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= Electric Vehicles: a new storage system = The general environmental situation and the consequent energy transition from fossil fuels to renewable energy sources is something well known and it is characterizing the energy market year by year more and more. The intermittent nature of renewable sources especially solar and wind brings to some problems in the electric grid management, in fact energy supply and demand must be balanced. Aside, many scenarios forecast an huge spread of electric vehicles EVs. An emerging idea is to solve the electric grid problems using Electric Vehicles connected to grid as storage.

The duck curve
The duck curve points to four important problems as more renewable sources are deployed:


 * While load is low, solar generation is at a maximum bringing to problems with over-generation as solar capacity increases.
 * When load peaks for the day there is little output from solar generation.
 * Sharp mid-morning down-ramps, when solar output is rapidly increasing.
 * Substantial evening up-ramps, when load is increasing at the same time that solar generation is decreasing.

Having a sufficient amount of EVs connected to the grid make possible to mitigate the duck curve, using in the optimal way this green energy.

Future Scenarios
As we can see from many scenarios the role of EVs will be more and more important in the next years because it also matches the goal of Achieving deep global greenhouse gas reductions which is possible only with the electrification of transportation soon and at significant scale (example of California). Moreover a prior research has proven the capability for EVs to meet the travel needs of the vast majority of drivers. So EVs can provide a dual benefit of de-carbonizing transportation while lowering the capital costs for widespread renewable integration!

A key uncertainty surrounding the prospects for oil demand is the speed with which sales of electric cars increase over the Outlook. This depends on a number of factors, including government policy, technological improvements and social preferences, and as such is hard to predict with any certainty.

V1G and V2G Charging
Under controlled charging, V1G means that the car can only charge. V2G means that the car can both charge and discharge.

Matching electric utility grid and the light vehicle fleet
The basic idea of using electric vehicles as a storage is to Reconcile 2 big energy conversion systems: the electric utility system and the light vehicle fleet.

There are 3 main strategy in order to do that:


 * 1) add extra energy storage to vehicle, but this leads to an increase of costs and vehicle weight.
 * 2) fleet management, draws V2G only from vehicles with known, fixed schedules. Although the second strategy, using fleets, appears to be a good initial area for V2G, the combined markets for V2G are many times larger than total fleet vehicles. Thus, to realize the full potential of V2G, we need a third strategy so that non-fleet vehicles can also participate.
 * 3) idea that the needs of the light vehicle operator and the grid operator are complementary. Their needs differ in time, predictability, and in the fundamental difference between energy and power. The vehicle operator needs stored energy in one particular vehicle at one fairly predictable time—when a trip begins. The grid operator needs power (instantaneous flow from a source or sometimes, to a sink), possibly at multiple times, but does not care which power plant (or which V2G vehicles) that power comes from.

Most driving times are fairly predictable, regulation and spinning reserves calls are unpredictable. How are these two reconciled?

An early suggestion by Kempton and Letendre for managing complementary needs was a dashboard control that the driver would set according to normal or anticipated driving time and distance. Then, the on-boardV2Gcontrol system could run V2G when needed by the grid operator, as long as the vehicle storage is always sufficient for the driver-specified trip at the driver-specified time. Some drivers may find that the “next trip” settings require too much planning and attention. If so, an alternative would be for the vehicle to “learn” driving patterns for, say, a few weeks before beginning V2G service. Then, the user controls could be simplified to a single button: an override.

Technical management of an electric power system
The technical management of an electric power system having a large-scale deployment of EVs will require, for their battery charging, a combination of:


 * a centralized hierarchical management and control structure;
 * a local control located at the EV grid interface.

The latter control approach relies on the creation of an adequate communications infrastructure capable of handling all the information that needs to be exchanged between the entities of the hierarchical control structure and the EV. When operating the grid in normal conditions, EVs will be managed and controlled by a new entity the aggregator whose main functionality will be grouping EVs, according to their owners’ willingness, to exploit business opportunities in the electricity markets. However, due to high uncertainties related to when and where EV owners will charge their vehicles, the existence of a grid monitoring structure will be required, controlled by the DSO, with the capability of acting over EV charging in abnormal operating conditions, i.e., when the grid is being operated near its technical limits, or in emergency operating modes, e.g., islanded operation. In these situations, EVs might receive simultaneously two different set points: one from the aggregator and other from the monitoring and management structure headed by the DSO. To avoid violation of grid operational restrictions, the DSO signals will override the aggregator ones.

