Hydro-pneumatic Energy Storage Research Articles

Measurements and Modelling of the Discharge Cycle of a Grid-Connected Hydro-Pneumatic Energy Storage System

Hydro-pneumatic energy storage is a form of compressed-air energy storage that can provide the long-duration storage required for integrating intermittent renewable energies into electrical power grids. This paper presents results based on numerical modelling and laboratory tests for a kilowatt-scale HPES system tested at the University of Malta. This paper presents measurements of the discharge cycle, in which energy stored in compressed air within a pressure vessel is hydro-pneumatically converted back into electricity via a Pelton turbine and fed into the national electricity grid. The tests were conducted using a hydraulic turbine operated under different fixed-turbine rotational speed settings, with the pressure being allowed to decrease gradually during the HPES system’s discharge cycle. The system’s overall efficiency accounted for flow losses, turbine inefficiencies, and electrical losses. The tests showed that this efficiency was practically independent of the compressed-air pressure of specific water turbine runner speeds, despite the water turbine operating at fixed speeds. A numerical model developed in MATLAB Simulink (R2022a) was also presented for use simulating the hydraulic performance of the system during the discharge cycle. The model used secondary loss coefficients for the hydraulic circuit and derived velocity coefficients from computational fluid dynamics (CFD) for the Pelton turbine nozzle. We achieved very good agreement between the predictions based on numerical modelling and the measurements taken during laboratory testing.

The design and analysis of a hydro-pneumatic energy storage closed-circuit pump control system with a four-chamber cylinder

A decentralized variable electric motor and fixed pump (VMFP) system with a four-chamber cylinder is proposed for mobile machinery, such that the energy efficiency can be improved by hydro-pneumatic energy storage, and problems of closed-circuit pump-controlled systems including asymmetrical flow and speed limitation are addressed. One of the chambers is arranged to the energy storage accumulator to increase energy efficiency, while the other chambers are flexibly connected to the pump ports to achieve variable transmission ratios. The piston areas of the multiple chambers are designed at first to permit a symmetric single-rod cylinder, and secondly a switching system with three operating modes is presented to expand force-velocity capabilities. Then, the four-chamber cylinder system with three solenoid valves is designed to substitute for the traditional two-chamber boom cylinder in a 6-ton excavator. A valve switching logic, as well as a feedforward and feedback compound speed controller, are presented. Simulations conducted in a 6-ton excavator model show that the maximum velocity increases by 66 %, together with asymmetrical flows to diminish the low-pressure charging accumulator. Peak power and energy consumption are both reduced by more than 20 % compared with the VMFP using the two-chamber cylinder. The energy-saving characteristics of the 6-ton excavator are emphatically analyzed considering energy storage and re-utilization. At last, experiment verifications are conducted in a lifting mechanism to verify the proposed energy-storage system.

Analysis of the Wave Attenuating and Dynamic Behaviour of a Floating Breakwater Integrating a Hydro-Pneumatic Energy Storage System

Floating breakwaters have recently been generating increasing interest as a vital means to provide shelter and protect the ever-increasing number of structures deployed at sea. Notwithstanding the novel ideas being put forward, to date, floating breakwater deployment has been limited to inshore and shallow water areas. The scale of such structures has been restricted to the smaller spectrum. Furthermore, whilst some concepts to integrate floating breakwaters with other offshore systems have been proposed to benefit from cost-sharing strategies, studies related to floating breakwaters integrating energy storage are lacking in the open literature. The present research investigates the wave attenuating and dynamic performance of a large-scale floating breakwater in deep seas with a hydro-pneumatic energy storage system also integrated within the structure. This article highlights the arising need for floating breakwaters and sheds light on the present-day technological status of floating wave breakers. It then lays the ground for the proposed, novel floating breakwater concept that aims to address the current knowledge gaps in this field of study. The simulation results generated from numerical modelling via the potential flow solver ANSYS® AQWA™ have been promising, connoting that the addition of hydro-pneumatic energy storage to a floating breakwater will not lead to a degradation in the dynamic performance or wave breaking efficiency of the floating structure.

