Kraftblock's Thermal Storage Technology

01 The Thermal Storage System

Every energy storage is always integrated into a system that converts the three aspects of a storage cycle: Charging, Storing, Discharging. Kraftblock is a thermal energy storage, the energy going in and out of the storage is heat. For process heat, this is more efficient than storing electricity in batteries or energy in hydrogen. It also allows for a resilient and independent use while decoupled from other systems like the electricity grid.

Use cases of heat batteries

The benefits of an heat storage system vary depending on when and how much energy can be charged and discharged. For example, you can shift cheap electricity as heat to avoid times when electricity is expensive, or use energy from sunny afternoons at night or the next day. As Kraftblock’s system can charge a multifold of what it discharges, the low prices are used for a longer time of heat supply.

Waste heat from flue gases also becomes flexible when a thermal storage is integrated. Kraftblock serves industrial processes as well as utilities and energy suppliers with its thermal battery. The Kraftblock solution can store from a few minutes to two weeks, which means that there is great flexibility in linking energy generation with consumption.

Typical operation parameters of Kraftblock's thermal battery

• Storage temperature between 350 °C and 1,300 °C
• Minimum charging/discharging power: 300kW
• Discharging at storage temperature or any lower temperature

The benefits of a high-temperature storage are lower investment and operation costs than conventional energy storage. Due to the higher temperature the thermal capacity of the storage is very high. This translates to less storage footprint which means less material and installation.

The operation of the Kraftblock system is also very flexible due to the approach of multiple units. Different units can perform different operations at the same time, such as charging, storing or discharging. This makes it not only possible to secure supply a 24/7 process but also be resilient with systems like the electricity grid.

Flexibility and Adaptability

Kraftblock units can be configured individually for each use case. They are flexible too, with a range of power capacities for charging, storing and discharging.

This also means that the purchase of electricity or the amount of waste heat used can be adapted to achieve the most cost-effective operating schedule. This is necessary in the industrial reality as many variables such as footprint, grid access, distance between processes, and many more aspects determine the best fit of a thermal storage system.

Modular Thermal Storage System

Kraftblock's approach to flexibility is centred on adapting to the demands of industrial settings. Thus, Kraftblock's thermal energy storage plants are divided into units, which are in turn divided into modules of interacting equipment. These are the charging module, the storage module, and the discharging module. They are built outside the storage unit for easy maintenance and improved longevity. As they are connected via ducting, the modules can be installed flexibly to adapt to the footprint of the industrial site.

02 Charging and Discharging the Thermal Storage

The Kraftblock systems follow a platform approach. This means that the thermal storage module is at the core of the systems, independent of the energy source which can be renewable energy, waste heat recovery or concentrated solar.

The storage module is linked with different charging and discharging modules to integrate the respective energy source.

Charging the thermal battery

In the case of waste heat, we can charge the waste heat directly. The minimum requirement additional to the minimum charging power is a temperature level of 350°C or more. Depending on the composition of the flue gas and the application, we might integrate a heat exchanger. If we use electricity as an energy source, we convert the power into heat using a power-to-heat element, in our case a resistance heater which heats air.

The hot gas is blown into the storage where the material absorbs the energy by heating up. Charging stops at a defined point and the storage cycle begins.

Discharging the heat storage

When the heat is needed, ambient air is blown through the storage. The heat of the Kraftblock material is transferred to the air and the system releases the energy at the temperature level needed for the process of the customer. We discharge in a range between the maximum storage temperature down to 50°C.

A part of the discharge module in Kraftblock’s thermal energy system is the transfer to other heat media. The Kraftblock system can discharge heat as air, steam, gas, thermal oil, water or other transfer media, depending on the infrastructure of the individual industrial site.

Benefits of flexible thermal storage

Unlike battery energy storage, a Kraftblock thermal storage system also has no pre-defined charge/discharge ratio. While you can charge 3MW, you can discharge for example 0.5MW or 7MW and vice versa. This gives you more charging and discharging flexibility to manage your energy supply and reduces operating costs.

It also enables the exploitation of periods of low electricity prices in the market. This transports the prices of a few hours for the consumption of a larger time frame. In our whitepaper about flexible electrification you can read more about the cost savings using thermal storage in the electricity market.

As a third benefit of this flexible charge/discharge ratio, industrial supply is more resilient to changes in grid and the Kraftblock storage allows for a more secure energy supply.

The round-trip efficiency from the whole system, meaning power-to-heat, storing in the thermal storage to the supply of the industrial process is over 95%. In cases of waste heat, the efficiency is even higher. The storage's daily energy losses are minimal.

03 Kraftblock's unique Thermal Storage Material

Just as important as how we charge and discharge energy is how we store it. The material is the essential part in terms of thermal capacity, efficiency and sustainability. Kraftblock has developed an outstanding, sensible thermal storage material with a special recipe. Much of it is a sustainable and low-cost product: up to 85% is made from upcycled materials such as steel slag. It also has a long lifetime: It was tested for 15,000 cycles with no degradation discovered. This is 50% longer than the maximum of battery energy storages. Used once a day, Kraftblock material has a lifetime of over 40 years.

The mix of different materials, mainly the milled down slags, is bound together by a harmless phosphate binder. This binder also increases the thermal conductivity of the material, allowing the charged heat to get into the middle of the storage material and use all the capacity. Kraftblock thermal storage material is charged up to ten times quicker than conventional bricks. 

These enhanced characteristics and stability make it a low-maintenance product for the demanding operations in industries. In this article you can learn more about the differences between a sensible thermal storage material like Kraftblock’s and a latent one.

Storage Material with outstanding thermal characteristics

Our team developed the material for a number of reasons: Every solid storage material has a specific heat capacity and conductivity. These parameters cannot be changed and must be used as they are. Kraftblock has developed a material that can be easily modified and adapted to the application since it is mixed using different materials.

Most existing materials are limited to a certain temperature range. Kraftblock has developed a stable material that can withstand a high maximum temperature level and massive temperature drops, allowing it to be used in a wide range of applications.

Natural materials such as basalt are more or less sustainable depending on the supply chain. Artificial materials such as alumina, concrete or magnesia bricks require large amounts of energy to produce. Kraftblock has therefore developed a sustainable material using a circular economy approach, incorporating cheap materials from landfills into the recipe. 

Although the Kraftblock material can withstand temperatures of up to 1,300 °C, it does not need to be heated during production, which makes the production very sustainable and low-cost.

You still have some questions? Check the Kraftblock FAQs and dive into many industrial and energy topics in our KraftBlog.