Why Pumped Hydro is the “Standard” for Clean Energy
The development of clean energy is the key to achieving the “dual carbon” goal. In 2021, wind power and photovoltaic power generation will account for about 11% of the electricity consumption of the whole society. However, the sudden emergence of wind and solar energy also poses challenges to the safe and stable operation of the power grid. This is because renewable energy such as wind energy and solar energy has the characteristics of volatility and intermittence. Large-scale wind energy and solar energy connected to the power system will have a serious impact on grid-connected control, operation scheduling, power forecasting, and power supply quality.
China’s wind energy resources are concentrated in the western and northern regions, and the geographical span from the central and eastern power load centers is very large. It is a big
issue . Moreover, wind power generation is limited by the wind power, and cannot generate electricity when there is no wind, so wind power generation is random and uncontrollable, which brings difficulties to the grid connection of wind power. Usually, the output power of wind power generation will be larger at night, when the electricity load is at the trough. From the power consumption side, the power load level is generally fixed. If the volatile wind power is connected to the grid, it will inevitably affect the stability of the entire grid and increase the operating cost of grid companies. The volatility of wind power can also cause voltage deviation and fluctuation, which in turn affects the power quality of the power grid.
Photovoltaic power generation comes from the light energy of the sun, and the intermittency of sunlight determines that photovoltaic power generation is a kind of energy with poor regulation ability. This intermittency is restricted by seasonal changes, alternation of day and night and meteorological conditions, which will have a great impact on the power of photovoltaic power generation. If there is no energy storage device for adjustment, it will affect the safe and stable operation of the power grid and the power supply quality of the power grid.
To improve the grid’s ability to absorb large-scale clean energy, it is necessary to build a high-standard smart grid and seek breakthroughs in large-scale energy storage technology. When it comes to energy storage technology, the most common ones we see are chemical batteries, such as lithium batteries in smartphones and laptops. Although the technology has been commercialized and the number has been established, it has not yet reached the grid scale. Ability to absorb clean energy.
Practice has proved that pumped storage is a technically mature and economically feasible energy storage solution. The construction of pumped-storage power stations is an important part of promoting the large-scale development of clean energy.
Tianhuangping Pumped Storage Power Station, Anji County, Zhejiang Province, with an installed capacity of 1.8 million kilowatts, is also a national 4A-level tourist attraction
Why is pumped storage different from conventional hydropower plants?
A pumped storage power station is also called an energy storage hydropower station. As a special kind of hydropower station, it is not the same as a conventional hydropower station. Speaking of hydropower, almost no one will feel strange. Hydropower has a very long history and can be regarded as a pioneer in the power industry. A hydropower station is a technical device that uses water power to generate electricity. Therefore, power generation is the fundamental task of conventional hydropower plants. Although pumped storage can also convert the mechanical energy of water into electrical energy, its core value lies in “energy storage”. In fact, pumped storage power stations came into being to solve the contradiction between supply and demand between the peak and trough of grid load. The meaning of “energy storage” is that when electricity consumption is low, water is pumped to “fill the valley”, and power generation is “peak shaving” when electricity consumption peaks.
Based on this functional orientation, a pumped-storage power station needs to build two upper and lower reservoirs, and the water in the two reservoirs can be controlled in both directions, while conventional hydropower stations generally only have one reservoir. Generally speaking, the production and consumption of electricity are not matched. Within a day, the electricity demand during the day and in the first half of the night will be larger, and the electricity demand in the second half of the night will drop significantly. The same is one kilowatt-hour of electricity, and its value varies greatly in different time periods. When the load of the power grid is low, pumped storage uses the low-valley electricity to raise the “low-level water” to the “high-level water”, and then uses the “high-level water” to generate electricity when the power load peaks, so as to achieve the “peak shaving and valley filling” for the power grid. Purpose.
Why Pumped Storage is a “Public Good”
The pumped storage power station is different from the conventional power station, its service function is positioned based on the basic characteristics of “power reserve”. In addition to “peak shaving and valley filling”, pumped storage also has functions such as frequency modulation, phase modulation, emergency backup, special system load, special power consumption requirements, and black start. The beneficiaries of these service functions are not only the pumped storage power station itself, but a complex system including the power grid, the power generation side (such as thermal power, nuclear power, and new energy companies) and electricity users.
The “peak-shaving and valley-filling” function of pumped hydro storage can help to improve the quality of energy and turn waste energy into treasures, so as to ensure the stability of power grid operation and improve the utilization level of clean energy. At the same time, the use of pumped storage for peak regulation can reduce the peak regulation pressure of other power sources, thereby improving the efficiency of the system.
The frequency modulation and phase modulation functions of pumped storage can improve the power quality of the user side. The pumped storage unit has the characteristics of rapid start and stop, flexible and reliable, and can well adapt to the drastic changes in the system load to ensure the quality of power supply.
