"Friendly grid-connected" into a new standard for photovoltaic power plants

In recent days, Gansu, Inner Mongolia, and Liaoning have successively assessed a number of grid-friendly "friendly wind farms" and "friendly photovoltaic power stations." With the large-scale volatility of renewable energy power generation and large-scale access to distributed power of high-permeability, the security and stable operation of power grids are under increasing pressure, and “grid-friendly” has gradually become the new standard for photovoltaic power stations and wind farms. .

Recently, the “grid-friendly charging control technology” developed by Battelle in the United States allows electric vehicles to start or stop charging automatically according to the grid conditions, reducing grid pressure on the user side, allowing owners to spend less and make the grid more secure. “We need charging stations, and charging stations need to have a level of intelligence that matches smart cars and smart grid infrastructure to avoid straining the grid and provide flexible billing for energy consumption and the grid.” US Department of Energy Intelligence Dan Tang, project manager of the grid research and development department, said this.

“The construction of a strong smart grid and friendly grid environment requires the coordination of interaction between power generation or equipment and the grid to support grid safety and economic operation.” Yao Xiaoqin, senior member of the China Wind Energy Committee of the China Renewable Energy Society, told this reporter: “ In foreign countries, grid-connected friendship is a basic principle that has always been adhered to in the construction of photovoltaic power stations and wind farms, and now it has achieved results on the electricity side, and there is a wide gap between the country and the lack of standards, and more importantly, the implementation of established standards. It's very random, and the consequence of this is that large-scale wind farms and photovoltaic power stations blow the sun in the northwest."

Grid-friendly renewable energy generation

In recent years, China's renewable energy has developed rapidly. As of the end of 2012, China's wind power grid-connected installed capacity reached 63 million kilowatts, exceeding the United States as the world's largest wind power country. With annual power generation exceeding 100 billion kilowatt-hours, wind power has become China's third-largest power source.

Before 2010, the installed capacity of photovoltaic power generation in China was basically negligible, and more than 90% of the country's photovoltaic cell production depends on exports. In 2011, the installed capacity of domestic photovoltaic power generation increased by more than 3 times over the previous year and exceeded 3 GW; in 2012, this figure rose again to 7 GW; the installed capacity of new photovoltaic power generation in 2013 is expected to reach 10 GW, consuming nearly half of the country's total. The output of photovoltaic cells.

However, photovoltaic, wind power and other renewable energy sources have characteristics such as instability, unpredictability, and difficulty in control. Therefore, the problem of grid connection has followed.

The National Energy Administration stated that in 2012, the nation’s “abandoned winds” amounted to about 20 billion kWh. If calculated according to the current national thermal power coal consumption of 226 grams of 1 degree, 20 billion kilowatts of electricity is lost more than 6.78 million tons of standard coal, and direct economic losses caused by more than 10 billion.

The large-scale development of photovoltaic power generation is not long, but grid-connected problems have begun to appear. A person in charge of a photovoltaic manufacturing company told reporters: “We are very grateful to the country for opening up the domestic market, which has reduced the pressure on PV manufacturing companies. As for the difficulty of grid connection, this is indeed a problem, and it has already begun to appear. After installation, it may be even more serious, which requires everyone to pay attention to it and resolve it.Photovoltaic manufacturing companies need to make efforts in technological innovation, so that renewable energy power generation from 'waste electricity' into 'high-quality electricity', so that the power grid can be like receiving thermal power Easy to accept, reduce grid pressure, and solve grid-connected problems at the root.”

Lack of implementation of standards

How to make renewable energy power generation better and become a grid-friendly power source?

Yao Xiaoqin said that the main goal is to improve the predictability, stability, and controllability of renewable energy power generation, and "operate under conditions conducive to grid stability, such as low-voltage ride-through."

The so-called "low voltage ride through" means that when the voltage drop at the wind farm's grid connection point, the wind turbine can maintain the grid connection and even provide a certain amount of reactive power to the grid to support grid recovery until the grid returns to normal. Low voltage traverse can not only make the fan not disengage when the voltage fluctuates, avoid chain failure, but also effectively improve the safety and stability of wind farm operation.

