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The connection between smart meters and self-consumption

As Africa increases its adoption of electric vehicles (EVs), e-mobility and smart meters – that provide various benefits to end-users, retailers and network operators – what models from the European Union’s electricity market can African utilities take into consideration?

The article appeared in ESI Africa Issue 1-2021 on pages 62-65.
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Smart metering solutions are designed to provide end-users with information on a real-time basis about their domestic energy consumption. This information is intended to give consumers greater clarity on their consumption behaviour and help electricity suppliers with system monitoring and customer billing.

Considering the new changes in energy consumption by adopting smart charging for electric vehicles, monitoring of consumption behaviour must also adapt.

This article summarises advances from a paper that proposes a solution based on the combination of smart metering and smart charging that may help local European energy communities increase self-consumption.

The 2018/2001/EU renewable energy directive (RED II), as part of the European Clean Energy Package, underlined the strategic role of energy communities in helping the EU transition to sustainable and renewable energy. In this context, the paper proposes a feasible solution to improve the self-consumption of a local energy community.

Smart metering benefits

Analysts estimate that nearly 225 million smart electricity meters will be installed in the EU by 2024, thanks to government investments of about €47 billion. The benefits of smart metering are based on the flourishing prospects for the smart meter market. Taking into account the common European standards for the internal market of electricity and consumer protection, smart meters may provide a wide variety of benefits to a wide variety of actors, including end-users, retailers and network operators.

For example, smart metering deeply helps end-users to understand the link between their habitual use of energy and the energy consumption of each specific appliance. This link is a key to enable energy efficiency services such as peak shaving and load shifting, adopt time-of-use tariffs, and increase self-consumption and savings on bills.

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Solutions for utilities

In addition, smart metering benefits retailers because it allows elimination of the hated and expensive adjustment bills, especially if in combination with blockchain. Simultaneously, retailers may offer new tariffs, perfectly customised for how the customer wishes, and apply discounts for weekly payments in place of typical bimonthly payments, and apply discounts for prepaid consumption.

Lastly, smart metering also benefits grid operators. It supports the observability and control of the smart grid, monitoring power quality and generation from renewable sources, solving multiple daily checks such as identifying the phase of end-users’ connection to the low-voltage network. Grid operators can better manage the network and plan the investments while reducing operating and maintenance costs.

Smart charging variations Smart charging (V1G) and vehicle-to-grid (V2G) are two feasible technologies for integrating EVs and the electric grid smartly. V1G allows power flow control from the grid to the car, adjusting the time – start and end of the charge – and the amperes. V2G goes beyond V1G as it also allows reversal of the power flow. Therefore the EV is a programmable load and a programmable generator as well. V2G beats V1G since by implementing V2G, the achievable advantages are potentially greater than V1G. On the other hand, implementing V2G requires significant investments greater than V1G; these investments are because V1G and V2G impact battery-charge infrastructure in a very different way.

Figure 1: Off-board and on-board chargers for an EV

In general, an EV can be charged quickly at a charging station or slowly at home, as illustrated in Figure 1; in the first case, the batteries are connected to the onboard charger of the charging station, whereas in the second case, they are connected to the onboard charger. In general, both the onboard and the onboard chargers consist of a cascade of two electronic power converters, one AC/ DC and one DC/DC (see labels 1, 4 and 2, 3 in Figure 1, respectively) with high power density and high efficiency.

These converters are relatively cheap and structurally lean in the V1G case because they are unidirectional, although they are more expensive and structurally more sophisticated in V2G. After all, they are bidirectional. Further, firmware on microprocessors, communication methods, number of sensors, and converters’ certifications appreciably differ from V1G to V2G. For example, the off-board charger typically converts the phase-to-phase AC voltage of grid cables in a DC voltage, and the vehicle batteries are DC coupled to this charger directly. Therefore, a V1G off-board charger may consist of a conventional diode rectifier in a cascade with a DC/ DC buck/boost converter for power factor correction (PFC).

By contrast, the corresponding V2G charger may consist of a three-phase bidirectional AC/DC converter mounted with six insulated-gate bipolar transistors (IGBTs). If the battery voltage is lower than the voltage at the rectifier’s terminals, then a single or interleaved bidirectional buck/boost DC/DC converter is further placed in the cascade. Similar considerations apply to the onboard charger: it typically converts the phase-to-neutral AC voltage of the residential cable in a DC voltage. In V1G, there is a cascade of a diode rectifier and a DC/DC buck converter with power factor correction. In V2G, there are a full-bridge AC/ DC boost converter and a half-bridge bidirectional DC/DC converter or a bridgeless boost-type AC/AC converter in cascade to an interleaved DC/DC buck-type converter.

