Heat 2 Power:
New Thermo Storage Technology []

Advantages of the New Thermo Storage Technology

Optimum combination of the materials used in the heat storage mass

• The materials used are inexpensive, resource-efficient, ecologically harmless and easy to process.
• The selected configuration leads to high energy storage density, little space requirement, high temperature resilience and practically unlimited cycle stability. Due to the materials used and the smaller gap volume, the volumetric heat storage density is, for example, 4 to 8 times higher than a heat storage device made of lava rock.
• Comparatively low pressure loss when flowing through. Defined flow paths allow precise design.
• Homogeneous temperature distribution inside each module without a "heat front" migrating through the storage tank, therefore targeted use of the module with a defined current temperature in parallel or serial connection. There is no large gap volume as with coarse rock or granulate fills. Here the gas seeks the path of least resistance and leads to uneven flow and dead zones. A "heat front" is virtually not realizable.
• Only the combination of steel pipes and minerals allows the use of separate charging and discharging circuits (see below) and different media for charging and discharging.
• Heat input via hot gas flow and also directly via embedded resistance heaters (e.g. for targeted post-heating) possible.
• The idle losses of the stored energy depend on the individual parameters (temperature ranges, type of insulation, geometry, etc.) and, based on experience, amount to approx. 2 ... 4% per month for storage systems of this type.

Separate charging and discharging circuits

The function of previous thermal stores is usually limited to absorbing heat and then releasing it again. This is usually done by reversing the flow direction.

The New Thermal Storage Technology can absorb and release heat at the same time because loading and unloading takes place in separate pipework systems. Certain areas of the storage installation have a practicable minimum temperature for regeneration of electricity for as long as possible.

• The storage can be charged with excess electricity or industrial waste heat.
• The residual heat after delivering the energy to a subsequent heat engine is not waste heat, but is fed back to the storage modules. This will not work with existing storage systems: The returning gas flow would reduce the maximum temperature in the thermal storage continously since they do not dispose about a counterflow principle.

  

• Charging does not have to be stopped before discharging. No operation required on the device. No delay.
• A subsequent heat engine can therefore work continuously at a constant speed.
• A subsequent heat engine can also work continuously if the power or heat source (wind turbine, industrial waste heat, etc.) only provides heat fluctuatingly or cyclically. With previous storage systems, a downstream turbine would have to constantly start up and shut down.
• A subsequent heat engine can also work continuously if the heat conducted into the storage tank temporarily falls below the minimum temperature required for operation.

  The following graphic describes an example of the course over time of such a fluctuating introduction of heat. About 40% of the time (horizontal axis) the temperature (vertical axis) is below the minimum usable temperature (“T_min”) for reconversion. With conventional heat storage systems, a subsequent turbine would have to start and stop frequently. In addition, charging would first have to be stopped in order to enable discharging. The heat available during this period would be lost.

  With the New Thermal Storage Technology, on the other hand, the fed-in thermal energy is smoothed by diverting the heat to other modules at specific time intervals (vertical dashed lines), while at the same time discharging can continue continuously.

  

  The time axis is divided into sections a to t. Exemplary procedure for cyclical feed-in of heat:

  a) Serial charging module 3 - 5
  b) Serial charging module 2 - 4
  c) Serial charging module 1 - 3
  d) Serial charging modules 2 – 4
  e) Serial charging module 3 - 5
  f) Serial charging module 5 – 6
  g) Serial charging modules 4 – 6
  h) etc.

  The thermal energy below the usable level (“T_min”) is also fed in, stored and finally recovered.

• Only then it does make sense at all to feed such low-temperature heat into the New Thermal Storage instead of reducing it, discarding it or just using it for heating.

Modular design with flexible interconnection

• When absorbing thermal energy, the New Thermal Storage can also efficiently cope with very different feed-in capacities, for example peak capacities from wind energy.
• The heat can be taken from a place where the desired temperature prevails.
• Various operating modes and serial connection allow a gradual temperature change of both the charging and the discharging flow according to a countercurrent heat exchange between charging and discharging. Overall, this causes higher temperature differences between the inlet and outlet temperature of the medium and thus a more efficient operation.
• The gradual change in temperature from module to module means that the heat exchange between gas and thermal storage is maximized and only little residual heat remains in the gas. Large quantities of uselessly circulating gas or heat are avoided and would also increase the overall equipment costs (design fans for high temperatures, larger heat exchangers for reheating, etc.).
• Overall, a larger proportion of the heat fed in is converted back into electricity.

