Pic 1. 500 LPD solar water heating system Economic Solar Assessment of Installations at CAEPHT The College of Agricultural Engineering and Post Harvest Technology (CAEPHT), Ranipool, Gangtok, Sikkim, has installed 8 natural circulation solar water heating, 20 SPV street and 7 SPV home lighting systems on its campus. By R. Chandra, T. K. Khura, S. K. Rautaray, P. K. Srivastava, S. N. Yadav and N. S. Chauhan Sikkim receives an average solar radiation in the range of 5.2 to 5.4 kilowatt hours per square meter per day, with about 250-300 sunny days in a year (Indian Meteorological Department). Solar energy is fundamentally tapped in two different ways; by directly using the heat that is received from the sun and by application of photovoltaic to convert light energy into electricity. The solar radiation falling over Sikkim is about 8,000 billion kwh/year. The annual per capita electricity consumption of Sikkim is 429 kwh and stands at second position after Meghalaya in the north eastern states. The area required for installing photovoltaic array for electric conversion system to meet this demand of power consumption of the State is about 2.24 square 36
solar energy gadgets aim to harness the available solar energy for hot water supply in hostels, guest house and mess; street lighting; home lighting and operation of fans thus reducing the consumption of grid electricity. Table 1 shows brief details of the installed solar energy gadgets. Pictures (pic) 1 to 5 shows varied views of solar installations on the campus. Grid Electricity Savings The Fundamentals The grid electricity savings (alternating current) have been determined using energy required to operate the electrical heater in case of solar water heating system. Pic 2. 1000 LPD solar water heating system kilometer. The solar photovoltaic is a very important power source for meeting rural electricity demand in this region of the country. Thermal energy is required to fulfil several purposes in the domestic, agricultural, industrial, and commercial sectors of the economy. The College of Agricultural Engineering and Post Harvest Technology (CAEPHT), Ranipool, Gangtok, Sikkim, started in 2006, is one of the constituent colleges of Central Agricultural University (CAU), Imphal, Manipur, India. The College has installed 8 (7 units of 1000 litre and 1 unit of 500 litre) natural circulation solar water heating, 20 solar photovoltaic street lighting and 7 solar photovoltaic home lighting systems on its campus. The installation of E e E Cos Where, Ee = The amount of alternating current energy required to operate the device, MJ E = The amount of thermal energy required to heat water, MJ Cosφ = Power factor (0.80) The grid electricity savings by use of solar water heating system installed at CAEPHT CAU, Ranipool campus is presented in Table 2. Similarly, the electrical energy savings for solar street and home lighting systems have been also determined using the above fundamental relationship. The AC electrical energy savings by using solar photovoltaic street lighting and home lighting system is presented in Table 3. Sikkim is a small and beautiful State nestled in the inner Himalayan ranges. It has elevations ranging from 300 to 7000 m above mean sea level. Nearly two thirds of its high mountainous territory is perpetually snow bound. Sikkim is administratively divided into four districts, namely: Mangan (North), Gangtok (East), Namchi (South) and Gyalshing (West). It is a landlocked State and it is enclosed on three sides by Tibet (China), Bhutan and Nepal in the northeast, east and west, respectively and in the south by the Darjeeling district of West Bengal. The climate of Sikkim has been broadly classified as tropical, temperate and alpine. The general climate of Sikkim is cold and humid as rainfall occurs round the year. The mean temperature difference between higher and lower altitude varies from 1.5 to 9.5 o C. The maximum temperature of about 25 to 30 o C is recorded usually during the month of July and August. The minimum temperature varies from 5 to 6 o C during the month of December and January. Fog is a common feature especially during the monsoon months from May to September. 37