Numerical modelling of a hydro-pneumatic energy storage system for smoothing power fluctuations from offshore wind

Energy storage systems are imperative in tackling the regulation of electricity supply and demand mismatch to avoid curtailment of wind energy. Co-locating energy storage in the same operating region as the offshore wind farms allows for an unobtrusive environment while also steering away from rising land prices. The presented work involves an offshore Hydro-Pneumatic Energy Storage (HPES) system made up of a subsea accumulator pre-charged with compressed air. The Energy Conversion Unit (ECU) of the system consists of a megawatt-scale hydraulic pump and a turbine. This paper discusses a novel numerical model developed in Python™ for simulating the operation of the ECU pump and turbine of the offshore HPES system by using a simple moving average, based on a time window of wind data, whilst also introducing a one-step-ahead forecasting model. The results of the research are split into two parts; Firstly, the analysis and validation of the Seasonal Auto Regressive Integrated Moving Average (SARIMA) forecasting model is performed. Secondly, results on the pump and turbine performance based on the smoothened power are shown. The research found that despite the centrifugal pump limitations due to variable head operation, a smoothened power output is efficiently (> 90 %) attained in retaining the intermittent power generated.

Sensitivity analysis of levelized cost of hydro-pneumatic electricity storage for grid support applications

The first sensitivity analysis of hydro-pneumatic levelized cost of electricity storage for a set of twelve power system applications, ranging from primary response to seasonal storage, is done, using as parameters the specific power and energy investment costs and round-trip efficiency. The electric-to-electric round-trip efficiency for hydro-pneumatic energy storage systems is discussed, using a lab-scale hydro-pneumatic energy storage system that was built using commercially available bladder hydraulic accumulators. In general, the results show that hydro-pneumatic energy storage can be very competitive whenever the number of annual cycles is sufficiently high, as happens in the case of primary response application but, even for applications with a low number of annual cycles, it can be competitive for applications with a high ratio power/capacity. A comparison with the dominant technologies, pumped hydro and Li-Ion, shows that, for the highest hydro-pneumatic energy storage investment costs considered, this technology will only be competitive for primary response, but, for the lowest investment costs considered, hydro-pneumatic energy storage is more cost-effective than Li-Ion for all applications, and can even be more cost-effective than pumped hydro in four of the twelve applications. The main challenges to the development of hydro-pneumatic energy storage systems are discussed.

A Numerical Model Comparison of the Energy Conversion Process for an Offshore Hydro-Pneumatic Energy Storage System

Energy storage is essential if net zero emissions are to be achieved. In fact, energy storage is a leading solution for reducing curtailment in an energy system that relies heavily on intermittent renewables. This paper presents a comparison between two numerical models which simulate the energy conversion unit performance of a hydro-pneumatic energy storage system. Numerical modelling is performed in PythonTM (Alpha Model) and Mathworks® Simulink® and SimscapeTM (Beta Model). The modelling aims to compare the time-series predictions for the simplified model (Alpha Model) with the more physically representative model (Beta Model). The Alpha Model provides a quasi-steady-state solution, while the Beta Model accounts for machinery inertias and friction within hydraulic flow circuits. Results show that the energy conversion performance simulations between the two models compare well, with a notable difference during system start-up due to the inclusion of transients in the Beta Model. Given its simplicity, the Alpha Model has high computational efficiency, while the Beta Model requires more computational time due to its complexity. This study showed that, despite its simplicity, the Alpha Model is able to generate results that are very similar to those from the Beta Model (with the average RMSE being less than 5%).

Assessing the Potential Increase in the Energy Storage Density of Subsea Hydro-Pneumatic Accumulators Using Carbon Dioxide in Lieu of Air

Abstract The integration of energy storage systems (ESS) on a large scale is becoming essential to mitigate intermittency issues in power supply from offshore wind farms. This paper deals with an offshore hydro-pneumatic energy storage (HPES) system comprising of a subsea accumulator pre-charged with a compressed gas. The paper applies a simplified thermodynamic model to investigate the potential increase in the energy storage density of the proposed HPES system by replacing air with carbon dioxide (CO2) that is able to undergo a phase change (gas-liquid-gas) during the storage cycle when limiting the peak operating pressure below the critical point. The study is based on a numerical model for simulating the thermodynamics of the entire storage cycle. A sensitivity study is conducted to examine the influence of main operational parameters, primarily the seawater temperature, peak working pressure, and sea depth, on the storage density of the HPES system operating with a dual phase fluid. It is shown that the storage density of HPES accumulators can be increased substantially by using CO2 in lieu of air. The increase in density is found to depend considerably on the seawater temperature and sea depth.

