Jun-2022

Digital twins heat up the capabilities of energy storage plants

How to support future energy security by enhancing energy storage with automated digital twins.

Alan Messenger
Optimal Industrial Automation

Article Summary

Renewable natural gas (RNG), solar, wind and other sustainable resources are at the core of decarbonisation and energy transition strategies. To effectively support their large-scale adoption, it is necessary to ensure dispatchable generation and predictable supply to the grid. Future-oriented energy storage plants that leverage cutting-edge industrial automation, such as digital twin technology, can succeed in this by taking advantage of accurate, real-time simulation models.

Renewable energy sources, such as RNG, provide multiple benefits. In addition to supporting ambitious decarbonisation and net zero goals, they also offer the most economical way to create a decentralised power system. This, in turn, can help achieve universal, reliable and affordable access to power.

For these reasons, the use of alternative energy sources is increasing in popularity, representing almost 11% of power generated globally and forming a major part of the energy mix in many counties (1). For example, renewable energy use in Norway covered more than 60% of total consumption in 2018 (2) .

One of the key challenges that must be overcome to support the increasing adoption of renewable natural gas and other replenishable resources for power generation is balancing fluctuating electricity demands with the intermittent nature of some renewable sources. For example, to succeed in decarbonisation efforts and avoid any wastage, it is essential to prevent curtailment. This occurs when a power generation system is prevented from exporting to the grid, usually because of a temporary constraint caused by congestion, essentially wasting potential low-carbon energy supplies.

The importance of advanced energy storage solutions
To fully utilise generation capacity, robust, reliable and highly efficient energy storage solutions are required, as they can provide the level of flexibility needed to maintain stable and consistent supply to the grid. Strategies such as these can support peak shaving and load shifting activities.

Compressed-air energy storage (CAES) in its various thermo-mechanical forms, is among the most promising technologies available at a commercial scale for high-capacity energy management. By saving potential energy in the form of compressed air, these systems are able to generate large amounts of power on demand.

Also, apart from access to a cavern, CAES facilities are not dependant on specific geographies, unlike pumped hydropower, and their daily self-discharge is very low, making it possible to effectively keep the stored energy for long periods without any considerable losses. In addition, due to the well proven nature of the underlying equipment, CAES plants typically have a designed lifetime of over 40 years, which keeps the overall costs per unit of energy (or power), among the lowest for all available storage technologies.

To achieve these results, CAES facilities can utilise different configurations, one being the innovative liquid air energy storage method, which leverages thermo-mechanical principles to advance the benefits of CAES. In the liquid air variant, air is purified and cooled to its liquid state during the charge phase. It is then stored at cryogenic temperatures and low pressure in suitable tanks. When discharged, the liquid air is pumped to a high pressure, evaporated, and heated to expand the liquid air stream. The resulting high-pressure gas drives a set of turbines in a power recovery unit.

Liquid air energy storage is the way forward
The liquid air energy storage cycle described above utilises components that are commonly found in conventional power stations and industrial air separation plants. Therefore, they offer multiple advantages. Firstly, they are well-proven and broadly accepted. Secondly, this equipment is widely available to support commercial-scale facilities. Finally, they have well-understood maintenance requirements.

Furthermore, the use of liquid air energy storage systems leads to energy densities that can be up to 8.5 times higher than conventional compressed air alternatives (3). Therefore it is possible to create compact plants that are more economical, efficient, easier to implement and suitable for sites with limited available space.

In addition, the power generation cycle eliminates the need for combustion and the associated carbon emissions while also supporting ‘cold recycle’ practices. Waste heat from the liquefier compressors is recovered within the process for highly efficient operations and the storage and recycling of thermal energy released during discharge can be used as part of a closed-loop system to support air liquification activities during charging.

Automating energy storage process control
A liquid air energy storage process offers per se unique financial and environmental benefits. Nonetheless, with temperatures ranging between -200 and +600 °C and pressures reaching up to 200 bar, small variations in these can impact performance significantly. This means that the optimum control of processing parameters throughout the different phases is key. This is essential to maintaining energy efficiency and low costs while maximising the end results.

By supporting real-time feedback and feedforward systems as well as remote monitoring, industrial automation technologies provide an ideal solution to consistently deliver peak performance and efficiency. More precisely, fully integrated automated process control provides a highly available, responsive and secure framework for monitoring and visualisation, trending and analysis as well as the management and synchronisation of all pieces of electro-mechanical equipment onsite.

By using this type of automated setup, liquid air energy storage plant operators can ensure the proper sequencing of all processes and promptly address any alarm to maximise uptime, ultimately delivering high efficiency and productivity. As a result, it is possible for facilities to realise dispatchable and predictable power distribution to the grid while also maintaining a low — or even net zero — carbon footprint.