Pod Z: The Redflow Grid-Scale HVDC Energy Pod

Simon Hackett, Redflow System Integration Architect

introducing Pod Z

Redflow is in the midst of building a new “Pod” based energy storage architecture, with the first customer for that deployment also being its largest customer to date.

The story below includes a link to a short video about the new architecture Redflow has designed to support entry into the Grid-Scale energy storage market:

Redflow Pod Z grid-scale architecture using Trumpf HVDC modules

When we made that video, we hadn’t formally announced our partnership with TRUMPF Hüttinger, the company we’re working with to deliver this scalable architecture. A few days later, we were able to make that announcement:

How Does Pod Z Work?

Now we’ve made that announcement, I can explain how this nifty stuff works.

Here’s a photo of a Redflow Pod Z with some of the covers taken off:

Redflow Pod Z internal elements

On the left is the battery cabinet with one of four covers removed. This cube-shaped cabinet holds 16 x ZBM2 storage modules, 8 to a side.

Ventilation paths run inward at the base of each pod. Air flow then rises via a ‘cold aisle’ in the middle of the pod, proceeds through each ZBM2, and exits as warmer air via fans installed behind each cover door.

While the Redflow modules you can see here are the existing Redflow ‘Gen2.5’ devices, the upcoming Redflow Gen3 modules will also be a perfect fit, in both physical and electronic terms (and they are designed to be).

To the right is the electronics cabinet for the pod. Inside that cabinet, at the lower right, is a cluster of six Trumpf DC1010 units with a Trumpf System Controller.

The DC1010 module achieves something quite special. It is a bidirectional DC/DC converter that can shift voltage up to a very high ratio (around 15:1).

These modules are clustered together and driven in a unified manner via the the system controller.

On the the low-voltage side, these modules interface to a standard 48V telco standard voltage bus (compatible with Redflow ZBM2 modules).

In fact, beyond merely being ‘compatible’ with Redflow ZBM2’s – the Trumpf product has been specifically designed for flow batteries!

This product line has been created by Trumpf in response to the rising demand for the use of flow batteries in large energy systems.

Flow batteries are long duration, 100% depth-of-discharge, durable and high-temperature-tolerant workhorses. They compliment, rather than conflict, with the use of shorter-duration/higher-peak-output capability Lithium batteries.

Trumpf have developed this product line at a time and in a manner that is an ideal complement to Redflow energy storage modules, and that paves the way to create grid-scale hybrid deployments that include flow batteries.

Flow battery support in the DC1010 includes a capability to have the low voltage DC bus operating all the way down to zero volts. The units then support smoothly raising the voltage of a flow battery back up to its normal operating voltage range, smoothly ramping a current-limited/current-controlled energy supply to the modules, as part of commencing the next charge cycle.

The DC1010 modules are each rated at 200 Amps continuous on the low voltage bus, meaning that this cluster of six units can support up to 1200A on that bus.

In the first Pod Z configuration, Redflow has rated each pod at a nominal continuous energy throughput of 50kW.

The low voltage bus comes together on the left hand wall of the control cabinet. On that wall is a pair of DC bus-bars sandwiched around insulation layers, with built in ‘comb’ connectors that allow the battery circuit breakers to bolt straight on to the bus-bar.

A set of 48V bus cabling (visible on the left hand wall) fans out from the bus-bar to all 16 batteries on the left, and additional cables run down to the DC1010 cluster at the lower right.

On the high voltage side, the DC1010 units support a (software selectable) interface voltage in the 765-900 Volt range.

On the lower part of the rear wall, you can see the output side cables for the high voltage side. Those (small!!) wires run at circa 800 volts and come together to the high voltage interface terminals. At a 50kW power level, across six DC1010 units, at (say) 800V, the current being carried from each of the cluster modules is a mere 10 amps (50,000 / 6 / 800). This is why those wires are so small – because they really don’t need to be larger.

This is one half of the key to grid scale battery deployments. That high DC voltage means the total cable size – even for a DC bus visiting many Pods in parallel in a single site – really isn’t all that large.

The other half of how this architecture supports high scale deployments is the way that voltage management happens on that high voltage DC bus. We are operating these modules in a mode that Trumpf call ‘Voltage Static Mode’.

