VPP (Virtual Power Plant) Primer — Bundling Distributed Resources and Selling Them as a Power Plant

On its own, a few kW of rooftop solar or a home battery has no value to a grid operator as a "power plant." But bundle thousands or tens of thousands of them, and control them simultaneously through communication and software, and the combined output can rival that of a single thermal power plant. That's the basic idea behind a VPP (Virtual Power Plant). A VPP isn't a new way of generating power — it's an information platform that packages existing distributed resources into a unit that can be traded on the market. The communication and metering foundation for bundling distributed resources was covered in the Smart Grid Primer. This article focuses on the business structure built on top of that foundation, along with Japan's institutional design and real examples.

The Bottom Line in 30 Seconds

A VPP is a mechanism that bundles distributed resources with very different characteristics — rooftop solar, home batteries, EVs, and factory demand response (DR) — through communication and software, treating them as a single controllable power plant.
In Japan, the system is designed around a two-tier structure: "resource aggregators," which contract directly with consumers and control their resources, and "aggregation coordinators," which pool the output offered by multiple resource aggregators and handle wholesale trading. In April 2022, the specified wholesale supplier system began, and ENERES became the first certified aggregator in Japan under it.
The resources a VPP targets differ in response speed, duration, and predictability. Batteries and EVs respond quickly; solar is hard to control in the upward direction; and DR from factory HVAC and production equipment is large in scale but constrained in flexibility.
The main battleground for Japanese VPPs isn't the wholesale power market (JEPX) itself so much as the balancing market, where general transmission and distribution utilities procure regulating power. It offers several product categories divided by response time and duration, and a VPP chooses which product to bid into based on its resources' characteristics.
As a working example, during the tight power supply-demand conditions of summer 2022, REXEV and ENERES put V2G — using the batteries of car-share EVs — into practical use to provide regulating power. VPP is a technology where institutional design and real-world operation are increasingly moving forward together, past the demonstration stage.

1. What Is a VPP — the Meaning of "Virtual"

The "virtual" in VPP means it holds no physical power plant of its own. Solar panels, home batteries, EV onboard batteries, and a factory's demand-response capacity are each, physically, just a small resource in a separate location. Connecting these over a network, central software grasps the state of each individual resource (remaining charge, generation forecast, operating schedule, and so on) and sends output-increase or -decrease commands at the necessary moments. From the perspective of a grid operator or the power market, this collection behaves as if it were "a single power plant."

Figure 1 — In a VPP, resource aggregators directly contract with and control distributed resources of different characteristics, and an aggregation coordinator pools them to trade with the balancing market, the wholesale power market, and general transmission and distribution utilities — a two-tier structure.

2. Japan's Aggregator System — a Two-Tier Structure

Japan's VPP system is divided into two roles: the resource aggregator and the aggregation coordinator. A resource aggregator signs a VPP service contract directly with a consumer (a household or a factory) and controls their solar panels, batteries, or DR equipment. An aggregation coordinator pools the output collected by multiple resource aggregators and conducts direct power trading with general transmission and distribution utilities or retail electricity providers.

Backing this structure institutionally is the specified wholesale supplier (aggregator) system, which began in April 2022. It gives legal footing to the business of bundling distributed resources and wholesaling power the way a generation business would, and ENERES became the first certified aggregator in Japan under this system. Even before institutionalization, METI's VPP demonstration project (conducted from FY2016 through FY2020) had already validated the division of roles between resource aggregators and aggregation coordinators, along with standardizing the communication interfaces between them.

Role	Main duties	Relationship with consumers
Resource aggregator	Contracting with consumers, direct equipment control, baseline management	Direct contract
Aggregation coordinator	Aggregating output from multiple resource aggregators, trading with the market and grid operator	Indirect (no contract)

3. The Types and Characteristics of Resources a VPP Bundles

The resources a VPP targets aren't uniform. Response speed, duration, and output predictability differ greatly by resource, so aggregators design the character of the regulating power they can provide based on how they combine resources.

Resource	Response speed	Approximate duration	Direction of control	Characteristics
Home battery / grid-scale battery	Fast (seconds to minutes)	Tens of minutes to a few hours	Both charge and discharge possible	Fast response and highly versatile, but limited capacity
EV / V2G	Fast (seconds to minutes)	Depends on the vehicle's operating status	Both charge and discharge possible	Balancing driving demand against providing regulating power is a challenge
Rooftop solar	—	Depends on sunlight	Mainly downward (output curtailment)	Essentially unable to be controlled upward
Factory/building HVAC and production equipment (DR)	Moderate (minutes to a little over ten minutes)	Depends on contract terms	Mainly downward	Large in scale, but constrained by comfort and production needs

Because solar can't increase output without sunlight, it's a poor fit as an upward-DR resource. Batteries and EVs, on the other hand, can be used in both charge and discharge directions, making them likely to become a VPP's core source of regulating power. V2G (Vehicle to Grid) using EVs is the idea of using an onboard battery not just as an energy source for transportation, but as a source of regulating power during the hours the vehicle isn't in use.

