Towards net zero: is battery storage leading the way?

As the UK decarbonises and real time balancing of the electricity system becomes more challenging, battery energy storage will play a crucial role in maintaining a stable system. The UK’s Electricity System Operator, National Grid ESO, has the ambition of operating a zero-carbon electricity system by 2025. This growing requirement for robust real time balancing of the system has been the dominant revenue driver for battery storage projects over the last few years, via Firm Frequency Response. As the ESO begins a journey of reform in UK frequency regulation via new services such as Dynamic Containment, and 2025 draws closer, we look back at how the system has changed and the impact that batteries have already had, through the lens of grid frequency. 

The UK’s electricity system has been rapidly decarbonising over the last few years: renewables accounted for 19.1% of generation in 2014. In 2020, this figure stood at 44.1%. As we move towards a zero-carbon grid, a higher proportion of electricity comes from renewables with no rotating mass, and this has an impact on how the system is operated – not just in dealing with GW swings in wind generation within a few hours, but in the delicate balance of supply and demand over a matter of seconds. 

The spinning turbines of traditional power generation give rise to system ‘inertia’: similar to a bike wheel that keeps turning when you stop pedalling, inertia is an important part of the stability of a power system. Grid frequency is then the needle showing the stability of that system; when all things are equal, it is 50Hz. When they are not, blackouts can occur – frequency plummeted to 48.8Hz on August 9th 2019, leading to nationwide power cuts. 

Here, we look in some detail at grid frequency since 2014: at the trends in frequency ‘events’ (when frequency spikes or dips in response to an outage), and in the way the system recovers. Because we have many more renewables now, system inertia has decreased. We see that year on year, grid frequency is becoming more volatile (see Figure 1), and events are becoming longer. However, the rate of change of frequency (RoCoF) is becoming less severe (Figure 2).  

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So why would RoCoF, a key indicator of system stability, be getting ‘less’ bad with decreasing inertia? One explanation for this is in the new technologies which have been coming onto our system in recent years. National Grid ESO, the UK’s Electricity System Operator, procure an array of services to balance supply and demand in real time. One of the most important of these is dynamic firm frequency response (FFR), in which a plant moderates its output to help balance the system in real time, given the system frequency. It has become dominated by batteries, which, when operated well, can respond reliably and nearly-instantaneously to frequency events – and crucially for net-zero, cleanly.  

Figure 3 shows the volumes of frequency response from different technology types. Since 2014, batteries have gone from providing no FFR volume to now providing virtually all FFR volumes. This, alongside frequency regulation volumes delivered by batteries via Enhanced Frequency Response (EFR) tenders, and more recently the Dynamic Containment (DC) auctions, mean the UK now has close to 1GW of low carbon, ultra-fast battery storage providing real time frequency regulation to balance the electricity system. 

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Looking at two comparable frequency events, one from summer 2017 and one from summer 2019, we can corroborate this theory. There were similar conditions on these days – a similar national demand (INDO), wind outturn, and a sudden power loss equivalent to around 2% of total demand (Table 1). The event in 2019 is after the evening peak, when national demand is decreasing, while the one in 2017 is during the evening ramp. Figure 4 shows the frequency trace for these two events, on a common time axis. 

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Despite the slightly smaller loss in generation causing the 2017 frequency event, it was more severe – with a larger RoCoF and reaching a lower frequency: 49.57 vs 49.70 Hz. The post-event response overshoots and subsequently the frequency remains high for a couple of minutes, whereas the 2019 event returns to a frequency close to 50Hz. While time of day considerations may be at play, it is interesting to consider the volumes of frequency response on the system during both of these periods: see Figure 5. The earlier event had around 30% more dynamic FFR volume. Logic then says the system should stabilize more quickly to a comparable loss, but the opposite is true. However, there is a marked shift in the makeup of that volume; batteries in both FFR and EFR provide significantly more of the stack in 2019.

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The fault recovery of the system appears much better in 2019, suggesting all of these batteries are really improving our response to unplanned plant outages. Returning to the bicycle analogy, it’s much easier to stop a bike from falling over if you catch it just as it starts to topple rather than just before it hits the ground. Batteries are so much faster as compared to the gas, pumped storage and hydro plants which dominated just a few years ago, and it means the system operator needs less volumes to provide the “same” service, so it’s more efficient. Batteries are also very happy performing these low utilisation services – we see very low levels of cell degradation in battery systems performing FFR over long periods of time, and it can be easily stacked with other services. 