Table 1. Details of solar energy gadgets installed at the CAEPHT CAU Campus Item Specification Unit price (Rs) Quantity No Amount (Rs) Solar water heating system (Pic 1,2) Solar photovoltaic street lighting system (Pic 3) Solar photovoltaic home lighting system and fan (Pic 4, 5) Rated capacity in litres per day: 1000 Minimum aperture area of collector: 20 square metre electrical heater back-up: 9 kw Capacity of make up tank: 10 litre Rated capacity in litres per day: 500 Minimum aperture area of collector: 10 square metre electrical heater back-up: 6 kw Capacity of make up tank: 5 litre 12 V, 74 Wp SPV module 12 V, 75 AH Battery 1 CFL of 11 W Model - 1 (MNRE approved) 16.8 V, 20 W SPV module One 9 W CFL Rating: 1 DC Fan of 9 W Battery: 12 V, 20 AH Model - 2 (MNRE approved) 16.8 V, 37 Wp SPV module Two 9 W CFL Rating: 2 DC Fan of 9 W Battery: 12 V, 40 AH *As per the DGS & D rate contract for 2009 1, 97, 374* 07 13, 81, 618 91, 420* 01 91, 420 24, 209* 20 4, 84, 180 7, 356* 02 14, 712 12, 500* 05 62, 500 DC fan of 9 W 850 07 5, 950 Total 20, 40, 380 Economics of solar water heating system The economics of installed solar water heating systems has been worked out considering the life of the system as 15 years (Kothari et al. 2009), and with annual maintenance cost @ 2 per cent of the unit price for regular cleaning of flat plate collectors and filling water in make up tank after every 20 days. The economics of the 500 LPD and 1000 LPD systems is presented in Table 4. Economics of street lighting system The photovoltaic module The photovoltaic module has 74 W power at rated voltage of 12 V. The module charges the connected battery whenever the solar radiation is available. Battery and photovoltaic charge controller The solar water heating systems in the Campus resulted in savings in grid electricity of 8,700 units per year for 500 LPD and 17,400 units per year for 1000 LPD systems. The battery of photovoltaic street lighting system is of 75 AH at rated voltage of 12 V. The module is connected to the battery via a solar photovoltaic charge controller. CFL lighting A CFL of 11 W is connected with the battery via the same solar photovoltaic charge controller, which provides illumination during the night (with an automatic on/off 38
Capacity, litre/day Initial water temperature, o C Table 2. Grid electricity savings by using solar water heating system Final water temperature* o C Thermal energy required to heat the water, MJ Electrical energy required to heat the water, MJ Savings of grid electricity per day, kwh Savings*, per day approx. (Rs) 7 1000 30 80 (4.5 h) 1463.0 (7000 1829.0 508.0 2032 litres in 7 units) 1 500 30 80 (4.0 h) 105.0 (500 litres 131.0 36.4 146 in one unit) Total 1567.5 1960 544.4 2178 *Depending on sunshine hour and intensity of solar radiation; Figure in parenthesis shows duration of heating. **Commercial electricity charge = Rs 4.0 per kwh. operation system available on solar photovoltaic charge controller). The connected 11 W CFL can be continuously operated for about 75 to 80 hours provided that the 12 V, 75 AH battery is fully charged. The economics of installed solar photovoltaic street lighting system has been worked out considering the life of system as 15 years and with annual maintenance cost @ 2 per cent of the unit price for regular cleaning of module, lamp and maintenance of battery such as filling distilled water when the voltage of the battery falls. The operating life of the battery is assumed to be 3 years. Therefore, in a period of 15 years, the battery is to be replaced with a new one 4 times. The cost of 12 V, 75 AH battery is assumed as Rs 3000. Therefore, the total cost on battery will be Rs 12000 Pic 3. Solar photovoltaic street lighting system Item and No. installed Solar street lighting system: 20 No. Solar home lighting system: Model - 1: 02 No. Solar home lighting system: Model 2: 05 DC Fan: 07 Energy use per hour Table 3. Grid electricity savings by using solar lighting systems Electrical energy required to operate 40 W Incandescent lamp to get same lumen intensity (450 lumen) as of 11 W CFL Savings** (Rs) per / hour Savings** (Rs) per/ annum 220 Wh 800 Wh 3.20 9,344 2 9 = 18 Wh 2 40 = 80 Wh 0.32 934 5 2 9 = 90 Wh 5 2 40 = 400 Wh 1.6 4, 672 7 9 = 63 Wh 78.75 Wh If AC current is used to operate these fans, 63 Wh/0.80 = 78.75 Wh 0.315 927 Total savings (Rs) 5.435 15,877 **Commercial electricity charge = Rs 4.0 per kwh 39
Table 4. Economics of the Installed Solar Water Heating System Sl. No. Particular 500 LPD 1000 LPD (A) Fixed cost 1 Depreciation (assuming salvage value 5, 485 11, 842 @ 10 % of unit price) (Rs/year) 2 Interest (@ 14 % on the investment) 6, 783 15, 198 (Rs/year) 3 Repair and maintenance (@ 02 % of unit price of the system) (Rs/year) 1, 828 3, 947 Total fixed cost (Rs/year) 14, 096 30, 987 (B) Variable cost 4 Charges to fill the cold water tank (assuming one labour may fill 500 litre of water in tank in 2 working hours and 1000 litre of water in 4 working hours, labour charge @ Rs. 100 per day of 8 hour), (Rs/year) 9, 125 18, 250 Total cost (A+B), (Rs/year) 23, 221 49, 237 Assuming the working of the