In this mode, the DC1010 cluster converts the variable ‘48V rail’ DC voltage into a fixed voltage outcome on the high voltage side. All the pods are programmed to have the same HVDC voltage when idle, and they are just wired together in parallel.

To connect the DC pods to an AC energy grid, third party AC inverter/chargers are used.

When those inverter/chargers wish to discharge or charge from the overall Pod array, they simply ‘pull’ or ‘push’ against that DC voltage. If the inverters try to discharge, they naturally draw the DC voltage down in the process. The external draw-down on the DC rail acts as an automatic signal to the DC1010’s to start to deliver output energy. The amount of energy they deliver is proportional to the voltage shift that the inverter/charger initiates on the DC bus.

In the reverse direction (array charging), the inverter/charger drives the DC voltage up, and the DC1010’s respond to this by moving energy from the DC rail into the Pods. Again, the amount of current that flows is controlled via the voltage shift that the inverter/charger initiates.

Here is a diagram showing this result, just to make it clear (taken from the Trumpf system documentation):

The deep point of this operating mode is that each pod acts like an ‘ideal’ battery on the HVDC side, that:

  • always sits at the ‘perfect’ voltage, waiting for work to do
  • can be wired to an arbitrary number of similar pods
  • can be wired to, and commanded by, inverter/chargers

… all using the chosen DC link voltage – and shifting of that voltage – as a command mechanism that requires no software interface and no real-time cluster synchronisation for it to work.

In the initial deployment site there will be twelve pods sitting in rows on concrete plinths, delivering 600kW throughput via 12×16 module pods, for a total of 192 Redflow ZBM2 modules on site:

Deployment arrangement using 12 x Pod Z modules

Meantime, back inside each Pod Z, the Redflow ZBM2 modules are coordinated and controlled by Redflow’s purpose designed BMS, operating in a cluster-friendly ‘Slave’ operating mode.

Each Pod Z’s BMS:

  • Drives the Redflow ZBM2 module operating cycle internally in each pod, including coordinated maintenance cycles for batteries at appropriate times
  • Actively controls the operation of the Trumpf equipment cluster using a newly developed Trumpf operating module in the BMS. This code sends continuous updates via MODBUS-TCP to the Trumpf cluster, keeping it informed about the present operating limits of that particular cluster of ZBM2 modules. The key parameters sent are the maximum charge capability, maximum discharge capability, and the target charge voltage for the ZBM2 cluster.
  • The BMS provides secure remote management access to the Trumpf system controller and manages the high level configuration of the pod (including setting the HVDC operating voltage and current limits in Voltage Static Mode).
  • The BMS also watches over the Trumpf cluster, monitoring and logging operating parameters including voltage, current, and three temperature measurement points inside each DC1010 cluster member

With each Pod Z being fully managed by its internal BMS, all that remains is to aggregate the status of all Pods together, for the benefit of, and the coordination of, the on-site inverter/chargers and on-site Microgrid controller.

A Redflow BMS operating in in ‘Master’ mode is interfaced over ethernet to all the downstream Slave BMS in each Pod Z that it watches over.

The Master BMS passes overall status data to the on-site microgrid controller. This includes System State of Charge, overall site charging and current discharging capacity, temperature, and state of health. This information is provided via industry standard CANBus ‘Smart Battery’ protocol, MODBUS-TCP, and/or JSON queries to the Master BMS.

Summary

The Redflow Pod Z architecture has been designed with, and around, the Trumpf ‘TruConvert’ DCDC power system architecture.

The combination creates a powerful, integrated high voltage energy storage system that can be scaled to an essentially unlimited extent.

The interface mechanisms being used allow the high energy, high voltage Pods to be parallel-wired without complex or difficult real-time synchronisation or balancing mechanisms. Instead, the software-mediated Trumpf cluster creates a ‘perfect’ battery voltage for every Pod, driving the simplest possible integration path for high scale site designers.

The Redflow BMS acts as a per-Pod orchestrator for the Redflow ZBM2 modules downstream, and as a coordination and control point for the Trumpf DCDC converters in each Pod, and passes aggregated energy storage status data upstream to the on-site master Microgrid controller.

This architecture plays to the strengths of all of the components concerned. It is is designed for reliability, redundancy, and scale.