All this is great news for net-zero. Leaps and strides in energy storage technology over the last few years, alongside the platforms which operate them, mean we can integrate far more intermittent renewable generation into our electricity mix – whilst ensuring the system remains robust and secure, crucial in our highly electrified society. As we build more wind and more solar, the importance of battery storage technologies in operating a decarbonised, digitalised, democratised and decentralised system will continue to grow. And, not just in frequency regulation but across the board of balancing requirements. 

Written By Grecia Monsalve

The Open Energi Podcast – Lessons from the 2019 Blackout

The blackout that struck the UK on the 9th of August 2019 was a once in a decade event: a lightning strike causing near simultaneous drops in output from both a conventional gas power plant and the UK’s largest offshore windfarm.

This led to widespread blackouts and travel chaos in London as passengers were left stranded on depowered trains. It also raised conversations about the systems necessary for the stability of the UK’s power grid into the mainstream.

Open Energi has been actively working for over ten years helping the UK’s National Grid deploy the technology and software necessary to underpin a reliable renewable power network.

Our first podcast features insight from Dr Robyn Lucas, Open Energi’s Head of Data Science and Sebastian Blake, Head of Markets and Policy, as they discuss what made this blackout so important as a moment to reflect on the evolution of the UK’s power infrastructure, including:

  • how systems designed to offer resilience to the grid responded (or failed to respond) to the blackout.
  • how assets – like batteries – are managed through software to react to both changes in frequency and market prices.
  • the most important lessons emerging from the blackout and subsequent investigations for everyone looking to help answer the UK’s future energy needs.

Listen here:

 

 

 

V2X: how ‘storage on wheels’ can reshape our energy system

EV smart charging

Dagoberto Cedillos, Strategy & Innovation Lead at Open Energi

As Electric Vehicle (EV) uptake accelerates we’re starting to see a radical transformation in the way transportation influences the power system. Vehicle-to-X (V2X) technology, which can be used to discharge an EV battery back to the grid, or to power our homes and businesses, has a pivotal role to play.

By unlocking ‘storage on wheels’ V2X can bring down the cost of EV ownership; reducing the need for infrastructure upgrades and cost effectively integrating more renewable generation. Open Energi’s analysis suggests that by using vehicle batteries to optimise electricity demand against prices, EV owners could benefit from a new income stream in the region of £1,500 a year.

EV momentum

The UK currently has over 130,000 EVs on the road, and National Grid expects this to rise to over 10 million by 2030. Globally, BNEF forecasts 130 million EVs in the same timeframe.  As 2019 gets underway, all the indicators suggest EV growth is well on its way to hitting these targets, breaking records month-on-month. The graph below shows how EV forecasts have increased year on year. It’s possible we will see a very visible step change in the mid-2020s, as EVs hit up-front cost parity with Internal Combustion Engines (ICEs).

 

BNEF rising consensus on EV adoptionRising Consensus on EV adoption, source BNEF

Quantifying EV flexibility from smart charging

Last year Open Energi analysed the potential to manage EV electricity demand (one way) using smart charging.  Taking National Grid’s 10 million by 2030 forecast, we identified some 12GW of flexibility which could turn EVs from a threat to grid stability to an asset that can benefit the grid, drivers and the environment alike.

Smart charging flexibility comes from the energy that can be shifted (e.g. moving a period of charge, or part of it, from one time to another) and is determined by the amount of energy a vehicle will require at a given charge.

An average vehicle in the UK drives 21 miles per day, which translates to 6-7kWh. It is also limited by the speed of charging, typically 3, 7 or 11kW for an EV charging at home or in the workplace.  These scenarios offer the most smart charging potential because vehicles are parked and charging for longer periods, which makes their charging more interruptible.

There is no need for an expensive rapid charger outside your office or home if you are parked there for several hours. You will have ample time to charge your vehicle with a cheaper, slower charger.

