Abstract – Some of the most pressing and urgent question, which mankind faces today are the future availability and cost of the energy supplies. Are the available resources sufficient to meet the growing demand of energy? Will the decline in the conventional source of energy affect the quality of living in rural India?
Concern being expressed today for searching more and more renewable source of energy stems largely from the fact that the mankind today depends predominantly on fossil fuels such as coal, gas or petroleum products. Availability of these fuels is dwindling and may be consumed fully within a foreseeable future. Other concern about use of fossil fuels is its effect on environment and carbon foot prints. Solar energy is one convenient and clean source of energy and fully suitable for rural India even for the inaccessible areas. This implores us to find and ways to use this energy in rural areas, which is made possible due to availability of efficient and affordable solar photo voltaic cells and related equipments.
Keywords - solar, energy, rural, India
1.0 INTRODUCTION
Rural India is starved of electricity. Many villages are yet to be electrified. Even those which are electrified received electricity only for limited hours in a day.
For Indians till now the crisis meant whether the millions will have enough food to cook and fuel to cook it. With declining world reserve of not so environmental friendly conventional fuel we had developed gobar gas plants as source of alternative energy and fertilizers, Now the emerging technologies such as solar / wind power or hybrid units enable us use of affordable source of un conventional and convenient source of power.
Use of solar power is steadily getting popular in rural area for domestic lighting, community and street lighting, solar Sun is the brightest object in the heaven, but for its light & heat life would be impossible on earth. The light and heat from Sun is the ultimate source of nearly all the energy which maintains plant and animal life and also the prime cause of weather, climate and wind. Sun is also source of all energy resources mankind uses viz coal, gas, petroleum, hydroelectricity, tidal power, wind mill, fire wood et al
| powered pumping units, solar powered heating and cold storage units.
2.0 AVAILABILITY ASPECT OF SOLAR ENERGY
The Earth receives enormous amount of energy in the form of sunlight. The amount of energy received can be estimated as follows:-
As per solar power hand book (2) radiation received by an area of one square kilometer perpendicular to sunrays in India = 1.36*106 kW
Projection of total area of the Earth normal to sunrays at any time =π*R2 where R= radius of earth. (Fig-1)
Energy received annually = 1.5*1018 KWh
As far as India is concerned this will mean that radiation over just 200 square kilometer (just .006 % of land area of India) can supply total power
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requirement of the country.
Use of Solar energy is needed for 2 reasons:
- No other energy source is available at the location, e.g. communication satellites. Street lights and community TV in remote areas.
- Solar energy is cheap e.g. heating of houses, swimming pools, water heaters or pre heaters for hotels etc.
It shall be interesting to scan through some of the recent news on use of Solar Power in India:
Solar water pumps can help India surpass 100 GW target.-PTI| Jul 31, 2018
US agency signs MOU with Indian company for 41 MW power project in Andhra - PTI Jul 31, 2018
The road to 100GW: lighting up India with solar power-3rd April 2018
Farmers to pay only 10% cost of solar pumps under Budget scheme: Minister, IANS February 03, 2018
Kochi airport becomes world's first to operate completely on solar power-First Post Aug 19-2015
Guwahati, (Assam) [India] May 16 (ANI) Guwahati now has India's first railway station run by solar power.
Solar power can be put in use in 2 ways:
i) Solar Thermal System (Use of Solar thermal energy directly)
In Solar Thermal System heat from sunrays are directly used through a collector or concentrator to heat up, e.g. solar powered water heating system, solar powered cold storage, solar cookers or even power plant where water is heated and steam formed is used for power generation by using solar power concentrator. Solar powered water heating in its simplest from was in use even in 1900 when water tanks were painted black.
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We are well aware of concentration of sun rays by using convex lens. In 1772 diamond was cut using this technique by Lavoisier. In experiments in France using large concave mirror built up with segments, temperature of 35000C in 1946 and 59000C – which is surface temperature of the Sun itself in 1968 were acheived.