“There are many uncertainties such as environment and weather in new energy power generation industries such as photovoltaics, wind power, biomass, etc. It is very difficult to predict. At present, power grid friendly power generation technology with the main purpose of improving new energy power generation forecast has been preliminary in China. Research and application; In the aspect of improving the stability of new energy generation, low-voltage ride-through technology applied to wind farms is currently the more popular grid-friendly technology; we have also applied remote control of wind power, Yao Xiaoqin said.

“But these applications are demonstrations, and there is no universalization.” Yao Xiaoqin said that the domestic renewable energy applications have a short application time and are developing rapidly. In many aspects, there are problems with the lack of standards, and the published standards are limited in their implementation. .

Take low voltage ride through as an example. As early as in 2003, the German wind power grid-connected guidelines required that wind turbines must have low-voltage ride-through capability. This problem was only recognized in China in 2007. In 2008, the country applied for the 863 program, and at the end of 2009, it had the detection capability. . However, until this time, the low-voltage ride-through capability was not included in the relevant national standards.

In 2011, a number of wind farms suffered from wind power off-grid accidents, and even thousands of turbines were off-grid at the same time, causing heavy losses. “This prompted the National Energy Administration's “Technical Code for Design of Large-Scale Wind Farm Grid Connections” issued in August 2011 to require large-scale wind farms to have low-voltage ride-through capability. At the same time, the State Electricity Regulatory Commission mainly aims at 'low voltage ride through' 'In the national wind power security inspections.' Anonymous wind power industry sources told reporters, 'But even if this is the current wind turbine low-voltage ride-through capability is still a problem. Some companies in the inspection, a fan If you pass a test, you will need to replace a dozen turbines before finally passing. Can you say that the fans of these companies have low-voltage ride-through capability?"

A friendly environment requires the concerted efforts of the three parties

To cope with the increasingly prominent operational control, acceptance, and delivery issues of wind power and photovoltaics, the National 863 Program “Grid-friendly New Energy Power Generation Key Technologies and Demonstration Applications” project was launched in Lanzhou at the end of 2012.

According to Shu Yinzhuo, Deputy General Manager of State Grid, “photovoltaic equipment manufacturing companies should increase the research and development of technology and equipment to improve battery quality, life and performance; increase inverter harmonic control technology research, improve equipment low-voltage ride-through capability, and have merit. Reactive power regulation capability; perfect main control system operating performance and indicators, and building a grid-friendly photovoltaic power generation system.”

“At present, Germany and other national and international Electrotechnical Commission (IEC) standards are preparing to test the ability of high-voltage ride-through capability of wind turbines. Foreign wind turbine manufacturers eliminate backward technologies through standard upgrades and upgrade product competitiveness through technology upgrades, so domestic wind turbine manufacturers should also Actively develop grid-friendly fans and use technology to drive the market,” said experts from China Electric Power Research Institute.

On the user side, the “grid-friendly charging control technology” developed by Battelle in the United States can ensure the stability of the power grid by continuously monitoring the frequency of changes in the grid current and the charging speed of different vehicles. If the grid unexpectedly causes the current frequency to drop rapidly, the charging system will stop automatically. This applies to the large-scale application of renewable energy such as wind power and photovoltaics. When the power grid fluctuates frequently, it will ensure stability of the power grid.

“The research and implementation of 'grid-friendly new energy power generation key technologies and demonstration application' projects can solve the key technical problems facing the development of new energy power generation and promote the construction of smart grids. At the same time, the project construction will promote the optimization and efficient energy structure in China. Utilizing, securing electricity supply security, cultivating strategic emerging industries, etc. are of great significance.” Yao Xiaoqin said, “We have achieved some results and passed some standards, but an important issue is that these standards have not been effectively implemented. It has not been applied in a timely manner, and the promotion of new standards and new achievements has met with many resistances, but many backward technologies are still being vigorously promoted.The construction of a friendly power grid environment, the promotion of new energy applications, the need for equipment manufacturers, the electric field and the power grid to work together , so that new energy sources have a harmonious ecological environment for production, transportation and consumption."