In Knowledge Section

Industry is responsible for around 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 global comparison.

To be able to operate competitively despite rising electricity prices, the energy supply must be made renewable and energy efficiency must be increased to relatively reduce electricity consumption. This will reduce greenhouse gas emissions and reference size at the consumer and reduce costs. The simplest way to reduce the reference variable from the grid is to integrate a battery storage system to smooth peak loads, minimize 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 capacity, output power and input channels. By being independent 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 more easily transformed to high voltages and is therefore subject to fewer losses over long transport distances. The disadvantage of alternating current in applications, 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 purchase costs of the companies.

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, some 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 power-intensive industrial sites, the loss accumulates and creates enormous inefficiencies. Relative electricity savings can be made by switching to DC industries.

Conventional AC grid architecture

In DC Industry, a central inverter directly feeds the site’s power grid with DC power and all applications are powered by a central DC bus. This eliminates significant efficiency losses and realizes other smart benefits. Reducing the number of copper conductors from three to two in the power lines can save up to 40% copper, which lowers the overall cost of the lines. Currently, it is being evaluated whether it is possible to use the existing AC lines in locations, as well as in the power grid, to build a DC network.

Industrial smart DC grid architecture

ENROME EFFICIENCY INCREASE THROUGH DC-INDUSTRY

Efficiency losses in AC networks 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 powered directly from the DC bus, which in most cases requires no conversion. Most devices and machines are operated with DC current. For this, only the voltage must be adjusted the DC bus to that of the consumer. Due to the space and material savings on the power electronics, it can be installed closer to or in the consumer directly and fewer frequency converters are needed.

Basically, robot arms, for example, are accelerated and decelerated. A DC network now additionally allows the recovery of braking energy. This principle is known to most 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. In DC networks, this problem does not arise. The electricity recovered through braking energy is absorbed into the DC grid and can be consumed again directly by other consumers.

BATTERY STORAGE IN DC-INDUSTRY

To additionally 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. Particularly in energy-intensive industries such as the steel industry, the chemical industry or in the case of frequent load peaks due to welding work or similar, 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 accordingly can be connected to the DC grid or battery storage without large conversion losses. Thus, the excess generation on off days can be used to mitigate the reference from the grid. The DC grid simplifies the direct exchange between the generator and the consumer.

In addition to the benefits to their own energy consumption and machine efficiency, battery storage systems can theoretically trade on the market when there is too much stored capacity and release power to 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 site’s grid connection point.

OWN CONSUMPTION OPTIMIZATION, PEAK LOAD CAPPING AND GRID CONNECTION COST REDUCTION

Currently, it only makes sense to set up a site powered by direct current in the case of new buildings or conversions at existing sites. For existing halls, plants, and machines, on the other hand, an optimization of self-consumption through the integration of a battery storage system and corresponding renewable generators is recommended as a first step. The integration of renewable energy alone can result in energy savings of up to 15%. Battery storage can already be used to increase self-consumption of self-generated electricity. The high fluctuations of renewable generation plants due to external influences usually do not allow to use the total generated capacity by oneself. Especially for existing plants that are or have been removed from the EEG subsidy, it makes sense to install an appropriately scaled storage system as an extension. By flexibilizing high generation loads in the midday and afternoon, excess power generated in-house is made available in the evening or at night (peak shifting). Battery use can also contribute to relieving the load on internal and external grids and help to absorb the power peaks of photovoltaic systems at midday.

If designed appropriately, battery storage can additionally 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 – ONE PLATFORM FROM THE STORAGE SOLUTION TO THE ENERGY SYSTEM

The AXSOL Energy Container Solutions offer all necessary basics to be able to map the mentioned application examples for industry and commerce. They serve as a platform for pure storage solutions for integration into existing generation plants up to complete microgrids and energy systems for individual sites. Each ECS is customizable to meet application and consumer requirements. From the modular storage capacity to the connection of different generation sources simultaneously, to the modular power electronics, each component can be individually assembled.

AXSOL GmbH’s storage solutions are based on an integrated DC bus. This means that all generators and storage units can be freely interconnected. Everything is controlled by a higher-level control software, which manages the energy flow and thus feeds out the ideal and most efficient energy mix from the DC bus.

Our ECS are modularly adaptable and can be built up in a network to large-scale storage systems. For smaller requirements, our selected technology can be integrated into outdoor enclosures, increasing the flexibility of our storage solutions, and enabling each customer to find the perfect solution for their requirements.

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