Frequently Asked Questions


How does the thermal battery work?

Energy in form of heat is transferred to the Thermal Energy Storage (TES) using a heat transfer fluid (HTF). The HTF can in principle be any fluid with adequate heat transfer properties. In most cases this is either thermal oil or water/steam. Heat from the HTF is transferred to the solid-state storage material HEATCRETE® via cast in “U-shaped” carbon steel heat exchanger tubes. There is no direct contact between the heat transfer fluid and HEATCRETE®; the heat transfer occurs through the heat exchanger steel tubes only. The thermal storage element design using U-tubes ensures that thermal stresses in the axial direction are minimized. The thermal elements also include a steel casing which has three functions; being a permanent casting form, an external reinforcement reducing the risk of spalling or cracking, and HTF containment (in the very unlikely case of HTF leakage inside the element).

What makes EnergyNest different to electrochemical batteries?

Electrochemical batteries, such as lithium-ion and lead acid, need electricity to charge, whereas the EnergyNest thermal charges with heat. This means that the thermal battery can be used for applications (such as combined heat and power) which are not physically possible with electrochemical batteries. Moreover, the thermal battery has a significantly longer lifetime, near-zero performance degradation, in addition to being made of fully recyclable materials. These materials primarily consist of steel and concrete, which are cheap and globally available commodity materials. This is why the system comes at a significantly lower cost than batteries.


How do you generate savings and reduce carbon emissions for industrial facilities?

EnergyNest project developers will start by evaluating process data from the facility. This includes analyzing different heat sources and heat sinks, in terms of temperature, pressure, and flow rates. Many industrial facilities have processes that are either intermittent or highly variable in their energy production and consumption. By recovering thermal energy from high-temperature waste heat sources, storing it, and discharging this energy into downstream processes at a later point in time, EnergyNest opens up entirely new possibilities for waste heat recovery: instead of consuming fossil fuels to generate the heat that they need, industries can simply rely on stored thermal energy. The reduction in fossil fuel consumption allows an equivalent reduction in carbon emissions. The thermal battery effectively grants industrial plant owners optimal management of their energy use.

What kind of revenue opportunities do you create for independent power producers?

The thermal battery is the ultimate flexibility solution for thermal power plants. It can be directly integrated into existing steam cycles, effectively providing a steam storage buffer between the boiler and the turbine. This allows plant operators to run their boiler continuously while boosting or reducing the electric output on demand. Depending on the case, the system reaction time can be less than 7 seconds. This makes the thermal battery a perfect solution for providing thermal power plants with the flexibility required to respond to primary frequency response. The thermal battery can thus be designed to provide a short or long response time, depending on what provides most value in electricity markets.

How much does the thermal battery cost?

The material cost for our basic storage modules can be as low as 25 USD/kWhth of storage capacity in favorable project conditions. This includes the storage medium, the containment of the medium and the means to input and extract heat from the medium. However, this indicative cost figure excludes local EPC costs which tend to vary significantly from one project to another. The total system cost will therefore vary depending on its size, functionality, subcomponents, and geographic location.


What kind of temperatures can your thermal battery handle?

Our storage material HEATCRETE® has been tested up to 550°C, and is guaranteed to perform as intended up to 450°C.

How does the thermal battery withstand the stress from thermal expansion?

The storage material is designed to have a similar coefficient of thermal expansion to that of the cast-in carbon steel pipes.

How many charging/discharging cycles can your thermal battery handle?

With daily cycling, a TES would experience less than 20,000 cycles during 50 years operation. Since the stress values are far away from the failure values for concretes, the stress and fatigue pose no operation issues to our TES system over 10,000 – 20,000 cycles.

Does the performance of the thermal battery degrade over time?

The thermal battery itself does not have any performance degradation during operation, because the system entirely made of durable concrete and steel, which can tolerate tens of thousands of stress cycles. All materials are operated within bounds that preserve their integrity for up to 50 years.

How do you minimize technical risks?

EnergyNest has designed the thermal battery to have the lowest possible technical risks. Our technology has undergone a significant number of tests, both in laboratory settings and with real operational pilot facilities, which have been certified by third-party auditors. Data on exact material performance can be shared upon request. The modular system design allows material malfunctions and contingencies to be dealt with swiftly, by shutting down the part of the storage that is affected.


Who is responsible for building the TES?

We offer our customers the most convenient option for their situation, which is typically one of these two:

  1. The Customer brings its own EPC contractor to site, and EnergyNest offers site advisory services, to guide them during the construction of the thermal battery.
  2. We are in charge of a turnkey solution, together with one of our international EPC partners.

How do you assure the quality of your system?

We only work with ISO 9001:2015 certified suppliers and partners, who provide top-confidence on our products and services. Additionally, we perform 2nd Party Audits, together with certified bodies, and on-site supervision during the critical phases of the construction process.

What is the lead time for installing a TES? (assume: delivery of materials + construction)

3 months after the closure of the TES design, key components are ready to be shipped to site. Transport to site duration will very much depend on project´s location: from 1 week in an European project, to 1 month, if it is overseas. The construction process duration depends on the size of the storage, but a good reference is 3 months for a small project, from civil works to cold commissioning, to 6 months for a bigger project.

What are the carbon emissions associated with building a TES?

Emissions are highly dependent on context and likely to vary from one project to another. What is certain is that their effect will generally not be substantially more significant than that of cement. A conservative total estimate would put overall emissions at 15 kg per kWh of storage capacity. Comparing this number with about 300g CO2 per kWh from burning fossil fuel, one can see that a reasonable number for payback of the CO2 debt for a TES is less than 2 months. Therefore, no matter what type of project, the EnergyNest TES will recover its carbon debt very quickly. The EnergyNest TES thus constitutes an elegant and cost-effective solution for reducing carbon emissions in heat-intensive industries and electric power generation.


What are the heat losses over time?

Thermal losses will be less than 2% over 24hrs for large-scale projects. Smaller projects will have somewhat higher losses as the surface-to-volume ratio increases.

What maintenance does the thermal battery require?

The TES system requires very low maintenance as there are no moving parts other than a few control valves on the TES piping interface with the plant.

How fast can the thermal battery respond?

The EnergyNest thermal battery can respond very quickly, and can provide anything from short term frequency response (30 min charge/discharge) up to longer cycles over several days.

How do you measure the performance of the thermal battery?

The performance of the thermal battery is based on measurements of the inlet and outlet HTF temperature and mass flow through the system. These parameters allow for accurate performance monitoring. In case of water/steam, the performance is measured based on mass flow of fluid in either liquid form (water) or vapor (steam), combined with temperature and pressure.