What are the benefits of Electrical Energy Storage Systems? | NAPIT

What are the benefits of Electrical Energy Storage Systems? | NAPIT

Steve Humphreys, Technical Commercial Manager at NAPIT, throws light on the battle to use self-generated green energy.

With the continuing rise in energy costs, consumers are looking at ways to mitigate against rising bills and recoup some benefits through renewable technologies.

Solar PV systems have been on the market for many years with homes fitted with Solar PV benefiting from a fairly generous feed in tariff (FIT). However, this scheme was closed to new applications on 1st April 2019. It was not until 1st January 2020 that the government introduced the Smart Export Guarantee (SEG).

The SEG tariffs still allow customers to receive payments for electricity generated and exported back to the grid, but the rates are much lower and vary between energy suppliers.

So, if homeowners with Solar PV systems are not receiving the historic financial benefits, what is the alternative?

Electrical Energy Storage Systems (EESS), also known as battery storage, offer an attractive alternative. Instead of exporting back to the grid, the energy generated from Solar PV can be stored in the EESS and used in the home at certain times of the day, as shown in Fig 1.


Can an EESS System be installed without Solar PV?

There’s a common misconception that an EESS can only be installed when combined with a Solar PV system. Whilst it’s true that combining these renewable technologies would be the most cost-effective way over time, that doesn’t mean that an EESS can’t be installed on its own.

A few energy suppliers are now offering time-of-use electricity tariffs. This is where homeowners purchase electricity from the grid to charge the battery when the prices are cheaper and then use it in the home at peak times to avoid buying it from the grid, see Fig 2.

Benefits of installing an EESS The main question that gets asked by homeowners when they’re thinking of installing renewable technologies is: “what’s the payback period?”

While the costs of installing Solar PV and EESS are becoming increasing affordable due to increased demand, it’s worth pointing out that there can still be a considerable up-front investment for the installation of these systems.

The payback period depends on various factors such as the size and type of the system. In the UK, the average payback time for a domestic EESS is around 10-12 years (source: Electrify Wales/Solar & Battery Payback/28 April 2023).

Installing an EESS offers many additional benefits, including:

• Off-grid independence,

• Lower energy bills,

• Low maintenance,

• A greener environment.

Which EESS should you choose?

The wide range of manufacturers and equipment available can provide a minefield of choices when deciding which system to install.

All installed systems should be carefully designed beforehand to meet the requirements of the individual customer and installed in accordance with current regulations and standards.

In general, Electrical Energy Storage Systems come in two types – packaged or discrete component.

Packaged EESS

Packaged systems are complete solutions available commercially as an off-the-shelf product. They could have all the component parts in one single enclosure or comprise of separate components all from the same manufacturer.

The potential benefit of this type of EESS is that the manufacturer is responsible for all its component parts, its safety and its stated performance, as shown in Fig 3.

Discrete component EESS (Bespoke)

Discrete component systems are assembled from two or more discrete component parts, perhaps from different manufacturers.

This does provide a wider range of choice and can make the installation more bespoke to the customer’s needs (see Fig 4). However, a bespoke system creates a greater reliance on the designer and installer to ensure safety and compatibility between components.


Meeting the Standards

All electrical installations need to be designed and constructed to meet the safety requirements of the Electricity at Work Regulations 1989 (EAWR).

To meet the statutory requirements of the EAWR, designers and installers need to refer to BS 7671 and other documents, such as:

• The IET Code of Practice for Electrical Energy Storage Systems,

• MCS Standards Document MIS 3012: The Battery Standard,

• ENA Engineering Recommendations G98, G99 and G100.

BS 7671 contains specific information concerning battery installations in Section 551 and Chapter 82. These guidance documents are displayed in Fig 5.

It is of the upmost importance that designers and installers comply with these regulations, standards and guidance documents. The manufacturers’ instructions shall also be taken into account in addition to the requirements of BS 7671.

This will ensure that the correct equipment and installation methods are used for safe operation, use and maintenance of the EESS.


As with Solar PV installations, Electrical Energy Storage Systems are notifiable to the Distribution Network Operator (DNO). This is because these systems work in parallel with the grid supply and have the potential to feed energy back into the grid. The notification process is published by the Energy Networks Association (ENA) and follows Engineering Recommendations G98, G99 and G100.

G98: Single Premises

This process is very straightforward and uses a ‘fit and inform’ procedure.

The DNO notification is required within 28 days after the installation has occurred. To follow the recommendations for a simple G98 fit and inform process, the EESS installation shall:

• Have a total site generation/inverter capacity of less than or equal to 16 A per phase,

• Be a single installation on a single property,

• Use a G98 type tested approved inverter.

G98: Multiple Premises

This process requires DNO approval before the installation proceeds. This is due to the potentially larger impact on the electricity network with multiple systems within a close geographical proximity.

The DNO notification is required within 28 days after the installation has occurred. To follow the recommendations for this process the EESS installation shall:

• Have a total site generation/inverter capacity of less than or equal to 16 A per phase,

• Use a G98 type tested approved inverter.

G99: Installations

Systems over 16 A per phase will generally fall into the G99 procedure and will vary depending on the size and type of system. The three routes are:

G99 Fast Track (Route 1)

The fast track process is to provide a simplified connection process for a small scale EESS that is being installed in addition to existing local generation such as an existing domestic Solar PV system.

G99 Standard (Route 2)

This process is for an EESS with type A generators less than or equal to 16 A per phase and a total generation of less than or equal to 32 A per phase. In addition, only type tested inverters are used.

G99 Full (Route 3)

This process is for all other systems. This will include type A generators rated over 16 A per phase and all other type B, C and D generators.

The standard and full G99 process requires a written connection application and a formal DNO approval prior to proceeding with the installation.

A G99 commissioning form is to be supplied to the DNO within 28 days or alternatively could be witnessed by the DNO if requested.

G100: Export Limitation

This scheme measures and controls the amount of power from generation systems that are to be exported to the grid. This can be achieved by restricting the generation output and/or by balancing the customer’s demand. This is done to prevent the agreed export capacity being exceeded.


Electrical Energy Storage Systems provide a good option for consumers to make the transition to prosumers, consumers and producers of electrical energy. This gives the customer greater flexibility in how they use and pay for their energy.

When combined with a Solar PV system, an EESS allows for greater grid independence and contributes to a carbon neutral future for the UK.

Technology and innovation within renewable systems is improving all the time and this will make their design and installation more accessible.

This is an exciting time in the renewables world and could create a great opportunity for electricians to get involved in designing, installing and commissioning Electrical Energy Storage Systems.

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