Large offshore wind farms tend to direct a high-power capacity at a single location. Notably, the magnitude of the power fluctuation can reach extremely high values due to wind speed variations. Wind power fluctuations are visible at different time scale such as short intra hour and long several hours [ 6 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. Furthermore, wind power and PV are known as non-dispatchable energy sources since the active power production is variable over time [ 6 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ].
The transmission system operator TSO plays a significant role in ensuring the balance between consumption and production at all times including at intra-hour time scale. Importantly, the research has majorly focused on the potential contribution of EVs to facilitate the integration of RESs in the power system. The research topic has been developed within the paradigm of the smart grid, and it is centred on the EVs potential of establishing mutual benefits to both the electric power system with RES and future EV users.
Regarding this vision, an EV is in a position to act as a controllable load or as storage, charging or discharging part of its battery capacity back to the grid, conferring to the vehicle to grid V2G notion, as stated by Kempton and Letendre [ 19 ]. If the charging of EVs is uncoordinated, their impact on the grid is equivalent to a large electric load resulting in higher power systems peak-load and to distribution grid congestion issues [ 20 ].
To avoid such scenarios, the study has researched on what impacts EV coordinated charging can have in correlation with RES production. To be precise, the research has focused on the solutions using EVs for the provision of ancillary services for wind integration as well as energy storage for PV integration.
Using EVs in power systems together with wind power has been reported to be ideally suited for the provision of ancillary services [ 18 ]. The EV owners are likely to experience lower price despite a higher initial value compared to the ICE cars. Pillai and Bak-Jensen [ 23 ] examined the benefits of ancillary services provisions by EVs in the western Danish power system. They mainly checked at the disposition of secondary reserves, load frequency; control LFC , which is assessed through simulation models. The authors explain how EVs can efficiently control power mismatch resulting from the variability of wind power, therefore eliminating the use of conventional power plants.
Renewable Energy Solutions
Regarding the simulation results, it is observable that vehicles batteries are subject to extensive energy excursion, which tends to pass from empty to full state of charge. The authors affirm that using EVs to offer monitoring power in Denmark is one of the most effective solutions for substituting the reduced reserve power generated from conventional power plants in the future.
The research also looked at micro-grid applications. It was discovered that the penetration level of wind power could be increased even more by using a coordinated EV load. In a different study, EVs and power systems are believed to be perfect as controllable loads in simulation environment; however, the research failed to address the possible hindrances like EV control requirements as well as EV elements response during moments of coordination.
The research on the usage of solar power through EVs is significantly diversified as compared to various studies focusing on wind power and EVs. Substantially, it is possible to generate electricity PV at both medium and low voltage levels within the power systems. Besides, this alternative additionally motivates the concept of incorporating the PV generation with EVs [ 6 ]. Additionally, research reveals that during the daytime when the solar radiation is at the peak, solar power can be easily stored in the car batteries for future usage.
On the contrary, Birnie [ 30 ] also recognised another application.
The scholar introduced a concept in which EVs can be charged during the day at the parking areas situated, for instance, within the workplaces. In addition, EVs can be re-energised entirely during the working periods to realise the solar-to-vehicle SV2 approach.
Furthermore, the research also illustrates that energy generated in each parking area is essential in the extra generation of adequate electricity for transportation requirements for the EVs operator. Although grids may have high penetration capacity of PV, they may too have lower voltages. In such situations, the primary constraint is linked to variations of voltage magnitudes along the feeders. Moreover, such discrepancies can be noticed particularly within the periods of high production as well as the conditions of low load [ 31 , 32 , 33 , 34 ]. Unsurprisingly, these events are likely to occur regularly, but on areas majorly the places of residence that have highly concentrated roof-top PVs.
Conversely, many studies have examined various alternatives in the mitigation of voltage capacity, for instance, the grid reinforcement [ 32 ], approaches to reactive power control [ 34 , 35 , 36 , 37 , 38 ], harmonised active power curtailment [ 33 ], as well as permanent storage of energy [ 39 ]. Research exposes that the application coordinated EV load within the feeders using high PV penetration has not been satisfactorily analysed. The need for a transition to a more sustainable energy system leads to a deep change in the energy, building and transports sector. Power installation from RESs is becoming more and more relevant, new mobility schemes, namely car sharing, are growing more popular and particular attention is paid to energy efficiency in buildings.
Moreover, each of these aspects is related to another important concept that is energy storage. The greatest change in the energy sector has occurred due to the development of distributed or diffused generation DG. DG plants exploit primary energy sources—in the majority of cases renewable—which are distributed on the territory thus the name distributed generation and that could not otherwise be exploited in a traditional centralised plant; they supply local loads and they can be operated in a co-generative mode.