Numerical Modeling of the Thermal Behavior of Subsea Hydro-Pneumatic Energy Storage Accumulators Using Air and CO2

This paper numerically models the thermal performance of offshore hydro-pneumatic energy storage (HPES) systems composed of a subsea accumulator pre-charged with a compressed gas. A time-marching numerical approach combining the first law of thermodynamics with heat transfer equations is used to investigate the influence of replacing air within an HPES system with carbon dioxide (CO2). The latter is able to experience a phase change (gas–liquid–gas) during the storage cycle in typical subsea temperatures when limiting the peak operating pressure below the critical point. The influences of integrating a piston and an inner liner within the accumulator to mitigate issues related to gas dissolution in seawater and corrosion are explored. It is found that the energy storage capacity of subsea HPES accumulators increases substantially when CO2 is used as the compressible fluid in lieu of air, irrespective of the accumulator set up. It is also noted that the length-to-diameter ratio of the accumulator has a considerable influence on the round-trip thermal efficiency for both air- and CO2-based accumulators. Another factor influencing the round-trip thermal efficiency is the presence of the inner liner. Moreover, the CO2-based HPES system yields a lower round-trip thermal efficiency over that of air.

Modelling and Performance Analysis of Cyclic Hydro-Pneumatic Energy Storage System Considering the Thermodynamic Characteristics

The energy storage system of electric-drive heavy mining trucks takes on a critical significance in the characteristics including excellent load capacity, economy, and high efficiency. However, the existing battery-based system does not apply to harsh cold environments, which is the common working condition for the above trucks. A type of cycle hydro-pneumatic energy storage system for the trucks was proposed in this study. The dynamic model of the system, including the dynamic and thermodynamic models of hydraulic and pneumatic parts, was built to analyze the performance of the system. Subsequently, the thermodynamic characteristics were clarified during the energy storage and released through the real test condition-based simulation. The power and energy performances of the system were studied in practice based on the above characteristics. The analysis of the results showed that the system reduced 22.03% driving power at the optimal braking energy recovery rate, the energy density was nearly 12.6 MJ/m3, the maximum input power was higher than 230 kW, and the cycle efficiency was about 40.6%. The results of this study will be conducive to the application of the hydro-pneumatic energy storage system for the electric-drive mining trucks and reducing the resulting carbon emission.

Repurposing Offshore Pipeline as Energy Storage Opens Market Segment

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 31703, “Repurpose Offshore Pipeline as Energy Storage (ROPES): Opening a New Market Segment Offshore,” by Azril Syazwan Hazim, SPE, Subsea 7, Daniel Buhagiar, FLASC, and Alasdair Gray, Xodus. The paper has not been peer reviewed. Copyright 2022 Offshore Technology Conference. Reproduced by permission. _ The repurposed offshore pipelines as energy storage (ROPES) solution repurposes aged offshore installations into energy storage systems based on proven hydropneumatic principles toward a cost-competitive, reliable system. Findings from a recent concept-assessment study show the cost competitiveness of the solution as a result of a low levelized cost of storage (LCOS) paired with the value of deferring full decommissioning of existing assets. The ROPES solution enables the storage of renewable power while allowing for the optimization of time and expenditure for decommissioning of infrastructure. Background Energy-storage technologies address a fundamental problem related to the integration of renewable energy production into conventional energy systems on a large scale: the mismatch between intermittent energy supply and consumer demand. Balancing supply and demand is quickly becoming the greatest obstacle to increased uptake of renewable energy. An emerging industrialized energy storage solution (ESS) technology uses mechanical power storage based on proven fluid-compression principles. Hydropneumatic energy storage (HPES) relies on a large pressure containment system (PCS) that acts as a pressurized liquid piston—potentially a pipeline system—with energy activated by a pump and recovered through a turbine. The solution is positioned to improve on economics for offshore wind farms either through remote units within each turbine or through the ROPES concept, with the energy conversion unit (ECU) on either the seabed or an adjacent decommissioned offshore platform. Overview of HPES Technology The proprietary HPES system stores energy by using it to pump seawater into a closed chamber to compress a fixed volume of precharged inert gas. The energy then can be recovered by allowing the compressed gas to push the water back out through a hydraulic turbine generator. The technology embodies a patented combination of two key features: - Pneumatic precharging allows the system to be installed in shallow water, making it suitable for both fixed-bottom and floating wind applications. - Using the ocean as a natural heatsink results in an efficient, isothermal system without the need for complex thermal-management systems.

