Associate Professor of Tsinghua University Dai Xingjian
April 2-4, 'Storage Energy Summit and Exhibition 2018' was held at the National Convention Center in Beijing. Associate Researcher Dai Xingjian from Tsinghua University gave a speech at the theme forum. The following are the contents of the speech:
Associate Professor of Tsinghua University Dai Xingjian:
Thanks to the invitation of the Energy Storage Alliance to introduce some basic concepts of energy storage in flywheels. Because energy storage is various, flywheel energy storage is a relatively special technology. Including three points, first introduce the research status and development trends at home and abroad. These parameters and applications are used as an introduction. Finally, we are very concerned about the cost. We also have an estimate because the time for doing it is relatively long. There is a demand in the energy storage, called high frequency, short high frequency. The number of charge and discharge described above may be 10,000 times, and the number of charge and discharge of the flywheel energy storage may exceed 100,000 times, or even longer. The flywheel energy storage also needs to pursue high performance, including large capacity, and the flywheel's stand-alone capacity can be very high. Big, we talk about the power. After several hundred flywheels are connected in parallel, they can be dozens of megawatts and hundreds of megawatts.
The technology of flywheel energy storage was started in the 1950s and 1960s. It has been done for 50 or 60 years. There are indeed some breakthroughs in technical indicators. We have said that the single-machine power has already been done in foreign countries by 3 MW, and Tsinghua made a MW in the previous year. The system, the energy, he took the electroplating to measure is not his long-term, high-power in a short time. Now abroad can realize the ten-speed electricity to the low-speed flywheel, medium and low speed. The three-megawatt system saves sixty trillion megajoules. The more important power supply occasions are more appropriate. The other set of flywheels is the high-speed flywheel, and the speed of the high-speed flywheel exceeds 10,000 rpm. At this time, the power can't go up. We can see that the highest in foreign countries is 330 kW, which can be achieved in China. Three hundred kilowatts, energy 90 megajoules and about 25 kWh, we are like batteries. The speed of foreign countries can reach 2200 rpm, domestic 1600 rpm, and the domestic level is also the prototype. Domestic from the beginning of the year to do flywheel energy storage, the recent few There are more units to do these things. This is because the industry of energy storage is developing rapidly and has its needs. The energy storage of the flywheel is aimed at short-time high frequency, and it requires high power, but its energy requirements are not high. For the occasion, it is With its use.
Domestically, there are some breakthroughs in the past few years. The stand-alone development is narrowing the gap. To achieve grid use, we can achieve several hundred kilowatts to several megawatts. There are two 20 megawatts of storage power stations in the United States. With 200 flywheels, there are still some gaps with foreign countries.
We recently wanted to make a flywheel array in our national key R&D program and we will use it as a demonstration application for short-term high-frequency applications. The stand-alone capacity can reach 600 kilowatts to 3 megawatts for high-speed flywheels, and high-speed electrode power. Can not do it, because of the loss of the motor, we can achieve a high-power energy storage system through 200 to 1000 stand-alone machines. So we think that the flywheel energy storage is still a short time, his charge and discharge in sub-seconds, High power.
For such a large energy storage system, we can also extend the time without his rated power. For example, if you insist on 30 seconds, you can achieve 5 minutes. Just said capacity, the second problem is efficiency. Some do flywheel The unit's efficiency, say 99%, 98%, I don’t know what his efficiency is. For us to carry out energy storage, how many kWh you go in and how much electricity is taken out, this is the real energy Efficiency. Charging consists of two processes. We assume 98%. There are also two 98% discharges, plus other losses. So we think efficiency can be 86% to 94%. This interval is what we call cyclical. Energy efficiency, this number is a reasonable range. If 99%, 98%, I do not know what efficiency he said.
The third problem is life span, because the flywheel is made of metal material or composite material, its strength fatigue life, design can be done more than 100,000 times. Motor materials are also more mature, power electronic materials and other power conversion are the same Its two bearings and auxiliary systems can achieve longevity through maintenance. The question is, where does this long life go? We can see in many references that the life of the flywheel is more than 100,000 times. This is dependable. Yes, scientific basis, but where, based on our experience with flywheels for so many years, there is high frequency in the field of kinetic energy regeneration for vehicles. We have charged and discharged in the Zhongyuan Oilfield Project in just 4 months. It has reached 12,000 times. For high frequencies, we feel that it has its place to use it. The second purpose, if it is 10 times or 20 times a day, it is thousands of times every year, and it also has its use. There is also an idea that if you use peaks, you may not have enough peak adjustments, once per day, and more than 300 times a year. How many years will it take for ten thousand years? For 30 years, it will be difficult for many investors to accept , Or Willing to vote so far.
The last question is about cost. This table is a document of 2015. This is a reference for us. From this Euro per kilowatt, it is still a relatively low cost compared to others. Note that its unit is kilowatts. It's not kilowatt-hours. It's not competitive because of its power. To use its strengths, it's short-term high frequency, and it's measured by power. It still has advantages. This is about its maintenance.
Here, the final point is that after considering various factors, its cost is still relatively low. We emphasize that it measures its price in kilowatts under the conditions of high-frequency charge and discharge. In FM applications, it is compared with lithium batteries and lead-acid batteries. The annual cycle price is still a relatively low price. So if the FM market is used every year in the thousands of charging and discharging markets, we feel that the energy stored in the flywheel is still Competitive, its competitiveness is also manifested in its mature material, technology is relatively mature, and will not start from the basic material system.
This is a data from the U.S. Department of Energy, and it is also said that flywheel energy storage is the market for FM. The cost of single frequency modulation is still relatively low.
Third, on the application of flywheel energy storage. Several applications, for the aerospace applications in the 1980s and 1990s, the development of vehicles in Europe is more, mainly in the scene of frequent braking energy regeneration of public transport systems, including lifting machinery is also energy. Recycling, adding up to the market and dynamic UPS, as well as new energy generation, grid frequency tuning are all a small market. We just said a few thousand times of charge and discharge data from the United States of America's energy storage power station, which accounted for this grid system's The FM capacity is only 10%, but it takes 30% of the FM operation. It has advantages in the frequency of 3,000 to 5,000 times. We talk about more than 100,000 times to pay attention to my equipment investment period or Can we use this for 100,000 times during the operation? This should be taken into account. So we think that the 5,000 annual power usage is best for flywheel energy storage.
Another use, for energy use, this is in 2012. Want to compete with the battery, do a battery-type flywheel, he can do 0.4 per kilowatt-hour. Our conclusion is that the capacity of a single machine can be done very high, Efficiency is 86% to 94%, which is a reasonable range. The life expectancy is more than 100,000 times. Its cost is estimated at 1200-2500 kilowatts. It is more suitable for high-frequency frequency modulation applications. Thank you!