Flying On Electric Avenue

I am fortunate to own the first electric self-launch glider to fly under Australian skies. It is a Pipistrel Taurus Electro G2.

A few months ago, I wrote a story that explained the background and my journey to owning and flying this impressive little aircraft. The story was published in the Gliding Federation of Australia’s Gliding Australia magazine.

You can read the article here .

Alternatively here is the same article as a PDF file:

Electric Avenue – Taurus Electro G2

I’m posting these links as a precursor/background to a story I will write soon about three wonderful days of flying this aircraft from our airstrip in Tasmania.

Life, the universe, and Redflow

Today Redflow announced the appointment of John Lindsay as a non-executive director of Redflow Limited. John has deep skills and experience around technology and technology related business matters. He is, to use a favourite phase (for us both), ‘smart and gets things done’.

Its worth appreciating that John has specific expertise and experience in precisely the realms that Redflow needs. I sent John over to Brisbane when I originally invested in Redflow, to help me assess the technical merit of the technology. He, like me, has been a shareholder in Redflow ever since.

In addition to being a great businessman, John is also a technology geek at heart (as am I). He has been an active member of the electric vehicle and renewable energy community for many years. His daily driver is electric (as is mine) – of course. He knows which end of a soldering iron is the hot end.

His idea of a fun weekend hobby is (literally – and recently) to have set up a D.I.Y. solar and battery offgrid system in his own garage to charge up his electric car from renewable energy because… he can (and because he knows how to).

His appointment frees me up to transition my own head space in the Redflow context totally into the technology around making our battery work in the real world. Doing that stuff is what I really love about being involved with Redflow. I love helping to make this amazing technology sing and dance smoothly for real people, solving real problems.

It was just the same at  Internode – the company I spent more than two decades running. The ideal situation is to do things in business because you’re passionate about it. In the words of Simon Sinek: People don’t buy what you do, they buy why you do it.

I care about Redflow because I believe that Redflow’s technology can genuinely help to accelerate the world’s transition to renewable energy as a replacement to burning things to make electricity. Its really that simple.

The technical lever I designed, to help Redflow to move this particular part of the world, is the Redflow Battery Management System (BMS). I am very proud of the great work done by the technical team at Redflow who have taken many good ideas and turned them into great code – and who continue to do that on an ongoing basis.

So… while there can be a natural tendency, when looking at this sort of transition, to wonder whether my leaving the board (given how influential I’ve been at board level in the last few years) is because something ‘bad’ is happening, or because I don’t like it any more, or because I don’t feel confident about things at Redflow, the reality is precisely the opposite.

My being happy to step back from board level involvement over the next few months is the best possible compliment that I can give to the current board, lead by Brett Johnson (and now including John) and to the current executive (now ably lead by Tim Harris).  

I’ve put my money where my mouth is, to a very large extent, with Redflow. I am its largest single investor – and I have also put my money down as a customer, too, in my home and in my office.

At this point, I’m happy to note that we are seeing great new batteries turning up from our new factory. We are on the verge of refreshing our training processes to show our integrators – and their customers – how far the BMS and our integration technology has come at this point (and just how easy it all is, now, to make the pieces work). We are looking forward to the integration industry installing more of our batteries into real world situations around the world again – at last.

We do this with confidence and we do this with eagerness.

I am proud to be a shareholder in Redflow and I look forward to the next chapter of this story.

The Role of Flow Batteries in Dispatchable Renewable Energy Grids

At the Australian Energy Storage conference held in Adelaide, South Australia on May 23-24 2018, I delivered this keynote address about the role of flow batteries and other energy storage technologies in the context of building an energy grid with renewable energy in the majority and with “Baseload” generation on the wane.

The core thematic question I posed was this: Is a future grid with large amounts of renewable energy storage necessarily using Lithium-Ion (or other, otherwise conventional) battery systems for the majority of that large scale energy storage – or are there better ways?

A specific underlying aspect of that conversation is about environmental impact – around the notion of ‘environmentally friendly’ energy generation and storage being a notion that must factor in the ultimate environmental impact for each storage technology and not just its up-front cost.

The video below is a recording of my address synchronised to the slide deck that I used.