In an urban district, examples of DG are PV panels and solar collectors mounted on top of buildings. One of the drawbacks of DG is the high specific investment cost mainly due to the fact that, being medium or small plants, scale economy cannot be applied. Nevertheless, this can be faced thanks to a suitable incentive strategy. The real problem is the difficulty in predicting and controlling the power produced and put on the distribution network. So the distributed generation, together with other distributed energy resources such as EVs and energy storage, is the main driver for the shift to a new paradigm in the management of the grid: the passage to a smart grid.
Smart grid is defined as a modern electric power grid infrastructure that guarantees the reliability of the system and the security of supply, allowing to face problems related to the distributed power generation from RESs and to control the load, promoting energy efficiency and involving the passive final users. In order to do so, integration of the electrical grid with information and communication technology ICT is needed. The availability of electricity is of crucial importance for all human activities. Therefore, continuity and security of the supply service are necessary.
Since nowadays electrical energy cannot be stored at low-cost and in large quantities, electrical systems must guarantee a constant equilibrium between production and consumption. This means that the power generated has to correspond exactly to the one requested at any time interval. The electrical network is ruled in a way to ensure that this balance is respected despite any possible disturbance, from load fluctuations to faults determining the unavailability of some grid elements. The structure of the electrical grid is investigated in the paragraph below.
In a traditional network configuration, power generation occurs mainly in big, centralised power plants. Domestic and commercial users are generally connected to the LV network while the majority of industrial users are connected to the MV network. HV grid is designed to transfer bulk power from major generators to areas of demand; it has a network structure to ensure different alternative paths for the power flow in case some of its elements are unavailable owing to a fault. In Italy, for example, the transmission network has reached a high automation level, leading to a good reliability and security of supply.
On the other hand, MV and LV grids have a radial structure. To be more precise, even if in MV grids different possible paths are available for the power flow, these grids are operated in a radial way. Distribution networks have originally been conceived to transfer power just in one direction: from the substations to the final customer. This model is appropriate as long as only loads, with the exception of a very few generators, are connected to distribution networks so that they can be regarded as passive. Due to recent large spreading of distributed generation, mainly from renewables, this model needs to be re-visited.
At present, generators are connected to the distribution network according to the fit and forget approach. The capability of the distribution grid to accept a certain amount of diffused generation is called hosting capacity. The nodal hosting capacity NHC methodology is utilised to determine how much DG can be connected to a given network respecting performance limits. Typically, the operating limits are as follows: rapid voltage changes, short circuit currents, reverse power flow and line thermal limits. The DSO deals with the generator as a negative load, since; it puts power on the network instead of withdrawing it.
So, the DSO is forgetting it because it cannot control the generator during its operation: The generator can introduce power into the grid at any moment depending on the will of the producer or on the availability of the energy resources. Therefore, it is possible to identify three main issues related to the actual distribution network. First of all, the DSO is obliged to limit DG connection in order to keep the control of the grid, reducing the power that could be installed through DG.
A way to overcome this issue would be allowing the generators to collaborate to the management of the grid. The second drawback is related to the behaviour of DG in case of faults or contingencies. If there is an anomaly in the measured values of frequency and voltage at the connection point, DG is disconnected even if the problem is not related to the distribution network but to the transmission one.
This results in the sudden unavailability of the power produced by DG which could have dangerous consequences for the safety of the overall electrical power system.
Renewable Energy Overview
Last but not least, reverse power flow can occur if the installed DG grows. It means that the power does not flow anymore only from the substations to the users but vice-versa. Thus, the updating of protection and regulation systems is necessary. Provided all this, a transition to a new management of the electrical network and of the entire power system is needed; we refer to this new model as smart grid.
The aim is to move from a system in which power production is centralised and controllable while consumption is completely random, so the responsibility for the balance between generation and consumption is entirely on the production side, to a system in which part of the generation is non-programmable, but this can be counterbalanced by a controllable portion of consumption.
The idea is to move from a passive grid to an active one in which there is a bi-directional exchange between producers and users as it shown in Figure 2. An expansion in electric vehicle reception may mean greater adaptability for the framework to react to supply as well as demand. For this situation, reserve funds from vehicle-to-grid administrations could take care of the yearly expense of charging an electric auto. This improvement shows that vehicle-to-grid administrations could be utilised as a part of different nations amid peak hours to discharge stored power onto the grid and reduce charging costs.
Adjusting the supply as well as demand of power with electric autos additionally could bring about maintaining a strategic distance from exorbitant moves up to the grid, for example, putting resources into new power plants. In this way, transportation expenses and power bills could reduce with vehicle-to-grid administrations. As more clients embrace EVs, vehicle-to-grid administrations ought to be considered to help level out power supply as well as demand.
This alternative might be particularly helpful in urban communities that have embraced electric transports for public transportation. These electric transports could give power to the grid when not being used, diminishing expenses for the city as well as clients. Some alert ought to be taken as more EVs are associated with the grid. Huge spikes popular for power could cause anxiety that could influence soundness, productivity, and working expenses of the grid. Subsequently, the effect of charging an electric vehicle is subject to where it is situated on the grid and the season of day it is charged.
