They refer to virtual replicas of a process, a component, or an object able to reproduce the behavior of its physical counterpart in order to monitor and analyze its reaction in certain situations to improve its performance and efficiency.
As shown in the figure presented below, a Digital Twin comprises a “Real Space”, a “Virtual Space” and a link of “Data Flow” between them that allows us to experiment without running risks, or to carry out an exhaustive analysis of the information.
Since its introduction in 2002 by Dr. Michael Grieves, this technology has been connected to the fourth industrial revolution; also known as Industry 4.0.
In facts, reports such as “Beyond the hype of i4.0” published by KPMG clearly identifies this technology as a key tool to achieve this Industry 4.0.
To achieve this, the Digital Twin must go hand in hand with Big Data solutions, the Internet of Things (IoT) and Artificial Intelligence (AI). In this frame, an environment of real objects “Things” (equipped with sensors and software) and other technologies is created with the aim of exchanging data through the Internet, which can then be processed by a Digital Twin.
A Digital Twin is capable to be implemented in almost any industrial process for several purposes such as the optimization of a component performance in a determined process, to reduce raw materials consumption or to take fast operative decisions as a function of external conditions, among others. Main benefits identified when a Digital Twin is implemented in a process are the following:
Clear applications of Digital Twins are processes in which heat is involved. From CIC energiGUNE, we target mainly four areas: industrial processes (steel, cement, forging, glass…), renewable energies (concentrated solar power), the electric vehicle and domestic heat.
In intensive industrial processes like steel, cement, forging or glass, huge amount of energy is consumed in form of heat. Different studies indicate that between 20 and 50% of the energy required in these processes is released to the atmosphere.
Historically, this energy has not been recovered and reused as the required technologies presented high payback periods, not compatible with the industrial needs. One of the reasons behind this situation is the low price of fossil fuels like natural gas, used to produced thermal energy or the relaxed environmental regulations.
However, in the last years, environmental restrictions, carbon credits or the increasing price of fossil fuels are requiring industries to search for alternatives to valorize the generated waste heat. These alternatives are typically the production of electricity, its reuse in an internal process or its external commercialization (district heating).
A common characteristic of the waste heat is that it is not always produced at the same power and temperature level or in a continuous way. However, almost all possible applications of the heat require constant heat sources.
In this frame, a Digital Twin plays a key role in fostering the implementation of heat recovery systems in the industrial sector as it may allow, for example, an optimal exploitation of components like the thermal energy storage (TES), heat exchanger, power block or the district heating, as a function of the instantaneous thermal power production and demand.
As a consequence, this type of tools clearly contributes to the required payback time reduction of heat recovery systems. One example of the implementation is the case of the Rillieux-la-Pape district heating network near Lyon where, since a digital solution was installed by Engie Cofely, the rate of renewables energies in the network ascended to 91%. From which, 80% come from waste heat recovered from a nearby waste incineration plant, a biomass plant and a gas boiler.
In concentrated solar power (CSP) plants, solar radiation is converted into thermal energy to heat a fluid (a thermal oil or a molten salt). This fluid can be used either to produce electricity through a Rankine cycle (steam or organic) or to supply thermal power to an industrial process.
One of the advantages of CSP plants in comparison to other renewables energies is its dispatchability due to the low cost of storing heat. Actually, this property has promoted the appearance of new concepts like hybrid plants combining CSP and photovoltaics (PV).
The important reduction in the levelized cost of electricity (LCOE) achieved in the last years in the PV sector has make this technology more attractive than CSP. However, the relative high-cost of storing electricity at large scale makes PV less dispatchable and costly than CSP.
The combination of both technologies is called to be the solution: during the day, electricity is directly produced in the PV panels while, the captured heat in the CSP is completely stored, and used to produce electricity when sun radiation is not available (evening, night or cloudy periods).
In both cases, only CSP or in hybrid CSP/PV, a Digital Twin becomes of paramount importance as it allows stablishing a daily/hourly operation strategy as a function of the weather forecast or the price of electricity, or predict maintenance operations like mirrors/panels cleaning when the optical/electrical efficiency drops below a certain value, among other benefits.
