Electric Vehicles 101: V2G Charging & The Grid

How can electric vehicles (EVs) assist the aging US electrical grid as it tries to handle the rising demand for electricity during peak load times? The answer is the EVs themselves. Bidirectional charging refers to two-way charging — that means the EV both charges and discharges. Vehicle to Grid (V2G) is a charging technology that allows the flow of energy from the car battery back to the grid — from the vehicle to the grid.

How does bidirectional charging work? EVs with bidirectional (two-way) charging capability can be used to power a home, feed energy back into the electricity grid, and even provide backup power in the event of a blackout or emergency. A bidirectional EV can receive energy (charge) from electric vehicle supply equipment (EVSE) and provide energy to an external load (discharge) when it is paired with a similarly capable EVSE.

What is Vehicle to Grid (V2G) charging? The V2G model employs the bidirectional EV battery as a demand-side resource.

What are some of the possibilities of bidirectional vehicles? They can provide backup power to buildings or specific loads. These can be part of a microgrid, through vehicle to building (V2B) charging, or providing power to the grid through vehicle to grid (V2G) charging.

What’s the process that takes place in bidirectional charging? Bidirectional charging is a complex power conversion process from AC power to DC (direct current), unlike a regular unidirectional EV charger that charges using AC (alternating current). A bit different than standard EV chargers, bidirectional chargers operate much like an inverter and convert AC to DC during charging and the reverse during discharging.

Can any EV engage in bidirectional charging? No. Bidirectional charging is only compatible with V2G enabled electric cars. I co-own a Tesla Model Y, for example, and Teslas don’t offer it.

What’s the relationship between bidirectional charging and the grid? EV batteries allow us to store the excess of renewable energy and pull it back into use exactly when we need it. As the world is moving full force toward full electrification, energy shortage is a significant concern. Bidirectional charging comes in as a sustainable solution to manage momentary spikes in electricity consumption locally. Surplus energy in EVs can be sold back to the grid instead of being stored, and this could be used to power millions of households when they need it most.

How does bidirectional charging work alongside renewable energy? Renewable energy is unlimited and carbon emission-free; they renewable sources are also occasionally unstable and unpredictable. With bidirectional charging, this problem can be solved with better energy storage and management systems. Bidirectional chargers used to power a home do require additional equipment to manage the loads and isolate the house from the grid during an outage, known as islanding.

What is grid overload, and how does bidirectional charging help? Grid overload happens when a momentary energy demand spike greatly destabilizes the grid. That can cause local overload and energy shortages. With bidirectional EV charging, the energy stored in EVs circulates to where it’s needed first, thus meeting local needs and preserving the grid.

What is promising about bidirectional charging? It adds resilience, management, and demand response capabilities to a site’s building infrastructure. It can act as the conduit for a potential backup source of power for the grid.

Can a light duty battery power a building? Yes. An approximately 15–100 kWh battery is ideal for individual buildings. The benefit is that emergency diesel generators won’t be needed any longer.

Are there any examples of this already happening? Bidirectional charging is already being incorporated into the Ford F-150 Lightning — that’s the all-electric version of gas-powered F-150. Ford’s Intelligent Backup Power System is the first emergency power system of its kind that lets an EV power a home or business during an outage. The F-150 Lightning incorporates bidirectional EV capabilities to enhance its utility as a massive mobile energy source.

Can bi-directional charging work with solar? Sure. V2B and V2G power solutions can complement solar photovoltaic (PV) arrays and other distributed energy resources (DERs) or supplement diesel generators as backup power.

Does bidirectional charging need to be stationary? No. EVs can be employed as mobile storage, which means they can be moved to a site.

How can bidirectional charging help in emergencies? The EV can be moved to a site shortly after an unexpected power outage to supplement local generation or serve as an emergency reserve.

Can an EV make money with Vehicle to Grid Charging? By being prepared to act as a mobile battery to charge/discharge as a demand response asset, EVs can generate revenue.

Is V2G fully developed right now? No. While V2G presents tremendous promise for enhanced resiliency, the market for building on the benefits of bidirectional electric transmission is still evolving.

What is V2E charging? Vehicle-to-everything (V2X) car charging uses the EV’s battery to charge when energy is less expensive and then discharge that energy either directly onto the electric grid, or into the building the charger is connected to, as a way to reduce the building’s electric needs from the grid. V2X is often interchanged with V2G.

Final Thoughts

The idea of using EVs as battery storage — for other outside uses — may sound simple, but it’s a concept still in its infancy and is one that will require the coordination of car makers, technology providers, utilities, and regulators to work together to make bidirectional charging and discharging a common feature of owning and operating EVs. That was the lowdown from Jeni Reynolds, director for clean transportation at San Diego Gas and Electric (SDGE), in some of her comments at the Veloz conference in San Diego in September. SDGE is involved in a pilot project to use electric school buses to discharge power when they are not in use.

A number of energy companies are trying to figure out how bidirectional charging could work commercially. There are more than 100 V2G trials worldwide, most of which are taking place in Europe in collaboration with grid providers and electric vehicle and charger manufacturers.

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