More than 1.1 billion people worldwide (about 80 per cent population in rural areas including over 230 million in India) do not have access to electricity. Renewable energy (RE) sources-based mini and micro grids (small-scale versions of centralized electric grids) are proving to be one of the biggest rewards for the masses by providing basic electricity facility to the rural and remote networks in underdeveloped and developing countries. Enormous advantages can be availed through new supportive ecosystems by setting up economically-viable and environmentally-benign solar-based mini and micro grids. Rural folks are finding great relief in fulfilling their aspirational needs, such as cooking, clean running water availability, and primary rural health and learning centres. Besides meeting the essential energy needs of every household, these mini grid systems are also enabling increase in their income through cottage enterprise-based opportunities. Hybrid-based micro grid systems (combination of solar and diesel generator sets) for rural communities can help in meeting their electric load requirements and also increase in their economic activities. The mini grids have enormous potential and are a promising solution to access the energy challenge, especially in developing countries. By setting up these grids, an important milestone is achieved towards the holistic transformation in the lives of the villagers together with boosting of local economy. All over the globe, the installed capacity of green power systems based on solar energy is expanding rapidly. Decentralized RE systems being eco-friendly and cost-effective, are being deployed to provide electricity in every household in remote areas in many parts of the developing world. Use of clean technologies to generate affordable and reliable power is a high-priority area for the fast upliftment of villagers and in general the economic development of rural areas. New prospects are emerging for installing efficient solar PV systems (using the matured crystalline silicon technology) for energy access through decentralized or distributed mode systems (mini and micro) for multiple applications. Basically, their installation on different scales is relatively easy and can be done in any open, shadow-free ground, or a building rooftop. These systems being modular in nature get quickly installed and the energy produced can instantaneously power the designated applications at the source of consumption. The inherent advantages of solar energy systems have been discussed here.

Solar Power Systems (PV and Thermal)

A solar photovoltaic system (SPVS) is a concept of generating DC electricity from the sunlight falling on a solar array and converting it to AC power with the help of an inverter. The electricity can be used in a variety of applications, such as lighting, pumping, battery charging, etc. The SPV system can store electricity during day time in a battery for use in the night. It is also possible to integrate large solar plants including concentrated solar power (PV technology: CPV and thermal technology: CST) with the grid so that the generated power could be evacuated using a dedicated transmission infrastructure.

The solar PV-based clean power systems are useful for an individual dwelling unit, a community or on grid utility level, besides the space satellite applications. The upcoming technological innovations in mini/ micro grids are likely to create new developments and business opportunities.

Solar Mini and Micro Grid Systems

Renewable energy-based mini and micro grids offer the benefits of boosting rural local economy and enterprise development, thereby generating employment opportunities and raising individual/household income, while meeting their day-today energy needs. A well-planned and focussed approach is called for scaling up mini and micro grids installations as per the needs of a developing country.

Today, a range of reliable RE technologies to generate, distribute, and manage power for a wide variety of applications are making the installation of micro grids popular. In view of the decreasing costs of delivered solar power including batteries for energy storage, municipalities all over the world are turning to installation of a large number of micro grids.

As per GTM Research report, when it comes to reliability of micro grids as a growth driver, North America is leading the way. The region has reached a tipping point between technology development and commercial deployment.

Policy on Mini and Micro Grids in India

The Ministry of New and Renewable Energy (MNRE), Government of India, has issued a national draft policy on setting up RE-based mini and micro grids in the country. The objective of the policy is to promote decentralized solutions based on RE sources (such as solar, wind, biomass, and small hydro) with its enormous potential, for meeting the lighting needs and other electricity requirements in unserved rural parts of the country. It envisages RE-based micro and mini grid solutions and approaches for overcoming challenges, and being perceived as a durable solution to provide reliable and cost-effective energy access for rural homes, cater to productive and commercial loads, accommodate future loads, and connect with grid and feed surplus power, if needed.

The government equally encourages active participation from energy service companies (ESCOs) in the RE-based mini and micro grid programme for providing clean power to rural households. They are being empanelled as rural energy service providers (RESPs). The Ministry has set a goal to deploy at least 10,000 RE-based micro and mini grid projects in India. An estimated capacity of 500 MW RE-based mini/micro grids (average size 50 kW) are proposed to be set up to provide energy to every household beyond the basic needs during the next five years to attain a sustainable growth in the country.