Overall, the implementation of Digital Twins will boost the deployment of renewables energies as demonstrated by different studies. One example is the 20 MW solar farm of Invenergy which claims that, after implementing a Digital Twin system, 99% of plant availability can be achieved together with a US $200,000 worth of additional value annually.
The need of reducing the dependency of fossil fuels and the pollution generated by combustions cars in cities, together with the economic incentives from governments have caused an increment in the interest of the society on acquiring electric vehicles.
Starting from TESLA, almost all historical car manufacturers like BMW, Volkswagen Group, Toyota or Hyundai have introduced in the market electric models at affordable prices.
Even though the electric vehicle has been demonstrated as a mature and reliable technology it still presents an important optimization/improvement potential. Among them, increasing the battery capacity and durability have emerged as the two main targets to boost the electric vehicle.
From CIC energiGUNE we target both aspects. From the Electrochemical Energy Storage area (EES), with the search of disruptive new battery technologies with higher energy densities and better cyclability, and from the Thermal Energy Storage (TES) area in improving its durability by means of ensuring optimal operation conditions.
It is in the latter, where a Digital Twin acquires a relevant role. Depending on the battery technology, the operation temperature must be stuck in a certain range. This parameter is critical to avoid both, malfunctioning (sudden discharge) or reduction of the useful life (durability).
While the car is charging or accelerating, batteries suffer from inefficiencies leading to heat generation. If this heat is not properly removed, it may cause temperature rise above the recommended values.
Same undesirable situation occurs if the car is park outside at very low (winter) or high (summer) temperatures. In this frame, a Digital Twin able to take instantaneous decisions over the heat management system as a function of parameters such as ambient temperature, battery temperature, acceleration rate, state of charge, etc. is vital to ensure an efficient performance of the battery, as well as to extend its useful life.
Studies from General Electric (GE) claim that the insights gained from the “Twin” have enabled them to reduce the size of the battery by 16 cells and shave the cost by 15 percent.
Another clear application of Digital Twins is in the area of Domestic Hot Water (DHW) and Heating, Ventilation and Air Cooling (HVAC), not only in residential buildings but also in public ones.
There is not a unique solution to provide DHW and HVAC to a building. For example, old buildings used to incorporate diesel heaters while, newer ones use natural gas or, in the best of the cases biomass.
However, recent regulations for new buildings, together with Government incentives, are making current installed solutions to be a combination of systems based on fossil fuels (mainly natural gas) and renewable energies (solar thermal panels, heat pumps, biomass, etc.).
In addition to the implementation of more efficient and cleaner technologies/equipment, there is a clear need of improving the operation of the DHW and HVAC systems.
Many studies have demonstrated the viability of including Digital Twins in buildings. For example, IES indicates that, with the integration of a Digital Twin in the Riverside Museum of Glasgow, annual savings of £52.3k were achieved, with a Payback period below 6 months.
In order to achieve this savings, Digital Twins play a major role as they allow operate the system, for example, as a function of the weather forecast, historical data of demands, etc. in such a way nominal (more efficient) operation conditions are ensured in each scenario.
Furthermore, the use of this type of tools in the system design stage allow an optimized scaling of the components leading to cost reduction and to a more compact solution.
In CIC energiGUNE in general and, the TES area in particular, we are experts in the development of this type of digital tools as key solutions to boost not only the Basque, but also the European industries, towards the fourth industrial revolution.
The know-how acquired by the researchers and engineers in different public funding projects (Hazitek, Plan Nacional, H2020, RFCS…), as well as in private contracts with industry in the last years, has allowed the creation of initiatives like Thermlab to offer this type of solutions to the industry.
Currently, CIC energiGUNE counts with powerful modeling tools to accomplish this type of technological challenges such as ANSYS Fluent, ANSYS Icepak, TRNSYS or Matlab.
Author: Iñigo Ortega, Associate Engineer from the Systems engineering and technology transfer group of Thermal Energy Storage Area.
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