In recent years, with the rapid development of new energy sources, the problem of ensuring power consumption during off peak periods in the power grid has become prominent. At the same time, due to factors such as energy substitution, the pressure of ensuring power supply during peak periods in the power grid has gradually increased. In order to solve the problems of ensuring consumption and supply, the operation of power grid dispatching requires a large number of regulating power sources with both upward and downward capabilities. However, the drawbacks of constructing conventional regulated power sources such as pumped storage and electrochemical energy storage are obvious. One is the large fixed investment and long construction period; The second is that there is an energy conversion loss of 15% to 25%. In this context, virtual power plants with the same efficacy as conventional regulated power sources have emerged and gained recognition from the domestic capital and industry sectors, becoming a popular concept and development trend for new power systems.
Functional positioning and market space of virtual power plants
The power resources aggregated by virtual power plants include distributed new energy, energy storage, and power loads. From the perspective of the power grid, virtual power plants can be presented as power sources that provide output or as pure electricity loads. Under the incentive of price mechanisms, virtual power plants can achieve bidirectional state transitions from power sources to loads through internal control measures, in order to obtain maximum economic benefits. In China, due to the fact that the power resources aggregated by virtual power plants are usually smaller than the load resources, they generally exhibit net load characteristics to the outside world. Therefore, virtual power plants are classified as demand side resources along with load aggregators and adjustable loads.
The biggest difference between virtual power plants and microgrids is that the power and load of microgrids are located in the same geographical location, while the resources aggregated by virtual power plants can be located in different geographical locations of the same power grid. The most significant feature of virtual power plants is that their output or load can be flexibly adjusted, which creates conditions for virtual power plants to participate in the electricity market.
In the electricity spot market, virtual power plants can use more electricity during low price periods, and use less electricity or even provide electricity during high price periods. The price difference benefits obtained from this can be shared internally among the resources aggregated by virtual power plants.
In the electric power auxiliary service market, virtual power plants can participate in the peak shaving and frequency regulation auxiliary service market. Peak shaving is a unique auxiliary service in the absence of the electricity spot market, which will gradually disappear with the construction and improvement of the spot market. Frequency regulation is divided into primary frequency regulation and AGC frequency regulation. The response time requirement for primary frequency regulation is in the second level. Virtual power plants aggregate numerous resources, have different regulation performance, and have a long chain of control command issuance, making it difficult to meet the requirements for primary frequency regulation time. Therefore, the participation of virtual power plants in the frequency regulation auxiliary service market usually refers to their participation in the AGC frequency regulation market. The response time requirement for AGC frequency regulation is in the minute level. According to the latest version of the "Electricity Grid Operation Guidelines" (GB/T 31464-2022), the period for AGC to send instructions is not more than 30 seconds, which puts high demands on the regulation capability of virtual power plants. In fact, virtual power plants do not have an advantage in the two most important technical indicators of AGC frequency regulation market, namely regulation speed and regulation accuracy. Therefore, the AGC frequency regulation market may not be the main battlefield for virtual power plants to exert their effectiveness.
The development of virtual power plants will be limited in the electricity spot market environment
The domestic spot electricity market generally adopts a nodal electricity price system, and in some provinces such as Jiangsu, the segmented electricity price system is also used to calculate the nodal electricity price first, and then weighted average to obtain the segmented electricity price. The prerequisite for calculating node electricity prices is that all power generation and loads must be placed at specific nodes (in the domestic electricity spot market model, the minimum granularity of nodes is 220 kV busbars). In other words, the node pricing mechanism requires that the resources aggregated by virtual power plants must be located on the same node and cross node aggregation is not allowed. Because the node electricity prices of different nodes are different, the settlement electricity prices representing different node resources are different, and the economic incentive signals they emit are also not the same. For example, high priced nodes encourage load reduction in electricity consumption, while low priced nodes encourage load increase in electricity consumption. In this case, virtual power plants that aggregate resources across nodes cannot respond to different node electricity prices. If the aggregated resources cross nodes, the virtual power plant must be split by nodes. That is to say, under the node electricity pricing system, the scope of resource aggregation for each virtual power plant is strictly limited within a single node, and its aggregation scale will be greatly restricted. Therefore, the capacity scale of virtual power plants is destined to be small.
