frequenty asked questions

ask the flasc team

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With ambitious offshore renewable energy target all the way to 2050, it is evident that offshore will be a key pillar of the future energy system. Significant variable power generation will therefore be taking place in the offshore environment, far from the consumption side. This represents a mismatch in time (when the energy is produced vs when it needs to be consumed) and space (where the energy is produced vs where it needs to be consumed). This mismatch can result in a significant value loss from offshore renewables, jeopardising project bankability and the pace of the green transition.

Onshore storage alone is not enough since congested grids cannot deliver offshore power to onshore assets to be stored. Offshore storage of energy on the generation side, combined with onshore storage assets on the consumer side will maximise the value of the offshore resource and transmission infrastructure, resulting in a sustainable and cost-effective energy system.

Co-locating within the offshore environment also allows FLASC to maximise use of offshore infrastructure and well-established design principles, resulting in a solution that is cost-competitive with land-based storage.

Discover 5 reasons to go offshore.

No, FLASC is specifically designed for co-location with existing and upcoming offshore projects, specifically offshore wind and solar. Market research shows that most projects will be in waters not deeper than 300m (incl. floating wind).

Thanks to the pre-charged concept FLASC can reach very high energy densities in such relatively shallow waters (40-400m) since it does not rely on external hydrostatic pressure to store energy. In comparison FLASC can have an energy density (kWh/m3) that is 20 to 100 times greater than competing solutions using hydrostatic pressure: that means a significantly more compact solution for the same storage capacity.

FLASC has a minimal environmental impact: thanks to a high energy density the footprint of any offshore infrastructure is minimised. There is intake and release of seawater but this is managed using standard principles for water cooling in industrial processes. Temperature changes are minimal since the system is designed to be isothermal.

A risk assessment study has already been an carried out with an established offshore test site, and it was confirmed that the system remains within the pre-consented envelope for marine energy deployments.

It is an inherently safe solution, using inert non-toxic materials with no flammability hazards.

FLASC uses predominantly steel as a material, which is required to store the pressurised fluids in the HPES process. Steel is one of the most circular materials available and is considered fundamental to achieving a circular economy: steel components can be effectively reused, remanufactured, or recycled.

Moreover, the system does not require any rare-earth materials or elements that come from geographically restricted supply-chains.

Yes, a proof-of-concept prototype was deployed in November 2017, in Malta’s Grand Harbour, and underwent an extensive testing campaign spanning 15 months. The results were positive: indicating the technical viability of the solution and allowing for validation of internal numerical models being used to design larger systems.

The scientific results from the experimental campaign were subjected to extensive peer-review and published in the Journal of Energy Storage.

Yes, FLASC has already received a Statement of Feasibility from DNV. The company also works with leading offshore delivery partners and systems integrators in bringing the technology to market.

Yes. FLASC’s HPES technology is covered by international patents (WO 2016/128962 A1) covering:

  • Europe (EP32567161)
  • United States (US103447412)
  • China (CN107407248)
  • Japan (JP6709225B2)


Other developments are also subject to pending patent applications.

Early systems have been developed with energy densities of 2.2 kWh/m3, this is already 20x higher than competing hydrostatic solutions. On-going developments leveraging more advanced compression and expansion processes can result in more than 11kWh/m3, making the system potentially 100x more energy dense than competing systems in shallow-water.

Typical maximum pressures are in the range of 200 bar. The system can be designed for higher pressures, but 200 bar allows for leveraging standard pipeline supply-chains as a cost-effective means for storing large volumes of pressurised fluids.

A FLASC system power rating and capacity (duration) can be sized in a completely independent manner. From short duration (large pump / small tank) to longer duration (small pump / large tank) everything is technically possible. However we see that the optimum sweet-spot is in the range of 4-12 hour duration, which coincides with intra-day storage applications.

FLASC targets utility-scale applications of at least 10MW with no real upper bound given the modularity of the solution. Smaller systems are also possible for experimental or pilot applications.

Capital Costs (CAPEX) for a FLASC system can vary depending on the application type. But in general FLASC is cheaper than marinized li-ion batteries on a CAPEX basis, and cheaper than land-based long-duration assets on a levelized cost basis. 

The company has developed in-house sizing tools and methods to ensure an optimised solution, and we are happy to think along on specific projects…so please get in touch.

The Pressure Containment System (PCS) benefits from exposure to the marine environment to achieve a high thermal efficiency. So ideally it is located subsea or within a floating structure.

The Energy Conversion Unit (ECU) on the other hand can be located, topside or subsea, depending on the project requirements. Both options are being developed in parallel.

To ensure maximum versatility, we have developed our solution in a modular a manner, with a range of configurations that are scalable to the needs of specific projects.

We’re also happy to think along on other configurations and system architectures…so please get in touch.

No. Although systems have been designed for integration with floating wind, it is not necessary to modify or integrate anything inside the floater. The FLASC system can be deployed as a completely external plug-and-play solution.

If specific project requirements or synergies would benefit from floater-integrated components, the team can also support on these types of designs.

