With increased dependence on emission free technologies, the distributed grid is changing. One of the main challenges is to optimize grid efficiency and its stability vis-à-vis variable generation of green power. With a view to enhance deployment ability and provide continuity of service of renewable and low carbon technologies, the key to an innovative solution lies in provision of energy storage (ES) in RE power applications. A recent report from the World Energy Council, E-storage—shifting from cost to value, mentions that the current methods of evaluating energy storage are not accurate due to a limited focus on the cost of investing and thus hindering the progress on its large deployment. The report also estimates that energy storage costs will fall by as much as 70 per cent over the next 15 years due to the adoption of new technologies.

Solar PV Outlook

The state-of-the-art solar photovoltaic (PV) power systems have made significant progress and are now considered an affordable alternative for generating clean power for meeting the electricity needs of the developing and underdeveloped countries in an independent and sustainable manner. To face/tackle the challenge of an estimated 1.3 billion people lacking electricity access, governments across the globe are implementing clean energy programme by installing versatile solar PV technology based power plants in far-flung islands and rural hamlets together with energy systems. With this abundant renewable resource having excellent solar irradiation levels in regions nearer to the equator, harnessing of resourceful and untapped solar potential, remains high (including in India: the annual global horizontal solar radiation data is shown in Figure 1).

With consistent drop in panels cost per watt and other consumables, the levelized cost of energy (LCOE) of solar PV would be decreasing to competitive levels with all conventional power generation technologies by 2030. Solar has a promising future to challenge the intermittency with new storage innovations and market developments. With energy demands globally set to increase on year to year basis, these innovations in ES are likely to shift increasingly towards renewable technologies where the costs are continuously showing downward trend. With the biggest demands in economically emerging countries such as India, solar PV is going to be the primary energy and the major investment option.

In the long run, the increasing preference for solar power plus storage, by virtue of uninterrupted usage and affordability, would greatly help in decarbonizing the power generation technologies to help protect the nature, leading to revival of global economy and reducing carbon footprint.

Energy Storage (ES)

During the past two decades, the commercially matured renewable technologies (solar, wind) have made remarkable progress by making strong inroads in the global energy mix for deployment across all sectors, viz., industrial, commercial, institutional, and residential through cost competitiveness. This is bound to increase overall bankability on clean power at affordable rates in the foreseeable future. It is a known fact that both solar and wind technologies, though infinite sources, are variable in nature and lack dispatch ability in keeping the electric grid stable. The continuous and independent deployment of green power systems is not highly viable with these renewable sources unless there is a provision for energy storage, which permits storage of the surplus clean solar and wind power instead of exporting it. The ES systems have consistently been held against investment but safe, costeffective and rapidly evolving storage technologies could change the economics of bringing the clean power into the power generation stream. The energy storage demand is primarily driven by a changing utility landscape requiring more storage capacity. Investments on storage would get sufficiently enhanced with higher targets of renewable energy generation. Globally, the energy demands are set to increase every year and the storage innovations are likely to combine with renewable power, as new technological developments and automation in solar PV production processes are being commercially exploited in bringing down the costs. Delivery of reliable, stable, and uninterrupted supply of clean power, essential for energy security of the developing nations, having limited access to electricity, will be possible with electrical energy storage using batteries, which allow optimum usage of solar PV and wind system output.

WITH ENERGY DEMANDS GLOBALLY SET TO INCREASE ON YEAR TO YEAR BASIS, THESE INNOVATIONS IN ES ARE LIKELY TO SHIFT INCREASINGLY TOWARDS RENEWABLE TECHNOLOGIES WHERE THE COSTS ARE CONTINUOUSLY SHOWING DOWNWARD TREND.

The advanced international research work being done is leading to new developments for advanced storage systems, which are capable of storing high levels of energy. It is believed that the power systems built around storage shall increase round the clock availability of solar and wind power applications and gradually phase out the fossil fuels-based power systems. In PV technology also, electrical storage through advanced battery systems makes the variable solar power dispatchable and is considered a near-term, cost-effective replacement for peaking generation capacity. An integrated solar PV power system combined with smart storage shall provide the best economic opportunity by consuming energy sustainably and protect the ecosystem as well. This article examines the scope and transformative impact of the newly developed smart storage systems in overcoming the challenge of seamless energy delivery of variable green power.

Storage Battery Technologies

The technology developers, independent renewable power producers, and the utility industry together have been engaged on innovative solutions for quite some time which can seamlessly cater to 24×7 deploy ability of the solar power. Currently, out of the all major renewable sources, viz., solar, wind, hydro, biomass, the highly matured solar technology is showing an exponential rise globally, but its intermittent nature, greatly depends on energy storage facility for grid integration, reliability, and frequency regulation. Batteries can offer storage at economical costs. Fast responding batteries or flywheels (as quick acting load control systems) are deployed for ramping to full power virtually instantaneously and making the grid stabilized. The various types of batteries used for energy storage are: ‘lead-acid batteries’ (made up of plates of lead and lead oxide that sit in a bath of electrolyte solution); ‘deep-cycle batteries’ (similar to type of lead-acid battery that uses a thicker lead plate and requires less maintenance, these are used in off-grid situations for backup power and grid energy storage); ‘flow batteries’ (using a variety of different chemical combinations, a typical flow battery is made up of two tanks of liquids that are pumped past a membrane held between two electrodes and when the chemicals combine with the electrodes they produce electricity). Flow batteries are generally used in larger stationary applications, such as the grid for balancing or off-grid for power supply. At the same time, the industry is experiencing technical challenges in battery storage which are being met by large research grants and investments.