The standalone slide deck is also available here: Hackett-Keynote-Redflow-AES2018

How Redflow Batteries Work

I often get asked to explain how Redflow ZBM2 flow batteries work – compared to conventional batteries – and how batteries fit into your life in a home situation.

An interview I did a while back with the delightful Robert Llewellyn explains those things.

So… If that’s a subject you’re curious about, and you’d like to spend 15 minutes learning the answers… this Fully Charged show about Redflow ZBM2 flow batteries explains it !

 

The Base64 Redflow Energy System

Updated Feb 2019: System now operating at full battery capacity and with increased solar array size

The Base64 energy system has been a fantastic learning experience for us in general and me in particular.

The system is built around a large Redflow ZBM2 battery array. We call these configurations an “LSB” (Large Scale Battery). It is charged with solar energy harvested from a large solar array (most of which is ‘floating’ above the staff carpark).

We deployed it first some time ago now, prior to having got so deeply experienced with using Victron Energy inverter/charger systems. At the time we (Base64) purchased a big custom industrial AC inverter that didn’t come with any sort of monitoring or logging system and no control system to drive it to interact properly with on-site solar.

All of the necessary energy system control, management and data logging technology comes ‘out of the box’ with the Victron Energy CCGX controller unit in a Victron installation,  so I imagined ‘everyone’ provided such things. Well, I was wrong about that.

The big industrial unit we bought came with nothing but a MODBUS programming manual and created a lot of head-scratching along the lines of… ‘now what?’. For some reason industrial scale systems are in the dark ages in terms of the stuff that Victron Energy have ‘nailed’ for the residential/SOHO battery market – they supply great, easy to use, easy to understand, effective and powerful out-of-the-box energy system control software and hardware (entered around their CCGX/Venus system). It also comes with an excellent (no extra cost) web-accessible portal for remote data logging, analysis and remote site system control.

Meantime, we were exercising our large battery ‘manually’ – charging and discharging it happily on a timed basis to prove it worked – but we were unable to run it in a manner that properly integrated it with the building energy use, for the lack of that control system in the inverter we had at the time. We didn’t want to write one from scratch just for us – that’d be a bit mad. We also didn’t want to pay someone else thousands of dollars to set up a third party control system and make it work – a major consulting project – just to do what the Victron Energy CCGX does on a plug-and-play basis at very low cost.

In parallel, and importantly – it also took ages to get substantial on-site solar operating at Base64 – and there wasn’t much point in driving the LSB in production until we did have a decent amount of on-site solar to sustainably charge it with.

To the latter point – we are in an massively renovated and reworked heritage listed building and I was unable to get permission to mount solar on the massive north-facing roof of the main building.

Instead we commissioned a rather innovative mounting system that has (at last) let us complete the installation of a 50kWp solar array that literally ‘floats’ above our staff car park on four big mount poles supporting what we call ‘trees’ – suspended metal arrays holding the solar panels up.

That system was commissioned and imported from a company called P2P Perpetual Power in California to suit our site. There are lower cost systems – but (by comparison) they’re ugly. We wanted it to be beautiful, as well as functional – because Base64 in all other respects is…both of those things.

It was worth the wait.

The result is (in my humble opinion) quite spectacular.

Including that ‘floating’ 50kWp array, we have a total of 99kWp of solar on the site, though some of the rest of it is on ‘non-optimal’ roof directions, and so on a good day what we see around 80kW generated at peak in the high (solar) season.

That said, the advantage of some other parts of the solar system being on east and west facing rooftops is that our solar generation curve runs for more hours of the day. We get power made from earlier in the day (from the eastern array) and later into the evening (from the western one) – and that’s quite helpful in terms of providing a solar energy generation offset to local demand patterns.

In parallel, we pulled the LSB apart and rebuilt it using Victron Energy products and control systems, so that we could get a fantastic operational result and have optimal use of the solar energy to drive the building, charge the batteries, and support the building load at night – the very same stuff we do in houses with our batteries, just on a bigger scale – without facing a one-off software development exercise for the old proprietary inverter system we had been using.

Swapping the Victron Energy gear in has turned out cheaper and far better than the bespoke software exercise would have ever been. It has also created a signature example of a large scale Victron Energy deployment running a decently sized multiple building site. I hope that this, in turn, may inspire more of the global Victron Energy installation community to consider the use Redflow battery technology at this sort of scale.