Flexibility from EV charging with higher charging speeds is less interruptible, as it will tend to take place in situations where people want to charge quickly and continue with their journey, e.g. forecourt environments. These rapid charging scenarios will likely be complemented by stationary energy storage, which will help to reduce consumption during peak periods, manage local network constraints and provide grid services, as in the case of Open Energi’s project at South Mimms Motorway Services.

V2X capabilities

V2X tableOpen Energi’s 2017 analysis explored the potential to enable flexibility via smart charging. Turning our attention from smart charging to V2X provides food for thought. Instead of being limited by the amount of demand that can be shifted, V2X flexibility is defined by the amount of energy storage capacity in the vehicle battery (e.g. 40kWh for a Nissan Leaf) and its charge/discharge speed (3kW or 10kW based on current technology). This energy storage capacity could be used multiple times in a day, depending on its charging and discharging.

Conservatively assuming 5 million vehicles on the roads by 2030 – half of National Grid’s forecast – this translates to 200GWh of storage. Assuming they could charge/discharge at a low speed of 3kW, this equates to 15GW of capacity, enough to power 30 million homes! For comparison, National Grid’s most optimistic 2030 forecast of total (stationary) electricity storage capacity is 9GW.

Household demand

Given the battery accounts for some 50% of the car’s cost it is important to consider battery lifecycle and how using it could impact the vehicle’s warranty. However, keep in mind that a vehicle driving the average 21 miles a day will use less than a fifth of its capacity each day (7kWh/40kWh). The graph below illustrates a typical UK home’s daily consumption, which is in the region of 2kWh over the evening peak (4-7pm).

Daily Household Electricity ConsumptionResidential demand profile, source UKERC

Using V2X technology, an EV battery could discharge to the home during this time and already create substantial value by simply taking the household ‘off-grid’ when prices are at their highest. Adding this 2kWh to the 7kWh needed for driving gives a total daily throughput of 9kWh, or 22.5% of battery capacity.

EV storage on wheels

The batteries Open Energi operates in our portfolio of distributed energy assets usually perform a full charge/discharge cycle per day and comply with warranty conditions, so there is potential to extract further value by increasing the utilisation of the vehicle battery. However, in the example of a household we need to evaluate if the spread between the export price during the peak and the import price when energy is recovered is positive to justify exporting to the grid. This is not necessarily the case for larger demand sites such as an Industrial or Commercial user.

Opportunity for large energy users

Sites with greater demand could shift even more energy, and discharge more vehicles at once, without having to export. Essentially, a fleet of commercial vehicles becomes a behind-the-meter energy storage asset for a site when drivers have finished their shifts, displacing site consumption during the peak and recharging the vehicle battery when prices fall. Open Energi’s analysis suggests that this kind of demand optimisation could be worth up to £1,500 per vehicle per year.

The main obstacle today is the price and availability of V2G chargers but this should quickly change. While V2G chargers are relatively difficult to procure at present, V2G compatible vehicles are already being sold at a similar price to comparable EV models. For example, Nissan’s electric van, the e-NV200, does not seem to have a premium for the feature – it comes already equipped with V2G compatible charging technology. As charging technology catches up, V2G will be a standard bundled feature of these vehicles.

Storage on wheels

Projects such as Powerloop, the first large-scale domestic V2G trial in the UK, aim to demonstrate the benefits of V2X in action. Backed by Innovate UK and bringing together a consortium including Open Energi, Octopus Energy, Octopus Electric Vehicles, UK Power Networks and ChargePoint Services, the 3-year, £7 million project will see 135 V2G chargers rolled out on the UK’s electricity grid. EV drivers will be able to access a special V2G bundle when leasing a V2G compatible car.

A two-way charger will enable the driver to charge their vehicle intelligently, using their vehicle battery to power their home during peak times or sell spare power back to the grid. The project will also focus on the role of EVs in delivering flexibility services to the local network. Open Energi’s Dynamic Demand 2.0 technology will aggregate the cars’ battery power to integrate domestic V2G into UK Power Networks’ flexibility services.  Together, we aim to demonstrate the benefits of using EVs to support the grid and reduce costs for drivers.

