We introduce firm solar forecasts as a strategy to operate optimally overbuilt solar power plants in conjunction with optimally sized storage systems so as to make up for any power prediction errors, and hence entirely remove load balancing uncertainty emanating from grid-connected solar fleets. A central part of this strategy is the plant overbuilding that we term implicit storage. We show that strategy, while economically justifiable on its own account, is an effective entry step to achieving least-cost ultra-high solar penetration where firm power generation will be a prerequisite. We demonstrate that in the absence of an implicit storage strategy, ultra-high solar penetration would be vastly more expensive. Using the New York Independent System Operator (NYISO) as a case study, we determine current and future costs of firm forecasts for a comprehensive set of scenarios in each ISO electrical region, comparing centralized vs. decentralized production and assessing load flexibility’s... [more]

This paper presents the design and a short cycle repeatability test of a silica gel-based thermal energy storage system using low grade heat for the desorption phase. The system was designed to test the degradation in the energy storage density of the adsorbent material for a 2 h working period in a short number of cycles (5 cycles). Low grade heat of 70 °C is used for regeneration during the desorption phase in each cycle. It was found that a reduction of 1.6 W/kg per each cycle of energy storage was observed, up to 5 cycles. The maximal heat storage density was 292 kJ/kg at the first cycle and reduced to 225 kJ/kg at the fifth cycle. Furthermore, the total amount of water vapor adsorbed in the silica gel was observed as well. The test of energy storage was performed under a short time period (maximal approx. 165 min).

In many heat transfer related applications, there is a need for a stable, constant supply temperature. As a result, the integration of intermittent renewable sources of heat into these processes can prove to be challenging, requiring special temperature smoothing devices or strategies. This study focuses on the application of phase change materials integrated into a double tube heat exchanger as a possible thermal smoothing device. The objective of this study is to evaluate the ability of the exchanger to smoothen out temperature variations within the cold stream outlet while the hot stream is subject to oscillating inlet conditions. A computational fluid dynamics approach is used where a numerical model is developed, validated and then used to model the conjugate heat transfer within the heat exchanger. Four organic phase change materials (PCM) with different phase change temperatures were selected for investigation (myristic, octadecane, eicosane, and wax) to study the relationship b... [more]

Stationary battery systems are becoming increasingly common worldwide. Energy storage is a key technology in facilitating renewable energy market penetration and battery energy storage systems have seen considerable investment for this purpose. Large battery installations such as energy storage systems and uninterruptible power supplies can generate substantial heat in operation, and while this is well understood, the thermal management systems that currently exist have not kept pace with stationary battery installation development. Stationary batteries operating at elevated temperatures experience a range of deleterious effects and, in some cases, serious safety concerns can arise. Optimal thermal management prioritizes safety and balances costs between the cooling system and battery degradation due to thermal effects. Electric vehicle battery thermal management has undergone significant development in the past decade while stationary battery thermal management has remained mostly sta... [more]

The modular multilevel converter−bidirectional DC−DC converter (MMC−BDC) has been proposed to be utilized in the vessel integrated power system to interconnect the medium voltage bus and the distributed energy storage elements. In the shipboard applications, MMC−BDC faces unbalanced sub-module power operation because of the inconsistent state-of-charge (SOC) of the energy storage elements. Researchers have investigated into the unbalanced operation principle of MMC−BDC and proposed some unbalanced operation control strategies, but these traditional strategies do not perform well in both aspects of operating range and efficiency. Therefore, this paper proposes a novel Lyapunov-function-based feedback linearization control strategy for the independent sub-module voltage control of MMC−BDC, which not only shows wide unbalanced operation range and high efficiency, but also realizes the decoupling and symmetrical control of the sub-module capacitor voltages.

Solar Photovoltaics (PV) is seen as one of the renewable energy technologies that could help reduce the world’s dependence on fossil fuels. However, since it is dependent on the sun, it can only generate electricity in the daytime, and this restriction is exacerbated in electricity grids with high PV penetration, where solar energy must be curtailed due to the mismatch between supply and demand. This study conducts a techno-economic analysis to present the cost-optimal storage growth trajectory that could support the dynamic integration of solar PV within a planning horizon. A methodology for cost-optimal assessment that incorporates hourly simulation, Monte Carlo random sampling, and a proposed financial assessment is presented. This approach was tested in Japan’s southernmost region since it is continuously increasing its solar capacity and is at the precipice of high PV curtailment scenario. The results show the existence of a cost-optimal storage capacity growth trajectory that bal... [more]