  Portion of stored heat for reconversion:
  

  Existing thermal storages:  

  

  New Thermal Storage: 

  

Setup and Inclusion

• Decentralized installation with a thermal engine for reconversion directly at the energy source, for example a wind turbine, no additional network expansion required. An optimal configuration for the successful design of the energy transition should therefore provide the following:
  
  • At each renewable energy production site, the power is fed into the grid up to the annual average power of the system.
  • Performances above the average value are fed into the New Thermal Storage until it is fully charged.
  • The back-up power plants (gas, coal, etc.) now run at a lower but more even level they do not have to be designed for maximum performance anymore.
  • When RE production is below the defined base load, the stored heat is used to run a heat engine to supplement the missing power.
  • Optionally, it can be considered to operate the heat engine alternatively for a short time with bio-fuels if there is no renewable energy generation and the thermal storage is empty (long-lasting dark doldrums ).
    If the heat engine is capable of using bio-fuels (bio-LNG, H₂) and alternatively converting heat from thermal storage into electricity, there is no need for back-up power plants.
  • The heat engine only has to be designed for the base load, i.e. approx. 15...25% of the nominal power of the wind turbine. The overall costs therefore remain manageable. Example: The base load of a 15 MW wind turbine is approx. 2300 ... 3000 kW.
• Secondary circuits for extracting heat are usually not required. The separate piping systems for charging and discharging allows to use two different media (e.g. nitrogen, thermal oil, flue gases, steam, etc.).
• As a result, many additional devices are no longer required, and the system is less complex and less expensive.
• The flexible interconnection of the modules with the option of serial, parallel or successive interconnection makes the addition of cold air to achieve a specific target temperature obsolete.
• Overall, it is a minimalistic layout without numerous pumps, heat exchangers, compressors, etc.
• Low assembly effort. The modules can, for example, be delivered to the construction site pre-assembled in standard containers, provided they are in the form of a cuboid. In this case, the New Thermal Storage can be expanded with additional modules.
• However, cylindrical geometries are also conceivable, in which the hottest modules are on the inside and increasingly colder areas are added to the outside. In this way, heat losses are minimized.

Efficiency

Conventional thermal storages already claim very high "storage efficiencies" for themselves, without using the terms "exergy" and "anergy". How is such storage efficiency actually defined? Obviously not as a quotient "Recovered electrical work / Heat supplied". Overall, the New Thermal Storage Technology is more efficient than the existing systems at

• Charging: Current accumulators show a continuous loss of efficiency during charging, since the temperatures of the charging current and the heat storage mass continue to converge in the course of the process. Noticeably more and more residual heat circulates in the loading stream or is discharged. Manufacturers of previous storage devices do not address this issue for good reason.

  Small sub-units reach a maximum temperature somewhere in the system more quickly than a large mass. The New Thermal Storage is therefore ready for operation more quickly.

     Existing thermal storages:  

  

     New Thermal Storage: 

  



• Intermittent operation / cycles:
  Continuous operation of a subsequent heat engine is now possible, even if only lower temperatures are temporarily present.
• Discharging: It now makes sense to introduce fluids with a lower temperature: Modules with a lower temperature are used to preheat the discharge flow when connected in series.

  When discharging, the heat is first removed from the coldest module and used to preheat the other modules; very hot areas are initially spared if necessary. More stored heat is thus made available for reconversion and the withdrawal period increases.

  The storage is ready for discharge early because the first modules are charged quickly.
  

• Charging and discharging dynamics Overall, there is the possibility of charging and discharging the storage highly dynamically. In contrast to previous storage systems, it can be discharged continuously and with greater efficiency.

     Existing thermal storages:  

  

     New Thermal Storage: 

  

Compared to previous high-temperature thermal storage systems, the New Thermal Storage can

• be dimensioned smaller in order to enable the generation of the same amount of electrical energy.
• generate the same amount of electricity with less heat input.
• even if it works at a lower temperature level overall, achieve higher performance than previous thermal storage systems.

Calculation of an example system

Given a New Thermal Storage system with six cuboid modules. The internal dimensions of a module (heat storage mass volume) are L=4.4thinsp;m, W=1.8thinsp;m, H=2.2thinsp;m, which roughly corresponds to a standard 20-foot container size if the Thermal insulation has a thickness of 0.3thinsp;m all around and there is still room for piping along the length.

Round steel pipes 70.0thinsp;xthinsp;6.3 mm are provided for the internal piping for loading and unloading, the distances between the pipes are 20thinsp;cm. The piping systems are twisted by 90° to each other, so that there are 48 parallel pipes along the module length for loading and 128 pipes along the module width for unloading.

In addition, there are 56 melting cores (tube dimensions as above) with aluminum filling in each module.

The gaps are filled with a bulk material, of which it can be assumed that the heat capacity is 0.8thinsp;KJthinsp;/thinsp;(kgthinsp;K).

In total, approx. 5thinsp;600thinsp;kg of steel, 2thinsp;120thinsp;kg of aluminum and 19thinsp;500thinsp;kg of sand are installed per module.

If a module is used from 350°C (minimum temperature for microturbines) to 850°C, the following amount of energy results for reconversion:

Is the New Thermo Storage Technology superior to actual storage systems?

How efficient are the  competing products?