ROPES Offers an Energy Transition Solution to Pipeline Decommissioning

Oil and gas companies around the world are repositioning themselves to face the energy transition—whether that means embracing the fact that the green economy of the future calls for less hydrocarbon use or something more radical, like Lundin Energy’s (now called Orrön Energy) recent move to sell off its oil and gas assets to become a pure renewables player. One certainty is that as companies trend away from oil and gas and toward a lower-carbon frontier there will still be plenty of “cleanup” to do while players figure out exactly what to do with more than 100 years of oil and gas infrastructure. Offshore, decommissioning of platforms and pipelines is a capital-intensive business and one that is expected to grow in the coming years. Last year, IHS Markit released a forecast predicting global offshore decommissioning spending to reach almost $100 billion for the 2021–2030 period, up by more than 200% compared to the previous 10-year period. According to the forecast, nearly 2,800 fixed platforms and 160 floating platforms could be decommissioned. That represents 33% of fixed platforms and 43% of floating platforms currently in operation. Additionally, more than 18,500 wellheads, 2,850 subsea trees, and 83000 km of offshore pipelines and umbilicals currently in operation are subject to decommissioning during the same period. More than 50% of the expected activity is spread across four countries: the UK, US, Brazil, and Norway. The financial burden and safety liability of marine decommissioning have prompted some to look at the potential for repurposing the hardware and using it in moving toward the drive to net-zero emissions: platforms that could be used to host wind turbines, vessels that could be redesigned to collect hydroenergy, and pipelines that could be repurposed for potential battery storage. Repurposing offshore pipeline as energy storage (ROPES) is a concept that is being investigated by a partnership of offshore projects and services specialists Subsea 7 and offshore energy storage startup Flasc. Flasc was founded as a spinoff from the University of Malta in 2019 and is based in the Netherlands. The concept was described in a paper presented at the 2022 Offshore Technology Conference in Houston (OTC 31703). Subsea 7 and Flasc signed a cooperative exclusivity agreement in late 2020 to work toward the commercialization of Flasc’s patented hydro-pneumatic energy storage (HPES) concept offshore. HPES combines pressurized seawater with compressed air to create an efficient, large-scale energy storage device that can be applied across a wide range of offshore applications. Energy is stored by pumping seawater into a closed chamber to compress a fixed volume of precharged inert gas. The energy can be recovered by allowing the compressed gas to push the water back out through a hydraulic turbine generator (Fig. 1). The technology leverages existing infrastructure and supply chains, along with the marine environment itself as a natural heatsink. The first working prototype was successfully tested in 2018, and DNV has granted the technology a Statement of Feasibility based on a technical and commercial assessment. “The hydro-pneumatic technology is at the core of the ROPES concept, but can also be applied to other embodiments,” said Daniel Buhagiar, co-founder and chief executive of Flasc. “Within this collaboration, we’ve looked at doing some different designs and different products, and ROPES emerged as a very interesting opportunity. Typically, we’re looking at doing new infrastructure, [for instance] installing a bundle or a new piece of kit to store the pressurized fluids. ROPES, we thought, was really the low-hanging fruit because the pipeline infrastructure is already there, and we can create a use case for it beyond the typical applications, such as hydrogen and carbon capture, which are not always possible.”

Investigation on energy conversion instability of pump mode in hydro-pneumatic energy storage system

The pump mode of hydro-pneumatic energy storage (HPES) system often experiences off-design conditions due to the boundary pressure rises, and the resultant energy conversion instability has an adverse effect on the system operation. However, the evolutionary process of this instability and the corresponding flow events are still not fully understood. Experimental and numerical simulation studies of a centrifugal pump with vaned diffuser were conducted in a wide operating range, and the following notable results were obtained. The energy conversion of pump mode shows three typical stages as the pump head increases, stable work→stumbled work→shaky work, corresponding to the inner flow pattern development of stall-free→stall inception→stall deepening. In this evolutionary process, the attenuation of rotor blade loading gradually spreads from the inlet shroud side to the entire blade. This strengthens the natural adverse potential rothalpy gradient and induces the energetic vortical structures including leading backflow vortices, dynamic stall cells and trailing helical vortices. A strong coupling between large-scale vortical motions and energy conversion is observed and this yields a Logistic growth of the shaft power and pump head fluctuations. The critical condition for the energy conversion instability is the diagnostic function SI = 1, and this is recommended for determining the stability limit of the pump mode.