DELIVERY OF RELIABLE, STABLE AND UNINTERRUPTED SUPPLY OF CLEAN POWER, ESSENTIAL FOR ENERGY SECURITY OF THE DEVELOPING NATIONS, HAVING LIMITED ACCESS TO ELECTRICITY, WILL BE POSSIBLE WITH ELECTRICAL ENERGY STORAGE USING BATTERIES, WHICH ALLOW OPTIMUM USAGE OF SOLAR PV AND WIND SYSTEM OUTPUT.

The highly popular batteries for storage systems are Vanadium Redox flow and Lithium-ion type. The improved storage development benefits the application of flow batteries. Due to their long-life time and deep cycling ability to store large energy capacities, flow batteries are predicted to gain in market share especially in the area of power solutions for utilities. Vanadium (chemical element V) redox flow batteries using only vanadium ions (having unique properties with four iconic states), ideally suited for islands for long duration storage with zero degradation. The vanadium batteries with multi hours of storage under different environmental conditions (–20° to +40°C), are one of the most matured flow battery technologies (developed at the University of New South Wales, Australia during the 1980s). The capacity based redox flow storage systems have a few practical challenges, such as higher cost, energy density lower than lithiumion technologies (which are with power based solutions), and the space requirement for installation due to large electrolytes tanks is more.

DUE TO THEIR LONGLIFE TIME AND DEEP CYCLING ABILITY TO STORE LARGE ENERGY CAPACITIES, FLOW BATTERIES ARE PREDICTED TO GAIN IN MARKET SHARE ESPECIALLY IN THE AREA OF POWER SOLUTIONS FOR UTILITIES.

The lithium-ion battery has been the technology of choice over the past year. In the coming years, the trend for combination of storage and influx of new solar systems will gain popularity with economical viability for both off-grid and utilities services using lithium-ion batteries. Affordability shall be the key element in the outlook for energy storage technology. A recent report from Deutsche Bank estimated that the cost of lithium-ion batteries could fall by 20–30 per cent a year, bringing commercial or utility-scale batteries to the point of mass adoption before 2020. The bank report states that lithium-ion battery costs fell roughly 50 per cent, to about $500/kWh, between year-end 2014 and year-end 2013. In the wider market, consulting firm IHS expects continuing declines in lithium-ion battery prices. They fell 53 per cent between 2012 and 2015, and falling by half again by 2019 with economies of scale. Lithium-ion batteries (Figure 2) are lighter, more efficient, higher depth of discharge limit (> 75 per cent), require integrated controller that manages charge and can discharge more stored energy with longer expected life times.

The practicability of the smart storage systems using batteries with renewable power generation is widely predicted and is becoming highly visible internationally. Large scale usage of rechargeable batteries (smaller light weight and big shipping container size like stacks of large number of cells (Picture 1), used in off-grid RE systems for residential and commercial applications, has grown in to a big market (latest international projections are $60 billion in 2015).

These systems while complimenting the intermittent energy generation as well as realizing peak demand shifting pattern have smart technological features such as: (i) peak shaving, (ii) remote energy management, and (iii) grid services features. As costs for energy storage continue to decline, the applications, such as peak shaving and grid balancing continue to get recognition commercially by providing economical energy storage solutions. With large requirements of distributed batteries in energy storage systems, the need will grow for advanced batteries with better density at economical costs. According to GTM research, the solar- plus-storage is estimated to explode from a $ 45 million industry in 2015 to a $ 3.1 billion industry in 2020.

Applications

The IRENA report (2015) on battery storage for renewables divides the application areas into island (for converting power supplies from diesel sets to renewable) and off-grid systems. In order to integrate renewable, the distributed solar plus storage provides consumers with a viable alternative to the grid, the smoothing of energy supply shifts, the integration of storage systems in households with PV panels. Normally, the return on investments on solar PV systems improves with storage. Integrated solar plus storage economical products, being marketed with designs for residential and commercial systems, as backup or standalone applications are getting popular for quick installations. Stationary energy storage continues to show strong growth in the number of projects. These include output power stabilization for renewable power systems and for a variety of grid functions monitoring and improvements such as:

• Grid management asset
• Fast response frequency regulation
• Integrate more RE power in to the grid
• Primary control reserve
• Load balancing to the grid
• Valuable backup source during grid outages.

