- The concept of small hydropower
Traditional large and medium-sized hydropower stations have many negative impacts on the environment. For example, dams block the smooth flow of natural rivers, block the discharge of sediment, change terrestrial and aquatic ecosystems, submerge land, generate a large number of immigrants, and engineering construction causes soil erosion and vegetation. destruction and air pollution, etc. The impact of small hydropower on the ecological environment is much smaller, so it has gradually attracted people’s attention.
The definition of the installed capacity of small hydropower varies according to the national conditions of each country, but at present, 10MW is gradually recognized as the upper limit of the installed capacity of small hydropower. Small hydropower also includes small and micro hydropower stations, but small, small and micro power stations are generally completely limited to supplying electricity to local areas. The Second International Conference on Small Hydropower held by the United Nations Industrial Development Organization proposed to define the scale of small hydropower as follows: small hydropower stations are 1001~12000kW, small hydropower stations are 101~1000kW, and micro hydropower stations are 100kW and below.
When dividing small hydropower capacity in China, three main factors are taken into consideration: electricity load demand, local power handling capacity and the selection of unit equipment. Small hydropower mainly supplies electricity for county and township industrial enterprises and the vast rural areas. Considering that China’s rural electricity consumption level is still relatively low, it is not necessary to define the capacity of small hydropower. Local governments at all levels can solve the problem by themselves. At present, the investment cost of small hydropower stations is 80,000 to 10,000 yuan per kilowatt. If a 10MW small hydropower station is built, the investment may be close to 100 million yuan. At this time, the local power capacity must be considered; , China’s small hydropower unit product series specifications are also one of the considerations for the delineation of small hydropower capacity.
The capacity limit of China’s small hydropower is coordinated with the development of China’s national economy, especially with the development of China’s rural economy and the level of rural electricity consumption. In the 1950s, China generally referred to hydropower stations below 500kW as rural hydropower stations: by the 1960s, the capacity of small hydropower stations was limited to 3000W, and small power supply lines appeared in some areas. After the 1980s, with the development of small hydropower-based With the implementation of the rural electrification plan, the construction scale of small hydropower has expanded rapidly, and the definition of small power station has also expanded to 25,000 kW; after the 1990s, the State Planning Commission (now known as the National Development and Reform Commission) and the Ministry of Water Resources further clarified that the installed capacity is below 50,000 kW All hydropower stations in China can enjoy preferential policies for small hydropower, and some local power grids with a capacity of tens of thousands to hundreds of thousands of kilowatts have emerged.
The “Renewable Energy Law of the People’s Republic of China” promulgated in February 2005 (hereinafter referred to as the “Renewable Energy Law”) defines hydropower stations with an installed capacity of 50,000 kW and below as small hydropower. Figure 1 shows a small power station built on a mountain.
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According to the current relevant standards, those with an installed capacity of 50-250MW are medium-sized hydropower stations; those with an installed capacity greater than 250MW are large-scale hydropower stations.
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Like large and medium-sized hydropower stations, small hydropower stations are all hydropower generation and belong to the category of renewable energy power generation. But usually large hydropower belongs to traditional energy, while small hydropower belongs to new energy.
- Application characteristics of small hydropower
There are three types of hydropower development methods: dam type, water diversion type and hybrid type. Most of China’s small hydropower stations are water diversion types, such as using natural waterfalls, rapid beaches, river falls, river bends, mountain lakes, and cross-basin water diversion, etc. This is a relatively economical development method using the natural slope of small rivers in mountain areas. The number of dam-type and hybrid-type power stations is small, but because of their regulating reservoirs, they often become the backbone power stations in cascade development or regional power supply.
Hydropower stations can be divided into two types: runoff type and water storage type, according to the utilization and regulation capacity of natural water flow. The general small hydropower station is basically a runoff power station. This kind of power station is usually only a low flood barrier or diversion weir built, and little or no water is stored, so it is also called an unregulated hydropower station. When the flow of incoming water is greater than the water-passing capacity of the hydropower station’s turbine, the hydropower station will run at full power, and the excess water will not pass through the unit to generate electricity, but will be directly discharged downstream through the sewers (discarded water); when there is less incoming water, all the incoming water will pass through the unit to generate electricity , but some installed capacity has not been utilized due to water shortage. There are diversion-type hydropower stations with high or low head, and there are also dam-type hydropower stations with low head.
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The installed capacity of the runoff hydropower station is selected according to the average flow of the river for many years and the water head that may be obtained. It cannot operate at full load throughout the year, and the power generation guarantee rate is 80%, which generally only reaches normal operation for about 180 days; the power generation in the dry season drops sharply, less than 50%. %, and sometimes it doesn’t even generate electricity. The runoff hydropower station is restricted by the natural flow of the river, and there is a large amount of abandoned water during the flood season.
In order to reduce the cost of small hydropower, it is necessary to emphasize the principles of simplicity, economy and applicability in the design. Of course, for a power station with fewer units, it is technically necessary to ensure that the unit is of good quality and has a large unit operating range, which can operate at 50% or lower load, without affecting efficiency and stability, so that the load can be flexibly distributed. . In developed countries, small hydropower stations of less than 10,000 kW often use 1 to 2 units, the workshop is small, the degree of automation is high, unattended, economical and reliable.
The main economic indicators that need to be considered when investing in small hydropower stations are the investment per kilowatt, the investment per unit of electric energy, the cost of electric energy, the annual utilization hours of installed capacity, and the selling price of electric energy.
In addition, the dam-type hydropower station that only generates electricity is generally more expensive, but the dam-type hydropower station in the comprehensive utilization hub is still quite economical after the investment is shared.