The battery array is built with 45 x ZBM2 = 450kWh of Redflow energy storage.

We have 72kWp of Victron inverters installed right into the container as well. We could have gone larger (in terms of peak inverter power), but these have been ‘right-sized’ to the building demand at Base64, with summer peaks normally around 60kW (75-80kW worst case) and typical draw around the 30-40kW level when the building complex is in daytime operation.

It is all linked to that 99kW distributed solar array using via multiple Fronius AC solar inverters.

I’m thrilled with how well the system is working – its a monument to all of our Redflow BMS development work that the whole thing – at this scale – really is ‘plug and play’ with the Victron CCGX energy system controller and the associated inverter/charger equipment.

It is very satisfying to run an office in the middle of a major city that typically uses very little grid energy, that is resilient to grid faults, and that even still exports solar energy to the grid as well.

A subsequent step will be to interface with a grid energy ‘virtual power plant’ operator in the future, so that we can sell battery energy back to the grid during times of high grid demand.

Every battery system on an energy grid has the potential to also become a programmable grid-supporting energy source during peak load periods. The missing links are software, regulation, and attitude – with the software part being the easiest of the three.

We can easily set up to proactively control over when the battery charges and discharges in response to, for instance, wholesale market price. The Victron control system makes that easy.  What need to give that project legs is an innovative retailer who will work with us on that and a small amount of software ‘glue’ to make it happen on our local site.

Here is a little gallery of photos of the system that we’ve installed – click through them for a little more information about the system.

 

 

Redflow ZBM2 deployment at Bosco Printed Circuits

A case study in complex energy system optimisation

Bosco Printed Circuits is the largest maker of Printed Circuit Boards (PCB’s) in South Africa. The production line at Bosco needs a lot of energy. The direct and indirect consequences of losing energy supply to the line are substantial.

Johannesburg, where Bosco are based, has significant issues with energy supply – both in terms of reliability and also (as a consequence) in terms of energy cost.

Like most businesses, Bosco already had an extensive solar array installation, which certainly helps with the economics of energy supply. The solar array is not sufficiently effective, is isolation, to address the complex challenges for the business in terms of supply cost and supply security.

Energy supply to Bosco from the grid utility is time-of-day based. The energy supply cost is very high during distinct morning and evening peak periods, to discourage energy use in those times. These peak time bands are periods of high energy requirement for Bosco. The are the times when the potential for grid failure is greatest and are also the periods when the consequences of grid failure for Bosco are the most severe.

Of course, these times (early morning, late afternoon) are also exactly the periods when the solar arrays can’t help, as they are outside of the solar peak generation periods.

Grid outages are expensive for Bosco. Not only do they result in lost productivity, but they also have further economic consequences in terms of partially produced PCB’s having to be scrapped when the production machines are halted without warning.

The Challenge

Bosco had a variety of business aims and objectives across their daily operating cycle that their energy system had to address:

  • To ride over transient periods of grid loss seamlessly using battery energy
  • To support the operation of the production line for an extended period (hours, not merely minutes) in the face of longer periods of grid outage, so that the company can keep working, using battery energy augmented with any available solar energy, for as long as possible.
  • In cases of a very extended grid outage (several hours), to allow the production line to be closed down with plenty of warning (at least an hour) from the point at which the shutdown decision is made.
  • To time-shift energy obtained from the low cost overnight off-peak period into the morning peak period (0600-0800), prioritising battery energy usage at this time in order to minimise the use of very expensive grid energy.
  • To also minimise afternoon peak-period grid usage by again prioritising the use of battery energy in this second daily period
  • To use the residual battery energy, harvested from overnight off-peak charging and from any excess of daytime solar power, to supply the background energy needs of the building into the evening.
  • To recharge the battery array again using off-peak power from midnight to 6am ready to commence the next daily cycle.

This need set required a battery energy system capable of consistent hard work and capable of daily 100% energy discharge, working in a hot environment, and without loss of output capacity over time.

The Solution

The solution uses 14 x Redflow ZBM2 batteries (140kWh) interfaced to a large array of Victron Energy inverter/chargers and a large solar array.