It’s clear that V2X unlocks a huge opportunity for energy systems globally – with the potential to create a volume of ‘storage on wheels’ that will ultimately eclipse grid-scale and behind-the-meter batter storage many times over. Depending on how we shape regulation, develop technology and create new business models, this huge amount of flexible storage potential could be captured to lower the cost of car ownership, power our homes, and operate our electricity network more efficiently, whilst accelerating our transition to a net zero carbon future.

Cenex LCV event 2018

Cenex LCV 2018

Cenex-LCV is the UK’s premier low carbon vehicle event incorporating a seminar programme, technology exhibition, low carbon community networking and ride & drive of the latest research & development and commercially available vehicles.

LCV is run by Cenex, the UK’s first centre of excellence for low carbon and fuel cell technologies with assistance from Supporting Partners including the Department for Business, Energy and Industrial Strategy, the Centre for Connected and Autonomous Vehicles, the Office for Low Emission Vehicles, the Department for International Trade, the Advanced Propulsion Centre, the Automotive Council, Innovate UK, the Low Carbon Vehicle Partnership, the Society of Motor Manufacturers and Traders, and Transport Systems Catapult.

Date: 12-13th September 2018

Location: Millbrook, Bedfordshire

Speaker: Robyn Lucas, Head of Data Science

Further information is available from the event website.

Power Responsive success stories: South Mimms battery storage and EV charging

At South Mimms Motorway Services, Open Energi own and operate a 250kW/500kWh Powerpack alongside one of Tesla’s largest and busiest UK charging locations. The project, which is one of the first of its kind globally, was selected as a demand side flexibility success story and showcased by National Grid at their 2018 Power Responsive summer reception.

The Supercharger site can charge up to 12 cars at one time, and since popular charging periods often coincide with peak periods of grid demand – between 4pm and 7pm, when electricity prices are at their highest – flexible solutions are needed to ease the strain on local grids and control electricity costs.

Integrating a Powerpack at the location has meant that during peak periods, vehicles can charge from Powerpack instead of drawing power from the grid. Throughout the remainder of the day, the Powerpack system charges from and discharges to the grid, providing a Firm Frequency Response (FFR) service to National Grid and earning revenue for balancing grid electricity supply and demand on a second-by-second basis.

Combining batteries and electric vehicles makes vehicle charging part of the solution to integrating more renewables without affecting drivers, unlocking vital flexibility to help build a smarter, more sustainable system.

Robyn Lucas, Head of Data Science at Open Energi explained “[the battery] provides a source of flexibility to what is otherwise a very inflexible demand. We do frequency response for most of the time, and over the peak period we use the battery to charge the car up, rather than them charging from the grid.

“Open Energi hope to repeat this blueprint with multiple other stationary storage assets next to EV charging stations. Having stationary storage assets used in this way allows both transport and electricity networks to be decarbonised and allows for greater renewable penetration.”

Smart Energy Summit: Industry. Buildings. Cities. – 26/27.03.19

electricity pylons

Held in Moscow, the 3rd Smart Energy Summit: Industry. Buildings. Cities. is designed to unite the largest energy, industrial enterprises and leading world experts in the field of innovative, digital and Internet solutions for the energy sector to explore new models of generation, distribution, management and accumulation of energy. The 2019 programme includes:

  1.  Internet of Energy: Distributed generation, Smart grids and microgrid, Energy storage systems, Digital platforms, Big data analysis, New markets.
  2. Smart Energy Experience & Practice: Energy of industrial enterprises, Energy of buildings and infrastructure facilities, Energy of cities and regions.
  3. Energy Tech Hub: Startup expo, Pitch session, Hackathon.

Open Energi is delighted to be participating in the event. Our Commercial Director David Hill will be discussing new business models for battery storage and presenting practical examples of projects from the UK.

Date: 26-27th March 2019

Location: Moscow

Speaker: David Hill, Commercial Director

Further information is available from the event website.

2017 in review: breakthrough tech and tumbling renewable records demand greater flexibility

2017 was a year of dramatic change in the UK electricity market. Overall, total UK electricity consumption fell 2.8% compared to the previous year: 264 TWh compared to 272 TWh in 2016[1]. This follows the long-term trend of decreasing peak and total yearly energy use, while the proportion of renewable generation continued to rise: 2017 smashed 13 clean energy records, low carbon generation exceeded fossil fuels, and the resulting trend for negative prices (as recent as last week in Germany thanks to high wind) looks set to continue.

