Energy Dome – Written evidence (LES0020)


Thank you for this opportunity to comment on the proposed approach and design of the Capacity Investment Scheme (CIS) as described in the Public Consultation Paper.


Introduction to Energy Dome and the CO2 Battery technology


Energy Dome, based in Italy, has developed the innovative CO2 Battery long duration energy storage technology which is already proven at commercial demo scale and now being implemented at full commercial (20MW/200MWh) scale in Europe. The CO2 Battery is based entirely on proven industrial components and standard materials with well-established supply chains, which means that it can be deployed quickly and at scale on a global basis.


Key characteristics of the CO2 Battery include its high round-trip efficiency of 75% without performance degradation over a realistic 30+ year product lifetime.  When considered together with capital costs which are approximately half those of a corresponding Li-ion battery installation, it becomes clear that the CO2 Battery has a key role to play in enabling

the transition to a net zero emissions energy system.


In view of the significant interest and relevance of the CO2 Battery to the UK market, Energy Dome is actively exploring opportunities to deploy its technology in UK, both in terms of technology supply to third parties and as a potential developer, owner and operator of major projects. As such Energy Dome (“ED”) is pleased to provide comments on specific points raised in the Public Consultation Paper as detailed below.




The CO2 Battery is a long duration and large-scale energy storage system based on a thermodynamic process, that efficiently stores energy by manipulating CO2 under different state conditions (liquid/vapor) in a closed thermodynamic transformation.


The CO2 Battery is made of a 24.5 MW compressor and an 18.4 MW turbine, for a 10 h charge – 10 h discharge duration in nominal design conditions.


In charging mode, the CO2 Battery is withdrawn from an atmospheric gasholder (dome) and compressed into an adiabatic compressor, fed by a synchronous motor, which absorbs power from the grid. The heat generated from the compression is stored in a thermal energy storage system (TES). At the outlet of the TES, the CO2 stream passes through a condenser that condensates the CO2 , which is then stored under pressure in the CO2 liquid vessels.



Description automatically generated

Figure 1: Charging phase simplified process diagram


In discharging mode, the liquid CO2 is evaporated in the evaporator, previously used as condenser during charging. It then passes through the TES and expands into a turbine, which drives a synchronous generator, injecting back power to the grid. The CO2 is then cooled and stored in the dome at ambient temperature and pressure.


Figure 2: Discharging phase simplified process diagram.



Call for evidence answers and notes


  1. How much medium- and long-duration energy storage will be needed to reach the Government’s goal of a fully decarbonised power grid by 2035 and net zero by 2050, and by when will it need to be ready?


Energy storage is crucial to avoid massive curtailment or massive investment in new grid capacity. In particular, long-duration energy storage is required when renewable is in the range of 30 – 80 % of the energy production: a 10 hours duration allows the daily storage of the excess power production to have it available during peak demand. This means plants flexible in operation with a storage duration of 8 – 12 hours. When not-dispatchable renewable production overpass 80% of the total energy production also +12 hours storage duration is necessary for fully decarbonize the energy production. Renewable can already provide cheaper electricity compared to traditional fossil fuel generation.



Demand-side management can be considered but the main contribution is provided by utility scale solution and LDES, in order to assure the security of the grid electric system and its reliability. Apart from power injection and consumption, there are also secondary service that cannot be provided by demand-side management and that are of paramount importance, such as physical rotating inertia to stabilize the grid.


  1. Which technologies can scale up to play a major role in storage?


Lithium-Ion Batteries and other types of flow batteries have the important characteristic of being modular with units with small size and storage duration. They are the reference technology for small sizes and limited duration, while their specific cost is high and doesn’t make them competitive for utility scale with duration > 4 hours.


For Daily storage (5-15 hours) it is better having technologies with lower energy capacity specific cost, even if the cost related to power is higher. For example, Energy Dome CO2 Battery has a CAPEX around 30-40 % lower than lithium Ion Batteries for the same size, considering as example the commercialized unit of 20MW / 200 MWh (10 hours storage duration).


For weekly / seasonal storage (> 100 hours) other technologies with lower RTE but very long duration can be considered, such as thermal storage or hydrogen production.



Energy Dome is one of the few alternatives to traditional Lithium Ion Battery with already a commercial plant in operation (since June 2022) and with technology and process validated by third party performance test and report (Fichtner UK). Energy Dome is fully market ready to provide energy storage commercial plant.


The CO2 Battery is based on a proven thermodynamic process using components widely known to the mechanical and process industries, without employing any new materials nor technologies that would question its reliability as an efficient and durable long duration energy storage facility. Namely, the implemented turbomachinery, an integrally geared compressor and a multistage axial turbine, are reliable machines with proven availability in millions of hours of operation in thousands of installations currently operating globally. The CO2 Battery operating conditions (temperature, pressure, and power) are largely within the experience developed by multiple tier 1 manufacturers globally. This technology brings new life to components and skills already held by thousands of professional to enable and foster the energy transition, without compromises on performance, reliability, and timing.



Considering the high availability of wind resources, we believe this renewable resource can feed green hydrogen production. In this sense, LDES technologies can assist the 24/7 dispatchability of renewable power, limiting the off-design operating condition of the electrolyzer and increasing the overall capacity factors. Considering the very low RTE from RE power to Hydrogen to electricity, hydrogen should be considered as an energy vector rather than a storage of power. Indeed, it has multiple application apart from power production, for which is suitable on a seasonal timescale.


  1. What policy support is currently in place to support deployment of storage technologies? Is it sufficient to support deployment at scale?


The economic case for daily storage duration is improving, due to the increase in power price difference among different time of the day. The best way to give increase the revenue certainty for long duration energy storage is foreseeing specific capacity payment mechanism dedicated to storage duration >8 hours.


Reducing revenues uncertainty on the revenues and providing long term agreements will support the financial attractiveness of LDES, which is the one limiting their implementation.



Uncertainty in the revenue streams of the daily storage (arbitrage and ancillary services market revenues are extremely difficult to be foreseen) a supporting scheme such as capacity payment or auction with Contract for Difference support mechanism can push the installation of long duration energy storage.


  1. Beyond the cost of deploying long-duration energy storage, what major barriers exist to its successful scale up (e.g. the availability of a skilled workforce, the ability to construct the necessary infrastructure on time, or safety concerns around new technologies)?


Critical aspects for massive deployment of storage are uncertainty of revenue streams (see the answer to point 4) and not clear authorization process timing. The first point can be addressed with specific auctions or incentives. The second point needs clear procedures and definitions for storage technologies.


  1. What steps should the Government take now to ensure this storage can come online later in the current decade?



11 September 2023