At present, the load side of the domestic spot market mainly participates in the market by quoting quantity without quoting. The load side adopts a unified weighted average electricity price for power generation nodes as the settlement electricity price. In a certain sense, at present, the load side has not truly participated in the spot market, and cannot effectively respond to the high and low node electricity prices, nor does it have the corresponding flexibility to adjust. There are two hidden meanings here: firstly, user electricity prices are settled after the fact, without prior knowledge, and user loads lose the objective possibility of adjusting loads according to electricity prices; Secondly, the electricity prices for all users within the provincial market are the same, losing the geographical attribute of node prices varying with location. It is precisely because the load side has not truly participated in the settlement of node electricity prices at this stage that nodes have not become constraints on the aggregation scope of virtual power plants, and the capacity scale of virtual power plants has been expanded. The current situation is that as long as they belong to the same provincial market, their internal resources can be aggregated into a single virtual power plant regardless of their location. It is worth pointing out that with the deepening of the electricity spot market, the load side will participate in the spot market through volume quoting and settle according to the node electricity price of the node. At this stage, the situation of virtual power plants aggregating resources across nodes will no longer exist, and their development scale will be greatly limited. More importantly, under the node electricity pricing system, even virtual power plants that only aggregate internal resources of a single node will have their significance greatly reduced. Because individual resources can autonomously adjust node electricity prices and directly obtain corresponding benefits, the significance of participating in aggregation is not significant. It should be noted that only the node price based spot market has this constraint on the aggregation scope of virtual power plant resources, while the bilateral trading based spot market does not have this constraint. This is also the main reason why virtual power plants have not flourished in the US electricity market, which is dominated by node prices.
The bilateral trading spot market has high requirements for users to strictly follow the trading curve in their electricity consumption behavior, which may not be applicable to the domestic market. Therefore, the domestic spot market is a node price type spot market. Although there are many problems such as the difficulty in explaining the clearing results and the unreasonable negative electricity prices in the high proportion market of new energy, the node electricity price system is still the best spot market core psychology that perfectly combines the physical characteristics of the power system and the economic characteristics of the commodity market in the world, and there is no possibility of being replaced in the short term. Therefore, the limitation of the node electricity pricing system on the development of virtual power plants is a practical issue that needs to be carefully considered.
Exploration of the Development Direction of Virtual Power Plants in the Electricity Spot Market Environment
In the electricity spot market environment, the node pricing system only limits the expansion of virtual power plants, rather than eliminating their development. Within nodes, virtual power plants can still have great potential, but their development ideas should shift from aggregating ordinary resources to focusing on aggregating distributed new energy, especially distributed photovoltaic power generation. This can not only reduce the safety risks of power grid operation, but also fully leverage the size advantages of virtual power plants, improve the market returns of individual distributed new energy, and truly reflect the multiple values of virtual power plants.
With the rapid growth of distributed new energy installation, the problem of the lack of necessary control measures for distributed new energy has gradually become prominent, bringing significant safety risks to power grid scheduling and operation. For example, during the sunrise period, the output of distributed photovoltaic power generation rapidly increases from zero to full power, with a ramp rate far exceeding that of conventional thermal power units or even hydroelectric units, often causing high-frequency fluctuations in the power grid during certain periods. This is a real problem that troubles the operation of power grid scheduling and is also a new development direction for virtual power plants to make a difference. After aggregating dispersed distributed new energy into a virtual power plant, effective control of the output of distributed new energy can be achieved through the control means of the aggregation platform. In other words, virtual power plants can improve the grid friendliness of distributed new energy, which is also the safety value of virtual power plants. Although distributed new energy points are diverse and extensive, they are geographically close, and it is feasible to aggregate them according to nodes. The aggregation of distributed new energy from different nodes into different virtual power plants not only solves the problem of uncontrollable grid operation of distributed new energy, but also provides new development space for distributed new energy. In addition, in the electricity spot market environment, a single distributed new energy can only be a passive recipient of node electricity prices, while virtual power plants, as a cluster of distributed new energy, can participate in market operations through volume and price quotations, effectively improving overall revenue, and then increasing the revenue of individual distributed new energy through a fair and reasonable internal revenue distribution mechanism. Research and practice in this area are worth further exploration.