The system orchestrates this complex daily cycle of energy optimisation using the Victron CCGX and the Redflow BMS, to achieve the aims and objectives noted above.

Here’s a typical day in the life of this system, in terms of the sources of energy to run the plant:

Bosco Daily Cycle Example

Bosco Printed Circuits Energy Consumption

You can see the periods where the battery system energy (blue) is prioritised in order to minimise the use of grid energy during peak times. You can see the battery being fully utilised to supply energy during the afternoon and evening as the solar consumption falls away, and you can see the system recharging using off-peak energy again from midnight, ready for the following day.

You can use this Bosco Printed Circuits VRM Portal Link to see the live system running.

Bosco ZBM storage array

Bosco ZBM storage array (12 batteries shown – a further 2 were added later)

 

 

My home Redflow ZBM2 energy system installation

Here is some information about my home energy storage installation.

  • 2 x 10kWh Redflow ZBM2 zinc-bromide hybrid flow batteries
  • Redflow ZCell BMS
  • 2 x 5000VA Victron Energy inverter/chargers
  • 10 kWp solar panel array in four strings using 2 x SMA 5000-TL inverters
  • Victron Energy CCGX configured for solar self-consumption (Hub-4)

The Victron Energy Hub-4 software in the Victron CCGX optimises the system for solar self-consumption. In the presence of excess solar generation, that energy is applied first to the home loads, the surplus to charging batteries, and the surplus beyond that to export to the grid (if connected).

CCGX Solar Generation Example

High solar output period

When there is less solar generation than the home loads require, those loads are supported by the solar energy that is available, which is then automatically augmented with battery energy. The grid is used as required to further augment home demands as required (either when the peak load exceeds the battery inverter capacity or when the batteries are fully depleted).

The system allows the configuration of an adjustable reserve percentage of the storage battery energy to be kept in the batteries in case of grid failure. It also allows the system to be charge up proactively from the grid in periods of low grid energy cost or ahead of incoming bad weather that might increase the chances of a grid energy failure.

The system automatically reverts to off-grid mode if the grid is unavailable, including recharging the batteries from solar energy to help support loads in the home for extended periods during such outages.

The performance of the system is very good. On a sunny week, most of our home electrical energy is provided by direct and indirect (battery time-shifted) energy. Of course in weather conditions offering reduced solar energy, more grid energy gets used.

Like a home rainwater tank system, this system acts as an electrical energy buffer, doing the best it can to avoid the use of grid energy, and prioritising the use of battery energy first.

hackett-vrm-week-sample

System performance example during a good solar week

The system works very well indeed – and flawlessly from the standpoint of my family, who see a house that ‘just works’ – even when the grid doesn’t. We all appreciate seeing the house operating well into most evenings on time-shifted solar energy harvested during the day.

Hackett Home Energy Installation

Two Redflow ZBM2 zinc-bromide hybrid flow batteries

Note that this system doesn’t use Redflow “ZCell” enclosures because it pre-dates the existence of those enclosures. It was one of the earliest production deployments of Redflow batteries in a residential context.

 

The ‘Apple vs Android’ inflection point for battery energy storage

Tesla’s unveiling of its new Powerwall 2 battery with a built-in AC inverter in October 2016 – along with some upcoming solar roof tile products – takes a leaf from the Apple playbook of vertical integration.

It’s the latest step on a corporate path (including the imminent merger with SolarCity) that moves Tesla closer to being a vertically integrated provider of energy solutions.

As with the Apple product ecosystem, this aims to establish Tesla as a single entry point for energy generation and storage systems in the home environment. Tesla has both the name and the resources to become a strong player in this realm.

Tesla’s vertical stance contrasts with the ‘horizontal’ orientation of the rest of the industry – a commercial ecosystem that offers choice at all layers of the energy storage system, using standardised interfaces to allow mix-and-match assembly of devices in the solution ‘stack’.

Tesla’s evolving approach stands to put it into direct opposition to former allies – both existing inverter/charger vendors that may be cut out of the Tesla solution set and experienced energy system installers, who may see the presence of hardware ‘handymen’ installing generic/entry-level solutions to often complex underlying energy management problems.

