Can the unused electricity be stored?

This summer, Sichuan has been experiencing continuous high temperatures, and the power supply and demand tension has further intensified. In everyone's impression, Sichuan is rich in water resources and has many giant hydropower stations. Its installed capacity and power generation are both the largest in the country. Why is there a power shortage in the summer?

The extremely abnormal high temperature and drought this year are the main direct cause . The severe high temperature and drought disaster weather has caused Sichuan to face the highest extreme temperature in the same period in history, the lowest precipitation in the same period in history, and the highest power load in the same period in history.

Source: veer gallery

Part 1

The modern world cannot do without electricity.

As the operating basis of modern society, electric energy is widely used in all fields of production and life. Power stations convert wind energy, hydropower, chemical energy stored in coal and other types of energy into electric energy, which is transmitted to thousands of households through the power grid. People then convert the electric energy into other energy according to their needs. For example, the electricity produced by a distant power station is transmitted to your home, and you use it for lighting (electrical energy converted into light energy), cooking (electrical energy converted into heat energy), and washing clothes (electrical energy converted into mechanical energy).

Image source: Reference 1

The current power generation model has a very important feature: it produces as much as it consumes. The power generation of the power plant is adjusted in real time according to the power consumption at the other end of the power grid. When everyone turns on the lights at night, the power generation of the generator will be adjusted in real time according to the parameters of the power grid, and the power generation and power consumption are in a dynamic balance.

Of the power stations in Sichuan Province, 82% use hydropower for electricity generation, while run-of-the-river hydropower stations (generating electricity based on the amount of water flowing through the river, without a reservoir to store water) account for 60% of the total installed hydropower capacity. The power generation capacity of a hydropower station is limited by the amount of water in the river.

During the flood season, the water flow is large. If the hydropower station uses all the flowing water for power generation, the electricity cannot be consumed, so there is excess energy, and only part of the water can be released directly. During the dry season, the water flow is too small, and using all the flowing water for power generation cannot meet the power demand, resulting in energy shortage.

During actual operation, run-of-river hydropower stations will inevitably encounter the above two situations, which sometimes results in wasted power generation capacity and sometimes fails to meet electricity demand.

Image source: Author

Transmission lines are highly efficient but require time to plan and build. my country's power transmission technology is currently the strongest on the Blue Star (State Grid: low-key, low-key). In the early stages of power grid design, the power consumption of various regions and the power generation of power stations will be considered, and a suitable layout will be planned to maximize the power generation capacity of power stations and reduce energy waste. However, if an extreme situation occurs once every few decades, the designed power grid may not be able to cope with it.

Part 2

Energy storage technology is the backing of the power grid system

What should we do when the power grid is unable to cope? At this time, energy storage facilities are needed to come to the rescue. What is the purpose of energy storage facilities? For example, it is equivalent to a small treasury, storing the excess electricity in the energy storage facilities, and then taking it out when needed. This is the solution with the highest energy utilization rate. There are many types of energy storage systems, each with its own characteristics, mainly pumped storage, flywheel storage, compressed air storage, electrochemical storage, and supercapacitor storage.

At present, the largest grid energy storage facility in the world is the pumped storage power station. When electricity consumption is low, the pumped storage power station uses the excess power generation of the grid to pump water from the lower reservoir to the higher reservoir for storage; when electricity consumption reaches the peak period, the water pumped from the higher reservoir is used to generate electricity. In this way, the excess electricity can be stored in the pumped storage power station, and when the power station cannot meet the electricity demand, the pumped storage power station will generate electricity to share the pressure of the power station.

