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Study area and methods
The Indian power sector comprises five regional load despatch centers (RLDCs). These are the northern, western, eastern, north-eastern and southern RLDCs with a National Load Despatch Center (NLDC) at Delhi. The Southern load despatch center (SRLDC) monitors the electric energy scheduling and load balancing of Karna-taka, Andhra Pradesh, Kerala, Tamil Nadu and Pondicherry (four states and a Union territory). SRLDC covers the third largest geographical area of other RLDCs, which includes about 22 per cent of the country's total population and 29 per cent of total installed capacity. However, the installed capacity of RE based power plants is lesser in the region (7521 MW, 15 per cent), indicating lower exploitation of RE potential (Local Generating Balance Report, (CEA), 2013-14).
Long term spatio-temporal data are used to analyse the available RE potential in open source GIS platform. The assessment also gives the seasonal and geographical variability of the energy resources. Long term data sets acquired from NASA, SSE and Climate Research Unit (CRU) are reliable and depict the seasonal variability which is closely correlated with ground measurement.
NASA SSE Global insolation datasets are obtained from a physical model based on the radiative transfer in the atmosphere considering its absorption and scattering properties. The model considers visible and infrared radiation, cloud and surface properties, temperature, perceptible water, column ozone amounts and also the atmospheric variables includes temperature and pressure measured using various satellite instruments. The long wave and shortwave solar radiations recorded in the satellite sensors along with the effecting parameters are studied to generate global insolation for different locations and durations. The 0.1° x 0.1° spatial resolution SSE global insolation data derived from NASA SSE web portal (http://eosweb. larc.nasa.gov/sse/), for a period of 22 years (July 1, 1983 to June 30, 2005) were validated (RMSE of 10.28 per cent) with Baseline Surface Radiation Network (BSRN) data available as daily, monthly and annual averages obtained from measured values every three hours (Ramachandra et al., 2011; Guide to Meteorological Instrument and Observing Practices, 1964). Further, grids which essentially cover the entire southern region of the country are extracted and a geo-statistical Inverse Distance Weighting (IDW) interpolation is employed to produce monthly average Global Hourly Insolation (GHI) maps for the region. Taluk wise availability of solar potential is computed by over laying the delineated taluk boundary map.
3.1. Findings and analysis
Figure 1 shows the taluk wise seasonal variation of solar energy potential in southern states. During summer (February to May), solar energy reception varies from 5.6 to 7.1 kWh/m2/day. The region receives the highest insolation in April, while taluks in the northern and central region receive insolation of more than 6.8 kWh/m2/day. Solar insolation reception decreases as the south-west monsoon arrives during June and continues till mid-September (monsoon season). Taluks of the west coast are immediately affected by the monsoon, and receive lower insolation (4.2-5.0 kWh/m2/day) throughout the season. Even other-wise, insolation received in all the taluks is lesser during monsoon months, which slowly increases as the winter approaches. During winter (October to January), western and interior taluks receive higher insolation (5.3-5.9 kWh/m2/day) compared to the east coast taluks (4.1-5.1 kWh/m2/day).
Fig.1: Taluk wise seasonal variation of solar energy potential
Figure 2 shows the solar power density map for the region. Solar power density varies from 750 to 850 kW/m2 in the region where, interior taluks receive higher solar power (810-850 W/m2) compared to the coastal taluks (750-810 W/m2). Distributed genera¬tion and micro grid planning can be done with this knowledge which also helps in predicting the prob¬able energy output of the region.
Fig.2: Taluk wise solar energy density distribution
Seasonal variability analysis is carried out, dividing the entire area into three regions, that is, the west coast, the east coast and interior taluks,India has an installed capacity of more than 298 GW. Out of this 69 per cent of India's generation amounting to 201 GW is from thermal power plants.depending upon the geography of the region. Figure 3 depicts the variation in solar insolation across the seasons for all three regions. Insolation reception is highly variable in monsoon and winter due to cloud movements in all regions. However, insolation is less variable during summer in all the regions and west coast shows lesser variability of insolation in all seasons.
Fig.3: Seasonal variability of solar energy potential
Solar technologies, one finds, have the potential to offset a huge volume of GHG emissions and help realise a low carbon economy. They can also create numerous employment opportunities at the village level. Learning from other developing countries as well as its own past experience, India can be a world leader in solar power generation. With an ambi¬tious solar mission, and positively evolving policy instruments, the nation can easily earn the epithet of a 'Solar India' in the near future.
