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Battery storage webinar

Your questions answered

Is this primarily used for peak-lopping or to support voltage fluctuation?

Battery Storage can be used for peak lopping primarily on solar farms so that additional PV capacity can be installed above the allowable export limit, then at times of high irradiance, the generated power can be used to charge up the battery. Battery storage can also be used to support voltage fluctuations.

What winding configuration is used for the transformers?

The inverter transformers use a Delta Star configuration.

What are the life spans of these lithium utility batteries?

The life span of the batteries is dependent on the usage profile, the more you cycle the battery the more it degrades, projects are typically designed to have at least 12 years of usable life.

We are engineering a 400MW/400MWhr battery system for the Middle East - at what point does water-cooled technology become of interest? At present, there would appear to be no large installations to gain experience from.

Water-cooled battery products are readily available now from selected suppliers. In the UK the ambient temperatures are ideal for air-cooled HVAC systems, I understand that water-cooled may be more attractive for the Middle East.

Who is eligible for these auctions?

In theory, any battery system owner could bid into the FFR or DC service, the project just has to pass the test criteria and have the correct data provision. It would normally be a Route to Market Provider (Aggregator) who would bid the project into FFR or DC.

Can you please comment on battery response time/ramp rate required for FFR and Dynamic Containment? Certain areas on the network are struggling with step change (voltage fluctuation).

Battery system speed of response can be optimised for different services, currently, the most stringent service is the Irish DS3 service which requires a response time of 150mS from sampling the frequency event to full rated import of export of the battery.

Apart from energy storage, what are the benefits of BESS?

The benefits of BESS are generally to store energy for future use, either to support the network or to trade power.

How do you manage the limited short circuit capacity of these systems?

Limited short circuit infeed from inverter-based generators can be a help and a hindrance.

It's good when you are trying to connect generators to systems that already have fault levels close to network operators existing circuit breaker ratings but not so advantageous when you need short circuit current/fault level to be maintained at a reasonably high level and you are displacing conventional generators and this lowering short circuit/fault level. You might need high short circuit level to stabilise other inverter-based generators.

If extra short circuit fault level is needed then the options are to either constrain on a conventional generator (may cause constraint off of renewable generators) or to install a synchronous condenser as per the NGESO Stability Pathfinder projects.

Is there a need for a fire wall between the battery banks to prevent flashover?

Some projects, particularly where space is constrained will fit firewalls between enclosures - minimum clearances defined in EN 61936-1 allowed around all electrical plant. If the separation is 3m or more then firewalls are not required.

Is it common practice to have batteries to work either on island mode or grid-connected? Or is it similar to PV where the equipment used needs to be tuned depending on the use?

Battery systems can operate either grid-connected or in island mode. All utility-scale battery storage projects are connected to the grid but there are options for islanding domestic or light industrial batteries.

What happens to the batteries once they have reached the end of their useful life? can they be recycled?

Batteries can be repurposed, EV batteries can be used for utility-scale purposes and utility batteries reused as domestic or agricultural systems. They will need to be recycled eventually.

Could you give us some guidance on £/kWh stored?

Unfortunately, I am unable to give commercial details

How many charge/discharge cycles are these installations good for? How quickly do the batteries age, how often will they require replacement and are the old batteries readily recyclable?

The number of cycles depends on the manufacturer, the chemistry and the operating conditions, batteries that are operated in hotter conditions will degrade quicker. Projects will typically be designed to ensure that batteries do not degrade more than 40% within 12 years, full replacement is likely at this point and batteries will then be either repurposed or recycled.

On a domestic battery installation, is it best practice to install the batteries within the home or due to potential fire risks should they be stored outside?

Whilst locating batteries outdoors is an obvious preferable choice for fire safety, it should be noted that active heating and cooling may well be necessary to keep batteries in the optimum temperature range, otherwise the battery life and/or instantaneous storage capacity could be seriously affected.

The UK does not currently have standards that prohibit storage batteries for electrical energy storage systems from being installed indoors. However, it would be up to the installer (or manufacturer, if the installer is following the manufacturer's installation instructions) to determine the safety of doing so. There is some guidance on this in the IET Code of Practice for Electrical Energy Storage Systems to assist, but the final decision would rest with the installer or manufacturer.

