Storing thermal energy in tanks or underground facilities saves excess energy for later use - days, hours or even months. Thus, the concept of Thermal Energy Storage (TES) bridges the gap between energy supply and energy demand.

By 2050, world energy consumption is expected to increase by 50 per cent. At the same time, the world's traditional energy resources are being depleted. In order to adapt to future energy consumption in a sustainable and zero-emission manner, more and more energy is coming from renewable sources, such as wind, wave and solar.

But with renewable energy comes loss of control - we simply cannot control when and where the wind is strong enough to generate electricity. Lack of control can lead to erratic production, and energy production can be mismatched with energy consumption, leading to excess energy. There are even examples of wind farms closing down, despite high production efficiency, simply because of a mismatch with consumer demand.

What is Thermal Energy Storage (TES)?

In order to prevent excess energy from simply sitting idle and going to waste because it is consumed at a time and place that does not match production, a race has begun to find ways to store excess energy. One method is so-called thermal energy storage (TES), which refers to the cooling or heating of storage media. Examples of storage media include liquids such as water or solid materials such as stone.

Allan Jørgensen, Key Account Manager at Senmatic, says: "Simply put, thermal energy storage allows energy to be stored during off-peak hours and distributed during peak hours so that renewable energy can be utilized when the price of electricity rises."

"Wind energy is one of the cheapest sources of electricity. When wind is strong and generation surges during off-peak periods, it lowers the cost of electricity. Saving cost-effective energy means we can utilize it during peak times when the cost of peak electricity is relatively high. With thermal energy storage, we can operate according to the price of electricity." Says Chan Nguyen and Dr. Chan Nguyen, special advisor to Danish district heating company Fjernvarme Fyn.

Mathematical modeling major with a focus on energy systems and heat pumps.

What do sensors have to do with TES?

We now know that temperature is critical to a successful TES operation, which is why sensors are vital. By installing sensors, whether in a tank solution or an underground solution, it is possible to monitor the two main risks associated with temperature: delamination and leakage.

Control Layers

Stratification is the division of the water column in a TES installation based on density caused by temperature differences. Water agitation occurs when water enters and exits the installation through diffusers located at the top and bottom of the tank based on off-peak and peak hours.

For example, if the top layer consisting of warmer and less dense water is 85°C and the cooler and denser water at the bottom is 40°C, an intermediate layer of about 60°C will be formed. In order to control that the dispensed water for consumer use is at the correct temperature, multi-point temperature sensors monitor the temperature of the entire installation. The sensor points are usually placed vertically at 50 cm intervals in strategic locations. If too much water enters the system and agitation causes the layers to mix, the sensors will detect unwanted temperature changes, allowing the operator to stop the water from being ingested or discharged. Since the tank installation is deeper than the underground installation, more water can be added without mixing the intermediate layers.

Multiple temperatures in different layers or sub-layers can be measured using Senmatic's Multi-Point Temperature Sensor Type NLI, which requires only one flange connection in the tank. Other customized solutions are developed in close cooperation with our customers to match specific applications. Alternatively, multiple thermocouple sleeves can be installed on the side of the tank where individual temperature sensors are mounted.

leak detection

Another important use of sensors involves leakage.

Here, sensors are used on the outside of the control unit: In underground installations, we may have to dig up a lot of soil to find the leak. By installing sensors in a tightly networked structure (e.g. placed at 50 cm intervals), we can obtain data showing the heat loss at the exact location, so we can repair leaks more efficiently in terms of cost and man-hours Excavating at the exact location of the leak gives a clear picture of the extent of the leak.