This paper is aimed at elaborating use of Solar Thermal systems for water heating systems and cold storages which are relevant to rural areas of India as well as use of Solar photo voltaic cells for production of electricity.
Let us discuss some of the use of Solar Thermal Systems.
Cooking is an important activity that occurs to prepare food for human survival. It is a well known fact that, most
Prominent cooking energy in most developing world is fire wood. One of the alternatives to fire-wood / fossil fuel energy is solar energy, but the major problem with the use of solar energy is that, it is very dilute and fluctuates with time and weather condition. Solar cooker was one of the first simple systems widely publicized and subsidized by Indian government. The system was simple with a mirror used as concentrator and a black painted or reflective insulated box with a glass cover as collector. Apart from being economical this type of cooker is smokeless and preserves nutrition value of the cooked food too.
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Payback period for such cookers (without any subsidy) in India is 4000/40/.67 = 149 days ; based on Annual sunshine at Delhi (see table-1) 2993 Hrs out of total sunshine of 4422 hrs / year i.e. for 67% in an year and fire wood need to be used for 33% of the days. Assuming cost of box type solar cooker as ₹4000/-( ₹1200/- after subsidy in Haryana) and consumption of 5 kg fire wood @ ₹ 8/- per kg for cooking one meal.
Cold Storage in Rural India:Storage and preservation of food have been the concern of mankind since they wandered as food gatherers. Then it meant storing food at times if plenty and using them during periods of short supply. However as man learnt the values of various vegetables, fruits and meats he became |
interested in preserving them too. It was sheer luck that low temperature was found useful for food preservation.
Refrigeration in true sense was first employed by Harappans, Romans and Greeks who cooled water and wine by storing then in porous earthen pots.
However the real breakthrough was achieved when ice was manufactured in early 19th century. Earliest patent for practical ice manufacturing was granted in 1834 to Jacob Perkins, an American who lived in London.
Present day refrigeration works on two principle vapor compression or vapor absorption.
Vapor Compression is best suited where electricity is available to drive compressors or where large systems are required.
fig-4
The cycle is clear from above diagram & elaboration is given below.
Compression:
The refrigerant ‘gas’ at low pressure and low temperature enters the compressor. Here due to compression the temperature and refrigerant pressure rises. The refrigerant then leaves the compressor and enters to the condenser. An electric motor is used for compressor.
Condensation:
The condenser is essentially a heat exchanger. Heat is transferred from the refrigerant to atmosphere through air or water. As the refrigerant flows through the condenser, it is in a constant pressure.
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| Expansion
The cooled refrigerant expands through a throttling valve, and pressure is released. Such expansion results fall in temperature and pressure.
Evaporation:
At this stage refrigerant is at a lower temperature than its surroundings. Therefore, it evaporates and absorbs latent heat of vaporization. At this stage heat from the load is extracted. Refrigerant at low pressure and low temperature then enters the compressor and the cycle continues.
Vapor Absorption Cycle:
This type of refrigeration cycle uses heat energy instead of mechanical energy to raise pressure and temperature of refrigerant, achieved in compressor of above described cycle. Due to this very reason this cycle can use alternative source of energy such as solar heater, wood fired heating etc etc. 
Absorption cycle based on solar power is shown in figure-5. The cycle is similar to compression cycle, but we have generator instead of compressor and absorber for absorption of vapor. The refrigerant used is Ammonia solution. The system does not need electricity and is a silent system. For the system to be suitable for alternative fuel source when the sun is not shining- the pumps between absorber and generator may be replaced by gravity flow where as air cooling may be adopted instead of water cooling shown above.
The system is quite suitable for use in rural area in India.
Solar Powered Cold Storage:
In rural India storing vegetables and fruits such as potato or apple grown in rural side area is of prime importance.
| Whereas mechanical systems are available for use in areas with availability of regular electrical power, in villages with no or irregular power supply it is essential to have a non mechanical system without moving part such as intermittent absorption system. Authors & designers Sri N.C. Srivastava(6) & S/Sri H. Abhichandani, V.K. Nayyar, N.K.Narula (5) have suggested this method for use in solar powered cold storage / milk chilling units.
