Industry is responsible for about 30% of CO2 emissions in Germany. Due to the successively increasing CO2 tax, the electricity price in heavy industry has almost doubled since the beginning of 2021, which endangers the business models of individual companies and reduces their competitiveness in a global comparison.
In order to be able to do business competitively despite rising electricity prices, the energy supply must be made renewable and energy efficiency must be increased in order to relatively reduce electricity consumption. In this way, greenhouse gas emissions and the consumer’s reference value are reduced and costs are lowered. The simplest way to reduce the reference variable from the grid is to integrate battery storage to smooth peak loads, minimise conversion losses and save grid connection costs. AXSOL Energy Container Solutions offer a scalable platform for building large-scale battery storage systems. These are freely configurable in terms of capacity, output power and input channels. Due to the independence from the power source, additional renewable generators can be integrated, further reducing consumption and CO2 emissions.
Currently, we almost exclusively use alternating current (AC) for work, power or heat. Alternating current can be transformed more easily to high voltages and is therefore subject to fewer losses during long transport routes. The disadvantage of alternating current in application, however, is the lower degree of efficiency compared to direct current. For short transport distances – such as the power grid of a production hall or an industrial site – the transport losses due to DC voltage are negligible. These are more than compensated by the higher efficiency level between secondary and useful energy. A switch to direct current industry (DC Industry) would reduce 30% of the electricity demand and thus reduce the companies’ procurement costs.
WHAT IS DC INDUSTRY?
The fundamental difference between DC and AC industry is the design of the factory and building internal power grids. Currently, a site is supplied by the public AC power grid and the current fed in before each machine or robot is directed by frequency converters to the variable voltage and frequency required for the respective electric motor. In the process, part of the energy efficiency is lost in the form of heat due to the double conversion from AC to DC and back to AC. Considered individually for each application, these losses are negligible, but in large and electricity-intensive industrial locations, the loss accumulates and causes enormous inefficiencies. Switching to DC industry can save relatively on electricity.
With DC Industry, a central inverter feeds the site’s power grid directly with direct current and all applications are supplied by a central DC bus. This avoids significant efficiency losses and realises other smart benefits. By reducing the number of copper conductors from three to two in the power lines, up to 40% copper can be saved, which reduces the overall cost of the lines. Currently, it is being evaluated whether the existing AC lines in locations, but also in the power grid, can be used to build a DC grid.
ENORMOUS INCREASE IN EFFICIENCY THROUGH DC-INDUSTRY
Efficiency losses in AC grids are largely due to heat losses. These are caused by the double conversion for controlling frequency and voltage and thus the variable speed in electric motors. In a DC network, all loads are supplied directly from the DC bus, which in most cases requires no conversion. Most devices and machines are operated with direct current. For this, only the voltage of the DC bus has to be adjusted to that of the consumer. Due to the space and material savings on the power electronics, these can be installed directly closer to or in the consumer and fewer frequency converters are required.
Basically, robot arms, for example, are accelerated and decelerated. A direct current network now also allows the recovery of braking energy. This principle is known to most people as recuperation from electromobility. In AC grids, the braking energy cannot be reabsorbed into the grid and it dissipates into heat. In large production facilities, this additional heat leads to the need for additional air conditioning and an additional increase in electricity consumption. This problem does not arise in DC grids. The electricity recovered through braking energy is absorbed into the DC grid and can be directly consumed again by other consumers.
BATTERY STORAGE IN THE DC INDUSTRY
In order to further exploit efficiency potentials, battery storage systems can be integrated into the DC grid. Batteries basically only store direct current. Through a direct connection to the DC bus, recovered electricity can be stored and used to smooth peak loads. Especially in energy-intensive industries such as the steel industry, the chemical industry or in the case of frequent load peaks due to welding work, etc., costs can be avoided by avoiding peak loads. Depending on the system design, up to 80% of the grid connection power can be saved. In addition, battery storage systems can compensate for fluctuations in the grid in the event of irregular operation of plants and consumers without the power leaving the grid.