Last year also saw a fall in the strike price for new offshore wind power to £57.50/MWh. Considering the government’s guaranteed price for Hinkley Point C is £92.50/MWh, it highlights just how competitive renewables, and particularly offshore wind, now are. However, the system must be able to cope with the intermittency that all this cheap, carbon-free power brings.

Figure 1 shows the huge variation in demand over the year: from peaks of nearly 50GW on winter evenings, to troughs of around 17GW on summer nights. Figure 2 shows the average daily profile of consumption. In 2017, the prize for peak demand goes to January 26th, which came in at 49.76 GW at 6pm. Compare this to the profile of June 11th, the day that the UK used the least energy: at 5am, it was 16.57 GW. This swing of over 30 GW presents many challenges for the system operator as more and more of the generation becomes intermittent and demand patterns shift: there is value in being flexible with one’s electricity consumption.

 

Figure 1. Daily demand over the year, and smoothed trend over the year.
Figure 1. Daily demand over the year, and smoothed trend over the year.

 

Figure 2. Peak and lowest demand of 2017, compared to the average daily profile.
Figure 2. Peak and lowest demand of 2017, compared to the average daily profile.

Historically, our electricity system has been built to cope with the peaks; and paying for this network accounts for around 30% of your electricity bill (and rising). What if, by being a bit smarter about when we use our electricity, we could flatten the swing out a little? Or better still, align it to renewable generation?

This is where demand flexibility comes in, empowering consumers and playing a vital role in providing the responsiveness needed to cope with huge swings in renewable generation as it makes up more and more of the UK’s generation mix.

Transforming the network

2017 will be known as the break-through year of batteries and electric vehicles (EVs). With the dramatic fall in battery prices we’ve seen a rush of parties buying up battery capacity, hoping to profit from what were lucrative flexibility markets. National Grid have seen batteries flooding into the Firm Frequency Response (FFR) market, attempting to secure profitable long-term contracts to satisfy investors. Market dynamics mean this is increasingly challenging. In a rapidly changing marketplace, a variety of revenue streams must be considered. Battery operation must encapsulate multiple markets to insure against future movements and maximise profits, while ensuring safe and careful operation of the asset such that state of charge, warranty, and connection limits are respected, an area where Open Energi has significant expertise.

EV take-up is accelerating more quickly than many estimated – UK sales of EVs and plug-in hybrids were up 27% in 2017 – and the need for managing this additional demand in a smart, automated way is crucial to alleviate strain on local networks. We have explored the enormous potential of EVs to provide flexible grid capacity and are working with a consortium to deliver the UK’s first domestic V2G trial.

While in the short term, as the big electricity players try to keep up with the changing needs of the system, flexibility markets present a degree of uncertainty, the long term need for demand-side response (DSR) and frequency regulation cannot be underestimated.

Grid Frequency and FFR

As the System Operator, National Grid must maintain a stable grid frequency of 50Hz. Generation and demand on the system must be balanced on a second-by-second basis to ensure power suppliers are maintained. Traditional thermal plant operates with physically rotating turbines, which carry physical inertia and act to stabilise the frequency. With the increase in generation from non-inertial sources (e.g. wind turbines, which don’t carry inertia in the same way, and PV cells), this stability is reduced. Larger deviations in frequency can result in the event of a power station, or interconnector trip, for example.

During 2017, the largest low frequency event (demand greater than supply) occurred on 13th July, when it dropped to 49.57Hz. Given that National Grid’s mandate is to keep it within 0.5Hz of 50Hz, this was rather close! Figure 3 shows the period, and we see a sudden drop in frequency which typically indicates the trip of a significant generator. In this case, the fault was at the French interconnector. Here, what usually functions to improve energy continuity and smoothen geographical variations in supply was the culprit for the biggest second-by-second imbalance in 2017!