Batteries in a domestic situation should be suitably housed and with monoblocs/cells accessibly only using a tool, and BS 5839-6 recommends that where batteries and power converting equipment (and similar items) are installed in locations in dwellings that are not visited frequently, such as storage cupboards or loft spaces, fire detection interlinked with detection and alarm system (or interlinked detection and alarm devices) in the rest of the dwelling. Loft spaces may not be a suitable location for batteries for a number of reasons, including accessibility for maintenance, weight, and ambient temperature extremes.

What is the cost per kWh installed cost for batteries?

Unfortunately, I am unable to give commercial details.

Does the national grid use dynamic containment in a similar way to their use of inertia on more normal turbine spinning inertia?

Dynamic Containment has been introduced to mitigate the effects of reduced inertia.

How much floor area would 1MWh of utility-scale battery require?

This depends on the battery manufacturer and the battery chemistry but typically you can fir 3-5MWh of batteries in a 40ft shipping container.

What is the round efficiency of these batteries?

Typical round trip efficiency is 88-90%

Feeding tariffs are no longer available. Are there any other incentives from the government available?

The Contracts for Difference (CfD) scheme is the government’s main mechanism for supporting low-carbon electricity generation.

Are the cheap rate tariffs easily accessible or advertised such as Economy 7?

We are likely to be moving to a situation where the management system interacts with the SMART Grid in real-time. Consumers would be able to integrate this with their energy provider's packages.

Do you need to wire an essential circuit to use with batteries or can they be used with the main wiring and just the supply is switched when there is no power available from the network?

A switching arrangement is usually required to form island mode, so that 'maintained loads' are powered from the grid-connected system in normal operation and local generation (including batteries) in island mode.

For the domestic type would all property load be via the system with source as either mains or battery, like a UPS and so providing power conditioning effect?

Not with most simple electrical energy storage systems. There is nothing to prohibit this arrangement, but the relevant parts of the system would also have to comply with BS EN 62040 series for UPS.

At present when my solar panels generate more than 200W any excess is diverted to an Immersion heater for hot water. Could I benefit even more with a battery system as well, or will I lose the diverted energy to the immersion heater?

Potentially, but only modelling would be able to determine whether you would benefit more from installing a storage capacity. This would ideally let you know the anticipated payback period for the hardware cost involved.

If there is a G98 or G99 installed in the PV inverter,  do we need another one for the batteries when connecting batteries on the DC side?

If another AC inverter is not installed, the battery is installed on the DC side only, and no additional components to effect island mode (i.e. the system operates as grid-connected, or 'connected mode' only), it is unlikely a new notification or application will be required.

Can solar PV be used in island mode for EV charging only?

It can, although the charging current would have to be curtailed below the current limit of the inverter. It may also be preferable to leave the vehicle connected if it has vehicle-to-grid enabled charging equipment, to facilitate vehicle-to-home functionality. However, in installations where PME conditions apply, certain open-PEN detection devices may not operate effectively in island mode - see Regulation 722.411.4.1 of BS 7671:2018+A1:2020, sections and 10.6 of the IET Code of Practice for EV Charging Equipment Installation.

Why is G99 possibly necessary if the system operates only in island mode?

If the system is totally grid-independent, no notification is required. The term island mode is not used for this arrangement. If the system switches between connected and island mode, G98 (or more likely G99) notification is usually necessary.

What proportion would the fault current be relative to the inverter?

In island mode, the available fault current is limited by the overcurrent limits of the inverters connected in the system - the rule of thumb typically being 1.2 times the sum of all inverters connected in island mode.

Have there been any cases of fire in domestic battery installations, how safe are they please?

I am not aware of any in the UK at present. Battery systems should comply with relevant standards.

Some countries have implemented standards that dictate the maximum "size" (in arc flash incident energy and stored energy terms) of batteries that can be installed in or adjacent to habitable rooms. The IET Code of Practice has a suggested risk assessment approach in Appendix E, although this is not currently reinforced by other standards applicable in the UK.