system for 300 days in a year with effective sunshine hour of 8 hrs to 8.5 hrs in a day, the system would work 2400 hrs or 2500 hrs (approx) in a year. 5 Operating cost of the system In Rs/hour 9.30 19.70 In Rs/litre of hot water 0.15 0.16 (C) Grid electricity saving 6 Energy saving (MJ/day) 105 209 7 Unit electricity saving (kwh/day) 29 58 8 Amount of savings (Rs/day) 116 232 9 Annual saving (Rs) 42, 340 84, 680 10 Payback period (years) 2.16 2.2 2.33 2.5 The payback period of the installed systems in CAEPHT in reference to the investment made would be 2.2 years for 500 LPD capacity and 2.5 years for 1000 LPD capacity. Pic 4. Solar photovoltaic home lighting system for 15 years of operation of solar photovoltaic street lighting system. The economics of the installed solar photovoltaic street lighting system is presented in Table 5. Economics of solar home lighting system Battery and photovoltaic charge controller The battery of photovoltaic home lighting system is of 20 AH at rated voltage of 12 V (for Model 1) and 40 AH at rated voltage of 12 V (for Model 2). CFL/Fan A CFL or direct current (DC) fan of 9 W is connected with the battery through the same solar photovoltaic charge controller, which helps operate the CFL/fan. If one 9 W CFL or 9 W DC fan is connected with 12 V, 20 AH battery (fully charged), then the battery can work for about 25 hrs. If both (CFL and fan) are connected then the battery can work for about 12 hrs. However, if one 9 W CFL or 9 W DC fan is connected with 12 V, 40 AH battery (fully charged), then the battery can work for about 50 hrs. If both (CFL and fan) are connected then the battery can work for about 25 hrs. The economics of installed solar photovoltaic home lighting system has been worked out considering the life of system as 15 years and with annual maintenance cost @ 2 per cent of the unit price for regular cleaning of module 40
Table 5. Economics of the Installed Solar Street Lighting System Sl. No. (A) Fixed cost Particular 1 Depreciation (assuming salvage value @ 10 % of unit price) (Rs/year) 1, 453 2 Interest (@ 14 % on the investment) (Rs/year) 1, 864 3 Repair and maintenance (@ 2 % of unit price of the system) (Rs/year) 484 Total fixed cost (Rs/year) 3, 801 (B) Variable cost 4 Average annual investment on replacement of battery, per year 800 Total cost (A+B), (Rs/year) 4, 601 Assuming the working of the system for 365 days in a year with one light for 8 hrs in a day, the system would work 2920 hrs or say 3000 hrs in a year. 5 Operating cost of the system In Rs/hour 1.50 (C) Grid electricity saving (comparison is based on, if the same CFL is powered by grid electricity) 6 Energy saving (kj/day) 316.8 7 Unit electricity saving (kwh/annum) 32 8 Amount of savings (Rs/day) 0.35 9 Annual saving (Rs) 128 and maintenance of battery such as filling distilled water when the battery voltage falls. The operating life of battery is assumed to be 3 years. Therefore, in a duration of 15 years 4 batteries need to be replaced. The cost of 12 V, 20 AH battery is assumed as Rs 1500 and the cost of 12 V, 40 AH battery is assumed as Rs 2000. Therefore, the total cost on battery will be Rs 6000 for 12 V, 20 AH battery and Rs 8000 for 12 V, 40 AH battery for 15 years of operation of solar photovoltaic home lighting system. Conclusions The grid electricity savings of solar water heating system; Savings in grid electricity of 8,700 units per year for 500 LPD and 17,400 units per year for 1000 LPD systems. Pic 5. Solar photovoltaic fan system The annual savings for heating of water using solar water heating system having 500 LPD and 1000 LPD capacity were worked out to be 42,340 and 84,680 units, respectively. The payback period of the systems in reference to the investment made would be 2.2 years for 500 LPD capacity and 2.5 years for 1000 LPD capacity. The grid electricity savings of solar street lighting system; Savings in grid electricity of 32 units per year per street light and the annual saving has been worked out to be Rs 128. The operating cost of solar photovoltaic street light has been worked out as Rs 1.5 per hour (approx). The grid electricity savings of home lighting system; Savings in grid electricity of 21.6 units (for Model-1) and 43.2 units (for Model-2) per year per home lighting system. The annual saving has been worked out to be 86 and 174 units for Model 1 and Model 2, respectively. The operating cost of solar photovoltaic home lighting system has been worked out as Rs 0.68 and Rs 1.10 for Model 1 and Model 2, respectively. Authors are from Department of Farm Power and Machinery, CAEPHT CAU, Ranipool, Gangtok, Sikkim 737 135, India, ram.chandra6dec@gmail.com 41