The largest high frequency event (supply greater than demand), during which frequency reached 50.41Hz, occurred at the end of October, was much more gradual and seems to have been due to a combination of several effects. Demand typically drops quite steeply this late in the day, so large CCGT plants are reducing their output and on this occasion a sudden drop in wind-generation seemed to have been over-compensated by pumped storage.

Figure 3. Lowest and Highest frequency extremes in 2017.
Figure 3. Lowest and Highest frequency extremes in 2017.

As well as these relatively rare large frequency events, there are excursions that can last for several hours. Figure 4 shows two periods where the frequency deviated from 50 Hz. In general, the average frequency is 50Hz, and therefore any response to frequency regulation averages out to zero. However, over these medium-term time periods the average frequency is not 50Hz. For flexible assets like batteries, that are dynamically responding to correct grid frequency during such periods (performing FFR) the state of charge is affected.

For this reason, the state of charge of the battery must be actively, and automatically, managed – so that optimal state of charge is quickly recovered after such events. The battery is then able to continue to perform FFR, or other services such as peak price avoidance or price arbitrage in wholesale markets. The state of charge (bottom panels in Figure 4) can also have strict warranty limits set by the manufacturer.

Figure 4: Extended frequency events and impact on battery state of charge
Figure 4: Extended frequency events and impact on battery state of charge

Interestingly, 2017 saw an increase in both the number of frequency events (usually defined as frequency excursions larger than 0.2Hz away from 50Hz), and frequency mileage (defined as the cumulative deviation of the grid frequency away from 50 Hz), shown in Figure 5, particularly during the spring and autumn.

Could this be due to the large, somewhat unknown amount of PV on the system? It is distributed, meaning National Grid see PV generation as a fall in demand; they also have no control over it (unlike most other generation). PV efficiency is high in cold weather, so perhaps unexpectedly high and erratic solar generation on cold, sunny days in the Spring and Autumn led to a more unstable system this year, compared to 2016.

Figure 5. The grid has experienced more mileage and more events in 2016 than 2017, especially in March and October. Frequency “event” here is defined as a deviation of 0.1 Hz around 50Hz.
Figure 5. The grid has experienced more mileage and more events in 2016 than 2017, especially in March and October. Frequency “event” here is defined as a deviation of 0.1 Hz around 50Hz.

Figure 5. The grid has experienced more mileage and more events in 2016 than 2017, especially in March and October. Frequency “event” here is defined as a deviation of 0.1 Hz around 50Hz.

The rise of distributed generation, accelerating EV uptake, and plunging battery storage costs, are all driving a rapid transformation in the UK’s electricity system.  Managing these changes requires new approaches.  Demand-side response technologies, like Open Energi’s Dynamic Demand 2.0 platform, mean patterns of demand can be shifted in a completely carbon neutral way; enabling electricity to be consumed when it’s being generated: as the wind blows, or the sun shines. Rather than inefficiently changing the output of a gas fired power station to meet demand, we can make smart changes in demand up and down the country to meet generation, deliver local flexibility, and put consumers in control of their energy bills: delivering completely invisible, completely automated, intelligent DSR which paves the way for a more sustainable energy future.

By Wouter Kimman, Data Scientist, Open Energi

[1] For demand here and throughout this post we use INDO values as reported by ELEXON Ltd.

All-Energy

All-Energy
Our Head of Data Science, Dr Robyn Lucas, is joining a panel on Energy Storage at this year’s conference to share our views on the business case for behind-the-meter battery storage.
Date: 2-3 May
Location: SEC Glasgow
Session: Smarter energy storage at the local level
Topic: Beyond FFR: making the business case for BTM battery storage
Time: 15.00-16.30, 3 May
Further information is available from the event website.

The future of flexibility: making the most of behind-the-meter storage

Camborne Energy Storage

The slowdown in the Firm Frequency Response (FFR) market, where prices are falling and volumes have been capped – in large part thanks to the decreasing cost of battery storage – has been a big talking point of late.

National Grid has now procured much of the low response it needs for the next two years, and average prices of accepted bids have decreased 20% over the last 7 months. National Grid has also announced proposed changes intended to rationalise and reform the current suite of balancing services it procures, including a streamlined FFR-type product.