Experimental and thermodynamic investigation on isothermal performance of large-scaled liquid piston

Hydro-pneumatic Energy Storage (HYPES) is one of the research hotspots by introducing liquid piston's isothermal/near-isothermal compressed method to compressed air energy storage. This paper focuses on heat transfer behavior of liquid piston according to experimental result. Firstly, a case is proposed to show the isothermal compressed performance of liquid piston with a 24.71 m3 cylinder: average temperature rises 10.59 K with a compressed ratio of 1.86. Models have been validated by experimental data. Secondly, heat transfer of compressed process has been investigated. The temperature distribution is uniform and exergy efficiency during compressed process is 86.9%: 85.4% of input exergy transfers into the pressure exergy of air. Additionally, availability analysis has been conducted. Ambient temperature has little influence on isothermal compressed process. Initial pressure affects liquid piston through air mass while pump flow rate affects liquid piston through compressed time. Moreover, cycle performance on practical process considering residual air has been studied with two scaled cases. Starting at ambient condition, both cases keep stable since the second cycle and show a good isothermal performance with large compressed ratio. The highest temperature is at the end of compressing, while the lowest temperature occurs in expanding process.

Offshore Wind-to-Hydrogen Production Plant Integrated with an Innovative Hydro-Pneumatic Energy Storage Device

One of the main technical challenges of wind-to-hydrogen production plants is to couple intermittent and variable renewable power sources, such as wind turbines, with an electrolyser. Most hydrogen production concepts rely on electrical storage to smoothen the power input to the electrolyser. In this study, the use of a hydro-pneumatic energy storage system is proposed as an interface between the green, fluctuating electricity supply and the electrolyser. The performance of the proposed solution is analysed and compared to that of a conventional offshore wind-to-hydrogen production plant in order to identify potential advantages and drawbacks. The results of the simulations show that the FLASC energy storage system provides a stabilized, yet green power supply. Short-term fluctuations of the power input to the electrolyser can be avoided. A 70% reduction of the On/Off cycles can be obtained. Moreover, if compared to an offshore wind-to-hydrogen production plant with no storage there is no substantial difference in terms of hydrogen production observed over the analysed period of one year in spite of a 70% round-trip efficiency of the energy storage device.

Nested Optimization of Oil-Circulating Hydro-Pneumatic Energy Storage System for Hybrid Mining Trucks

In order to recover and utilize the potential energy of mining trucks efficiently, this paper proposes a nested optimization method of a novel energy storage system. By analyzing the multi-objective optimization problem of the oil-circulating hydro-pneumatic energy storage system, a nested optimization method based on the advanced adaptive Metamodel-based global optimization algorithm is carried out. Research shows that this method only requires a short time to solve the complex nonlinear hybrid optimization problem and achieves better results. The optimized energy storage system has higher system efficiency, energy density, and volume utilization rate, thus obtaining a smaller system volume and weight. Verified by the bench experiment of its powertrain, the hydro-pneumatic hybrid mining truck with the optimized energy storage system significantly reduces its fuel consumption and CO2 emission. Thus, it lays the foundation for the practical application of hydro-pneumatic hybrid mining trucks.

A Software Tool for the Design and Operational Analysis of Pressure Vessels used in Offshore Hydro-pneumatic Energy Storage

Despite the breakthroughs and rapid growth in the global installed offshore wind capacity over the last two decades, a prevailing major challenge is the intermittent nature of the wind resource itself. Consequently, co-locating energy storage systems with wind turbines deployed out at sea is perceived as a key component that will help to overcome this crucial challenge and address the mismatch between the supply of green energy and actual energy demand in real time. Of particular interest are hydro-pneumatic energy storage solutions that can deliver a safer and more reliable operation for a longer life span when compared to electro-chemical storage solutions.This paper presents a smart software tool named SmartPVB, which has been specifically developed for the optimisation of the design of pressure vessel bundles used in offshore hydro-pneumatic energy storage systems. The optimised design parameters obtained through the software SmartPVB help drive the material requirements to a minimum. A sensitivity study to analyse the influence of various parameters on a hydro-pneumatic energy storage system mounted on the seabed at a water depth of 200 m is also outlined. Results suggest that the optimal operating pressure ratio to minimise steel requirments for the pressure vessel bundle lies between 2.4 and 2.6. Furthermore, it is shown that the overall mass of the pressure vessel bundle per unit of storage capacity increases with sea depth, while it decreases with increasing peak operating pressures up to 200 bar.