Given the different impact of V1G and V2G on the battery charging infrastructure and economics, today’s investments are mainly aimed at supporting the massive deployment of EVs and ensuring the extensive presence of charging points with one-way chargers. Therefore, due to technical potentials and promising practices of smart charging, V1G seems to be ahead in the competition with V2G. It is preparing to become the most popular technology for coordinating hundreds of EVs charging.

Coordinating the charging of many EVs via V1G can also reduce the total costs of ownership. For a single user, demand charge management via V1G can synchronise the charging to the over-generation of the roof-mounted PV plant so to maximise self-consumption; similarly, V1G can apply a time-of-use tariff to reduce the electricity bill. Similarly, demand charge management via V1G can coordinate charging EVs in a car park or a narrow geographical border, applying machine learning methods. These methods consider the users’ preferences or the batteries’ state of health, thus limiting the demand during peak hours and, in general, providing valuable grid services to network operators.

Figure 2: The energy community
Figure 2b: The community members’ equipment

Local energy community: smart metering and charging framework

Figure 2 illustrates a local energy community composed of four families; their residential homes are connected to the electricity distribution grid, downstream a unique medium-low voltage substation. Each user has a solar PV rooftop installation or an EV. Figure 2b illustrates one user or prosumer with detail. The smart meter is installed just behind the meter and measures the power flow with high temporal resolution. It also measures the power flow of the PV generator and to the EV.

For the latter, a smart charging service is available. Therefore, it is possible to start/stop the charging and adjust the power for small or large steps in general. The smart charging service is provided by an aggregator that supervises the power flows at meters enabled by continuous communication with the smart meters.

Figure 3: Communication between aggregator and smart meters

The communication architecture

The data flow scheme for communication between the aggregator and the smart meters is illustrated in Figure 3: the aggregator is at the top of the diagram. The smart meters are at the bottom, and a database is placed between them. This diagram shows an important assumption, i.e., the aggregator and smart meters do not communicate directly with each other; the database acts as an interface between them.

This assumption inevitably influences the operation of both the aggregator and the smart meters, as illustrated. Each smart meter measures voltages and currents, processes the measurements, performs calculations and then saves the numerical results both on a local memory and on the database.

Figure 4: Sending a command, receiving an answer: from aggregator to smart meters

Similarly, the aggregator retrieves the numerical results held by the smart meters’ database, processes these results, performs calculations and saves the Since the aggregator also implements decision-making processes, some new results are commands that the aggregator must send to the smart meters and that the smart meters must execute. Since direct communication between the aggregator and smart meters is not allowed, a cyclic read/ write procedure such as the one illustrated in Figure 4 is implemented.

The figure illustrates how to send a command for the i-th smart meter and how to receive its answer. The aggregator sends the command setting the value of a given variable, specific for the i-th smart meter, namely Asked_for_a_Service (ASi); this variable belongs to the database, and the i-th smart meter frequently reads this variable.

Figure 5: The aggregator, the smart meter and the EV supply equipment
Figure 5: The aggregator, the smart meter and the EV supply equipment
Figure 6: Connection of smart meter at a user’s home
Figure 6: Connection of smart meter at a user’s home

The smart meter enabling smart charging

Figure 5 and 6 illustrate how the smart meter enables smart charging. In Figure 5, the aggregator permanently communicates with all smart meters. Therefore it is aware of power flows at users’ meters; based on this information, the aggregator manages the smart charging service, establishing which vehicles can be recharged. The smart meter measures the meter’s power flow, but it also enables the smart charging service as it receives and implements the decisions of the aggregator. In this sense, the smart meter communicates to EV supply equipment (EVSE) so that batteries’ charging begins.

Figure 6 illustrates the connecting schema for the smart meter; rapid installations and minimal changes to the existing wiring are the basis of this schema. The smart meter is installed in the home switchboard, and it calculates the power flow measuring the voltage and the current at the switchboard input. The smart meter also measures the current of two main distribution lines: the line that supplies the EVSE and the line that connects the solar PV system to the grid.

– your smart metering partner –
Solutions for utilities

In closing, the paper presents a combination of smart metering and smart charging to help local energy communities increase self-consumption and achieve economic benefits. Without the proposed solution, i.e. in the absence of the combination of smart metering and smart charging, the community self-consumes only a fifth of its generation; the community exports the remaining four-fifths to the utility grid and imports it again during the last hours of the day. By adopting the proposed solution, the daily synchronous self-consumption increases by 45%. ESI

Barone, Giuseppe; Brusco, Giovanni; Menniti, Daniele; Pinnarelli, Anna; Polizzi, Gaetano; Sorrentino, Nicola; Vizza, Pasquale; Burgio, Alessandro. 2020. “How Smart Metering and Smart Charging may Help a Local Energy Community in Collective Self-Consumption in Presence of Electric Vehicles” Energies 13, no. 16: 4163. The article above is based on the research paper published under Creative Commons. View the full paper online: https://www.mdpi.com/19961073/13/16/4163

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