These rapidly changing market conditions may leave some battery companies going back to the drawing board and asking how to guarantee income over a long period and satisfy investors that it is worth investing hundreds of thousands in the latest battery storage system, without the relatively high revenues that providing FFR has historically guaranteed?

Fig: The distribution of FFR accepted tenders for the period January - October 2017. Source: National Grid
Fig: The distribution of FFR accepted tenders for the period January – October 2017. Source: National Grid

But it is possible to turn to other markets for flexibility. FFR will remain a part of the revenue stream for batteries, and for the fast-acting Demand Side Response (DSR) that makes up most of Open Energi’s FFR portfolio; but being a bit smarter about where, and how, you employ the flexibility at hand can open up a wealth of other revenue streams. These, stacked up, provide a stronger business case than FFR alone.

Open Energi’s new platform, Dynamic Demand 2.0, is designed with exactly this in mind. By connecting to distributed energy assets which have inherent flexibility in their electricity consumption or generation, including industrial equipment, electric vehicle charging stations, and of course battery storage systems, it enables businesses to dispatch this flexibility in the most valuable place at any one time.

Tailored to the particular operational or site constraints of an asset, balancing services, energy trading, the capacity market, network constraint management, peak price management such as DUoS red-band and TRIAD avoidance are all opened up as stacked revenue streams, as well as operational energy efficiencies automated with machine learning.

For behind-the-meter batteries, this means considering any on-site generation or demand, the import and export limits of the site, the warranty particulars of the battery, and evaluating all the potential revenue streams of the asset. By taking a holistic view of the energy market, using state of the art machine learning techniques and cloud based technology, we remotely operate the asset to maximise its return on investment: FFR is just one slice of the cake.

In many ways, a battery is the perfect asset for flexibility. It has a defined storage capacity; it can discharge power up to a maximum well-defined rate; and it has a known state of charge (SoC) at any one time. However, to operate a battery across multiple markets, careful management of the SoC of the system is necessary.

While batteries very naturally perform frequency response, charging up when frequency is high – removing excess electricity from the grid, and discharging when frequency is low – when more electricity is required, the operation is not quite that simple. To have the capacity, or availability, to both charge up and discharge in line with grid frequency, the ideal SoC of a battery is 50%.

Periods of high or low grid frequency can rapidly take the SoC of the system far from 50%, and batteries have an inherent efficiency (around 90% in the best systems): active state of charge management is required to maintain the availability for frequency response.

The figure below shows the same 500kW, 800kWh battery over the same 52-hour period, with and without state of charge management. The availability to fully charge or discharge at the capacity of the battery for 30 mins (equivalent to a frequency 50.5Hz or 49.5Hz for half an hour) – is quickly impeded on when no SoC management is present, and SoC will eventually tail off to zero due to the non-perfect efficiency of the battery. Battery throughput, defined as the cumulative discharge of energy through the battery, is also higher without SoC management, eating into that allowed by the warranty.

Fig: The state of charge (%, top), availability for FFR (kW, middle) and throughput (kWh, bottom) of a 500kW, 800kWh system are shown across 2 days of frequency data. With no SoC management in action, state of charge is routinely out of the dotted lines which signify ½ hour of storage capacity being available to charge and discharge at full power; here, state of charge is low. As a result, low availability for FFR is diminished. Throughput of the battery, defined as the cumulative sum of the battery discharge, is also higher when no SoC management is used.
Fig: The state of charge (%, top), availability for FFR (kW, middle) and throughput (kWh, bottom) of a 500kW, 800kWh system are shown across 2 days of frequency data. With no SoC management in action, state of charge is routinely out of the dotted lines which signify ½ hour of storage capacity being available to charge and discharge at full power; here, state of charge is low. As a result, low availability for FFR is diminished. Throughput of the battery, defined as the cumulative sum of the battery discharge, is also higher when no SoC management is used.

When introducing revenue streams in addition to FFR, as we do with Dynamic Demand 2.0, battery operation gets rather more complex. For a behind-the-meter battery, electricity bills can be significantly reduced by discharging over peak periods to either avoid importing electricity when it is most expensive (if the site has demand), or exporting to grid and taking advantage of the various network charging revenue streams (DUoS, TRIAD, CM Levy).