The underlying principles of the policy are as follows:

ƒ Mainstream RE mini grids for enhancing access to affordable energy services and improving the local economy;

ƒ Streamline project development procedures for ESCOs;

ƒ Provide operational frameworks to operate along with the distribution company (DISCOM) grid;

ƒ Optimize access to central financial assistance and other incentives.

ESCOs interested to deploy micro grids (less than 10 kW) are recommended to install projects in a cluster format (in contiguous areas) to improve operational and cost efficiency. The cluster format offers the possibility of interconnecting projects in the future. The policy favours deploying large-sized mini grid projects and permit ESCOs to deploy projects with capacities above 10 kW.

The International Scenario

Besides India, a few other countries (Tanzania, Nigeria, etc.) have also formulated policies to accelerate mini grid market growth. Internationally, the deployment of distributed renewable energy is getting an appreciable investment from utilities. Another online platform created by the International Renewable Energy Agency (IRENA)—The Project Navigator, facilitates access to project planning and financing. Through this platform, the navigator guides project developers with the help of guidelines and tools. The detailed technical information on off-grid, mini and micro grid technologies is provided. Based on the IRENA report, with the guidance, the developer achieves the optimal technical solution by considering three major components: site and resource assessment, technology assessment, and logistics and construction. Additionally, the IRENA Project Navigator offers financial help for the mini and micro grids, which supports project developers in evaluating the financials, sustainability, and reliability impacts of the project.

But the biggest technological change in recent years has been a rapid rise in the use of solar PV generation in both standalone home energy systems and mini-grids. Diesel- or gasoline-fuelled mini-grid hybrid with renewable and standalone off-grid generation systems are well established in many countries such as Mali, which has probably more success in the development of isolated mini-grids with more than 200 numbers small diesel minigrids supplemented with renewable technologies in operation.

Technology Capabilities and Criteria

During the last few years, as the prices of PV and energy storage are plummeting, micro grids are becoming cost-effective and attractive for a variety of power applications. Mini and micro grids using highly efficient/smart grid inverters are more than an alternative way to maintain energy supply or cut operational costs for any facility or municipality.

These grids generally operate in isolation to the electricity networks of the DISCOM grid (standalone), but can also interconnect with the grid to exchange power. In general, the grids enable key power system operational and which in turn can benefit developers in achieving a variety of added objectives, such as grid reliability, resilience in the face of harsh climate or natural disasters, and in meeting emissions reduction targets. The technology capabilities and criteria of the mini and micro grids are discussed here.

Mini Grids

An RE-based electricity generator with a capacity of more than 10 kW used for supplying electricity in a community in a rural area or island for household usage, commercial, productive, institutional, and industrial set up, etc., through a public distribution network. Combination of both alternative current (AC) and direct current (DC) systems are acceptable. Electrical parameters of an AC mini grid system are given here and include components, such as generation plant, storage systems (batteries), inverters, distribution network. AC mini grids:

(i) 220 V 1 phase — up to 10 kWp (ii) 440 V 3 Phase — beyond 10 kWp

Micro Grids

An RE-based system with a capacity below 10 kW, supplying clean electricity to a cluster of houses in a remote area. DC generally generated through solar power is normally preferred where the loads are of low voltage/power, such as lighting, fans, radio, etc., and is closely located. DC micro grids:

(i) 24 V DC — up to 1 kWp (ii) 72 V DC — above 1 kWp to 10 kWp

Quality Standard of Systems

All the components for a mini and micro grid systems, such as PV panels, charge controller, inverter, storage battery, cables, circuit breakers, junction boxes, etc., shall conform to the technical specifications/requirements and quality standards specified by MNRE across its various programmes.

Case Studies

ƒ A Pacific island Ta’u in American Samoa (4,000 miles from California) has power with solar mini grid from M/s Tesla Solar city, US. The island has three villages (average population of about 400 people) and were earlier powered by 100 per cent diesel generated (requiring 11,000 L of diesel as fuel). Located on seven acres of land on the northern coast of the island, the system includes 5,328 solar panels, generating 1.410 MW of electricity (Picture 1). The energy can be stored in 60 Tesla Power packs that allow the island to stay powered for up to three days with no sunlight.