What is the minimum size of PVs for a house that battery storage should be considered?

Battery storage does not have to be connected to solar PV. It can be used to charge at cheaper-rate, and discharge at peak periods.

If a Solar PV system is present or being installed at the same time, the benefit of battery storage depends also on the occupation profile (e.g. whether occupants are in and/or loads likely to be connected when the solar PV is generating). More benefit is seen from a battery storage system where local loads are heaviest at morning and evening peaks.

For the arc flash PPE requirement of CAT2, is this calculated or assumed?

This has been calculated

Re: Grid scale storage - Do you expect flow batteries to play a major part?

Flow batteries are likely to be of more interest when duration requirements are longer, there are more suited to 8 hour plus services.

Can the heat generation from the batteries be utilised as well?

We have not heard of this being done as yet.

We know that there are issues with Lithium-Ion batteries, are there any other battery types being considered or developed?

The industry is predominantly using Lithium-Ion batteries at the moment but also looking at flow batteries and Sodium Sulfur (NaS) batteries.

Do you have examples of where battery systems have been used as secondary supplies for life safety systems and compliance with BS 8519, that are not residential developments?

In these cases, the system would be required to comply with appropriate standards relevant to the application. Depending on the functionality and performance required, this may include BS EN 50171 and BS EN 62040 series, or relevant parts of BS 5839 series and BS EN 54 series.

For the domestic type systems, it seems it could be tricky to install in existing buildings and would be more suited to new build so it can be considered and designed in from the start. Do you know if this is happening at all in the new build housing market?

There is no reason that the technology could not be included in a new build scheme, but we have no information to indicate the scale on which this is happening at the present time.

What is the methodology of battery chemistry and capacity selection, inverter/charger, Battery management?

Sadly, it is not possible to answer this question in a brief Q&A. However, the battery performance (charge/discharge speed, capability and frequency) must be matched to the protected system usage and performance required.

The nominal battery capacity (in terms of cost-benefit) depends on the amount of local generation and power usage profile. The battery management system must be selected to match the battery chemistry, internal monitoring, and also be able to integrate with the inverter/charger and control system of the EESS. See the IET Code of Practice for Electrical Energy Storage Systems for basic details.

What considerations would need to be taken in order to use an EV battery within a residential setting?

If we are talking Vehicle-to-Grid, or Vehicle-to-Home, there are a number of considerations. Both the vehicle and charging equipment need to be V2G capable. There may be electrical safety issues, see sections 10.5 and of the IET Code of Practice for EV charging equipment installation. Finally, there is the issue of how the system management is arranged so the user is not left with a depleted range at the wrong time.

Please advise H2 detector is required for the batteries storage room?

Not all battery chemistries evolve hydrogen. In cases where hydrogen may be evolved, it would be preferable to have sufficient fresh-air ventilation (based on the size of the battery) and suitable battery management system functionality, to avoid an accumulation of hydrogen in the first place. See BS EN IEC 62485-1 and BS EN IEC 62485-2.

Are alternatives to Lithium batteries available - such as Vanadium Redox - to reduce fire risk, increase life and because of ethical supply chain concerns of lithium batteries?

Battery chemistries are evolving all the time. The standards and IET Codes of Practice do not mandate lithium chemistries. Ethical and sustainable supply chains are certainly a consideration, but should this not also be applied across all aspects of the electrical installation?

For Domestic type battery storage what prevents excess discharge energy from being exported to the grid?

Control systems can be arranged to control the discharge rate of batteries, as well as the charge rate. It depends on the system you buy.

Given the need to de-carbonize, is there a thirst from industry leaders to move towards island mode for the future of British homes?

If I understand the question correctly, I guess that would be a grid-independent system rather than "island mode" (the latter being only an operating state of a system that was normally grid-connected)?

Being wholly grid-independent … never connected to the grid ... is possibly not desirable, as there would be no opportunity for export to the grid to support the local network at peak periods. It may be difficult to service heavy current-using loads due to limitations of power converting equipment, without a lot of expense.