Electricity generated earlier in the day, from on-site PV generation, or stored when it was cheap to import, can be exported to grid at peak times. Energy arbitrage on the wholesale market: charging up when the N2EX price is low and discharging when it is high, or hedging against pre-bought volumes, can give a day-ahead price signal, as in the figure below; playing on the intraday market can similarly offer additional uplift. If the asset owner is exposed to the Balancing Mechanism through their supplier, short notice calls to discharge in line with a large system imbalance offers another revenue stream.

Battery Storage Energy Arbitrage
Fig: Energy arbitrage using the N2EX day-ahead market is shown for a 60kW, 300kWh system over one day. The stored capacity of the battery is varied to minimise the cost of electricity over the day, such that the battery charges when electricity is cheap, and discharges when it is more expensive. By layering on additional price signals closer to time and re-optimising the power profile, additional revenues from energy arbitrage across a range of markets can be achieved.

These requests to charge and discharge in line with ahead-of-time and real-time price signals must be dispatched depending on the import and export constraints of the site and of the capacity of the battery. It needs enough stored energy to be able to discharge for the duration of the price spike, while maintaining the availability to do FFR in accordance with any pre-contracted volumes required by National Grid, and such that recovering the SoC afterwards does not cost more than earnings during the call itself. It also needs to do so without overly increasing the throughput of the battery such that the valuable warranty is violated.

Open Energi has experience of doing this with assets already in operation behind-the-meter. At South Mimms Welcome Break services, we are managing a Tesla Powerpack alongside an EV charging station, to displace site demand from EV charging throughout the day, while providing FFR, and providing energy savings by doing a full discharge of the battery during peak periods.

In a Somerset field, we operate a battery integrated with a solar farm, using PV generation to charge up the battery for free during the day, discharging at peak times, and managing the SoC so that FFR availability is maximised the rest of the time. By stacking these additional revenue streams alongside FFR we increase the income of the asset, and with our Dynamic Demand 2.0 platform, will be able to extend these services across a host of other assets and services.

This includes managing fleets of battery storage systems, where the optimal control strategy goes beyond revenue stacking each asset individually. A central intelligence that is aware of the state of each battery can determine how hard to work different assets to maximise revenue or minimise the number of charge-discharge cycles performed, extending each asset’s life. Dynamic Demand 2.0 can combine revenue stacking with fleet management strategies to meet these objectives.

As we look to the future of energy, it is clear that behind-the-meter battery storage has a huge role to play in creating a more sustainable system. As renewable energy becomes more prevalent, value is emerging in new places, and the key to optimising this value, without negatively impacting battery performance, is technology.

Robyn Lucas is Head of Data Science at Open Energi

Battery storage project a ‘blueprint’ for EV charging infrastructure globally

Tesla South Mimms Supercharger and PowerPack

Pairing batteries with EV charging stations can help to align sustainable transport and energy needs for the future.

At South Mimms Welcome Break Motorway Services, we have installed a 250kW/500kWh Powerpack alongside one of Tesla’s largest and busiest UK charging locations. The Supercharger site can charge up to 12 cars at one time, and since popular charging periods often coincide with peak periods of grid demand – between 4pm and 7pm, when electricity prices are at their highest – flexible solutions are needed to ease the strain on local grids and control electricity costs.

Integrating a Powerpack at the location has meant that during peak periods, vehicles can charge from Powerpack instead of drawing power from the grid. Throughout the remainder of the day, the Powerpack system charges from and discharges to the grid, providing a Firm Frequency Response (FFR) service to National Grid and earning revenue for balancing grid electricity supply and demand on a second-by-second basis.

Open Energi own and operate the Powerpack, which is part of our portfolio of assets that help maintain the frequency of the grid. Combining batteries and electric vehicles makes vehicle charging part of the solution to integrating more renewables without affecting drivers, unlocking vital flexibility to help build a smarter, more sustainable system.

The project at South Mimms Welcome Break Motorway Services provides a blueprint for the development of electric vehicle charging infrastructure globally. Moreover, by reducing National Grid’s reliance on fossil fuelled power stations as a means of balancing electricity supply and demand, the Powerpack helps to reduce UK CO2 emissions by approximately 1,138 tonnes per year.