No. FLASC stores energy as compressed gas but uses a liquid piston to manipulate the gas. During the storage process electricity drives a hydraulic pump which pushes liquid inside a closed chamber, the liquid is incompressible, so it compresses the gas within the chamber.  During the discharge process, the gas is allowed to expand, pushing the incompressible liquid out through a hydraulic turbine or motor to produce electricity.

This approach combines the energy density of a compressible gas with the power density of an incompressible liquid. It also avoids inefficiencies and maintenance issues typically associated with air compressors/expanders.

During the storage process electricity drives a hydraulic pump which pushes liquid inside a closed chamber, the liquid is incompressible, so it compresses the gas within the chamber.  During the discharge process, the gas is allowed to expand, pushing the incompressible liquid out through a hydraulic turbine or motor to produce electricity.

Learn more about Our Solution.

The target efficiency is 70-75% round-trip (electricity in to electricity out). This is achievable thanks to a high thermal efficiency that is achieved by keeping the process isothermal, leveraging the marine environment as a stable heat sink. A thermal efficiency implies that most of the work done to compress the gas can be recovered during discharging. In the case of our prototype campaign, values 96% thermal efficiency were consistently measured.

Combining this high thermal efficiency with the conversion efficiency of proven hydraulic and electrical components from established suppliers makes the 70-75% target achievable for large-scale deployments.

With an energy density of 11kWh/m3, only 90m3 are required to store 1 MWh of energy.

To put this into perspective consider:

– 125MW/400MWh (4-hr duration) FLASC system to be co-located with a 1GW Wind Farm.

– This FLASC system would require 36,400m3.

– Installing this volume as a slender 36” pipe (0.9m) would require 57km of pipe that can be installed within the inter-array corridor.

– A 1GW offshore wind farm with have around 300km of inter-array distance (space between the wind turbines that is typically occupied by electrical cabling).

→ The co-located FLASC system occupies less than 20% of the inter-array distance while delivering the required storage capacity.

Designed using standard principles for offshore technologies, with standard monitoring and periodic preventive maintenance, FLASC systems cast last for 30 years in the offshore environment.

Lifetime is independent of charging/discharging cycling, so it is also highly predictable. 

Subsea structures and equipment can be designed for minimal maintenance requirements, typically some basic monitoring is required, but other than that it is fit-and-forget.

Topside hydraulic equipment would typically require some preventive maintenance every 5 years, and this can be combined with, for example, wind turbine maintenance to minimise offshore logistics and down-time.

Yes. FLASC requires structures to store pressurized fluids. This is typically new infrastructure but can also be an existing pipeline approaching end-of-life or sub-surface structure. Some of these assets are already ear-marked for hydrogen transmission or carbon capture, but these are not always viable. The FLASC system offers an alternative use-case, and since it uses inert materials, can be easily adapted to the residual integrity of the existing structure.

Through it’s collaboration with Subsea 7 and wholly-owned subsidiary Xodus, FLASC has evaluated specific applications of the HPES technology to existing pipelines. Titled ROPES (Re-purposing Offshore Pipelines for Energy Storage), the study showed that in some cases the cost of retrofitting storage is already offset by the deferred abandonment cost.

At the early stages FLASC undertakes concept development, sizing and system optimisation. The company then sells the Energy Conversion Unit (ECU) part of the solution as a standardised hardware module. The ECU embodies the control and operational principles and serves as the grid interface.

The full offshore system, including the Pressure Containment System (PCS) is then deployed via collaboration with leading strategic partners to deliver the full EPCI and integration scope.

FLASC B.V. is a Dutch-registered company (KVK: 76566404) based in Delft, The Netherlands. The company was spun-out from the University of Malta in December 2019.

Apart from The Netherlands, the company leverages strategic relationships to reach key regions in the North Sea (UK, Norway, Belgium). FLASC has also supported feasibility studies in Australia and the US.

Thanks to its close collaboration with the University of Malta, FLASC also actively participates in projects in the Mediterranean.

Yes. Theoretically FLASC systems can be installed onshore. However, a sufficiently large body of water is typically required to stabilise temperatures as the system charges/discharges. The company currently focusses on offshore applications, where the marine environment can contribute to this effect, and the technology’s unique selling points can be better leveraged. 

Yes. Theoretically this is possible but would require careful consideration for how the PCS can be integrated within the vessel. For fully mobile applications this can be challenging, but vessels already capable of storing fluids under pressure could be re-purposed as stationary energy storage system to support ports and coastal areas.

No. FLASC is a complementary technology to the production of green hydrogen, since the latter benefits from stability of the input power to maximize hydrogen output and electrolyser lifetime. The technology is therefore a great fit, especially when hydrogen is produced offshore since batteries or other storage technology are difficult to integrate in these applications. FLASC can also provide pressurised seawater to the desalination stage, as well as cooling water for the compression stage (if required).

A patent combining the FLASC system with an offshore Green Hydrogen production plant was submitted in late 2021 and is currently pending. 

Discover our ongoing projects on FLASC + Hydrogen.

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