Some of the largest storage energy plants set up internationally with RE (mainly solar, wind) during 2015 have been listed below:

• 2X31.5 MW with lithium-ion installation for wind energy (Picture 2) by Invenergy (at Grand Ridge Wind Energy farm, Chicago, USA)
• 40 MW with Lithium-ion battery system (by Toshiba at Tohuka Electric Power Substation, Nishi Sendai, Japan)
• 28 MW with Lithium-ion array (at Korea Electric Power Corporation, Seoul)
• The US Department of Energy has announced in 2016 funding of $18 million for six new energy storage (Figure 3) demonstration projects across the country. » These projects to be carried out with utility companies as partners, will enable the development and demonstration of integrated, scalable, and cost-effective solar technologies that incorporate energy storage to power American homes after the sun sets or when clouds are overhead.
• Sonnen Co. (Germany) is providing solar PV plus battery storage with digital controls (Picture 3) to create microgrids that allows sharing of renewable power among users.
• Tesla Motor’s new innovation has led to continuous fall of prices. Its new product “Powerwall”, a rechargeable lithium-ion battery for residential/electric vehicles applications is an advanced wall-mounted home battery that provides 10 kWh of storage, storing solar energy and allowing customers to cache grid electricity from non-peak periods to use during peak times.

Other significant applications where the combined solar plus energy storage will be of important use are as follows:

• Mines
• Gas and oil sites
• Pumping stations
• Water management processes
• Weather tracking stations.

Invariably, the trend towards remote power applications is driven by the fact that utility power often is unavailable or is available as a delayed resource, and that service is not meeting the needs of the remotely located projects.

The Mining sector in Australia plays an important role since mines are not grid-connected due to remote locations and utilize electricity generated at sites often through diesel generators. In 2014, the Australian Renewable Energy Agency (ARENA) and AECOM estimated the total off-grid generation capacity at mines is estimated at 3.9 GW with an annual electricity consumption of 12 TWh. Typically 20–30 per cent of the operating costs of mines are related to energy. A large part of that on-site power is generated by diesel generators. Diesel energy is expensive due to transportation to remote places. At the same time, several health hazards causing disease to the workers are serious in nature with the use of gensets. Mines normally run 24X7 with a constant load, which means that intermittent sources of energy, such as solar and wind installations cannot fully power the mines without storage. PV is typically used for solar-diesel hybrid power plants. The share of variable PV can be increased to 100 per cent by integrating storage into the PV-diesel hybrid system. This is important as the price for solar power has come down mainly driven by falling component prices of modules and inverters. If the PV plant generates peak energy, the diesel gensets can be switched off and the mining operations are fully powered by solar. If clouds pass over the PV array, the power drop can be compensated by storage.

A memorandum of understanding (MoU) on clean energy storage development project has been signed between Canada and India under the protocol of the governments of the two countries. The development work shall be on “grid simulation and testing to be conducted in Ontario by Ryerson University while the onsite integration and deployment will be managed by Anna University on the Tamil Nadu Generation & Distribution Company grid”. It is likely to provide improved reliability of the grid and enhancement of renewable energy production on the electricity distribution system, while ensuring environmental and climate change mitigation benefits.

Balance of Systems (BOS)

The BOS component supply for the grid-scale energy storage projects is ready for renewable power industry. With the widespread use in home storage and utilities, the battery costs (with better density and advanced innovations) and that of BOS (energy storage by $/kW magnitude) will cut down. The report predicts the BOS costs in storage (Figure 4) during the next five years should see a 40 per cent decline to values lower than $400/kW.

Solar plus storage applications tend to occur behind the metre, while utility mandates are most often front-of-metre applications. About the future of energy storage and how the grid will be shaped by behind-the-metre and front-of themetre installations, the current incentives for behind-the-metre installation, e.g., those installed by end users at their homes are greater than for front-of-the-metre installations, e.g., large-scale utility installations. In the short term, these incentives will drive growth of behind-the-metre applications faster than front-of-the-metre, which are used for utility purchases of power from large-scale energy storage projects. The trend for behind-the-metre storage increased significantly during 2015 and is likely to show strong growth for 2016.

Solar and Storage Futuristic Trends

For the rapid growth of the green power industry, Green Tech Media analyst and the PA consulting group experts have predicted “a decentralized, digital and dynamic grid system, with dropping cost of sensors, power electronics and renewable technologies like solar” for the next generation utilities. International consultancy firm KPMG’s report (2015) predicts major changes in power generation industry, with “Solar prices in India falling substantially (lower than coal) by 2020, helping the technology shall become a major part of the country’s energy mix, and that over the next decade solar will scale up significantly, reaching a 12.5 per cent market penetration by 2025.” Further the ‘significant evolution’ expected in storage technologies, will make self-consumption of solar power generated particularly in residential settings more attractive. The bigger contribution may come from the solar rooftop business. This will be supported by a rise in storage technologies, and together they could change the energy landscape.

Dr Om Prakash Nangia, Senior Consultant in Solar Energy, Director at New Era Solar Solutions Pvt. Ltd, New Delhi. Email: om.p.nangia@gmail.com; nangiaom@newera-solar.com