According to the specific conditions of micro-hydropower resources and power supply needs, there are four technical solutions for micro-hydropower systems: 1) AC direct supply system, 2) battery type system, 3) water storage power system, and 4) hybrid system.
1) AC Direct Supply System
The AC direct supply system is similar to the utility power used to supply electricity to urban households, and it supplies loads directly. It is suitable for areas with grid access and off-grid areas. The AC direct supply system uses the same standard transmission facilities and appliances as the utility, and it is generally more economical than custom-designed systems (e.g., DC systems, non-standard voltage systems) and, therefore, is widely used. This system is managed with an electronic load controller, which requires that the electrical power emitted by the system (which is generally constant) is always equal to or greater than the electrical power output by the system (which is generally variable). In order to keep the system power constant, the electronic load controller may consume some energy.
2) Battery type system
A micro-hydro with very little power can produce large cumulative power if it works continuously. When the accumulated power (KWh) of a micro-hydro system per unit time (e.g. 24 hours or 48 hours) is greater than the power consumed per this unit time (KWh), but the power cannot meet the peak load power demand, batteries can be used available to store power for nighttime use and to meet the peak load during the day. Battery type systems use rechargeable battery packs, the principle is similar to the use of solar and wind power systems. A DC generator is used for the generator and an inverter is used to power the AC load in the system, as shown in Figure 2-6.
The advantage of the battery type system over the AC direct supply system is that it requires much less water flow and can make the best use of the energy available in the system. The disadvantage is that the battery pack needs to be replaced once every few years.
3) Water Storage Power System
When the power or electric power that can be generated from micro-hydraulic resources is less than the power or electric power that the system needs to output, and although the conditions for the use of battery-based systems (Battery-Based Systems), but due to economic reasons can not use battery-based systems, water storage power generation systems can be used. For example, water is stored during the day and generated at night for lighting or water is stored at night and generated during the day for production. This system generally uses the same method as AC-Direct Systems for interval power supply.
The characteristics of this system are that it can guarantee the most basic electricity requirements and requires a certain amount of power generation storage capacity, and there are still many applications in areas without electricity in China.
4) Hybrid System
Hybrid system refers to the micro-hydro power generation and other power sources to form a hybrid power supply system. Other power sources can be wind power generation system, photovoltaic power generation system, internal combustion engine power generation system, etc. This system has many advantages over micro-hydro power supply alone, in many places, due to the different operating hours of water, wind and solar energy at the apex of the day / year, there is a good complementarity, coupled with the emergency protection of the internal combustion engine power generation system, even in the season of dry water flow, the hybrid system is also a completely independent and reliable power supply system.
Among the hybrid systems, Grid-Connected Systems (GCS) should be especially mentioned as a special case of hybrid systems, where micro-hydro power is built where there is already a grid, in order to obtain power from both micro-hydro power and the grid. The use of such systems allows the owner of a small renewable energy system such as micro-hydro to have better economics and reliability than a direct utility system, without the use of expensive combustion engine generation systems or battery packs for security. At the same time, the owner can even sell the excess power to the grid for a profit. This is the ideal model for the use of micro-hydro power as a renewable energy source. The many issues of grid management using grid-connected systems vary from place to place at different stages of development. Each locality has its own policy on grid connection.