"Grid-independence" (being a situation where the local generation and battery storage serves all the local energy needs of the installation) may be achieved without island-mode.

Why is G99 possibly needed (you said it was) in island mode? If it's island mode surely it's never connected in parallel?

The definition of island mode is an operating state in a prosumer's installation, which is normally connected to the grid, but where [part of] the installation continues to operate in the absence of the grid supply. Switched alternative systems are covered by Regulation 21 of the ESQCR. Therefore G98/G99 (probably G99) applies. If generation operates in parallel with the grid as well, then Regulation 22 also applies, and again G98 or G99 apply.

If the question relates to a system that is 100 % grid-independent, and never connected to a public supply, or is only a switched alternative (and the inverter NEVER connected to the grid) then I would agree, as ESQCR Reg 22 is unlikely to apply, and therefore neither G98 nor G99 would be necessary. See the first row of Table 9.1 of the IET CoP for Electrical Energy Storage Systems ... But this is not what is meant by island mode.

Is there interest in the battery condition being monitored centrally to determine end of life or disconnection in the event of fault/fire?

Each battery rack has a rack BMS which monitors state of heath of that rack.

Is there an installation method or requirement that can be used with lithium-ion batteries to increase longevity and reliability?

The critical thing is to keep the batteries within the optimum temperature range which varies between manufacturers but is typically 18-24°C.

What British standard would the flash over PPE need to conform to in the UK?

BS EN 61482-1-2 – Protective clothing protects the wearer against the hazards of an electric arc.

What is the efficiency of the PCEs used nowadays and how do we decide how many levels these converters should be?

You would have to examine manufacturer data/claims and conduct a cost-benefit comparison between different products.

Do you need a DSEAR assessment to install batteries at your domestic residence?

Storage batteries are already present in many domestic installations, including VRLA batteries that evolve hydrogen. The safety of these is usually covered by product standards. Not all batteries evolve explosive gasses.

Given changes in UL9540A and NFPA855 do you see the IEC 62933 series taking over for International and or EU applications (for Utility scale)?

While we do see IEC62933 as taking over a number of requirements for International and EU applications there are still a number of gaps in the standard which are filled well by both UL9540A and NFPA855. Specifically, there is currently no IEC large scale fire test equivalent to UL9540A defined, and IEC 62933 itself makes specific reference to UL9540A as an example test of this type. Likewise, NFPA855 makes specific recommendations for minimum clearances and FSS requirements which remain relevant outside of NFPA markets.

Do the utility batteries only supply active power or can they also supply reactive power, and is there an advantage to providing reactive power?

The batteries (through the inverters) can provide active and reactive power and this can be beneficial in supporting some grid connection points.

What kind of take-up are we having with domestic and commercial BSSs and does there seem to be a tend toward proliferation in the near/medium future?

At the moment the data we have seen is only projected. There are various reports on the projected market reach to compare and contrast.

What's more popular on the utility scale battery systems Modbus or DNP3 for SCADA communication?

When integrating Batteries and Inverters to an Energy Management System (EMS) the standard Protocol Used by battery and inverter suppliers is Modbus TCP. Communication between the EMS and the Utility/Market Operation Center is typically DNP3 or some other higher-performing protocol.

Is the utility size battery bank tested to UL9540 and UL9540A fire testing, if so what was involved and who was responsible for applying this testing?

Mainstream battery manufacturers are tested to UL9540A by using a test house to put the batteries into thermal runaway to ensure that the fire does not propagate to adjoining modules or racks.

Based upon the duty cycle of maximum discharge to 60% of the battery, is there any particular rule of thumb for sizing battery storage to pair with a 4kW solar PV array?

There is no rule of thumb - it will be dependent on how long you require the duration of the charge/discharge to be. As an example, you may choose to size the battery to 2kW and 6kWh allowing you to charge at rated power during the 3 peak hours of irradiance.

Reading a 2020 Government report It is my understanding that several standards that will be applicable for domestic battery storage are currently under development. Meanwhile how confident can the house-holder be that their system is safe?

