Introduction

Energy is synonymous with social and economic prosperity of civilizations. Natural resources utilized through various energy conversion devices for domesticwater heating to energy intensive commercial steel production have made significant improvementto lifestyles. However, exorbitant usage of natural resources especially exhaustible fossil fuels for meeting the ever increasing energy demands has costedour environment and health. In recent times, the impact of fossil fuels on local environment and global climatic changes are conceded by a large populace. The global energy scenario is witnessing a gentle shift from these polluting fuels which dominated the industrial era. This transition iswarranted by the fact that limited reserves ofextractable coal and petroleum cannot sustain the ever increasing energy demands of inhabitants in the planet who are 7 billion in number today. Today, renewables like sun, wind, biomass, hydro et al are gaining acceptance as locally available and clean energy resourceswhich couldminimize fossil fuel dependency to a great extent.

In the global context, the share of renewable energy consumption grew from 0.6% in 2000 to 1.8% viz. 158.6 Million tonnes oil equivalent (Mtoe) in 2010. This is a considerable shift in energy priority, although the impact of global warming pushes for intensive growth in the sector. Renewables share of total global electricity generation is nearly 1.7% of which installed solar photovoltaic power is 39.8 GW, wind power is 199.5 GW and geothermal power is 10.9 GW. Major part of the renewables based electricity capacity addition is driven by Europe and Eurasia. Renewables have been consistently contributing to 14% of the growth in global electricity generation. Due to congenial government policies in many parts of the world, renewable energy is the fastest growing source of electricity globally and is projected to be above 5 times the existing generation capacity by 2035 [Figure 1]. Biofuels account for 0.5% (59261 ktoe) of the global primary energy consumption, three quarter of which is contributed by the Americas. Biofuel remains one of the only possibilities to sustain a post-petroleum economy^[1-3].

Figure 1: Electricity generation from renewable energy resources projected till 2035^[3]

India, a nodal economy in the developing world is part of a slow changeover from polluting fuels towards cleaner alternatives. Fuelwood continues as the mainstay of domestic thermal energy (water/room heating and cooking) needs with obvious stresses on local vegetation resulting from increasing demand. This energy demand is also met by kerosene, biogas and LPG in rural and urban areas. Inefficient fuelwood stoves contribute to higher carbon emissions, health problems and are essentially being replaced by fuel efficient chulhas (stoves). The studies have shown that there is a scope for saving to the order of 42-45% by switching over to energy efficient devices at domestic level^[4,6]. Transport sector in India thrives on petroleum products largely imported due to limited availability of indigenous crude oil. Biofuel mix in petroleum fuels are being realized in smaller scales as the national policies fail to make a tangible impact. Coal is the principal fuel of Indian electricity basket with 99503.38 MW installed capacity. Other centralized power sources like hydro (38,206.40 MW), gas (17,706.35 MW), nuclear (4,780.00 MW) and oil (1,199.75 MW) contribute to the rest of the capacity. The total electricity generation in 2010-11 reached 811.143 Billion Units (BU) with nearly 10% deficit in supply. The Aggregate Technical and Commercial (AT&C) loss of the order of 30.93% and Transmission and Distribution (T&D) loss of 27.2% are phenomenally high. Even so, India follows further centralized capacity addition with marginal efforts on end user efficiency improvement in actuality. It is in this scenario that locally available renewables achieve significance as decentralized energy resources minimizing losses and pollution to a large extent^[4].

As the global energy preferences are taking a paradigm shift, India is challenged to initiate aggressive methods to infuse renewables into its energy mix.  India is endowed with renewables like solar, wind, biomass (domestic, agricultural, commercial) and small-hydro, in addition to limited geothermal. These account for 5% of the total primary energy supply and an installed electricity capacity of 20162.24 MW in the country. Encouragingly, renewables contributed to nearly 18% of the total electricity generated in 2007/2008 and the installed capacity today stands at ~10% of the total. Large scale wind power is the most matured segment of Indian renewable energy industry, with installed capacity at above 50 m hub heights speculated to scale up to 65000 MW 10. Solar energy availability of 5 kWh/m²/day over a large landmass as well as conducive solar energy policies hold excellent prospects for power generation in the country^[5]. The National Solar Mission intends to bank upon the 20 MW/km² solar potential for grid interactive and off-grid power generation. Rural electrification has become speedy with the introduction of photovoltaic technologies in rural markets. Bioenergy from domestic and commercial organic wastes is a renewable energy source with immense possibilities in meeting our increasing energy demands, especially thermal^[4]. The maturity of renewable energy conversion technologies, costs involved in design-operation-maintenance, sporadic availability of resources etc are factors observed to impede this awaited growth. Nevertheless, in a scenario where the environmental impact of energy generation and usage is considered, renewable resources with an added advantage of decentralized production are competent over any of the conventional fossil fuels.

Energy planning in India continues to be focused on enhancing energy supply with centralized sources rather than local resources, generation rather than efficient utilization and economics rather than environment. It is imperative to move towards Regional Integrated Energy Plan (RIEP) considering locally available renewables in the region, inevitable conventional energy as supplements, optimal energy mix, efficient energy conversion technologies,regional energy demand, viable energy supply, overall system efficiency and minimal local/global environmentalimpact.Such a decentralized energy plan favour economic development with the sustainable energy and least cost to the environment. The exercise essentially begins with renewable energy resource assessment in pockets of human habitation. It identifies available renewables like solar, wind, biomass, small-hydro, geothermal etc and estimates their spatiotemporal variability. Regional level resource availability studies yield accurate and site specific information. These studies could be in the state, district, taluk and most preferably village level accounting for all the regional aspects, which a national level study might overlook. With the understanding of renewable energy resource availability in a region, based on local energy demands, socioeconomic conditions as well as technology available, a decentralized energy plan could be drafted for the interest area. This minimizes the need for centralized grid extension and also effectively caters to increasing energy needs of heating and cooking, especially in remote areas^[6].

Further, national energy policies doesnot always reflect the requirements of specific regions. For example, Himalayan mountains are unique in terms of their landscape, climate, vegetation, economic activities and socio–cultural aspects. This brings along complex dynamics of energy usage in the Himalayan states. Earlier development in these regions neglected the richness of their ecosystems and impacted the environment adversely. Fuelwood continues to be the major source of thermal energy, although inefficiently utilized. Due to fossil fuel based energy consumption, there has been increased pollution and glacial melting in the Himalayan terrain. With increasing population, commercialization and higher energy demands, grid extension for electricity supply appears like an inevitable solution. However, this results in further ecological damages to an already fragile landscape. The holistic development of mountain regions is essentially linked to responsible management and utilization of natural resources^[7-11]. A decentralized energy strategy utilizing locally available renewable energy resources through efficient conversion technologies for meeting the regional energy demands in Himalayan states presents an ideal solution. In the broader picture, this helps to intensify renewables intrusion in the global energy mix through decentralized energy plans executed in different regions of the world.