Innovative Ideas on Power Sector: Use of Solar Power in Residential Townships of India

Use of Solar Power in Residential Townships of India

SUDHIR KUMAR SRIVASTAV

Additional General Manager-RAPDRP

NTPC LIMITED, NEW DELHI

India lies in the sunny regions of the world. Most parts of India receive 4–7 kWh (kilowatt-hour) of solar radiation per square meter per day with 250–300 sunny days in a year. The highest annual radiation energy is received in western Rajasthan while the north-eastern region of the country receives the lowest annual radiation. Solar energy, experienced by us as heat and light, can be used through two routes:

· The thermal route uses the heat for water heating, cooking, drying, water purification, power generation, and other applications.

· The photovoltaic route converts the solar energy into electricity, which can then be used for a number of purposes such as lighting, pumping, communications, and power supply in un-electrified areas.

Solar photo-voltaics (SPV) is the process of converting solar radiation (sunlight) into electricity using a device called solar cell. A solar cell is a semi-conducting device made of silicon or other materials, which, when exposed to sunlight, generates electricity. The magnitude of the electric current generated depends on the intensity of the solar radiation, exposed area of the solar cell, the type of material used in fabricating the solar cell, and ambient temperature. Solar cells are connected in series and parallel combinations to form modules that provide the required power. When the PV module is in use, the terminals are connected either directly to a load, or to another module to form an array. Single PV modules of capacities ranging from 10 Wp to 120 Wp can provide power for different loads. For large power applications, a PV array consisting of a number of modules connected in parallel and/or series is used. The wattage output of a PV module is rated in terms of peak watt (Wp) units. The peak watt output power from a module is defined as the maximum power output that the module could deliver under standard test conditions (STC). The STC conditions used in a laboratory are

· 1000 watts per square meter solar radiation intensity.

· Air-mass 1.5 reference spectral distribution.

· 25 °C ambient temperature.

In India, a crystalline silicon module generally contains 36 solar cells connected in series. The module provides a usable direct current (DC) voltage of about 16.5 V, which is normally used to charge a 12-V battery. In an SPV system, the components other than the PV module are collectively known as ‘Balance of System’ (BoS), which includes batteries for storage of electricity, electronic charge controller, inverter, etc. These batteries are charged during the daytime using the DC power generated by the SPV module. The battery/battery bank supplies power to loads during the night or non-sunny hours. An inverter is required to convert the DC power from the PV module or battery to AC power for operating the load. Some loads such as DC pumps do not require an inverter or even a battery bank.

The capacity of a stand-alone SPV Power Plant varies from 1 kWp to 25 kWp, and in some cases even higher. A stand-alone power plant functions like an uninterrupted power supply system (UPS) and provides a constant, stable, and reliable supply to the loads. The capacity of its battery bank depends on user requirements. Depending on the system voltage, SPV modules are arranged in series and parallel combinations.

A solar generator is a small capacity, stand-alone SPV power system based on a PV array, connected to a battery bank and an inverter of appropriate size. This system is designed to supply power to limited loads (such as lights and fans) for a period of two to three hours daily in situations such as conventional power failure or load-shedding. The MNES currently promotes four models of solar generators, with capacities of 150, 350, 450, and 600 Wp. These solar generators are mainly meant to replace the conventional small-capacity petrol-based generators that are used during routine load-shedding periods in urban areas by shops, clinics, and other small establishments. The components of a typical solar generator are a small SPV array connected to a battery bank of appropriate size and an inverter based on 12, 24, or 48 V. The system is designed to supply power to loads such as lights, fans, credit-card operating machines, and personal computers for a period of two to three hours.

In a Building-integrated photovoltaic (BIPV) system, PV panels are integrated on the roof & sides of a building. The SPV panels generate electricity during the daytime, which is used to meet a part of the electrical energy needs of the building. BIPV systems have significant potential in India, where a large number of buildings are constructed every year for different purposes, and where energy consumption in buildings is growing at a rapid rate. Although the initial costs of a BIPV system are high, long-term savings result from a reduction in electricity consumption. India needs more experience in the field of BIPV technology. In order to encourage this application and to prepare manufacturers and users, the Ministry of Non-conventional Energy Sources supports BIPV projects by meeting 80% of the cost of PV modules installed in the systems on government and semi-government buildings.

Use of BIPV in Townships

Roof of the residential towers in townships is mostly un-utilized by the resident. Rather intense heat due to sunlight on roof top gives uncomfortable hot and humid environment to top floor residents.

If we can utilize the sunlight falling at roof top of residential tower for solar power generation through SPV route, it can fulfill the power requirement of common facilities and can be used as backup power during power outage also. Also

Sample Calculation:

Approximately 7000 sq.mtr. area is available at roof top of medium size townships, on which direct sunlight is falling with 250–300 sunny days in a year. This sunlight can be utilized for solar power generation as follows:

Solar power generation capability for SPV installation	150 watt/sq.mtr.
In 7000 sq.mtr area, Power generation capability during sunlight	150 x 7000 watt = 1050000 watt = 1050 KW
Average hours of sunlight in a day	07 Hours
Solar energy generation capability per day in 7000 sq.mtr. area with 07 hours per day sunlight	1050 x 7 KWh =7350 KWh
Solar energy generation capability per year in above area assuming 300 sunny days in a year	7350 x 300 = 2205000 KWh Say 22,00,000 KWh
Cost saving per year @Rs. 4.00/KWh	Rs.88 Lacs
Cost of installation @Rs120/watt	Rs.12.6 Crore
Ministry of Non-conventional Energy Sources, Government of India, supports BIPV projects by meeting 80% of the cost of PV modules installed in the systems on government and semi-government buildings.

Advantage:

· Environment friendly, hence most suitable for claims under CDM (Clean Development Mechanism).

· Abundant solar radiation is available in most parts of India. Hence, SPV systems can be used anywhere in the country & solar energy can be optimally utilized.

· SPV systems are modular in nature. Hence, proto type cane be developed at initial stage in any one township and can be expanded as desired and used for small and large applications.

· There are no running costs associated with SPV systems, as solar radiation is free.

· Electricity is generated by solar cells without noise. Other form of electricity generation produced heavy noise. So noise pollution is also reduced considerably by optimally use of solar energy through SPV route.

· SPV systems have no moving parts. Hence, they suffer no wear and tear.

· As most of the components of SPV systems are pre-fabricated, these systems can be installed quickly. Hence, SPV projects have short gestation periods.

· SPV modules have long-life, and require no maintenance. Only BoS components such as batteries and inverters require minor maintenance.

· The system may be role model, for adopting the same by other organisations.

· Also, it can promote the use of green energy (solar energy) by society.

· With use of SPV in mass scale by society, the cost of SPV will be drastically reduced, because of bulk production and technological innovations.

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