The advent of a whole new range of rooftop integrated solar electricity generating or photovoltaic (PV) products has the industry and consumers buzzing with the potential of ‘invisible’ rooftop power generation.

The long-term potential for community-wide carbon reduction of domestic electricity depends, however, on more than just the increased use of renewable energy generation. Because of the inherent fluctuation of most renewable energy generation potential due to daily solar cycles and weather changes, when combined with the implications on variable size and timing of peak demand loads, the ability of renewables to be able to replace coal and gas fired grid energy to meet the various new state and territory zero carbon goal of the ACT, NSW, QLD and VIC by 2050 is limited by the availability, efficiency and cost of storage (battery) technology.

There has been a race to market in the last few years, culminating in a range of new technologies in recent times. Some of the newer technologies are already losing out to the ‘newest’ technologies and while there is still a long way to go before there is an obvious single preference, here are the current technology leaders and their various characteristics and top line benefits and uses targeted at residential scale developments:

Flow batteries

Flow batteries are different to conventional batteries in that they are effectively a cross between a conventional battery and a fuel cell. A liquid electrolyte of metallic salts is pumped through cores that consist of positive and negative electrodes, separated by membranes. The ion exchange that occurs between the cathodes and anodes generates electricity. There are several flow technologies that use different metallic salt combinations, and they can be used from small-scale to large grid scale applications.

An Australian company is a global leader and the first to commercially release a residential scale flow battery into the local market.

The Redflow ZCell flow battery is designed by ASX-listed company Redflow. Founded locally in 2005, it has developed a unique – and the world’s smallest – production zinc-bromide hybrid flow battery, one that can nonetheless shift energy in large volumes.

One ZCell unit can deliver 10 kilowatt hours (kWh) of stored energy each day, with genuine 100 per cent cycle depth, supporting daily delivery of 10 kWh of energy at a 100 per cent depth of discharge with no risk of battery damage, and comes with on-board smart battery control and smart monitoring system. ZCell’s bromide-based electrolyte is a natural fire retardant, while mechanical damage does not risk explosion or ‘thermal runaway’ and it has high temperature operation capability without active cooling because it has an electrolyte operating temp of up to 50 Celsius.

Some of their other advantages include:

  • no battery damage from full discharge or from overcharging
  • expectation of retaining the full output capacity over the useful life of the battery compared to the large loss of output capacity that comes with age for most other battery types
  • high ambient operating temperatures well above 50 degrees Celsius
  • on-board power control means the battery can actively disconnect for self-protection
  • essentially unlimited shelf life
  • can be switched off at any state of charge and hibernated for storage
  • made with major components that are easy to recycle or reuse
  • cycle life: can be discharged to a depth (DoD) of 100 per cent without damaging the electrolyte, and theoretically can be charged and discharged indefinitely

Other technologies

Aquion’s Aqueous Hybrid Ion (AHI) Salt batteries use saltwater electrolyte, manganese oxide cathode and a carbon titanium phosphate composite anode together with a synthetic woven separator. These are all plentiful and non-toxic internal components and they are combined with stainless steel and recyclable polymer casings and connectors. They are maintenance-free, optimized for daily deep cycling and are not flammable, corrosive, or explosive under any conditions, states of charge, or normal use conditions.

Here are some other benefits:

  • have a safe water-based electrolyte, as compared to the flammable organic solvent in lithium ion batteries and caustic sulfuric acid in lead acid batteries
  • their water-based system moderates the maximum temperature that the battery can reach – it is impossible for any internal reactions to drive the battery above 100 degrees Celsius, since at this temperature, all of the water will evaporate leading to an open circuit condition
  • the thermal mass of the water-based electrolyte means they neither heat nor cool rapidly. Therefore, they can operate in a very wide range of operating temperatures
  • can sit indefinitely at partial, or even no state of charge, without irreversible capacity loss like lead acid batteries
  • do not require the high levels of ventilation that lead acid batteries require, as no gases are generated
  • Cradle to Cradle Bronze certified
  • cycle life: 3,000-plus cycles at 100 per cent DoD


The Sony Corporation commercialized the first lithium-ion battery in 1991 and many other manufacturers have followed suit, including LG Chem, Samsung SDI, and now Panasonic and Tesla with their newly opened battery ‘gigafactory’ with a range of different chemistries.

The energy density of lithium-ion is typically twice that of older technology like nickel-cadmium. Lithium-ion batteries are safe provided certain precautions are met when charging and discharging. That said, the recent experiences with Samsung’s Galaxy 7 Lithium-ion batteries are a warning to manufacturers who push innovative manufacturing techniques too far when assembling the batteries given the small tolerances they are dealing with. In the Galaxy 7’s case, they unintentionally introduced short circuits into some phones that created overheating problems.

Lithium-ion is a low maintenance battery, an advantage that most other chemistries cannot claim. They have no ‘memory’ and scheduled cycling is not required to prolong battery life. Despite overall advantages, lithium-ion batteries do have some drawbacks. The technology is somewhat fragile and requires inbuilt protection circuits to maintain safe operation. These limit the peak and discharge cell voltages during charge and use. In addition, they monitor cell temperature to prevent overheating.

