The Perfect Symbiosis – E-cars as power storage devices at home

The idea is simple and forward-looking: Why not use parked electric cars as a storage facility for excess green electricity and thus compensate for fluctuations in the power grid? Efficient storage technologies for solar and wind energy are still rare. However, with the continuously growing number of e-vehicles, a large number of batteries are coming into circulation– a great potential for energy management in the home, for example, if this storage capacity can be used intelligently. With bidirectional charging technology, electricity can flow in both directions between home and car. IAV is developing the communications software relevant to this– thus creating an important lever for the success of the change in energy policy.

When switching to renewable energy sources, a key objective is to ensure a balance between energy demand and availability at all times. Intelligent storage systems and networks are needed to effectively distribute or store solar or wind energy from peak periods. Battery storage systems for electric vehicles can contribute towards the temporary supply of electricity to homes, especially at peak loads when electricity from the grid is expensive, during bottlenecks such as when winds are calm or at night when the home’s own photovoltaic system is not generating electricity. Charging takes place either during the day via a PV system or from the grid at favorable electricity prices, for example by using wind power at night.

With the introduction of e-mobility, vehicles with battery capacities of more than 25 kWh on average are becoming increasingly available on the market. According to the German Federal Association of Energy and Water Industries (BDEW), the average consumption of a 3-person household in Germany in 2019 was about 3,500 kWh per year, i.e. about 10 kWh per day.

In this way, e-cars can not only be used for environmentally friendly transportation. By using the storage capacity provided by the high-voltage batteries, e-vehicles become a central component of the so-called “smart home system.” In this way, they stabilize not only the energy management in the connected private home, but also the energy grids as a whole. Intelligent interconnectivity is necessary for this to work in practice. Most smart home concepts are based on the Internet of Things, whereby electrical devices such as the PV system, heating and consumers are integrated into the “Home Energy Management System” (HEMS) by means of intelligent control. The aim of the system is to use an analysis of the energy flows induced by the consumer to store the solar power generated at home as efficiently as possible and to use it for personal consumption via an intelligent distribution system.

Battery electric vehicles can also be integrated into the HEMS, the key technology here being bidirectional charging: This not only enables electric cars to draw power from the grid at times when general electricity demand is lower, but also to feed it back into the grid via a charging point during phases of particularly high demand for electrical energy. Intelligent software enables the automated control of charging and discharging processes. The holistic integration of e-vehicles into the charging infrastructure and energy system is currently being researched in various projects, including by IAV, and the legal and regulatory framework is being evaluated.

As part of the “Bidirectional Charging Management – BDL” research project, companies and institutions from business and science are developing technology and system solutions in the field of energy and charging management at the Forschungsstelle für Energiewirtschaft e. V. in Munich and analyzing possible use cases. As a technology leader in future-relevant drive systems, IAV has a deep insight into the development of fully and partially electric vehicles and supports the joint project, which is scheduled to run for three years until April 2022 and is funded by the German government.

As an engineering specialist, IAV develops and tests the communication protocols between the electric car, charging infrastructure and power grid, thus creating the conditions for controlled charging. The individual needs of the consumers and the availability of electrical energy are coordinated with each other with the help of intelligent tariff offers and appropriate scheduling of the charging processes. Numerous current solutions for HEMS work with a proprietary communication system into which devices from other manufacturers often cannot be integrated. IAV develops communication modules for all international standards, thus creating the basis for competitive and future-proof solutions for so-called “smart charging.”

«In theory, e-vehicles could be connected not only to the HEMS but also to the public power grid and thus contribute to general supply security.»

Ursel Willrett — Senior Technical Consultant for infrastructure systems in the field of e-mobility at IAV

Regulatory changes must therefore be made in parallel with technical implementation.
“E-cars have great potential to cover the two central use cases – mobility and stabilizing local load management in the home,” says Willrett. “They are predestined to secure the electricity grid and provide meaningful support for the change in energy policy.”

The article was published in automotion 03/2020, the automotive engineering magazine of IAV. Here you can order the automotion free of charge.

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