Small-scale Experimental Testing of a Novel Marine Floating Platform with Integrated Hydro-pneumatic Energy Storage

Co-locating energy storage within the floating platform of offshore renewable energy systems is an effective way of reducing the cost and environmental footprint of marine energy storage devices. However, the development of suitable, non-hazardous technologies, and the influence of the marine environment on their efficiency remains an open problem. Research at the University of Malta has culminated in the Floating Liquid-piston Accumulator using Seawater under Compression (FLASC) concept, a solution involving hydro-pneumatic energy storage tailored for offshore renewables. A small-scale prototype was deployed at a sheltered marine location in the Maltese Islands, in the central Mediterranean Sea. The aim of the experimental campaign was to measure the performance of the energy storage system, and to quantify the effects of different system parameters along with the surrounding meteorological conditions. Results from selected charging-discharging cycles are presented, these include different scheduling schemes and pressure ranges. Overall, results indicate that the experimental system consistently demonstrated a high thermal efficiency (> 93%) across hundreds of charging cycles. Operating pressure range and charging schedule play a limited role on the hydro-pneumatic process, whereas seasonal temperature changes play a more significant role, in that such changes can slightly alter the effective storage capacity of the system. Results from this experimental work provide a practical proof-of-concept for hydro-pneumatic marine energy storage, and can enable key conclusions to be drawn providing a basis to numerous ongoing developments in fluid-based energy storage systems for offshore implementation.

Surrogate Modeling for Capacity Planning of Charging Station Equipped With Photovoltaic Panel and Hydropneumatic Energy Storage

Abstract Due to the promising potential for environmental sustainability, there has been a significant increase of electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEV) in the market. To support this increasing demand for EVs and PHEVs, challenges related to capacity planning and investment costs of public charging infrastructure must be addressed. Hence, in this paper, a capacity planning problem for charging stations is developed and aims to balance the current capital investment costs and future operational revenue. The charging station is assumed to be equipped with the solar photovoltaic (PV) panel and an energy storage system, which could be electric battery or recently invented hydropneumatic energy storage (ground-level integrated diverse energy storage (GLIDES)) system. A co-optimization model that minimizes investment and operation cost is established to determine optimal solution while considering capacity planning and following operations. EV mobility is modeled as an Erlang-loss system. Meanwhile, stochastic programming is adopted to capture uncertainties from solar radiation and charging demand of EV fleet. To provide a more general and computationally efficient model, main configuration parameters are sampled in design space and then fixed in solving the co-optimization model. Sampled parameters include EV charging slots number, PV area, capacity of energy storage system, and daily mean EV arrival number. Based on the sampled parameter combinations and its responses, black-box mappings are then constructed using surrogate models, which could provide insights for charging station placement in different practical situations. The effectiveness of the proposed surrogate modeling approach is demonstrated in numerical experiments. The results indicate better profit advantage of GLIDES over battery system with the increased power capacity

Hydro-pneumatic storage for wind-diesel electricity generation in remote sites

Unlike the majority of Canadian population, which benefits from reliable, guaranteed and affordable electricity, most Canadian remote communities do not have these benefits because they rely on locally generated electricity. Diesel generators are the main sources of electrical energy that supply most of these remote isolated areas. The operation and transportation cost of diesel fuel in addition to its price have led to the procurement of a more efficient and environmentally greener supply methods. Therefore, the combination of these generators with renewable sources, such as wind energy, in a wind-diesel hybrid system with compressed air energy storage can reduce these deficits by reducing the fossil fuel consumption, operating time of diesel engines, operation costs and environmental harm. Many recent studies have shown that the optimal management of the stored air reserve is to overcharge an existing diesel engine with compressed air. Based on this concept, a novel wind-diesel hybrid system with adiabatic air compression and storage at constant pressure is proposed. This concept combines adiabatic compressed air energy storage and hydro pneumatic energy storage technologies with a wind-diesel system. Based on a real wind speed and temperature data from the village of Tuktoyaktuk in Northern Canada, a study case was achieved. Simulation results show that the annual fuel savings can reaches 60% for the diesel consumption. This results in a significant decrease of electricity production cost and diesel engine gas pollution reduction. In addition, this system made it possible to maximize the benefits of available wind energy. Indeed, the results show that 70% of electrical energy is produced from renewable sources. Furthermore, this system prevents diesel generators from running on low loads and enable the diesel engine to be switched off in several situation while maintaining a reliable electric power supply. This was not possible in the previously proposed systems. Furthermore, the storage volume required for optimum operation in this system is relatively small compared with a large storage volume that has been already proposed in other systems. Finally, a cost study and a sensitivity analysis have demonstrated the feasibility of this system.

Cost Evaluation of Two Concepts for the Integration of Hydro-pneumatic Energy Storage in Floating Wind Turbines

Cost Evaluation of Two Concepts for the Integration of Hydro-pneumatic Energy Storage in Floating Wind Turbines