Ultrasonic sensors used in AquaBattery's innovative Blue Battery

AquaBattery was founded a few years ago by five young men who had specific ideas about a cheap but effective way to store electrical energy: an important theme at a time when there is a risk of a surplus of energy as a result of over-production of PV panels, and supplying back is not always possible or lucrative (anymore).

There are many options for storing energy, of which the regular 'battery' - which works with lead or lithium cells - is the best known. A major disadvantage of these types of batteries is that the materials used are partly toxic, expensive and flammable, up to the risk of explosion. How could this be changed?

With everyone having a background in 'water', the solution for Blue Battery was to store energy by making use of the potential difference that exists between salt and fresh water. COO Emil Goosen says: "The technology for producing electricity by allowing salt and fresh water to flow past membranes is already known from the 1960s. However, by reversing the principle, it is also possible to save energy with the same membrane technology, and that is exactly what happens in our Blue Battery. A system that consists of two or three tanks connected with pipework, pumps and the membrane sets. Based on the conductivity of the media, the level in the tanks and the pressure and direction which liquids have to flow in order to charge or discharge the battery is determined by the control system.

Green Village pilot

"Many tests have been carried out in our own workshop in Leiderdorp with membrane packages and capacities up to approximately 1kW. This has resulted in a setup which will be tested in our first pilot in "the Green Village' in Delft. This project was mainly carried out within the framework of "scaling up'; an important step because such a pilot must show that the successful operation on a laboratory scale also works well and reliably in larger systems. This first pilot uses 10 cubic metres of fresh water, spread over different tanks. At this point everything is working satisfactorily, leading to the start of a second and third pilot, where we are moving to even larger capacities."

In order to measure the level in the tanks, experiments were initially conducted with capacitive sensors. However, these were not accurate enough and, more importantly, gave too many fluctuations. At the Aquavak fair in March 2018, elobau was introduced to the project of AquaBattery and proposed the use of ultrasonic sensors.

This type of sensor includes both a transmitter that produces ultrasonic sound, and a receiver that captures the reflected sound. Based on the time it takes for the sound to return, the sensor determines the distance to the object or surface to be detected. In addition to the fact that this is always a non-contact measurement, ultrasonic sensors detect independent of shape and colour. This means that they also detect mirrored and transparent objects or surfaces, as well as smooth or very grainy variants. This makes ultrasonic sensors suitable for a wide range of applications, and certainly for the Blue Battery.

Gerard van de Griendt, sales manager industrial applications at elobau says: "The innovative AquaBattery has experimented with various ultrasonic sensors which we provided samples of. After tests had shown that ultrasonic measurement was indeed suitable for this application, we looked at the best suited variant of the selected sensor. For example, there is a choice of a plastic or stainless steel housing, and we had to find out whether a long or short version would suit best. In addition, the degree of protection is important, as well as the resistance to salt water, and of course the measuring range."

Emil Goosen adds: "The reading of the sensors, based on which, for example, the pumps are controlled, is done via our own written software and industrialised PLCs. These are easy to program and robust enough for use in industrial applications."

Efficient electrical energy storage

With the final design of the Blue Battery, end users are not only assured of efficient and guaranteed storage of electrical energy, but they also benefit from a product that is safe for people and the environment. After all, leakage of the liquids does not present any risk so this battery can also be transported without problems or need for extra permits. Furthermore, "overcharging' of the batteries is not possible and charging and discharging has no influence on the life of the battery.

In follow-up of the successful pilot in Delft, a larger set-up in Gorinchem is being worked on now. In this set up double the amount of fresh water is being used with 20 cubic metres being distributed among different tanks that are connected. The ultimate goal is to arrive at a total system of 2,000 cubic metres. Emil Goosen says: "The system in Gorinchem is housed in a sea container where the assembly of components has now started. This should be ready around the end of March. In this pilot the ultrasonic sensor from elobau is not being used because the choice was made to use a number of smaller tanks with integrated sensors. However, these sensors only indicate full or empty. In the final application, we do want to use the sensors that we have selected in consultation with elobau.

"I assume that this will happen in the third pilot, but for this we also depend on other partners who work with us in the context of an H2020 project. On the other hand, it is simply the best solution, because then we again change to a larger system with larger and higher tanks. The required sensors must then have a sufficiently large measuring range and an accuracy of around 0.1 per cent; and that is one of the big benefits of the ultrasonic sensors previously selected."

The ultrasonic sensor that AquaBattery selected for its "Blue Battery' is the UC18PIC-220S. This is a plastic (PBT) sensor with an M18 external thread and a measuring range of 200-2200mm. In addition to an analogue 4-20 mA output, this ultrasonic sensor is also equipped with a push-pull output. Due to the relatively large measuring range, this variant is suitable for the larger tanks planned for the third pilot. The plastic housing also makes the sensor suitable for use in tanks with salt water; this in contrast to stainless steel versions that were initially chosen.

Follow the link for or more information about the Blue Battery.