert to usable format.
- Feasible for quick transfer from place to place.
- Widespread grid network for anywhere anytime energy dump and draw.
- Least energy wastage by rejection, leakage and self-use.
- Well-developed control system for regulation.
- State of art protective system for reliability.
Following five Natural Phenomenon available to transform other form of energy to electricity:
- Piezoelectric Effect: Pressure is converted to electricity. Widely used in Gas Lighter. The trial is going on for getting electricity from pedestrian walk. Still no scheme is developed for bulk power production.
- Electrochemical Effect: Electricity produced by chemical reaction. Popular use is in Dry Cell. Other major applications are energy storage for various applications like vehicles, phones, toys etc. Bulk energy storage is also tried for grid and EV etc. But no scheme has yet been developed for power production on a large scale.
- Hydrogen fuel cells convert the chemical energy in hydrogen and oxygen into direct current electrical energy by electrochemical reactions.
- Thermoelectric Effect: Temperature converted to electricity. Mostly used as in Thermocouple used mostly in instrumentation as temperature sensor. No scheme yet available to developed power.
- Photoelectric Effect: Light is converted to electricity. Solar radiation is converted to electricity by photovoltaic cells. Recently there is fast development in power production by this method.
Another form of energy available from solar rays is heat. This heat is absorbed and utilized for various purposes like cooking, drying, steam generation for cooking, industrial applications and producing electricity by conventional method.
- Electromagnetic Effect: Interaction of magnetic flux with conductor produces electricity. Electricity produced due to changes in magnetic flux linked to conductor is electromagnetic inductions. This is the most used principle for production of bulk electricity. Steam turbine, gas turbine, hydro turbine, wind turbine / mill or any system that has rotary motion uses this method to produce electricity.
Following three is basic requirement to produce electricity by electromagnetic induction:
- Magnetic flux is produced by permanent magnet or electromagnet.
- Conductor coil linked within magnetic field.
- Continuous change of magnetic flux linked to coil.
The magnetic field of permanent magnet is limited – and so the electricity produced using permanent magnet is also limited. So is useful for small power applications.
Mostly electromagnets are used for producing magnetic fields.
Change in flux linkage is accomplished in three ways.
- Magnetic poles are stationery and conductor coils are moving: Conductor coils are used instead of single piece of conductor to multiply the induction effect. Coils are laid in armature (rotor) such that its sides cross opposite poles at the same time. Magnetic poles are stationary on stator. Electricity is induced in the coils on armature by electromagnetic induction when rotor is moved by prime mover due to changing flux linkage to coils. Electricity produced on armature is picked up by brushes commutator. This is a DC generating system.
- Conductor coil is stationary and magnetic poles are moving: DC supply is fed to rotor through slip rings to produce electromagnets on rotor. Coils are stationary on the station. Electricity is induced in stationary coils by electromagnetic induction when rotor is moved by prime mover due to changing flux linkage. This is an AC generating system.
- Electromagnet and conductor coils are stationary: In transformer primary and secondary windings are stationary. Primary is producing magnetic flux in core. Secondary is on the same core linked with flux produced by primary. Magnetic flux is produced by DC (unidirectional current) in the case of AC and DC generators. Transformer cannot work when DC is supplied to primary because there is magnetic flux linked to secondary but is fixed. But magnetic flux produced by primary changes when AC is supplied to primary. Now secondary is on the same core linked with changing flux. So, electricity is produced in secondary.
There are many energy sources in various forms. Some of them are already in use since long whereas some sources are employed recently and still efforts are ON to find ways and means to harvest energy from few identified sources. The possibility is that new sources having potential for energy are identified in future.
Characteristics of various raw energy sources:
- Availability over the day (Day/Night)
- Availability over the year (Season)
- Regularity (Predictable)
- Storage scope (Dormant / Use or Let go)
- Ease of transfer.
- Convenience of handling
- Reliability
- Recurrence (renewal) cycle.
Analyses of few known energy sources on above line:
Fossil fuels: This is available under the ground in the solid form of coal and lignite, in liquid form as crude and in gaseous as natural gas and petroleum gas. Various derivatives of crude like petrol, diesel, kerosene, naphtha and residual RFO are obtained to suit different applications.
All these are chemical energy sources as they release energy in the form of heat by exothermic reaction with atmospheric oxygen. These are dormant sources, naturally stored and remain available till explored. One after another such sources were available and used in the past. There was no idea for exhaust. These were used mainly in power plants to produce electricity, in transport as fuel and to produce heat for industrial and domestic purposes. It has been in use for a long time and hence referred to as a conventional source of energy. It has a major drawback that it produces carbon dioxide and flying ash polluting the environment. But now advanced techniques have made it possible to estimate the total stock of such sources on earth. This revealed limitation of stock and alarmed for future energy crises. This gave rise to the concept of energy conservation and judicious use.
Coal and lignite are solid fuels used in boilers to produce steam and run steam turbine generators to get electricity. Rise or drop of generation is slow as numbers of auxiliary has to follow. Frequent start stop is not economical, not suitable for thermal stresses.