Implications for inverter/charger vendors – polarising innovation into distinct camps

Tesla’s Powerwall battery packs are high voltage devices that are not compatible with most industry battery inverter/chargers, which typically operate at 12, 24 or 48 volts DC.

The Powerwall 2 unveiling is an interesting day for inverter/charger vendors such as Solar Edge, manufacturer of the inverter of choice for the original Powerwall, which is no longer required with Powerwall 2. Likewise it is an interesting day for Fronius, which makes a three-phase inverter that supports support the first Powerwall version. The launch also impacts SMA, which recently released its SMA Sunny Boy Storage, a high voltage DC Tesla Powerwall-compatible battery inverter – that is now superfluous to requirements.

The bottom line for the emerging energy storage sector is that each time Tesla sells a Powerwall 2 with integrated AC inverter, an existing inverter/charger/energy control system vendor books one less sale.

As a result, this new approach from Tesla may tend to polarise the market into two camps over time – with a distinct sensibility developing that is akin to the long term battle of Apple vs Android in the smartphone market.

Implications for the industry – flexibility vs convenience

In the US, Tesla’s sales proposition adds US$1000 (and adds AU$1450 in Australia) to the Powerwall 2 purchase price to cover installation and associated ancillary hardware costs. One wonders whether this Tesla-determined margin for installers will be sufficient and sustainable for the provision of a professional-grade storage solution to the consumer.

This approach may also fail to accommodate specialised situations such as two-phase or three-phase installations, installations that require flexible interconnection, those that requite sophisticated energy flow management; or those that may require the integration of multiple DC or AC energy sources.

DC battery optimised applications

There are many commercial, industrial and telco environments where a 48-volt DC battery is more appropriate (and often, required), such as:

  • Data centres
  • Telco facilities such as mobile phone tower sites; and
  • High efficiency off-grid sites based on direct DC power systems, as in developing countries where pure DC-based energy systems are increasingly the norm.

In many cases, it can also be more efficient and effective to DC-couple solar panels to batteries using MPPT trackers than it is to use AC coupling, which requires separate inverters for solar and battery. This is especially relevant in pure off-grid or in grid-failure-backup scenarios, where DC coupled solar-to-battery charging can remove the need to have an AC generator available to ‘bootstrap’ the system in black-start scenarios.

(See this page for a comparison of AC coupling vs DC coupling approaches in the deployment of solar plus battery systems)

Challenges inherent with lithium-based batteries

While lithium-based batteries offer a core advantage – generally lower upfront cost – this energy storage chemistry presents substantial challenges that include:

Alternative battery technologies

Lithium based chemistries are the undisputed preference for transport applications (such as electric cars). Their high energy density and high peak power output makes them entirely appropriate in such use-cases.

However, a number of great alternatives to Lithium based chemistries exist (and can often be preferable) for stationary energy storage in home, commercial and industrial energy storage and delivery scenarios.

For example, Redflow ZCell batteries are a completely different energy storage approach that avoids the downsides of Lithium based batteries as noted above.

The ZBM2 storage module underlying the ZCell product also has other unique advantages, such as support for ‘Standby Power System’ (SPS) mode – a ‘virtual generator set’ operating mode.

The history of generator set deployment is littered with examples where backup generators simply don’t start up when called upon to do so.

In SPS mode, ZBM2 battery arrays can be fully charged and placed into indefinite hibernation. The full stored energy capacity held in the storage array can automatically be brought back online within 30 seconds (and yet with indefinite shelf life while on standby). This acts very much like a generator set but without the ongoing maintenance costs and also without the uncertainty around reliable startup that consistently challenges diesel generator sets.

The role of price in the purchase decision

Many industries demonstrate that price is not the only factor when consumers decide to buy. Whether choosing a product – such as a car, a plane ticket, clothing, Internet access plans, or even a seat at the theatre – price is just one decision factor.

If price was the sole determinant, we would all drive identically cheap cars, airplanes would have no business class seats and we would all wear identical beige clothes 🙂

Safety factors such as the thermal runaway potential for many lithium-based battery chemistries are an example of a non-price consideration that can be extremely significant in many markets.

The way forward is win-win

There is plenty of room in what is now a rapidly expanding market for a wide variety of energy storage alternatives.