ƒ In the Ladakh region in India, there are about 100 villages on harsh mountain terrains at an altitude ranging between 2,900 m and 5,900 m, with no access to grid electricity. The region receives incredible solar irradiance—1,250 W/ sq. m on a clear day in summer and in winter it touches–30°C temperature. The habitants sustain their livelihood from the limited crops and animals. The Global Himalayan Expedition (GHE), a nonprofit NGO along with volunteers from IEEE smart village volunteers have installed 110 solar micro grids (total capacity about 21 kW) in monasteries, homes, elementary schools, and dormitories in 25 villages (Picture 2). Energy access intervention has acted as a tool for further development and growth in these remote areas and has led to increase in income.

As per a report (GHE website), each micro grid of 24 V DC includes a 150 W– 250 W PV panel, a pair of 12-V leadacid deep-discharge tubular batteries and 2.5 W LED lamps. A schematic diagram of the micro grid system is shown in Figure 1. Each PV panel of 250 W can support 30 LED lights. Each LED lamp is energy efficient and provides 250 lumens. All micro grids are automatic in operation and switch ON and OFF as per the sunlight levels.

New Developments and Growth Opportunities

In the current scenario, economics and customer preferences are driving micro-grid owners to integrate higher concentrations of non-dispatchable renewable energy of varying capacity into their system. Several key factors, such as resilience and reliability, influence commercial-scale expansion in the micro-grid. For remote industrial operations, fuel prices and access to electricity via weak grids continues to drive specialized solutions, especially in developing countries. This leads to technical and operational challenges, including intermittencies, system-balancing problems, and power quality issues. However, with proper planning and use of appropriate technologies (automated controls and storage), micro-grid operators can effectively address the challenges.

As per GTM Research and ABB report, “The future of micro grids is bright and getting increasingly powered by renewable resources. Catalysed by dramatic decreases in the cost of deployment, the share of renewable energy generation and storage will continue to make up an increasingly larger portion of the growth. Although renewable energy production is variable and often intermittent, it provides longterm certainty on operating costs by offsetting fuel consumption and reducing engine run times.”

Hybrid Solar–Diesel– Wind Micro Grid Projects

M/s ABB has installed around 40 installations all over the world serving remote communities, islands, utilities, and industrial campuses with micro grid technology. The report highlights that these factors enhance the economics of high-renewable micro grids while improving system reliability and flexibility. This can enable both grid-connected and off-grid systems to support wide-reaching benefits, such as minimizing fuel and net energy costs, reducing peak demand or emissions, etc. Figure 2 shows the micro grid market till date in the USA (ABB Report). It has relied primarily on conventional resources, specifically diesel- and natural-gas-fired generation, however, advances in PV generation technologies are initiating a rapid change to the future scenario for micro grids.

In the near future, it is expected there will be a large volume (in millions) of distributed energy renewable (DER) connections in the US (California) and elsewhere. To meet the growing requirements, M/s Southern California Edison (SCE) is planning to invest capital (about $ 9 billion), over the next three years on upgrades in its electric distribution system in California. SCE expects that as DER adaption upgrades, behind the meter solar deployment together with energy storage systems will take lead.

Installation of the new RE-based mini/micro grids for remote off-grid location, may offer a reliable and cost-effective alternative to building additional generation or transmission and distribution capacity. If a feeder or substation upgrade is required to meet an increasing demand or address power quality concerns, a local micro grid with on-site generation could meet the need without significant capital investment. Similarly, the grid-connected micro grids can also reduce projected costs of service for local utility purposes.

Conclusion

Globally, the micro grid capacity is likely to grow rapidly. Looking in to the future, the momentum and focus on mini and micro grids shall be more with renewable technologies. With the selection of a suitable technology and equipment for setting up micro grids, especially with high-renewable portfolio, the technical challenges such as inherent intermittences of renewable sources can be adequately overcome. Considerable decline in solar technology and energy storage costs have mainly triggered the growth while changing the economics of installing mini and micro grid systems. These systems with the integration of solar offer tremendous potential to enhance reliability, resilience, and long-term energy security while decreasing both fossil-fuel dependence and overall energy costs.

The integration of micro grids with the distributed systems shall continue to grow in future and take care of capacity enhancements with cost effectiveness and power quality issues. As micro grid technologies are taking up a leapfrog from niche application to viable advance systems, commercial projects are beginning to fructify in recognition of the tremendous benefits these systems offer in terms of energy cost reductions, both to the remote communities and the project developer. New technical challenges may surface, but with the right approach and tools, mini and micro grid projects are surely to continue increasing in number and size and with a decrease in system’s costs.

Dr Om P Nangia , Senior Consultant–Solar Energy, Director at New Era Solar Solutions Pvt. Ltd., New Delhi, India.