physics

Vehicle-to-grid

Vehicle-to-grid is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Vehicle-to-grid rather than just read about it. In short: Vehicle-to-grid (V2G) describes a system in which plug-in electric vehicles (PIEVs) sell demand response services to the electrical grid. Such services are either backfeeding electricity to the grid, or reducing the rate of charge from the grid at different times of the day.

Key takeaways

Vehicle-to-grid belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Vehicle-to-grid to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Vehicle-to-grid from memory before moving on to harder problems.

Reference excerpt

Vehicle-to-grid (V2G) describes a system in which plug-in electric vehicles (PIEVs) sell demand response services to the electrical grid. Such services are either backfeeding electricity to the grid, or reducing the rate of charge from the grid at different times of the day. Demand services reduce demand peaks for grid supply, and hence reduce the probability of disruption from load variations. Vehicle-to-load (V2L) and vehicle-to-vehicle (V2V) are related concepts, but the AC phase is not synchronised with the grid, so the power is only available to "off-grid" loads. Plug-in electric vehicles include battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs). They share the ability to store electricity in their on-board battery modules, which are typically used to propel the vehicle's electric engine. V2G allows some of this energy storage to be sent to the grid, turning the vehicle into a small-scale grid battery that is eligible for claiming feed-in tariffs. A 2015 report found that vehicle owners could receive significant payments by charging their EVs at off-peak times when grid electricity is cheaper, storing it in their car battery, and selling it back to the grid at peak times when electricity prices are higher due to congestion pricing. Rechargeable batteries have a finite number of charge cycles, as well as a limited shelf-life, so V2G can reduce battery longevity. Battery capacity is a complex function of battery chemistry, charge/discharge rates, temperature, state of charge and age, but is improving as technology improves. Most studies of the effects of V2G on battery life show that slower V2G discharge rates lessen degradation, while one study suggested that using vehicles for grid storage could improve longevity. Some hydrogen fuel cell vehicles (HFCVs) are also equipped with V2G functions. HFCVs with fuel tanks containing 5.6 kg (12 lb) of hydrogen fuel can deliver more than 90 kWh of electricity. Vehicle batteries may hold 100 kWh or more. Uni-directional V2G (UV2G) charging is technically simpler than delivering power from an EV battery, which many PIEVs are not equipped to do. As of 2024, most EVs require a separate inverter than the one used to power the propulsion motors in order to output AC power from the battery. UV2G can be extended by throttling other activities such as air heating and cooling.

History V2G began as vehicle-to-vehicle (V2V) charging, as introduced by California company AC Propulsion in the early 1990s. Their two-seater Tzero car featured two-way charging. V2G allows charging and discharging between vehicle and grid.

Applications

Peak load leveling V2G vehicles can provide power to help balance grid loads by "valley filling" (charging at night when demand is low) and "peak shaving" (sending power to the grid when demand is high; see duck curve). Peak load leveling supports regulation services (keeping voltage and frequency stable) and provides spinning reserves (to meet sudden demands for power). Coupling these services with "smart meters" enables V2G. V2G could buffer variable power sources by storing excess energy and providing it to the grid during high-load periods. It has been proposed that public utilities would not have to build as many coal-fired and gas-fired power plants to meet peak demand or as an insurance policy against power outages. Local demand is easily measured, so dynamic load leveling can be provided as needed on a highly local basis. Carbitrage, a portmanteau of 'car' and 'arbitrage', is sometimes used to refer to the process of buying and selling power stored in a vehicle.

Backup power Electric vehicles can generally store more than an average home's daily energy demand, and supply emergency power to a home for several days, using vehicle-to-home (V2H) transmission. Though the concept of V2H charging is simple, putting it into action requires a technologically complex system. Charging stations must integrate software that communicates with the central grid to monitor real-time system demand.

Types California's grid operator, CAISO, defines four levels of Vehicle-Grid Interface (VGI):

Unidirectional power flow (V1G) V1G with aggregated resources V1G with fragmented actor objectives Bidirectional power flow (V2G)

V1G/Unidirectional V2G V1G involves varying the time and rate at which an electric vehicle is charged. It is also known as unidirectional managed charging services, unidirectional V2G or "smart charging". V1G approaches include charging in the middle of the day to absorb solar power that would otherwise be discarded (load shedding) and varying the charge rate to provide frequency response or load balancing services.

Bidirectional local V2G (V2H, V2L, V2B, V2X) Vehicle-to-home (V2H), vehicle-to-load (V2L), vehicle-to-vehicle (V2V), and vehicle-to-building (V2B)—sometimes collectively termed vehicle-to-everything (V2X)—use the vehicle to provide power during a power outage or to displace grid energy with energy from possibly other energy sources stored in the vehicle's battery. The source energy may be renewable; for example, vehicles charged using solar power at work during the day could power a home through the night, without pulling power from the grid. In Japan commercial V2H solutions have been available since 2012. In 2022, Utrecht was installing thousands of bidirectional chargers in anticipation of the arrival of vehicles that support bidirectional energy flows. By 2023, several vehicles supporting V2X energy transfer had come onto the market. The Ford F-150 Lightning supports 9.6 kW of V2L or V2H power. Tesla began deliveries of a new light truck Cybertruck offering 11.5 kW of V2H or V2L capability.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Vehicle-to-grid

Start with the simplest possible case. Write down what Vehicle-to-grid claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Vehicle-to-grid before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Vehicle-to-grid ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Vehicle-to-grid

In research: Vehicle-to-grid appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Vehicle-to-grid in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Vehicle-to-grid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Automotive technologies, Electric vehicles, Energy storage, so understanding it makes those chapters shorter.
In everyday life: Look for Vehicle-to-grid outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Vehicle-to-grid in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Vehicle-to-grid means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Vehicle-to-grid out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Vehicle-to-grid in simple terms?

Why does Vehicle-to-grid matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Vehicle-to-grid?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Vehicle-to-grid.