The bottom line is that Tesla’s presence in this market will drive increased interest in energy generation, storage and use. It will help to deliver further momentum to drive demand and adoption of energy storage systems in general.

It will also act as a catalyst for other energy generation and storage systems – using a variety of technologies and deployed a variety of physical scales – to each find their own appropriate ‘place in the sun’.

 

How State Governments can save money and drive the battery revolution

There is a great opportunity for Australian state governments to offer home battery storage incentives to consumers and to funding this incentive by repurposing existing, committed government expenditure. The mechanism I’m talking about is a voluntary trade-in offer, built around the residual payment stream for existing (and often very generous) solar Feed-In Tariffs (FITs).

These solar Feed-In Tariffs have already achieved their goal of kickstarting solar panel adoption in Australia. Indeed Australia is now among the world leaders in its per capita deployment of PV solar panels.

From a public policy point of view, continuing to pay solar Feed-In Tariffs well beyond the point where the underlying consumer investment in their solar installation has been fully paid off represents a substantial forward liability that does not deliver improved public good outcomes. However, state governments are clearly sensitive to the political risk of simply cancelling these long-running tariff schemes, some of which hold liabilities to as far as 2028.

However, Governments have an attractive way out of that problem, which serves both a public policy and industry development agenda while removing these long term liabilities from the public purse.

This involves inviting consumers to voluntarily trade in the residual life of their FIT in exchange for funding to buy a home battery energy storage system. This would have the dual benefit of eliminating a long-term forward liability for governments while kickstarting a home energy storage industry in Australia.

The remaining forward liability for a given customer can be readily estimated based on past subsidy payment patterns for that customer.

Past subsidy payment patterns are also likely to underestimate the remaining forward liability from the FIT schemes to governments. Each time a consumer reduces their home energy usage during daytime hours (through buying new and more energy-efficient appliances, installing automatic energy optimising control systems, and also through government-funded incentives such as this LED lighting replacement scheme), their future FIT payments from the government are set to rise still further in the future.

Accordingly, it seems likely that governments can likely save money overall by offering such a voluntary trade-in, even if the trade-in offer funds the entire capital cost of a home battery energy system. That up-front payment now could well be below the net present value of the (rising) forward liability of the FIT payments to the customer concerned.

Over the past year, Australia has emerged as a global battery proving ground because of its widespread deployment of PV solar panels and high electricity costs. Home batteries based on Lithium battery chemistries have been launched here by companies including Tesla, Enphase and Panasonic.

Redflow, an Australian company of which I’m Executive Chairman and a major investor, has recently launched its ZCell home battery, which is based on Redflow’s unique ZBM2 flow battery. This is a different kind of battery entirely. We believe it is far better suited to the long term demands and the daily ‘deep cycling’ required to store daytime excess solar energy generation and to let you use it to power your home at night.

The solar FIT buyout concept note here has been widely discussed in the Australian renewables sector and is reportedly under consideration by the Queensland Government. It has the virtue of re-using funds previously committed to kickstarting the PV solar panel sector to encourage the new home energy storage sector – with associated jobs and business growth.

Its important to appreciate that in many areas, the solar installation industry is now starting to saturate – with installers starting to struggle to find new growth areas in what has become a highly competitive pricing realm. The big opportunity for renewal in this industry is (now) the installation of battery energy storage systems in the same homes that have previously installed solar – but the high cost of battery systems at this early stage of the battery industry cycle is getting in the way. This voluntary FIT trade-in scheme could be just the growth catalyst the industry needs.

Just as with solar PV incentives, it will prove politically popular with citizens who increasingly regard home energy storage as a way to increase their energy independence and reduce electricity costs.

Widespread energy storage will also benefit far-sighted electricity companies by reducing demand during peak power periods and providing them with the possibility of buying home-stored energy as a ‘virtual’ on-demand power source rather than relying on fossil-fuelled driven peaking gas generators.

At a national level, widespread energy storage, both at the consumer and the grid level, will help Australia achieve its international carbon reduction commitments by time-shifting renewable energy so it can be used 24/7, not just when the wind is blowing or when the sun is shining.

Swapping solar Feed-In Tariffs for home battery installations is not just a win-win: It’s the gift that keeps on giving.