Direct current grid into injection molding machine

 

 

Photovoltaic systems are no longer a rarity on the roofs of industrial companies. High energy prices, purchase restrictions and unstable grids in some countries and regions make it lucrative to be somewhat independent of the electricity market. Especially as the use of renewable energies also contributes to sustainability goals. Yet, there is still plenty of untapped potential for using renewable energy efficiently. Together with its partner inesco AG, WITTMANN is helping injection molding companies to tap into this potential. The key is to use direct current as a direct energy source.

 

It is 2022 and we are at the K trade fair in Germany. What visitors to the WITTMANN booth in Hall 12 are experiencing is bordering on a revolution. An injection molding production cell is making electronic parts from a flame-retardant polyamide and boasts eye-catching solar panels – this is a conceptual study presented by  WITTMANN in collaboration with a customer. Supported by the appropriate infrastructure, the injection molding machine and the robot are being powered directly by solar energy via a DC link. The two partner companies have jointly filed a patent for this development.

 

Fast-forward a year and, at Fakuma 2023, WITTMANN is again presenting a production cell powered directly by direct current (DC) obtained from solar energy. This is no longer a conceptual study, but a production-ready solution that includes solar power storage. WITTMANN has joined forces with another partner company with the aim of industrializing and marketing DC injection molding technology. The partner company, which has been operating under the name inesco AG since autumn 2024, has been working for more than ten years on the question of how renewable energy can be used sensibly and stored efficiently on a large scale.

 

This presentation at Fakuma 2023 sets the ball rolling. The injection molding industry is now very interested in the direct use of solar power via DC grids. As a result, WITTMANN and inesco are currently evaluating and processing a number of inquiries on specific projects. The first DC-capable injection molding machines have been sold.

 

WITTMANN has pioneered DC technology in the injection molding industry. It is the first supplier to offer injection molding companies machines and production cells that can use solar energy sourced directly from a DC grid.

 

 

Focus on security of supply

 

Like other types of renewable energy, such as that generated in wind farms and biogas plants, solar power is direct current (DC). However, national power grids use alternating current (AC). Before alternative types of power can be used, they need to be converted into AC. DC is converted into AC so that it can be transported and distributed – and in some cases the AC is transformed back into DC at the consumer, many of which work with DC. The converters employed are primarily frequency inverters used for infinitely-variable control over the speed of electric motors, which account for 70 % of power consumption in industrial environments. Other examples of DC consumers are computers, televisions, LED lamps and electric vehicles.

 

In industrial production as well as in everyday life, DC is constantly being converted into AC and vice versa. With each transformation, there is a loss of energy, in the order of 2 to 4 %. This lowers the energy efficiency of the applications. It was this consideration that prompted the idea of making direct current directly usable via decentralized DC networks, called DC microgrids, without converting it first into alternating current.

 

Aside from energy savings and the associated smaller carbon footprint, there are other motivations for looking into the possibilities afforded by DC technology. First and foremost is security of supply. Rising electricity consumption due, among other things, to the proliferation of electric vehicles and heat pumps, as well as advancing electrification of industrial production are placing ever-greater loads on existing power grids, which are often not expanding in line with developments. This situation is being exacerbated by the rapid rise in feed-in solar power, which is putting additional strain on the grids and making them more unstable. Experts say that even countries which have very good electricity supplies, such as Germany and Austria, could increasingly experience grid failures and restrictions on consumption in the future. Direct-current grids could therefore evolve into an important building block for ensuring security of supply and climate neutrality. One argument supporting this is that direct current is easy to store in batteries, providing an efficient way to cover expensive power peaks.

 

Another is greater resource efficiency when it comes to the expansion of power grids. Thanks to modern technology, three-wire DC grids require substantially less copper conductor material than five-wire AC grids, as well as fewer electronic parts: There are no rectifiers at all in the equipment.

 

 

Solar Storage Batteries Keep Output Constant

 

What does the direct use of solar power in injection molding operations look like in practice? WITTMANN's solution is based on three components: A WITTMANN injection molding machine or production cell modified to use DC technology, inesco’s DC network “DConnect”, and a sodistore max storage battery based on natrium salt. The salt battery was developed specifically for sustainable use by industrial companies.

 

The DConnect forms the backbone of the DC power supply during operation. It is a self-regulating DC microgrid into which DC producers and DC consumers can be easily integrated and interconnected. DConnect works without an external controller and does not require an internet connection. This means that the system is securely protected against cybercrime.

