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

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 – we also took ages to actually 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 big 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. We (at last) have a total of around 70kWp of solar on the site, though now I’m casting about to find some more ‘hidden’ roof spaces on the main complex where we might squeeze in just a bit more – you can’t have too much solar 🙂

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 big 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 far 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.

At the time of writing (January 2018), we have had 15 x ZBM2 batteries installed and running (150kWh total) for a few months now, with another 30 x ZBM2 units slated for delivery into the container later (its all wired up and ready for them). When installed, we will have a grand total storage capacity of 45 x ZBM2 = 450kWh.

There is 72kW of Victron inverters installed right into the container as well. We could have gone larger, but these have been ‘right-sized’ to the building demand at Base64, with demand peaks normally around 60kW and typical draw around the 30-40kW level when the building complex is in daytime operation.

Its all linked to a 70kW distributed solar array connected via multiple Fronius AC solar inverters. The main 50kW array is ‘floating’ above the staff carpark and the battery and the rest is distributed on other small, non-heritage, rooftop areas around the campus.

I’m thrilled with how well the system is working – its a monument to the last year or two of the 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 grid-supporting energy source during peak load periods. The missing links there are software, regulation, and attitude – the technology part is easy.

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’.

 

ZCell Launched

I’ve been working very hard with a wonderful team for quite some time now on launching the home-optimised version of the unique and very nifty Redflow ZBM2 battery.

Today we launched a new web site to announce that product (shipping mid year).

We’ve called it “ZCell”.

ZCell Logo

ZCell Logo

You can read all about it at http://www.zcell.com

For a variety of reasons (that you can read about at our FAQ section), we think this really is a better mousetrap. Its materially different (in better ways) to lead-acid and lithium based batteries.

We’ve been beavering away very busily here in Adelaide at Base64 on key aspects of taking this industrial-strength battery technology and reframing it as an easy to use, easy to install home energy storage system.

This technology is a huge passion of mine. I am quietly hopeful that we can make a positive difference to the world with it.