The urgent energy transition needs a better penetration of renewable energy in the world’s energy mix. The intermittency of renewables requires the use of longer-term storage. The present system uses water displacement, in a lined rock cavern or in an aerial pressurised vessel, as the virtual piston of compressor and expander functions in a carbon dioxide heat pump cycle (HPC) and in an organic transcritical cycle (OTC). Within an impermeable membrane, carbon dioxide is compressed and expanded by filling and emptying pumped-hydro water. Carbon dioxide exchanges heat with two atmospheric thermal storage pits. The hot fluid and ice pits are charged by the HPC when renewable energy becomes available and discharged by the OTC when electricity is needed. A numerical model was built to replicate the system’s losses and to calculate its round-trip efficiency (RTE). A subsequent parametric study highlights key parameters for sizing and optimisation. With an expected RTE of around 70%, this CO2... [more]

In recent years, power-to-gas technologies have been gaining ground and are increasingly proving their reliability. The possibility of implementing long-term energy storage and that of being able to capture and utilize carbon dioxide are currently too important to be ignored. However, systems of this type are not yet experiencing extensive realization in practice. In this study, an overview of the experimental research projects and the research and development activities that are currently part of the power-to-gas research line is presented. By means of a bibliographical and sitographical analysis, it was possible to identify the characteristics of these projects and their distinctive points. In addition, the main research targets distinguishing these projects are presented. This provides an insight into the research direction in this regard, where a certain technological maturity has been achieved and where there is still work to be done. The projects found and analyzed amount to 87,... [more]

Power systems are subjected to a wide range of disturbances during daily operations. Severe disturbances, such as a loss of a large generator, a three-phase bolted fault on a generator bus, or a loss of a transmission line, can lead to the loss of synchronism of a generator or group of generators. The ability of a power system to maintain synchronism during the few seconds after being subjected to a severe disturbance is known as transient stability. Most of the modern methods of controlling transient stability involve special protection schemes or remedial action schemes. These special protection schemes sense predetermined system conditions and take corrective actions, such as generator tripping or generation re-dispatch, in real time to maintain transient stability. Another method is the use of a real-time feedback control system to modulate the output of an actuator in response to a signal. This paper provides a fundamental evaluation of the use of feedback control strategies to im... [more]

The large-scale storage of hydrogen in salt caverns, modelled on today’s natural gas storage, is a promising approach to storing renewable energy over a large power range and for the required time period. An essential subsystem of the overall gas storage is the surface facility and, in particular, the compressor system. The future design of compressor systems for hydrogen storage strongly depends on the respective boundary conditions. Therefore, this work analyses the requirements of compressor systems for cavern storage facilities for the storage of green hydrogen, i.e., hydrogen produced from renewable energy sources, using the example of Lower Saxony in Germany. In this course, a hydrogen storage demand profile of one year is developed in hourly resolution from feed-in time series of renewable energy sources. The injection profile relevant for compressor operation is compared with current natural gas injection operation modes.

The transition of residential communities to renewable energy sources is one of the first steps for the decarbonization of the energy sector, the reduction of CO2 emissions, and the mitigation of global climate change. This study provides information for the development of a microgrid, supplied by wind and solar energy, which meets the hourly energy demand of a community of 10,000 houses in the North Texas region; hydrogen is used as the energy storage medium. The results are presented for two cases: (a) when the renewable energy sources supply only the electricity demand of the community, and (b) when these sources provide the electricity as well as the heating needs (for space heating and hot water) of the community. The results show that such a community can be decarbonized with combinations of wind and solar installations. The energy storage requirements are between 2.7 m3 per household and 2.2 m3 per household. There is significant dissipation in the storage−regeneration processes... [more]

A battolyser is a combined battery electrolyser in one unit. It is based on flow battery technology and can be adapted to produce hydrogen at a lower efficiency than an electrolyser but without the need for rare and expensive materials. This paper presents a method of determining if a battolyser connected to a wind farm makes economic sense based on stochastic modelling. A range of cost data and operational scenarios are used to establish the impact on the NPV and LCOE of adding a battolyser to a wind farm. The results are compared to adding a battery or an electrolyser to a wind farm. Indications are that it makes economic sense to add a battolyser or battery to a wind farm to use any curtailed wind with calculated LCOE at £56/MWh to £58/MWh and positive NPV over a range of cost scenarios. However, electrolysers, are still too expensive to make economic sense.

