Plug-In Battery Storage Systems: Alternating Current Without Inverter

Expert Interviews – Monday, July 5 , 2021

The Sax Power home storage tank converts direct current into alternating voltage without an inverter. This is made possible by cascaded bridge circuits between the battery cells. Managing Director, Dipl.-Ing. Lei Shen, explains the benefits of what the company call their unique balancing method and how SAX Power wants to challenge Tesla as an equal rival.

You are proclaiming a “revolution in the battery market” and want to show Tesla that you have the better storage system. That’s confident and ambitious. What does your “Sax battery” do differently and why do you think is it better suited to electric cars than Tesla batteries?

Our battery brings many benefits to the table that are particularly relevant to the e-mobility sector. First of all, our battery is smaller and lighter than in conventional systems. And weight and space play a huge role when it comes to electric cars. Safety is also extremely important: The electronic control unit completely and instantly switches off our battery should something go wrong, for example in an accident. Therefore, voltage is very low, eliminating the risk of high heat generation. Our lithium iron phosphate cells are also much safer and more durable than NMC cells. For those in the workshop, it is a huge relief when the voltage level falls below the safety voltage as soon as it has been switched off. Staff can safely touch any area – something which is a huge problem with conventional systems. Finally, our technology is up to 50% more long lasting than current batteries thanks to our unique balancing method. Our batteries require half the charging time, without the need for any additional equipment.

Tell us more about the balancing method, how does that work? And how can your storage system convert direct current into alternating voltage without an inverter?

The cornerstone of our technology is that the cells are interconnected, either individually or grouped, forming what is called a cascaded H-bridge circuit. So not in a row where they are just one behind the other. This, in combination with the digital control system, enables rotating charge balancing in which the cells with more capacity are used for longer, and those with less capacity for a shorter period of time. This way we can use each cell to its full capacity, maximizing performance to a much higher level than with a conventional system. In order to achieve an alternating voltage from the DC battery, the electronics add the voltages of the individual cells in a way that the desired sine wave is achieved. When the inverter is not needed, it saves not only costs but also on space and weight, and the digital process is far more efficient. We achieve a 99% efficiency rate for the conversion to alternating current. Hardly any conventional IGBT inverters achieve such an efficiency rating.

You target the e-mobility sector as your main market. However, the first product you launched was the solar home storage tank. With that product you were nominated as an ees AWARD finalist. Why did you do that?

Bringing a new piece of technology onto the automotive industry market is extremely complex and entails huge costs. We simply couldn’t afford that investment as a start-up business. Therefore, we’re starting by laying foundations for the business through the production of solar storage systems. There’s a high demand for it and with it we can show that our technology works. We can also gain experience and grow our business.

What are the advantages of your batteries in combination with a PV system for residential buildings?

Since no inverter is required, it just consists of a compact battery model which is easy to install. It is up to 40% smaller and lighter and fits in any corner so you don’t have to cram even more into your cellar. It even works as a simple plug-in solution with a secured plug, meaning you don’t have to go to the hassle of redoing the plasterwork on the walls. The installation work for electricians is reduced by up to 80%. As with other systems, there is an app to control the system, an uninterrupted power supply system (UPS) in case of a power cut, and the possibility to connect it to a wall box for electric cars. Our battery is compatible with all PV systems.

Your storage system can be increased from 5.2 to 15.6 kilowatt hours of storage capacity. Can even more storage capacity be added?

Our modular battery systems can be extended to reach any capacity and performance level. In the near future, we will develop a battery with the same performance and double the capacity for the US market. There is already high demand for this. A new mega storage system with 200 ampere is also in progress. Product development will start in the fall.

How did you end up with the company Ms. Shen?

I already worked for SAX and was involved in the development of the new technology. In the beginning, we didn’t expect there to be so much potential. Then in 2019, we fell under the radar of an overseas ship building company. They studied our plans thoroughly and came to the conclusion that we had a groundbreaking idea. For that reason, we had research institutes in Germany assess our technology. Their feedback was also very positive. We already had requests to completely sell the technology abroad. But within our SAX team, we decided that we wanted to produce a market ready product with our own hands.

You secured funding from the region of Baden-Württemberg. The crane manufacturer Liebherr and the bank Sparkasse Biberach are also financially involved. Not long ago, the Venture Capital specialists Walden International also got on board. How does a Californian investor become aware of a young start-up from Ulm?

We knew that Walden only invests in innovative technologies with huge potential. For example, they are involved with DJI, the world market leader for drones and have already helped 116 companies to get an initial public offering. We got in touch with Walden and for months they scrutinized us within an inch of our lives, both on the technical and business side of things. Only then, when they were convinced we were worth investing in, did they get involved.

At the moment, the first Sax Home storage tanks with private PV installations are being tested in Germany. From 2022 onwards, it is to be available in other EU countries, the US, Brazil and South Africa. How important is the German sales market for your company?

We have had requests for our solar powered storage tank from different countries, but first we want to build good foundations in Germany. We also have to bear in mind that every country has different technical and certification requirements and that is something we can only afford to do one step at a time. The US is of course an important market and Walden would also like to see us operate there. But entering that market is very expensive and risky, many things are easier within the EU. ees will raise the profile of our company and I’m sure that will help us gain new contacts in different markets more quickly.

In a press release you mentioned your multi-cultural team from a multitude of different walks of life. For example, the team at Sax Power includes a retired construction manager of a large industry corporation, university graduates, an international sales specialist, a software engineer who came to Germany as a refugee, and you have Chinese roots and came to Germany to study in 1988. So that really is a melting pot of different cultures and ages. How does that work and what can you learn from one another?

We respect each and every team member, regardless of where they come from and which position they work in. Everyone is allowed to express their opinion. Each one of us brings not only our own knowledge to the table, but also a different background and different way of thinking. If you stay open-minded, there’s always something you can learn from your fellow teammates, and it always ends up bringing positive results. Our team is very cheery and dynamic, we only take on the best. We grow our team gradually so that new members can be well integrated. The atmosphere in the company is very important. Resources can be best used via a controlled growth and structured organization.

What do you expect from your participation at ees Europe?

We are really excited about the conversations we will have there and to hear feedback from industry professionals. We want to get the best possible insight into customer requirements – that’s where the exhibition is of huge value to us. We are also certain that the guests, as industry experts, will recognize the innovativeness of our development and will be interested in it. We are really looking forward to the exhibition! This is our first international presentation and we are going to present a new technology that has never before been used in network-ready solar storage systems.

Why did you submit an entry for the ess AWARD?

When you achieve such a big breakthrough on the scale that we have done with our technology, at first many people don’t want to believe it. You have to convince them that it is a serious and well-founded idea. That’s where the independent expert opinions and assessments really help us. As does the neutral position of a panel of judges of such an important award as the ees AWARD. We have a big goal and need this recognition in order to hit the ground running with this technology in the e-mobility sector.

ees AWARD Finalists 2021

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