Gas is either used in boiler for electricity or a gas turbine is operated by burning gas in combustion chamber. Heat energy left in exhaust gas is used in heat recovery steam generator to produce steam and run steam turbine generator. Close cycle plant has limitation for start or stop but open cycle can be regulated as required.
Oil is used in boiler for electricity as above or used
in oil engines to generate electricity or use rotary motion in industries and transport etc. No restriction for start / stop.
Hydro energy: Basically, hydro energy is available in two forms – potential and kinetic.
High head: River with regular flow may have drop (fall) on pathway way due to uneven land. Potential energy of water at the upper level is used to run water turbines and produce electricity. Small natural or artificial reservoir developed at upper side receives and stores water. This facilitates short term regulation of generation.
There is a limitation on the use of potential energy. Head pressure at bottom of penstock and turbine will be unmanageable when level difference is very high. Such very high head is utilized by cascade stations. Part of the total available head is utilized in the top stage. The second stage station just below intake is discharge of upper stage and so on.
Low head: River flowing on moderate gradient and having continuous heavy flow is good source of kinetic energy. Here situation is use or lose condition. Low head water turbine is used for production of electricity. There is no scope for storing and regulating generation. Reducing generation means wasting energy. So, this can be base load generation.
Dam site: River having very wide catchment area has heavy flow during monsoon. But availability is only for a few months. So, it is not economically viable to have a power plant of huge capacity due to very low load factor. But storing water in dams at suitable locations enables regulation of generation and full utilization of available energy. Dam has still more benefit of water for agricultural, industrial and population. Generation regulation is technically feasible but requires coordinate with water requirement. Energy available is fixed based on storage capacity and seasonal inflow but is an annually recuperating source and hence needs to be utilized before the next cycle.
Pump storage system is useful for short period energy storage to manage load variations over the day. Two reservoirs, upper and lower, are required. Water is pumped from lower reservoir to upper reservoir using surplus energy during light load period. Energy is thus stored in the form of potential energy of water. Energy is reproduced by normal hydroelectric system using water from the upper reservoir.
Hydro generation can be regulated in full range with start or stop also. Hydro generation is cheapest as only capital and operational cost is involved. So, regulation of generation on run off river is uneconomical.
Wind energy: Air in motion is wind has kinetic energy. It is available round the day and year, but the velocity of wind is unpredictable and uncertain. It is also a use or waste type of source.
Windmill: Wind energy harvesting is by windmill. Mostly high mast horizontal shaft wind turbines are used. This is expected to be cheap like hydro generation as no consumable input is required. But capital cost is yet high.
Other models like vertical shaft windmill, windmill tree etc. are on trial.
Parachute pull: Air trapped in parachute pulls the rope unwinding drum connected to generator through gear. After reaching a definite distance, the parachute is tilted, or top vent is opened to let air flow through and off load it. The unloaded parachute is drawn back up to fixed distance by winding drum run by motor. Energy generated by generator during pull by loaded parachute is much more than energy consumed by the motor during draw back unloaded parachute. The difference is the next generation in each pull / back cycle. This may continue repeatedly.
Solar Energy: Solar radiation is an unlimited source of energy available anywhere but for part of the day except on cloudy days. It is a use or waste type source and unpredictable to some extent.
Solar energy is available in two ways.
Insulation: Photo Voltaic Cell directly converts solar insulation to electricity. It is static, light weight and almost maintenance free device. Continuous R&D made it cheaper and compatible with conventional electricity and widely used.
It requires wide area. So, it was considered as suitable for waste land area only. But now better solutions are available. Covering roads with solar panels where no shadow of trees or building obstructing the sun rays has dual advantage of generating electricity and also prevents road heating. Similarly covering canals with solar panels and floating panels on pond prevents evaporation loss of water in addition to electricity. Installation has to be strong enough to secure during cyclonic weather.
Heat: Sun rays also produce heat where they hit. So, it is used for drying and heating in various manners.
- Solar cookers are mostly used for household applications.
- Solar water heaters are used for various purposes.
- Solar steam generators are used in large kitchens, industrial and to produce electricity in conventional way.
Air in wide heat collector at bottom of Solar Chimney is heated by sun rays. Hot air is passed through the chimney to set up air draft. The wind turbine generator set in the path of the draft produces electricity.
To be continued…
Natvar D. Makwana is a Retired Engineer from SLDC, Gotri Baroda, Gujarat. Post retirement, he has been working as a visiting faculty of Parul Institute of Engineering and
Technology. He was associated with various taskforces /committees related to power system operation at state/ regional/national level. He is a Fellow of Institution of Engineers, India (IE) and a Fellow of Society of Power Engineers (CBIP).
Paresh R. Modha is working as an Assistant Professor in the Department of Electrical Engineering, ADIT, New Vallabh Vidyanagar. He received his M.E. in Electrical Engineering,
specialized in Electrical Power Systems, from Birla Vishwakarma Mahavidyalaya (BVM), Gujarat Technological University, Ahmedabad in 2011. At present he is perusing PhD from CVM University, Vallabh Vidyanagar.