An additional benefit of battery storage for buffering in DC grids is the ability to easily integrate renewable generators. Most renewable generators are DC coupled and can accordingly be connected to the DC grid or battery storage without large conversion losses. In this way, the surplus generation on rest days can be used to reduce the reference quantity from the grid. The DC grid simplifies the direct exchange between producer and consumer.
In addition to the advantages for their own energy consumption and efficiency, the battery storage units can theoretically trade on the market if too much capacity is stored and release electricity into the AC grid. In this way, companies and businesses, just like private individuals, can act as prosumers on the market and actively participate in the energy transition. The prerequisite for this is a bi-directional inverter at the grid connection point of the site.
OWN CONSUMPTION OPTIMISATION, PEAK LOAD CAPPING AND GRID CONNECTION COST REDUCTION
Currently, it only makes sense to set up a site powered by direct current for new buildings or conversions at existing sites. For existing halls, plants and machines, on the other hand, optimising self-consumption by integrating a battery storage system and corresponding renewable generators is recommended as a first step.
The integration of renewable energies alone can result in energy savings of up to 15%. With the help of battery storage, the self-consumption of self-generated electricity can already be increased today. The high fluctuations of renewable generation plants due to external influences usually do not allow the total generated capacity to be used by the plant itself. It makes sense to install an appropriately scaled storage system as an extension, especially for existing plants that are or have been removed from the EEG subsidy. By flexibilising high generation loads at midday and in the afternoon, excess electricity generated in-house is made available in the evening or at night (peak shifting). Battery use can also contribute to relieving the internal and external grids and help to absorb the power peaks of the photovoltaic systems at midday.
If the battery storage system is appropriately designed, it can also serve as a UPS (uninterruptible power supply), especially in grid sections with greater failure probabilities and voltage fluctuations. The selection and installation of the storage system requires careful planning and preparation. High self-consumption with a good cost-benefit ratio is possible if the electricity storage capacity of the batteries is matched as closely as possible to the output of the photovoltaic system and the household electricity demand.
By integrating generator and storage units, an expensive expansion of the grid connection point can be dispensed with in the event of increasing electricity consumption or peak loads. The higher loads are served directly from the storage unit and the peak load is capped (peak shaving).
AXSOL ENERGY CONTAINER SOLUTIONS – A PLATFORM FROM THE STORAGE SOLUTION TO THE ENERGY SYSTEM
Die AXSOL Energy Container Solutions bieten alle benötigten Grundlagen, um die angesprochenen Anwendungsbeispiele für Industrie und Gewerbe abbilden zu können. Sie dienen als Plattform für reine Speicherlösungen zur Integration in bestehende Erzeugeranlagen bis hin zu kompletten Microgrids und Energiesystemen für einzelne Standorte. Jeder ECS ist an die Anforderungen der Anwendung und der Verbraucher anpassbar. Von der modularen Speicherkapazität, über die Anbindung verschiedener Erzeugerquellen gleichzeitig, bis hin zur modularen Leistungselektronik, kann jede Komponente individuell zusammengestellt werden.
Die Speicherlösungen der AXSOL GmbH basieren auf einem integrierten DC-Bus. So können alle Erzeuger und Speicher frei miteinander verbunden werden. Gesteuert wird alles über eine übergeordnete Steuerungssoftware, die den Energiefluss steuert und so den idealen und effizientesten Energiemix aus dem DC-Bus ausspeist.
Unsere ECS sind modular anpassbar und können im Verbund bis zu Großspeichern aufgebaut werden. Für kleinere Anforderungen kann unsere ausgewählte Technik in Outdoor-Gehäuse integriert werden, was die Flexibilität unserer Speicherlösungen erhöht und jedem Kunden die perfekte Lösung für dessen Anforderungen ermöglicht.
Image and information sources:
https://www.ipa.fraunhofer.de/de/referenzprojekte/DC-INDUSTRIE.html
https://experience.dc-industrie.zvei.org/01_acgrid.html
https://experience.dc-industrie.zvei.org/01_acgrid.html
