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Electricity transfer, distribution and storage

Introduction

Generating electricity is only the first step – it has to be transmitted to households, industry companies and other consumers. Check out the technological solutions making that happen!

Image Copyright: BMWi/Holger Vonderlind

© BMWi/Holger Vonderlind

The use of renewable energy is expanding steadily across the globe. If this is to be gradually integrated into the electricity system, the system is in need of radical restructuring. The challenge is to guarantee a reliable and efficient supply of electricity at all times. Power electronics and network control technology support an efficient overall system, minimise transmission losses and guarantee stable network operation.

A cutting-edge energy system must be capable of balancing out the variations that arise because of the fluctuating, decentralised generation of renewable electricity and of adapting to demand. This is possible thanks to system services, intelligent networks (smart grids), virtual power plants, flexible conventional power plants and various energy stores.

On the other hand, it is also important to make electricity consumption more flexible. With load management, companies only use electricity when it is very windy or sunny. To make renewable electricity available in other areas also, e.g. in heating supply or in transport, the various consumption sectors must be connected with one another in a strategic manner.

In this way, ever-increasing numbers of interfaces will be created between the grid, energy producers, consumers and energy stores. The use of digital technologies across the economy - “digitalisation” - therefore plays a crucial role.

In off-grid areas, micro-grids offer an economic alternative to expanding a central power grid. Based on renewable energy, they help minimise the costs of diesel generation and guarantee a round-the-clock supply of energy, for example.

German companies offer many products and services that enable efficient electricity management and are essential to the establishment of a modern electricity infrastructure.

Image Copyright: fotolia.com/thomaslerchphoto Enlarge

© fotolia.com/thomaslerchphoto

Power electronics

Power electronics are necessary in the power grid whenever the profile, amplitude or frequency of the voltage and the current intensity of current flows need to be adjusted, for example, when electricity is fed into the supply grid. The power electronics used here are converters. The converters convert the power in accordance with the technical connection rules with regard to the required frequency, voltage and phase position, for example, with direct current becoming alternating current.

Modern power electronics, such as those used in high-voltage direct-current transmission, can significantly reduce transmission losses during network operation. Current research and development is focusing on optimising costs, efficiency, service life, weight and volume as well as the system efficiency of power electronic components.

Application fields of power electronics

Power electronics play a key role in achieving a sustainable supply of power with a growing share of renewables, as these energy sources require a combination of AC and DC systems. While alternating current flows through most supply grids and domestic appliances are also powered by alternating current, direct current is generated or required during electricity generation. For this reason, an inverter nowadays acts as the standard interface between a photovoltaic system and the supply grid. However, in wind turbines, frequency converters are used to align the frequency of the variable-speed wind turbines with the grid frequency.

Modern power electronics, such as those used in high-voltage direct-current transmission, can significantly reduce transmission losses during network operation. Current

Network control technology

The term “network control technology” refers to the technologies used for data acquisition, transmission and evaluation and the monitoring, control and regulation of networks enabled by these technologies. It is used both in power grids and other supply networks such as heat, gas and water networks. In the past, network control technology was mainly implemented at the highest voltage level, since this is where the feed-in took place. Now, with the integration of multiple decentralised power generators in the grid and feed-in of these generators at low-voltage and medium-voltage levels, the application of network control technology has expanded to include these levels and is increasingly important in the field of feed-in management.

Power grid operators access system services in order to ensure a trouble-free and efficient power supply with the fewest possible supply interruptions and transmission losses. These include various measures designed to stabilise the frequency, voltage and load in the electricity grid when balancing demand and supply.

Digitalisation of the electricity infrastructure refers in particular to the development of smart grids. These smart grids enable better balancing of electricity generation with electricity consumption so that supply can be guaranteed at all times despite volatile sources.

The modern information and communication technology (ICT) incorporated in smart grids enables real-time acquisition and transmission of network states. These data can then be used for the precise connection and disconnection of loads and generators.

Digital technologies are also used in virtual power plants (VPPs).

Image Copyright: BMWi

Central control station of a Virtual power plant (VPP)

© BMWi

Virtual power plants (VPPs) are not power plants in the traditional sense, but a virtual network of multiple generating plants, loads or storage. While the individual plants can be in different locations, the electricity they generate is balanced across all plants before being bundled into the power grid.

VPPs can help make the power grid more flexible by, for example, consuming excess power by increasing demand and reducing production within the virtual power plant.

The operation of a virtual power plant requires a real-time monitoring system that allows producers to monitor their available power and operational readiness. If, for example, a virtual power plant comprises solar and wind power plants, weather data also needs to be considered within the monitoring system. The monitoring system determines how much power the VPP can feed into the power grid, since the amount of electricity that can be delivered by the plant varies depending on the weather.

Image Copyright: Franz Meyer/BINE Information Service

Lithium-ion storage batteries in standardised industrial racks

© Franz Meyer/BINE Information Service

For a sustainable energy supply with a high share of renewable energy and alternative fuels to become reality, energy storage is an essential part of the energy infrastructure. These storages can generally help to make the energy system more flexible, compensate for peaks in demand and supply, and also enable off-grid or mobile energy supplies. In the electricity sector, energy storages can also be used for voltage and frequency control.

Power storage systems can generally be broken down into electrical, electromagnetic, electrochemical or mechanical storage systems. Within these various categories, the individual power storage systems vary in terms of their injection and withdrawal rate, storage capacity, depth of discharge, service life, self-discharge, reaction times and costs. With regard to their fields of application, power storage systems can be either short-term or long-term.

For more information on short-term and long-term power storage systems, please consult the brochure Energy solutions - made in Germany.

Image copyright: SMA Solar Technologies AG

© SMA Solar Technologies AG

Mini- and micro-grids

Micro-grid systems or mini-grids are self-sufficient power grids that cannot be connected to larger interconnected grids, or only connected with difficulty, due to geographical conditions or cost-benefit considerations. In the case of cost-benefit considerations, micro-grid systems are used in particular for rural, remote areas with low electricity consumption or in countries with weak infrastructure in general.

The size of these micro-grid systems varies greatly: from the self-sufficient power supply of a single consumer, such as a remote hotel or remote mine, to the power supply of an entire village or island state.

Reduce costs of diesel with hybrid solutions

Traditionally, diesel generators have been a core element of the power supply within a micro-grid system. They provide a flexible, demand-driven supply of electric power. However, diesel combustion is also associated with environmental and health downsides such as exhaust gases and noise, as well as high fuel costs and a dependence on energy imports. An environmentally friendly, cost-effective and reliable alternative is to substitute or supplement diesel generators with renewable energy systems in conjunction with storage technologies. Photovoltaic systems, small wind power plants and hydroelectric power plants used together with battery storage systems offer good potential for application in micro-grid systems.

Hybrid systems, in particular, are widely used internationally. These include one or more diesel generators which are used in addition to renewable energy systems for emergency power supply. In general, several generating units are required within a micro-grid system.

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