Anhui Xiangshuijian Pumped Storage Power Station

(Photo source: Xinhua News Agency)

The power generation of wind power and solar power fluctuates greatly and rapidly. The wind blows for a while and then stops for a while, or the clouds cover the sun for a while, and the power generation of both fluctuates like a roller coaster. This is also an important reason why the energy utilization rate of wind power and photovoltaic power generation is not high at present. The fluctuation is too fast and the power grid cannot bear it. (Power grid: My little heart can't stand this kind of fluctuation). The way to effectively improve the utilization rate of these electric energies is to build energy storage facilities. When the power generation is redundant, the electric energy is stored, and then when the power generation is insufficient, the auxiliary discharge is performed to "iron" the power generation, so that the power grid can bear it.

(Image source: self-made by the author)

Can pumped hydropower stations do this job? No, for photovoltaic and wind power, the response speed of pumped storage power stations is always "half a beat slower" and cannot meet the requirements. It usually takes several days for pumped storage power stations to store energy, and the construction of pumped storage power stations also has relatively high requirements for the environment. Therefore, currently pumped storage power stations are almost all used to share the pressure of power generation when the power system is under a large load.

Chemical batteries are currently the most likely to meet the above requirements. Chemical batteries switch between charge and discharge quickly and react very quickly. The most common energy storage device in life is chemical batteries. The energy storage devices of mobile phones, tablets, and electric vehicles are all chemical batteries. However, although the performance of batteries is good, large-scale use still faces cost issues. Take the mobile phone power bank that we usually use as an example. Under ideal conditions without considering loss, 7.5 power banks with a capacity of 10,000 mAh are needed to store one kilowatt-hour of electricity. This is still the case when lithium-ion batteries with high energy density (of course, the price is also very touching) are used.

Part 3

The development of battery technology - there is no Moore's Law

Moore's Law is the experience of Gordon Moore, one of the founders of Intel. Its core content is: the number of transistors that can be accommodated on an integrated circuit will double approximately every 18 to 24 months. In other words, the performance of the processor doubles approximately every two years, while the price drops to half of the previous price.

In the battery industry, this can be said: the battery energy density doubles approximately every two years, or the price is reduced by half at the same energy density. Of course, this is simply a fantasy in the battery industry. For more than 20 years, the development of the lithium-ion battery industry has been concentrated in the communications, consumer electronics and electric vehicle industries. In the energy storage battery industry with a larger application scale, the application of large-scale energy storage batteries has always remained in the experimental stage due to the high cost of lithium batteries and their difficulty in coping with special environments such as puncture, collision, and high and low temperatures. The development of battery technology still has a long way to go.

(Image source: Reference 2)

At present, the main research direction of energy storage technology at home and abroad is electrochemical energy storage, and some new technologies have also made gratifying progress in the laboratory stage. However, there is still a long way to go for new technologies to move from the laboratory to the practical stage. When energy storage technology and power transmission technology develop to a new level, we are expected to get rid of our heavy dependence on fossil energy. Every major progress in the energy industry has brought mankind to a new stage of development. What will the future be like? What kind of changes will technological progress bring to the lives of ordinary people like us? Let us wait and see.

References:

[1]Hosein, Stefan & Hosein, Patrick & Kattick, Walter & Ratan, Varma. (2016). Web application for power grid fault management. 1-5. 10.1109/ICIAS.2016.7824052.

[2] Wu Haowen, Wang Jun, Gong Yingli, et al. Analysis on the development status and application prospects of energy storage technology[J]. Journal of Electric Power, 2021, 36(5):10.

[3] Zhu Xueyan. Analysis on causes and countermeasures of water abandonment in hydropower stations in Sichuan Province[J]. Industrial Innovation Research, 2019(9):2.

[4]Lai, Sing C, McCulloch, et al. Levelized cost of electricity for solar photovoltaic and electrical energy storage[J]. Applied energy, 2017.

[5]https://world-nuclear.org/information-library/current-and-future-generation/electricity-and-energy-storage

[6] Wu Haowen, Wang Jun, Gong Yingli, et al. Analysis on the development status and application prospects of energy storage technology[J]. Journal of Electric Power, 2021, 36(5):10.

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