Some standards are already in place, and protection against electric shock is ensured according to BS 7671. As with all installations, competent contractors (appropriately registered with suitable industry schemes) installing reputable products, would be recommended.

Many battery systems (utility) are edging up and 1500VDC becoming common, do you envisage even high voltages in the future?

I expect the voltage to be static at around 1500Vdc as above this will be classed as HV and brings about a whole host of other considerations.

What is the current possibility for dead or old batteries as they need to be disposed of? Any recycling capacity?

Currently, batteries which can not be repurposed are sent to recycling facilities in China, South Korea or the US.

Are second use EV batteries useful for buildings given their charging cycles? What sort of performance could you expect from a 2nd use EV battery?

Second use EV batteries can be used for utility applications and these can be repurposed again to domestic or agricultural settings, batteries repurposed from utility scale projects are likely to have degraded down to 60% of capacity.

Can Tracy please expand or advise on how Cat 2 AF rated PPE was arrived at? does this installation require an AF incident energy study? and does the general installation under normal ops constitute 'live working' controls?

An arc Flash study is carried out on each installation to calculate the potential risks which then determines the level of PPE required. All sites are treated as live working sites as the batteries have stored energy within them.

What is the required ramping rate/response time for a utility scale battery to participate in FFR and Dynamic containment? DNOs could struggle with step change/voltage fluctuation by a battery doing a full swing. Any proposed solutions?

FFR is more benign for voltage step, response in 2 seconds, full delivery in 10 seconds. DC is response within 500ms, full delivery within 1 second. Mitigation is to connect to a strong point (high short circuit level) on the local network where any active power swing will have less voltage change impact, and also to ramp the project response as much as possible (even within the 1 second for DC) to reduce the voltage step change.

What are the considerations for the power conversion equipment for loads that have substantial inrush currents? Both in the domestic and utility settings.

That is such a wide application range. However, the answer is how software in the inverter deals with the connected load to avoid nuisance-tripping, and how motor-starter systems are arranged to avoid start failure. It is an added level of complexity for the designer/specifier.

With certain battery types, hydrogen generation can be an issue under certain conditions do these installations allow for/require special ventilation and could the explosive atmospheres regs come into play leading to specialist electrical installations being required?

Yes, but the situation is best avoided by ventilation design, as recommended in BS EN IEC 62485-series. Not all battery chemistries evolve explosive gasses.

It has been touched upon about recycling. True that a battery that serves motor and dies for that application may be possible to be used for lighting or bump-less application for example, but I am asking about final stages of its life. What is currently in regulation is being said/set up for environment at end of secondary/thirdly usages?

Currently, batteries that can not be repurposed are sent to recycling facilities in China, South Korea or the US

How does the supplier maintain the equipment safely when the system is always live. Is there a safe system of work?

Safe systems of work must be used. To work safely on a point in an installation with island-mode capability is likely to require multiple points of isolation, and BS 7671, IET Codes of Practice, and G98/G99 recognise this and require adequate information and labelling to be provided. For many systems, even in domestic installation, it would be recommended to include a system diagram, along with any maintenance procedures.

The designer's duties under CDM Regulations, to design installations so that they can be safely maintained, applies regardless of whether the project/works are notifiable, and this would therefore extend to electrical energy storage systems in private domestic properties.

The batteries (i.e. monoblocs and cells) themselves are the primary concern - as you say, they cannot be switched off at all. For domestic use, the most sensible approach appears to be enclosed packs with a means of isolation or disconnection on their output, with a "return to base" approach for removal of cells or monoblocs.

With commercial/industrial systems, battery rooms, containers or enclosures should facilitate a safe maintenance environment, and BS EN IEC 62485 series of standards would be recommended, along with the provisions for batteries in BS 7671.

Does utility storage get planning permission via a Permitted Development route or is it not allowed via this route?

Utility scale battery storage projects must get planning permission in the same way as any other renewable energy project. In England, battery storage is exempt from the NSIP regulations however in Scotland projects above 49.9MW are still required to apply for an S36 rather than local authority consent. Most projects are also non EIA but this is determined by each local authority