Utilities plan to utilise disseminated assets, for example, sustainable power source generation, storage and demand reaction, to incompletely control charging effects of EVs.
Optimization of hybrid renewable energy power systems: A review | SpringerLink
Keen grid innovations, for example, progressed metering foundation could demonstrate accommodating in dealing with the charging of EVs. Such gadgets permit charging stations to be incorporated with time-based rates that support off-peak charging. They likewise enable utilities to examine charging station utilisation and charging practices to illuminate speculation choices. Moreover, calculations that successfully plan the charging and releasing of EVs are vital for the grid to work proficiently.
Be that as it may, growing such calculations is troublesome because of the irregularity and vulnerability of future occasions. More electric vehicle charging stations in advantageous areas are important to adjust request on the grid and increment accommodation. On the off chance that an electric vehicle needs to charge amid a lengthy, difficult experience trip, it would need to stop at the closest charging station. Microgrids could likewise support unwavering quality while charging EVs in an area or work zone. Small community areas with disseminated assets, for example, solar-power oriented, wind as well as storage would decrease the strain on our power grid.
Maybe circling capacity into nearby microgrids would additionally improve power versatility. As clients receive EVs, it is vital to consider all the potential advantages these autos could give to the grid. The grid could turn out to be more adaptable amid peak times for less cost and costly foundation updates could be kept away from with vehicle-to-grid administrations.
Providing supplementary services from EVs is a very plausible option in case the process involves large fleet vehicles [ 40 ]. The authors, therefore, suggested an aggregator technology, which may serve the purpose of intermediation between the automobiles, the utility organisations as well as the energy market. Figure 3 vividly demonstrates the aggregator frameworks alongside other forms of the framework [ 41 , 42 ].
In almost every circumstance, the EV aggregator produces essential signals for coordinating the EV fleet based on the data shared between the supply the energy market, TSO as well as the DSO. There are multiple reasons behind the deployment of EV aggregators. Firstly, under current market conditions small loads individual participation is prohibited. Also, it permits easiest interaction with the DSO for troubleshooting. With an appropriate strategy, it can lead to a reduction of the risk of forecast errors of the EV load. As PV penetration increases in LV grid, controlling the EV load can lead to an improvement in the feeder operation and a decrease in the need to invest in infrastructure upgrades of the grid.
In grids with such high penetration, there are constraints to keep in mind. Customers will evaluate improvements with respect to dependability, quality, and price. We expect a major change in the near future in the voltage quality improvement, which will aim to reduce long-term variations in voltage magnitude that arise in a decentralised RES generation context.
We know from theory, that EV load coordination can facilitate keeping a local balance between production and consumption, which can reduce under and over-voltages. Planning rules are currently being revised so as to allow for greater RES penetration by European energy suppliers. Above are the grid reinforcement options. Recently, automatic power curtailment is being looked at within DSOs, if RES induced voltage variations were to exceed the allowable bounds.
To do so, requires linking all units in a communication infrastructure network, which may not be convenient to owners and might imply compensating them for the inconvenience. Extensive research has been made into reactive power methods for LV grids, showing some limitations in the effectiveness of reducing voltage rise [ 46 , 48 , 49 , 50 ]. By providing reactive power contribution by all PV units, there can be visible voltage rise reduction in a feeder [ 50 ]. Besides, active power solutions can be utilised as an alternative one.
It is noteworthy that, the meaning of EV aggregator is also recognised by Brooks and Cage [ 44 ]; in this regard, the priority of EV aggregator is to check the driving needs of the operators. Some authors have suggested a strategy that allows the user to communicate their operation needs to the aggregator. Consequently, the aggregator works by processing the information about the driving data. Moreover, the estimation can be done per hour.
Further analysis was conducted a 2-year simulation on the Iberian market and concluded that; the agent of aggregation with augmented bidding is likely to reduce the costs of charging more than the coordinated system of billing. Secondly, in case the payment regarding the reserve capacity is convenient, then it is financially expedient to regulate EV participation. Lastly, if there is no reserve capacity compensation, the idea of optimised bidding can as well pay off.
Prediction of the EV loads as well as approximating the qualms is essential in problem-solving. Again, the aggregator in this context functions as interplay between the users of EVs and the energy market. In this case, these concepts are like to offer frequency regulation. Researchers Galus and Anderson [ 47 ]; introduced a different idea on an aggregator.
They asserted that an aggregator is not a corporation but an intangible computational unit that monitors and evaluates a control are: Adequately, it is a smart interface amid the electrical utilities and the EV. Harmonisation of EV is easy to detect if there is the likelihood of responding to the propagated indications.
Therefore, the need of EV to react to the secondary services as well as technological shortcomings arising from EV coordination process is addressed by Galus and Anderson [ 47 ].
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