Energy storage is a key solution to supply renewable electricity on demand and in particular batteries are becoming attractive for consumers who install PV panels. In order to minimize their electricity bill and keep the grid stable, batteries can combine applications. The daily match between PV supply and the electricity load profile is often considered as a determinant for the attractiveness of residential PV-coupled battery systems, however, the previous literature has so far mainly focused on the annual energy balance. In this paper, we analyze the techno-economic impact of adding a battery system to a new PV system that would otherwise be installed on its own, for different residential electricity load profiles in Geneva (Switzerland) and Austin (U.S.) using lithium-ion batteries performing various consumer applications, namely PV self-consumption, demand load-shifting, avoidance of PV curtailment, and demand peak shaving, individually and jointly. We employ clustering of the hous... [more]

Hybrid photovoltaic installations, defined as on-grid PV system in cooperation with battery energy storage system (BESS), are still rare among the typical investors because the investment cost of the hybrid installation is significantly higher than the one of the on-grid system. However, while considering the broader perspective, such as environmental or technological aspects, the mentioned solution can be competitive with photovoltaic on-grid systems and therefore should be carefully tested in the widest possible context. In this study, the authors compared 3.05 kW of peak power hybrid and on-grid installations operating in temperate climate conditions (Eastern Poland) using economic indicators, such as dynamic generation cost (DGC) and benefit−cost rate (BCR); environmental impact indicators (IMPACT 2002+ and GWP 100a) determined using Life Cycle Assessment (LCA); and technological aspects consideration, including the reliability of examined systems. Creating a ranking of the conside... [more]

This paper proposes a control system for the single-phase Three-Ports Active Neutral- Point-Clamped (ANPC-3P) converter, which can inject a sinusoidal current into the grid, balance the neutral point voltage, and regulate the energy storage system (ESS) current with reduced low-frequency ripple. Despite other applications, ANPC-3P inverter can be used in grid-tied renewable generation to allow the simultaneous connection of a photovoltaic (PV) energy source and an ESS to the AC grid. The ESS is connected directly to the inverter circuit without any auxiliary DC-DC converter, but due to the DC bus pulsed power, it can be subjected to low-frequency current ripple. This undesired current ripple is difficult to filter and can lead to shorter battery life. A control system based on well-known controllers is analyzed and designed. Theoretical analysis is validated experimentally using a single-phase 1-kW prototype.

This paper presents a detailed life-cycle assessment of the greenhouse gas emissions, cumulative demand for total and non-renewable primary energy, and energy return on investment (EROI) for the domestic electricity grid mix in the U.S. state of California, using hourly historical data for 2018, and future projections of increased solar photovoltaic (PV) installed capacity with lithium-ion battery energy storage, so as to achieve 80% net renewable electricity generation in 2030, while ensuring the hourly matching of the supply and demand profiles at all times. Specifically—in line with California’s plans that aim to increase the renewable energy share into the electric grid—in this study, PV installed capacity is assumed to reach 43.7 GW in 2030, resulting of 52% of the 2030 domestic electricity generation. In the modelled 2030 scenario, single-cycle gas turbines and nuclear plants are completely phased out, while combined-cycle gas turbine output is reduced by 30% compared to 2018. Re... [more]

The limitation of fossil fuel uses and GHG (greenhouse gases) emissions reduction are two of the main objectives of the European energy policy and global agreements that aim to contain climate changes. To this end, the building sector, responsible for important energy consumption rates, requires a significant improvement of its energetic performance, an obtainable increase of its energy efficiency and the use of renewable sources. Within this framework, in this study, we analysed the economic feasibility of a stand-alone photovoltaic (PV) plant, dimensioned in two configurations with decreasing autonomy. Their Net Present Value at the end of their life span was compared with that of the same plant in both grid-connected and storage-on-grid configurations, as well as being compared with a grid connection without PV. The analysis confirms that currently, for short distances from the grid, the most suitable PV configuration is the grid-connected one, but also that the additional use of a... [more]

There is the potential for hybridised gas engine-energy storage systems to participate in the Balancing Mechanism (BM) by offering a product that marries the advantages of both units. The higher price offerings are currently dominated by pumped storage (PS) assets. Given their high-flexibility, PS plants mostly offer at higher prices, but respond quicker and can run for a smaller minimum run time than a gas engine on its own. The operation of the hybrid system must match the operation of the pumped storage plants, to be able to claim a space in this part of the BM market including meeting a minimum run time and minimum start time. The business case is dependent on battery costs which in turn depend on size and operational strategy. This paper uses a case study approach to estimate Net Present Value of a hybrid system. The paper uses a mixture of publicly available data and industrially provided data within its analysis. The paper concludes that battery cost and lifespan are still issue... [more]

Driven by global concerns about the climate and the environment, the world is opting for renewable energy sources (RESs), such as wind and solar. However, RESs suffer from the discredit of intermittency, for which energy storage systems (ESSs) are gaining popularity worldwide. Surplus energy obtained from RESs can be stored in several ways, and later utilized during periods of intermittencies or shortages. The idea of storing excess energy is not new, and numerous researches have been conducted to adorn this idea with innovations and improvements. This review is a humble attempt to assemble all the available knowledge on ESSs to benefit novice researchers in this field. This paper covers all core concepts of ESSs, including its evolution, elaborate classification, their comparison, the current scenario, applications, business models, environmental impacts, policies, barriers and probable solutions, and future prospects. This elaborate discussion on energy storage systems will act as a... [more]