Uncoordinated charging of the batteries of PHEVs has a non-negligible impact on the performance of the distribution grid in terms of power losses and power quality. With respect to uncoordinated charging, the coordination of the charging reduces the power losses. Less grid enforcements are necessary with the coordination system. The maximum load is lower because the vehicles are not charging if the household loads are peaking. Therefore, the voltage drops, line currents and power losses are considerably reduced. These power losses are important for the operator of the distribution grid. The distribution system operator (DSO) will compensate higher losses by increasing its grid tariffs; hence the cost for the implementation and the possible additional power production will be passed on to the customers.

Market players
Currently spinning reserves and regulation are provided by large power generators. Operating V2G development, 100 electric vehicles (EVs) with at least 14 kW of battery capacity can provide 1MW of capacity for those services.

First V2G business model
The “fleet management”, the same party both manages time availability of fleet use for transportation and sells ancillary services directly to the grid operator. This model is very simple and effective but neglect the possibility to draw power from dispersed vehicles.

Second business model
Second business model regards the retail power delivery company: it contracts to buy hundreds or thousands of individual vehicles owners and sell 1 MW blocks to the regional power market.

Third business model
A third business model derives from the second: an independent party serves as aggregator of individual electric vehicles. An automobile manufacturer, who are increasingly using on-vehicle telematics to deliver information services between repairs, or a cell phone network provider, who might provide the communications functions and whose business expertise focuses on automated tracking and billing of many small transactions distributed over space and time. Finally, a company as Uber could have interest in managing connection and time of individual EVs, providing services to energy market in order to extend its business activities.

Transition path from actual system to V2G
Battery vehicles are the most adapt kind due the cost and the electric capacity.


 * The first step is to implement demonstration fleets. Initial fleet adopters will pay a cost premium over gasoline vehicles, which the V2G payments would reduce but probably not eliminate. However, as the vehicles move to volume production and battery technology improvements continue, V2G payments shift the fleet operator’s cost to breakeven with gasoline vehicles, then to lower costs.
 * Second step begins at the point that costs drop below break-even and ends at the point that the high-value V2G markets of regulation and spinning reserves are saturated. V2G revenues may stimulate aggregators and be partially reinvested to develop the charging grid itself.
 * In third step higher volumes of V2G capable vehicles and a more efficient aggregation industry have the benefits of making electric grid management cheaper and making power more reliable and stable. Power plants now used for regulation and spinning reserves can be freed up or even decommissioned.

California
California has issued ambitious targets through policy activities, as the ZEV Mandate. Goals are to reach 1,5 million of ZEVs in 2025, and renewable generation up to 33% by 2020 and 50% by 2030. This state has also commissioned 1,3 GW of electric storage by the end of 2024 to ensure continued grid reliability: there is a huge synergistic opportunity if EVs from the ZEV Mandate are used to provide grid storage. Renewable sources change the load curve, creating problems: evening peak net load is untouched while during daytime the net load is low due to over-generation. Moreover, transition period shows very shaped ramps.

These problems can be solved if vehicles are grid-integrated with controllable charging and discharging rates (V2G). Simulations performed show three main results: peak and valley load optimization and ramp mitigation optimization. Furthermore, the goal of 1,3 GW of storage of ZEV Mandate could be achieved with a significant reduction on capital investment in stationary storage.

Canary Islands
Lanzarote and Fuerteventura are an interesting case: an isolated system where irregularity of renewable energy limits their employment. Analysis regards 8 electric buses of 8 lines and 38 generation units, arranged in dispatchable (diesel) and intermittent (solar PV, wind) power plants.

For what concerns participation of electric vehicles in the different markets most of the volume of the traded energy corresponds to purchases in the day-ahead energy market and Primary Frequency Regulation (maintain constant grid’s frequency and voltage). It’s interesting consider relation between cost of capacity and amount of capacity available for the system for Primary Frequency Regulation (PFR). If cost is 100 €/MW basically EVs do not participate in the market. As the capacity cost decreases, the participation of EVs in the PFR increases while the total expected cost is reduced.

Obviously, annual operating costs are highly reduced as the renewable penetration increases, and therefore that they decrease as EVs are more involved in operation of the power system. For a high renewable penetration factor if electric vehicles can participate in energy, reserve capacity and PFR services, operating costs are reduced by 4,36% respect a situation where electric vehicles charge their batteries uniformly during their charging period without providing any kind of services.

About amount of energy exchanged, related to the maintenance costs of batteries, it’s clear that the uniform charge strategy is the most effective, but other results are quite interesting. First, the amount of energy discharged is significantly less than the energy charged. Second, the expected energy charged and discharged decreases if EVs can participate in capacity markets, mitigating batteries consumption. So, in V2G market, the best choice for an EV owner is to provide all services together, and this is also the best option for the grid operator, because correspond to lower expected costs.