Decentralised generation of electricity through rooftop SPV can help meet the electricity demand of households, apart from avoiding transmission and distribution (T&D) losses. Generation based incentives (GBI) can help decentralised electricity generation, and boost the regional economy. To encourage decentralised power generations, several incentives could be introduced. These incentives could be:
• Rs. 4.00 per unit for first five years (comparable to subsidies granted to mini hydro projects, the power purchase at Rs 3.40) and Rs. 3.50 for the next two years for the electricity generated from roof top solar PV. Several state governments (Karnataka, Tamil Nadu, and Andhra Pradesh) have recently come up with an attractive gener¬ation-based incentive scheme, which has given a boost to solar based systems.
• Buyback programmes for the electricity generated at household level and in micro grid-GBI of Rs. 5 to be provided for solar electricity photo-voltaic (<5 kW) feeding the grid .
• Implementation of solar rooftops in all new government and local body buildings could be done in a phased manner
• Commercial lighting in advertisement boards should only be from RE sources, with a complete ban on usage of grid electricity for these purposes.
• Impetus to energy research through generous funding for research and development to ensure further improvements in the grid technologies, two way communication energy meters (to connect rooftop generation with existing grid), efficient luminaries' production, low cost wiring, switchgears and appliances
• Energy education (focusing mainly on RE technologies, end-use energy efficiency improve¬ments, energy conservation) at all levels.
• Awareness about energy independence and the necessity of RE for consumers.
• Capacity building of youth through technical education for installation and servicing of solar photovoltaic panels.
• Setting up service centers in block development offices for service support for RE technologies (solar, biogas, and energy-efficient chulhas).
3.2. Smart Grid and New Energy Sources
Smart grid is an intelligent system which integrates all components of the power system (generation, transmission and distribution network, end users) for reliable, efficient and environment friendly energy supply. It also plays a key role in demand response, peak load management, and unit commitment to have an effective renewable mix in installed capacity. Well established information and communica¬tion technology and control networks are the backbone of a smart grid, which also needs a supportive grid network (Ten Minute Clima-tology, Vijayapriya & Kothari, 2011).
Power sector in India is evolving and adopting modern grid technologies such as supervisory control and data acquisition (SCADA), energy management system (EMS), distribution auto-mation (DA), advanced metering infrastructure (AMI) such as prepaid meters and the like. However, the communication network is limited to high voltage transmission equipment and feeble parts of the present power network need to be strengthened to have better smart grid architecture. India is planning to have a full phase smart grid by 2025, for which devices like (FACT) flexible AC transmission controllers and phasor measurements units (PMUs) are being installed. Around 14 pilot projects are being imple¬mented by the Government of India under the Restructured Accelerated Power Development and Reforms Programme (R-APDRP) and the US-India Partnership to Advance Clean Energy-Development (PACE-D) programmes (apdrp. gov.in). Data management technologies and automatic screening of data, collected through remote terminal units (RTUs) is the worldwide challenge to make the network smart and to take quick decisions (ISGTF 2013).
Yet, the smart grid vision needs contributions from industry, academic and research institutions. The architecture of a smart grid needs to be adapted considering the load dynamics and resource avail¬ability, as also future demand. The Indian power sector still suffers from huge unmet demand due to lack of peak load management and high AT&C losses. A Smart grid could reduce network losses and narrow the energy demand gap.
However, replicating the smart grid architecture may not be the solution for all problems that plague the Indian power sector. For this, we need radical government policies focusing on RE, revolutionary improvements in end-use technologies and changes in resource utilisation practices. Besides, there is a dire need to re-structure the energy portfolio to do away with the environmental problems that have resulted from the uncontrolled consumption of fossil fuel resources.
3.3. Endnote
India's southern region can easily use the ample solar insolation it receives for more than 300 days in a year to generate solar energy in a decentralised mode, and thus tide over its severe energy and peak power crisis.
For this, micro grids need to be promoted to meet community level demand through locally available energy resources. Wastelands in the inte¬rior taluks are best suited for grid connected hybrid energy generation, while, micro grids and rooftop generation can be promoted in metropolitan and biodiversity rich Western Ghats taluks. The exploitation of RE sources need to be promoted through appropriate policy intervention and grid integration. The share of energy sources can be decided depending on the variability of insolation and the geographical location. Aggressive tapping of renewable sources meanwhile, can also help mitigate GHG emissions and reduce dependence on fossil fuels.
Citation :T V Ramachandra, Ganesh Hegde, 2016, Distributed Solar Energy Systems, January - February 2016 P. Geography and You
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