This type of system has following advantages
- Such cold storages can be established even in remote non electrified or areas starved of electricity.
- Cold storages can be located near to production areas of potato or other perishable items.
- Transportation cost to conventional cold storages located in urban areas may be saved and spoilages avoided or minimized.
- Dependence of electricity is nil and alternative source of fuel to be used during rainy days are cheap and simple.
- Energy required are more in summer, which matches with available solar energy.
- The system has low noise.
Disadvantages of the system are:
- Initial investment may be heavy.
- System may not function in rainy days when alternative fuels may be needed.
- Ice making cannot be resorted to.
Typical design calculation for solar cold storage system:-
Basis of design of any cooling system is heat load that need to be pumped out. The heat load for the system comprises of:
a) Leakage Heat load
b) Product heat load
c) Heat load due to air change
d) Other heat loads due to solar radiation, light bulbs/lamps, humans etc.
a) Leakage heat load in (HL) is proportional to heat conductivity co-efficient (K=0.132 for insulation thickness of 250 mm and conductivity of .033 kcal / hr/m2 /deg C) of insulation, wall & roof, and proportional to wall/roof area (A = 350 sq m) and temperature difference between cold area (t2 ,5 deg C) and the ambient (t1, 35 deg C ). HL= K.A.( t1-t2). For 100T storage this is roughly 33,264 kcal / day.
b)Product heat load (HP) : For a storage capacity of say 100 T let us consider 10% withdrawal and replenishment i.e. 10000 kg per day. |
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If the product intake temperature is 350C and cold product temperature is 50C. Then with specific heat (S) of the product =1, product heat load =10000*1*(35-5)= 3*105 kcal /day.
c) Air change heat load: Air change due to door opening etc is (say) 2.7 per day. The volume (V) of storage of size 15*10*4 m=600m3, Heat gain due to air at 35 deg C at 60% RH = 40 kcal/m3. 600x2.7x40= 64800 kcal/day.
d) Heat load due to solar radiation, burning lamps/ bulbs in the storage, and heat load due to humans inside are ignored at present.
e) Total Heat Load per day = 398064 kcal. We consider that to maintain 5 deg C inside the storage, the refrigerant need to be kept at -9 deg C in evaporator. Thus the difference if temperature is 14 deg C. Similarly temperature difference between NH3 in Generator (75 deg C) and after cooling in condenser (35 deg C) is 40 deg C. The coefficient of performance = Q2/Q1= 14/40= 0.35, For removing heat load of 64800 kcal / day we need to input an energy of 398064/0.35=1137325.7=790 kcal/min. Solar radiation received is 1.36x106 kw/sq km = 19kcal/min. Hence area of solar collector needed @60% efficiency= 790/.6/19= 69 sq m.
ii)Photo Voltaic cells
Second method of using solar energy is via Photovoltaic (PV) cells, which directly convert solar energy to electrical energy. The electricity so generated is used directly or with storage batteries. This is most widely used method today and large solar farms are built up to feed entire locality or airport, such as 13.1 MW solar power plants for Cochin International airport.
During about 200 years of its existence photo voltaic cells have undergone lot of changes. As per Wikipedia Alexandre Edmond Becquerel discovered photo electric effect in 1839 by shining light on an electrode dipped in a conductive solution which produced an electric current.
Between 1873 to 1876 the photoconductivity of Selenium was discovered. It was found that Selenium became electrically conductive and that Selenium could produce electricity from light without heat or moving parts. This meant that solar power can be harvested for production of electricity. In 1883 first Selenium based solar cell was
| created and in 1956 first Silicon based more efficient & economical solar cells were commercially produced. Within 2 years in 1958 the solar cells were used as power source for satellites.
For about 100 years the photo voltaic cells remained very inefficient and were used only to measure intensity of light. Shortly after invention of transistor Russell Ohl invented a solar cell in 1941.
