Electrochemical Storage of Renewable Energy .....Initiatives taken by Exide Industries Ltd Dipak Sen Chaudhuri Research & Development Centre Exide Industries Limited, Kolkata September, 2017

We should not get into the mindset that ‘Renewable Energy (RE)’ is The Prologue We should not get into the mindset that ‘Renewable Energy (RE)’ is the intruder and ‘Conventional Energy’ is the main player. Why not consider RE to be the main occupant of the ‘house’ and then work out the rest of the system around RE, essentially because RE is the future? ........ Former Member (Energy), erstwhile Planning Commission, Government of India

The Opportunity One of India’s major advantages today and going forward is that its RE potential is vast and largely untapped. Recent estimates indicate that India’s solar potential is greater than 10000 GW and her wind potential could be higher than 2000 GW.

What is the Challenge here? One of the key features of Renewable Energy that differentiates it from Conventional Energy is the fact that the generation of the energy is intermittent. It can, and most usually does, change from: * minute to minute * hour to hour * day to day * season to season Therefore, to ensure availability of uninterrupted, consistent power in online configuration, storage becomes unavoidable! And there lies one of the principal challenge to increased introduction of the ‘RE’

What is Different here? Is this a new application? Electrical Energy is a rare example of a product that should ideally be consumed at the instant it is generated! ................Efficient storage of electrical energy had traditionally remained a technical challenge. Typical load cycles:

What would constitute a dream list of attributes for a storage technology Very high DC-DC storage efficiency Capable of charging and discharging at very high to very low rates. Long, long cycle life Safe Environment friendly High cost efficiency – low cost of storage per KWh

The Lithium-Ion Family of Products Strength Weakness 1. Excellent DC-DC storage efficiency ... 95% 2. High Cycle life .... 1500 – 6000 cycles at 80% DoD 3. Capable of very fast recharge ....@ 1C/2C/3C Amps 4. Compact, light weight 1. Safe operation dependent on electronic management system. Cannot be recycled .... as yet Lithium availability limited to few geographical locations 4. Manufacturing highly capital intensive Cost – on a downward trend, yet at least double that of lead acid at pack level.

Limitation in extended operation in Partial State of Charge What has held back Lead-Acid Technology in ESS Limitation in extended operation in Partial State of Charge (PSoC) operation. Limitation in high power charge – relatively poor charge acceptance at high power input Recharge Efficiency High space requirement

The Recent Breakthroughs in Lead Acid Domain Sandia National Laboratory, in their decennial report on ‘Energy Storage’, published in 2013, has listed three significant developments in lead-acid technology for ESS: Ultrabattery GS-Yuasa Advanced Lead Acid with Carbon Nano-tube additives in negative Hitachi Chemical’s LL-WS – High Density pastes and silica additives in electrolytes Hitachi has published report on successful operation for 9.5 years in the field for wind-power smoothing. There catalogue claim of 4500 cycles at 70% DoD, is highest ever in lead-acid history

Minimum Recharge Factor The Tubular GEL Advantage…… The Performance#: 1200 cycles at 100% DOD and lost only 14% Capacity! 555 cycles at 100% DOD at 45oC and no loss of Capacity! All this, with a Recharge Factor of 1.05 only! Battery Type Minimum Recharge Factor GEL VRLA 1.05 AGM VRLA 1.08 FLOODED TUBULAR 1.20 # CSIRO Data

The Tubular GEL Advantage……

The ‘ESS” Enhancements to Lead Acid Battery…. Improved ‘Partial State of Charge (PSOC)’ withstand capability Symmetric high power charge & discharge cycle capability Improved recharge efficiency The limitations are being overcome by: incorporation of recently available specialized additives in the carbon family development of suitable electronics for battery ‘State of Charge (SOC)’ management for optimum operation in the most energy efficient zones

Advanced Tubular Gel features… Handle extended PSOC operation without any deterioration of life or performance. Can be charged at 0.6C at 1 hour rate! Can be suited for symmetric as well as asymmetric discharge/charge cycles Deliver in excess of 3000 cycles at 50% DOD. Achieve a recharge efficiency of 90% and more In terms of cost, remain unchallenged if one take into scrap recovery - likely to be half of best expected of competing chemistries in future!!

A Note on the ‘Battery Management System’ In a ESS, the Battery Management System ‘actively’ participates in the delivery of the output at the rated levels by: Managing the SOC of the overall battery within the specified range. This is vital in delivering the energy efficiency at the declared levels. Monitor individual or group of 3/4/6/12 cells for health check and issue warnings on weak cells. Assess health of string/s and issue instructions for ‘string boost’ or ‘equalization’ when necessary Monitor overall health of battery bank

The ‘Ultrabattery’ Breakthrough…..

Hybrid Ultracapacitor (HUC) Asymmetric supercapacitor- Advanced Lead Acid Battery: Ultrabattery Advanced lead acid batteries combine the high energy density of a battery and the high specific power of a super-capacitor in a single low-cost device. The primary goals are to extend the cycle lives of lead-acid batteries and increase their power. Hybrid Ultracapacitor (HUC) Supercapacitor in parallel with a lead acid battery + electrode : PbO2 - electrode : sponge lead plate with sufficiently high-carbon content ‘Lead Carbon Batteries’ Asymmetric supercapacitor- + electrode : PbO2 - electrode : high surface area carbon Ultrabattery + electrode : PbO2 - electrode : part sponge Pb & part high surface area carbon

Advanced Lead Acid Battery: Ultrabattery UltraBattery is a completely new class of lead-acid technology: a hybrid, long-life lead-acid energy storage device containing both an Ultracapacitor and a lead-acid battery in a common electrolyte.

Ultrabattery Deliverables Best suited for extended ‘Partial State of Charge (PSoC)’ Operation Recommended range: 20 – 80% DC-DC Recharge efficiency is in excess of 90% Rechargeable at 1C, 2C and 3C rates Advanced version is suited for operation in high temperature environment without any protection. Standard range will be housed in ISO containers with appropriate HVAC features.

The Exide Advanced Tubular Gel Solution ....The Results Bank Voltage at end of Discharge AC – AC Efficiency Cycle Number

Thank you so much for listening. Any Question/s please?

Recharge Efficiency Zones of Lead Acid Batteries An intelligent BMS can continuously manage ‘range of charge’ of the battery bank in the ‘green zone’ during consecutive cycles and deliver a high recharge efficiency!