The intermittent nature of most renewable energy sources requires their coupling with an energy storage system, with pumped storage hydropower (PSH) being one popular option. However, PSH cannot always be constructed due to topographic, environmental, and societal constraints, among others. Underground pumped storage hydropower (UPSH) has recently gained popularity as a viable alternative and may utilize abandoned mines for the construction of the lower reservoir in the underground. Such underground mines may have complex geometries and the injection/pumping of large volumes of water with high discharge could lead to uneven water level distribution over the underground reservoir subparts. This can temporarily influence the head difference between the upper and lower reservoirs of the UPSH, thus affecting the efficiency of the plant or inducing structural stability problems. The present study considers an abandoned slate mine in Martelange in Southeast Belgium as the lower, underground,... [more]

Renewable energies are often subject to stochastic resources and daily cycles. Energy storage systems are consequently applied to provide a solution for the mismatch between power production possibility and its utilization period. In this study, a solar integrated thermo-electric energy storage (S-TEES) is analyzed both from an economic and environmental point of view. The analyzed power plant with energy storage includes three main cycles, a supercritical CO2 power cycle, a heat pump and a refrigeration cycle, indirectly connected by sensible heat storages. The hot reservoir is pressurized water at 120/160 °C, while the cold reservoir is a mixture of water and ethylene glycol, maintained at −10/−20 °C. Additionally, the power cycle’s evaporator section rests on a solar-heated intermediate temperature (95/40 °C) heat reservoir. Exergo-economic and exergo-environmental analyses are performed to identify the most critical components of the system and to obtain the levelized cost of elect... [more]

This paper presents an environmental sustainability assessment of residential user-scale energy systems, named solar home systems, encompassing their construction, operation, and end of life. The methodology adopted is composed of three steps, namely a design phase, a simulation of the solar home systems’ performance and a life cycle assessment. The analysis aims to point out the main advantages, features, and challenges of lithium-ion batteries, considered as a benchmark, compared with other innovative devices. As the environmental sustainability of these systems is affected by the solar radiation intensity during the year, a sensitivity analysis is performed varying the latitude of the installation site in Europe. For each site, both isolated and grid-connected solar home systems have been compared considering also the national electricity mix. A general overview of the results shows that, regardless of the installation site, solid state nickel cobalt manganese and nickel cobalt alum... [more]

This paper provides the result of a techno-economic study of potential energy storage technologies deployable at wind farms to provide short-term ancillary services such as inertia response and frequency support. Two different scenarios are considered including a single energy storage system for the whole wind farm and individual energy storage for each wind turbine (located at either the dc or the ac side of its grid-side converter). Simulations are introduced to check the technical viability of the proposal with different control strategies. Power and energy capability requirements demanded by both specific services are defined for each studied case based on present and future grid code needs. Based on these requirements, the study compares a wide range of energy storage technologies in terms of present-day technical readiness and properties and identifies potential candidate solutions. These are flywheels, supercapacitors, and three chemistries out of the Li-ion battery family. Fina... [more]

This paper aims at presenting and describing a dimensioning methodology for energy storage systems (ESS), in particular for one based on flywheels, applied for the specific application of reducing power oscillation in a wave energy conversion (WEC) plant. The dimensioning methodology takes into account the efficiency maps of the storage technology as well as the effect of the filtering control techniques. The methodology is applied to the case study of a WEC plant in operation in Spain, using real power generation profiles delivered into the electric grid. The paper firstly describes the calculation procedure of the efficiency maps for the particular technology of flywheels, although it could be extended to other storage technologies. Then, the influence of using future data values in the dimensioning process and the control of the ESS operation is analysed in depth. A moving average filter (MAF) is defined to compensate for power oscillations, studying the difference between consideri... [more]

There is an increasing demand in integrating energy storage with photovoltaic (PV) systems to provide more smoothed power and enhance the grid-friendliness of solar PV systems. To integrate battery energy storage systems (BESS) to an utility-scale 1500 V PV system, one of the key design considerations is the basic architecture selection between DC- and AC-coupling. Hence, it is necessary to assess the reliability of the power conversion units, which are not only the key system components, but also represent the most reliability-critical parts, in order to ensure an efficient and reliable 1500 V PV-battery system. Thus, this paper investigates the BESS solutions of DC- and AC-coupled configurations for 1500 V PV systems with a comparative reliability analysis. The reliability analysis is carried out through a case study on a 160 kW/1500 V PV-system integrated DC- or AC-coupled BESS for PV power smoothing and ramp-rate regulation. In the analysis, all of the DC-DC and DC-AC power interfa... [more]