On March 11 this year during an International Solar Alliance Summit in Delhi , Our Hon. PM has set a target of achieving 100 GW (Giga Watt) by 2020, out of 175 GW India plans to produce through renewable sources. Country has already achieved 20 GW of solar power production by now.
While the invention of Photo-voltaic cells found many usage for urban India and has been recently used for massive solar power plants to provide power for one airport or a railway station, rural usage are mainly for street or domestic lighting, water for irrigation and drinking, refrigeration and cooking. Recent developments is few areas also allows the residents of both urban and rural to offset their ever increasing electricity bills with reverse flow of energy using their roof top solar panels.
Solar energy is used from stand alone lanterns to cold storages. The solar panels generate D.C electrical power only during sunlight hours. There is some usage which may use DC power directly and only during sunlight hours such usage are simple and without much complicated electrical controls. One of such use in rural areas are pumping units which pumps water from bore wells or from other water bodies to places where it shall be used for drinking or irrigation purpose. DC motors driven by solar cells directly are available in simplest forms. Between solar panels and the pump a controller & regulator are used. Solar panels are usually connected in series to have little higher DC voltage matching the voltage of the pump motor. Such circuit allows using the pump only during sun-light times. It matches with the farm requirement since you do not need water for irrigation during those times when cloud restricts the sun light. For domestic use it means storing drinking water instead of electrical energy. A regulator is used to regulate DC voltage in the same way stabilizer is used for AC voltage.
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For those installations where continuous power is needed, not withstanding whether sun shines or not the energy is stored in batteries usually of 12-24 V DC and the using it for DC pump and lights (connected directly to battery bank) or for AC loads fed through VFD/ Inverter. The AC loads are pumps, lights, AC or heating units, Cold storages etc. Some of such loads are specific to rural areas.
Further for areas where electrical power is available and grid feedback is allowed solar powered system with grid feedback (Fig-7) may be used. The inverters in such cases work in parallel with utility power and inverter is duly synchronized with the utility. When the solar energy produced is more than the load requirement, the excess energy is fed back to the utility grid and the energy meter reverses and results in savings for such feedback.
| in parallel. For such cold storage no alternative source of energy is needed.
Payback Period:
While cost of PV solar systems is coming down, cost of electrical power supply from utility is going up. Thus feasibility of solar system is getting better day by day. We can briefly analyze the feasibility as following:
5 kW “On grid Solar system” with battery & inverter for a small building = Rs 6.80 Lakh, with 30% sale offer = Rs 4.75 Lakh. Installation cost Rs 0.75 Lakh Total Cost=Rs 5.5 Lakh (without Government subsidy but with grid feedback), Cost of capitals per month = Rs 4583/- For 3000 kWh consumption & feedback to grid and a cost of Rs 7.30 per unit (as in Delhi) saving in electricity bills = Rs 21900-4583 = 17317/-. Payback period = 550000/16417= 32 month.
Conclusion:
Need of the hour is use of renewable energy in place of fossil fuels which is likely to be exhausted in foreseeable future. Solar power is a very viable alternative today. In rural area the source and load are both are locally available & there is no need for transmission and distribution. Various types of usage have been discussed in this paper & use of solar power quite feasible. The need of hour is to promote Solar electrical units. Government of Jharkhand is likely to make roof top solar panel must for houses bigger than 3000 sqft. GOJ has even proposing 40% subsidy.
Acknowledgement / Bibliography
- Purnell’s New English Encyclopedia
- Handbook of Solar Radiation data for India by Sri Anna Mani.
- Resources, Demand and Conservation of Energy with special reference to India by Sri Chaman Kashkari
- Frank’s school atlas.
- Proceedings of fifth national symposium on refrigeration and air conditioning, IIT Madras
- SUN: Mankind’s future source of Energy : Proceedings of The Solar International Energy Society Congress, Jan-1978, New Delhi
- Journal of Basic and Applied Scientific Research, 2011, www.textroad.com
- Thesis by the author submitted as part of 2 year Business Management course of AIMA in 1988.
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