4. Control Architecture — Recalling the Layers of Communication

For a VPP to actually control large numbers of small resources, the communication layers covered in the Smart Grid Primer serve directly as its foundation. ECHONET Lite is often used for in-home device control, and OpenADR for automating business-to-business demand-response signals. On the aggregator's cloud-side system, the state of individual resources (SOC, operating schedule, generation forecast) is aggregated, and commands from the market are received and allocated out to each resource. The precision and speed of this allocation algorithm directly determine the quality of regulating power a VPP can provide.

5. Japan's Market Structure — the Balancing Market and JEPX

The main venues where a VPP earns revenue break down broadly into two: the wholesale power market (JEPX), where electricity itself is bought and sold, and the balancing market, where general transmission and distribution utilities procure regulating power to maintain frequency and supply-demand balance.

The balancing market has opened in stages since FY2021, trading products ranging from primary regulating power through tertiary regulating power ② — categorized by response time and duration (the detailed physical background of this classification is covered in the Grid Inertia and Frequency Regulation Primer). Fast-responding batteries and EVs suit product categories with a short response time, while relatively slower-responding factory DR suits categories with more leeway in response time. A VPP designs which product category to bid into by assessing the response characteristics of the resources it bundles.

Beyond that, "revenue stacking" — layering multiple revenue streams, such as selling electricity in the wholesale market, providing regulating power in the balancing market, and cutting a consumer's own costs through peak shaving — is what determines a VPP's business viability. Even a resource that can't recover its investment through a single market alone can sometimes pencil out once multiple uses are combined.

6. A Real Example — from Demonstration to Practical V2G

Japan's VPP sector, through METI's VPP demonstration project from FY2016 through FY2020, has had multiple companies participate as resource aggregators and aggregation coordinators, validating communication standards and operating rules. KDDI and ENERES have advanced a VPP initiative using 5G and MEC (multi-access edge computing), a known example of trying to improve VPP control latency and reliability from the communication-infrastructure side.

As a concrete case that has reached practical use, during the especially tight power supply-demand conditions of summer 2022, REXEV and ENERES put into practical use a scheme that discharges the onboard batteries of EVs used in a car-share business in the Odawara/Hakone area via V2G during hours the vehicles aren't in use, offering the output as regulating power for the Kanto region. It's an attempt to draw two kinds of value — use as transportation and providing regulating power to the grid — from the same vehicle battery, positioned as an example of V2G reaching the practical-use stage.

7. VPP's Relationship to Batteries and to the Smart Grid

A VPP doesn't replace the technology of a grid-scale battery itself (cell chemistry, BMS, round-trip efficiency, and so on). Rather, it's a "business layer" that bundles the individual batteries covered in the Power Battery Primer into a unit that can be traded on the market. Likewise, a VPP is an institutional and operational mechanism built on top of hardware infrastructure such as smart meters and communication protocols, and it can't function without the metering and communication infrastructure covered in the Smart Grid Primer. It's practical to understand VPP, batteries, and the smart grid not as competing technologies, but as different layers stacked one on top of another.

8. Current Challenges and Research Focus

Communication latency and reliability: a mechanism is needed to send commands simultaneously to large numbers of resources and confirm response within a specified time window. Using 5G and MEC is one answer to this challenge.
Baseline accuracy: measuring DR's effect requires evaluating it against the difference from an "estimated usage had it not been controlled" (the baseline), and the accuracy of that estimate directly determines the market's credibility.
Cybersecurity: with large numbers of home devices and EVs connected to the network, managing the attack surface becomes important.
Diversifying resources: incorporating new kinds of resources is being explored, such as heat-pump water heaters, industrial heat pumps, and data-center load adjustment.
Standardization: building standard interfaces to control devices from different manufacturers and communication standards across the board affects how easily aggregators can enter the market.

Summary: A VPP Is Not a "Power Plant" but a "Bundling Layer"

A VPP isn't a new generation technology — it's a mechanism that bundles existing distributed resources such as solar, batteries, EVs, and DR into a single tradable unit through communication and software. Japan has built a two-tier system of resource aggregators and aggregation coordinators, and with the balancing market providing a concrete venue for trading, the shift from demonstration to practical deployment is under way.

When evaluating a VPP initiative, it's worth checking the following:

Which resources (solar, batteries, EVs, DR) are being bundled, and at what response speed and duration?
Is it a resource aggregator or an aggregation coordinator, and how is the division of roles structured?
Which combination of revenue sources — wholesale market, balancing market, cost reduction — is being used, and how?
How is baseline measurement or communication reliability being assured?

Keeping these four points in mind lets you read a VPP announcement as a concrete structure — how the distributed resources are bundled, and where they're being traded.

References

#VPP #Virtual Power Plant #Aggregator #Demand Response #Power Engineering