Although aging is a concern with most lithium-ion batteries, manufacturers are constantly improving the technology with new and enhanced chemical combinations being introduced every six months or so. Such rapid progress means it is difficult to assess how each generation of the revised technology will age.

Storage in a cool place slows the aging process of lithium-ion (and other chemistries). Manufacturers recommend storage temperatures of 15 degrees Celsius (59 degrees Fahrenheit). In addition, these batteries should be partially charged during storage with the recommended storage level being a 40 per cent charge.

There is increasing interest in these batteries with French company Saft making the news recently when it agreed to a US$1 billion buyout of their Intensium li-ion battery technology from oil and gas giant Total, the largest ever merger/acquisition deal for an energy-storage provider.

The cycle life is 1,000 to 2,000 cycles, depending on cell chemistries.

Lithium iron phosphate (LiFePO) is another form of lithium-ion battery. These batteries have somewhat lower energy density than the more common Li-ion batteries but offer longer lifetimes, better power density (the rate that energy can be drawn from them) and are the safest of all lithium batteries. LiFePO batteries are finding a number of roles in vehicle use and backup power.

Enphase Technology’s AC lithium iron phosphate battery materials supplied by Japan’s Eliiy Power comes with a 10-year warranty. These bi-directional devices’ AC coupled configuration means the technology can be retrofitted to existing solar systems and installed in just over an hour and a half, the company claims.

LFP batteries are composed of copper, aluminium, plastic, graphite and lithium. They are non-toxic and 100 per cent recyclable. The fact these components are valuable and make up about 50 per cent of the battery cost encourages recycling.

They have a cycle life of 2000-plus cycles at 100 per cent DoD.

Lithium nickel-manganese-cobalt (LNMC) chemistry is used by Tesla in their new Powerwall 2.0 residential battery storage system. Launched a little less than a year after Powerwall 1.0, the model 2.0 has halved the price per kWh stored and re-used in less than a year. Indicative installed prices in Australia are a little over $10,000 according to a recent study by Bruce Mountain in Renew Economy. Mountain also states the commonly accepted wisdom has been that battery costs would decline more gradually than solar PV costs and that this has been proved decidedly wrong. LNMC batteries have a very low self heating rate.

Tesla now offers unlimited cycles and a 10-year warranty for the products.

Nickel iron

Encell’s Fused Iron (NiFe) batteries have an extremely long life compared to the other technologies. NiFe are an extremely old technology having been originally developed by Thomas Edison, but were limited by low energy density, poor charge retention, and high cost issues until recently. The ENCELL design is reputed to have removed the issues of the Edison NiFe battery and now according to the manufacturer, the Encell Fused Iron Battery has the capability of delivering the lowest levelised cost of energy (LCOE) in the market.

The extended deep-discharge performance results in a dramatic reduction in the number of batteries needed without compromising battery life and is estimated to cost up to one-tenth the price per kilowatt hour in comparison to a lead acid battery with similar capacity.  The LCOE advantage is even more pronounced versus Li Ion batteries.

That means these batteries can be used for up to 30 years (compared to seven years for lead acid) before needing to change the electrolyte. In general, these cells reputedly like to be worked hard with a heavy load; they apparently perform better with heavy use than if they sit.

Benefits include:

  • no capacity decrease for the first 75 per cent of total cycle life
  • easy to manage watering instructions (distilled water only)
  • widest operating temperature range of minus-30 to plus-60 degrees Celsius allows for operation in extremely rugged environmental conditions
  • environmentally friendly – contains no toxic metals
  • able to run under 50 per cent state of charge without harm, no stratification or sulphation
  • comes with Watering System (valves, tubing) and Battery Interconnect Hardware (busbars, covers, screws, washers)
  • cycle life: 11,000 cycles, with a storage life of 85 years

Leasing services

US company Sunverge has made headlines recently and attracted significant investment – around US$20 million – from Australia’s biggest utility, AGL, in the first quarter of this year for a Virtual Power Plant (VPP) that networks small numbers of houses into effectively single energy generators with installation based on a leasing model.

CEO of the Australian Renewable Energy Agency (ARENA) Ivor Frischknecht said recently the partnership “will accelerate the roll out of a state-of-the art grid integrated battery storage solution to Australia’s large household storage market.”

These networks will be able to ‘time shift’ their solar energy for the linked properties, applying ‘time-of-use pricing’ to residential customers. While these VPP projects are in the early stages, the results may offer new business models for utilities and additional opportunities to provide grid services with aggregated behind-the-meter storage for residential properties.

Smart grids

VPPs are essentially smart grids with the ability to integrate and enhance conventional energy generation and monitoring systems with renewable generation, storage, and controls with additional consumer participation.

Local, small scale smart grids are the future of low carbon communities, and battery storage is essential in offsetting renewable energy fluctuations as well as improving overall system efficiency, supply reliability, and ultimately sustainability and preferred economic viability.

With the cost of grid scale photovoltaic energy generation plummeting 25 per cent again in just the last three months, grid scale and smart grid battery storage is a game changer.

With the Mountain study showing the Tesla Powerwall 2.0 batteries are already cost comparative with grid energy in Adelaide based on a competitive offer from the grid, the days of coal fired energy appear limited. If the grid operators don’t do more to meet the community’s climate change mitigation expectations, there may very well be a mass exodus from the grid.