As a “power warehouse”, pumped storage has become the most prioritized emergency power source in the power system. It is reported that it only takes 1 or 2 minutes for pumped storage to go from start-up to full load, and it only takes 3 to 4 minutes to switch from pumping to power generation. The emergency backup function of pumped storage means that pumped storage can quickly adjust the load when the power grid fails and the load increases rapidly. The function of guaranteeing special power consumption requirements of pumped storage energy refers to ensuring the reliability of power supply for important power users.
Pumped storage is also a special kind of load. The system special load function of pumped storage means that pumped storage participates in the load test of high-power nuclear power and thermal power as a load.
In order to deal with a blackout accident, it is necessary to configure a certain scale of black-start power supply in the power system, that is, a power supply that can quickly self-start without external help. As the preferred black-start power source, pumped hydro storage can provide support for the rapid recovery of the power system under extreme accidents.
Therefore, as far as the service function of “pumped hydro storage” is concerned, it is a “public product” of the power system.
Why “4 kWh for 3 kWh” still wins
Pumped-storage power stations have attracted people’s attention because of their unique advantages in many aspects. However, from the operating characteristics of the pumped storage power station, it is both a power plant and a user. The so-called power plant means that it can use “high-level water” to generate electricity and feed it back to the power grid for “peak shaving”; the so-called user means that it is also a power user of the power grid, that is, the use of low-valley electricity or wind and photovoltaic power. Discarded energy for pumping, thereby converting electrical energy into potential energy of water and storing it for future use.
During an operation cycle, the pumped storage power station does not contribute much energy to the grid. Pumped-storage power plants inevitably suffer more or less energy loss in the process of water delivery, power generation and pumping, so the electrical energy generated by water discharge must be less than the electrical energy consumed by pumping. This is an indisputable fact!
We generally refer to the ratio of the electric energy generated by the water release to the electric energy consumed by the pumped water as the comprehensive efficiency coefficient of the pumped storage power station. This is an efficiency factor less than 1, usually in the range of 0.65 to 0.80. The question is is it cost-effective to use “4 kWh for 3 kWh”? How should this account be calculated?
In fact, as mentioned above, pumped storage is a “public product” of the power system, and its beneficiary is not only the enterprise itself, but the grid-related system. Therefore, it is a misunderstanding to measure the profit and loss of a pumped storage power station by the amount of electricity generated.
The transition to clean energy in the context of “dual carbon” requires the escort of pumped storage. Under the condition that the pumped storage power station cannot be fully introduced to the market at this stage, how to recover the cost has become the key point for the sustainable development of the pumped storage power station. The “two-part electricity price” policy currently implemented in my country fully reflects the value of the pumped storage service function. The so-called two-part electricity price refers to the electricity price and the capacity electricity price. The electricity price reflects the value of the “peak shaving and valley filling” service provided by pumped storage for the power grid. Electricity prices are formed in a more competitive manner, which reflects the characteristics of pumped storage for valley power and peak power generation. Through the movement of time and space, pumped storage can realize the jump from low-grade energy to high-grade energy. Pumped storage power stations can recover the operating costs of pumping and power generation through electricity tariffs. The capacity electricity price reflects the value of auxiliary services such as frequency regulation, phase regulation, emergency backup, special electricity requirements and black start provided by pumped storage for the power grid. According to the fair principle of “who benefits, who shares”, the pumped storage power station can recover the comprehensive cost except the operating cost of pumping and power generation through the capacity electricity price, and obtain reasonable income.
Why pumped hydro storage doesn’t have to be built along the river
Unlike conventional hydropower stations, pumped-storage power stations do not necessarily need to be built along rivers, except for hybrid pumped-storage power stations built in conjunction with new construction, reconstruction, or expansion of conventional hydropower stations.
However, not building along the river does not mean that there is no need for water security. Although pumped storage does not need to consume water resources during operation, it needs to use a certain amount of water as an energy carrier for energy conversion and energy storage. Therefore, when selecting the site, consideration should be given to the first water storage of the pumped storage power station, as well as the water source guarantee for subsequent water evaporation and seepage losses.
The leap-forward development of clean energy poses challenges for the safe and stable operation of the power grid. In 2030, the total installed capacity of wind power and solar power in my country will reach more than 1.2 billion kilowatts. In 2035, the maximum peak-to-valley difference of my country’s power system will exceed 1 billion kilowatts. It is an arduous task to maintain the safe and stable operation of the power grid. It is imperative to accelerate the development of pumped storage.
For a pure pumped storage power station, it is generally necessary to consider the proximity of the power load center and the economic and reliable power supply point. This is mainly to reduce line transmission losses during power reception and transmission. In the future, not only will the electricity load center be equipped with pumped hydro storage, but large energy bases will also need to develop pumped hydro storage.