 

The task of the sodistore max storage battery is to ensure a constant voltage, even when different consumers are connected and the supplied power fluctuates. Inesco’s solar power storage batteries come in various sizes and storage capacities of up to 500 kWh. These salt batteries achieve the same energy density and the same volume as conventional lithium-ion batteries, but can be charged and discharged at much higher rates. The sodium-ion battery is significantly more environmentally friendly and also safer than conventional lithium batteries. It does not require any hazardous materials and can be fully recycled at the end of its service life. In addition, it does not require any air conditioning and can be operated both indoors at higher temperatures (up to 55 degrees) and outdoors at very low temperatures (-20 degrees).

 

For integration into the DConnect Microgrid, WITTMANN is initially offering its EcoPower series of injection molding machines and the DC models of its WX linear robots. Further machine models and peripheral devices for integration into DC grids are in ongoing development. At its Competence Days Event in summer 2024, for instance, WITTMANN unveiled DC temperature control devices.

 

In order to operate these safely, the connection technology also had to be adapted. Specifically for this application, the HARTING Technology Group developed a prototype for an electrically lockable connector. During operation, this protects both the system and the employees from unintentional pulling and the associated electric arcs. The integrated signal indicator shows at all times whether voltage is present at the connector or not.

 

The all-electric EcoPower machines, which are equipped with highly dynamic servomotors for driving the main movements, are ideal for use in a DC grid. They feature a patented kinetic energy recovery system (KERS) that converts kinetic energy into electrical energy during braking. In a conventional AC set-up, this recovered energy can only be used inside the machine, e.g. to heat the barrel. When integrated into a DC grid, however, it can also be fed back into the DC grid for use by other consumers or for storage within the battery. The DC model of the WITTMANN robot, which is supplied directly via the DC link of the EcoPower machine, also feeds excess energy back into the DC link when braking.

 

The production cell presented at the latest trade shows comprised an EcoPower B8X 180/750+ injection molding machine with an installed salt storage capacity of 45 kWh. It operated non-stop over the entire eight-hour trade-fair day without the need to switch to the AC grid at any time.

 

 

 

 

 

 

 

Cutting Energy Consumption by up to 15 Percent

 

Initial practical tests show that the reduction in conversion losses alone shaves up to 15 % off the power demand of a production cell supplied direct with DC. Any decision-making about whether or not to create a DC grid should not focus on whether one technology is superior to the other. Instead, DC grids will be set up alongside AC grids in more and more areas. For example, if the battery storage becomes exhausted at some stage on an overcast day with little sunlight, the system developed jointly by WITTMANN and inesco will automatically switch to AC. The switch will not be noticeable in production; the machine will be fed with a continuous, steady supply of power.

 

In the long term, too, it is likely that AC and DC grids will exist in parallel. This will allow decisions to be made on a case-by-case basis as to which power supply offers the greatest overall efficiency.

 

 

Technical Challenges Solved

 

How quickly will DC become established in the injection molding industry? There is no easy answer to this question, as many factors are involved. The first task is to publicize the possibilities and advantages of DC technology more widely, to find reference applications and to share experiences more intensively across industries.

 

The technical challenges, at any rate, have been solved. Industrial-grade solutions, components and protection mechanisms are available. However, what is needed more than that is a change of awareness. Factory planners, architects, electricians and energy consultants need to be made aware of DC technology, so that it can be considered from the outset when new investments are being made.

 

Politicians and industry associations also need to play their part. Having recognized the key importance of renewable energies for the energy transition, the German government launched its first joint research project back in 2016. This led to the emergence of the Open DC Alliance (ODCA) working group within the German Electrical and Electronic Manufacturers' Association (ZVEI) in 2022. Many well-known global companies have joined the ODCA, including inesco.

 

 

ROI Possible in Just a Few Seconds

Although existing photovoltaic systems can be converted to direct DC power, replacing all inverters with DC-DC converters would be a massive undertaking. The fastest return on investment when setting up and operating a DC microgrid is made at the time a new DC-coupled photovoltaic system is being installed. That way, power and load management can be optimally designed from the outset. It is also advisable for the DC network to integrate not only the injection molding production cells, but also the peripherals and parts of the infrastructure, such as the compressed air supply, lighting and air conditioning.

What most affects the ROI, though, is the stability of the power supply on location. Where power supplies are frequently interrupted or the amount of supplied power is restricted, a DC microgrid with DC-coupled battery storage pays for itself particularly quickly. In the case of very critical components, the payback on a DC power supply can be made in a matter of seconds when a blackout occurs.