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Natural energy such as wind power and solar energy are renewable energy sources that do not emit CO2 when generating power.
Supplying this natural power in a stable and efficient manner is the first step towards achieving a low carbon society.
The goal of Hitachi's renewable energy business is to utilize the power system technology and expertise that we have cultivated over the years to help disseminate wind and solar power systems.
The Intergovernmental Panel on Climate Change (IPCC) concluded in its Fifth Assessment Report, issued in 2014, that limiting global warming "below 2°C relative to pre-industrial levels" would require "40 to 70% global anthropogenic GHG emissions reductions by 2050 compared to 2010."
The further popularization of renewable energy such as wind or solar power is expected to be one o of the main measures to reduce GHG emissions.
The Hitachi Group is using its advanced technology and products to deliver wind and solar power generation with high added value. These include our independently developed wind power generator and electric converter, high-capacity power conditioner *1 for a "mega solar" *2 generation system , and storage batteries.
Hitachi's strength is that we can provide total system deployment, from power generation devices to control systems that stabilize power transmission and distribution networks.
Hitachi has developed the downwind type wind power generation system at 2,000 kW, which suit the topography of Japan, with its many mountains and hills. At the bottom of mountains and hills, the wind blows along the topographical features. Downwind turbines use this wind efficiently. We are also developing power storage technology and our own power prioritization and control systems. These technologies allow wind power, which is unstable because of fluctuations in wind strength, to be connected stably to the power transmission and distribution networks.
The basic structure of a wind power generation system is shown in the figure below. A wind power generation system consists of components such as the wind power generator, storage batteries that absorb the output fluctuation, and SVCs *3 that regulate the voltage of the power transmission and distribution networks.
As shown in the following figures, stable operation of the power transmission network requires that the output fluctuations be restricted to within a certain range of the required power. Because the output of wind power depends on the strength of the wind, fluctuations in the wind strength can result in output outside the allowed range. When a storage battery is installed and the output from the wind power generator is higher than the allowed range, the storage battery is charged by the excess amount. When the output is less than the allowed range, the charged power in the battery is returned to the power transmission network. In this way, output fluctuations are kept within the allowed range.
The following explanation gives a little more technical detail. In power prioritization and control, the generated output is kept to a constant level by using the inertial energy of the generator and rapid-response electric control. In normal wind power generation, because the torque of the generator is controlled to a constant level, changes in the wind speed generate output fluctuations.
However, in wind power generation that uses power prioritization and control, electric control is used to change the generator rpm and keep the output at a constant level. In other words, when the wind speed drops suddenly, electric control is performed to discharge the inertial energy of the generator and reduce the generator rpm, which restricts the drop in the generated output. Conversely, when the wind speed rises suddenly, electric control is performed to absorb the inertial energy and increase the generator rpm. Electric prioritization and control can restrict rapid wind speed fluctuations that occur in about 1 second, and operate in coordination with turbine blade pitch control (a method of controlling the wind turbine rpm by changing the blade angle). This enables effective control of output fluctuations.
In addition, for large fluctuations that have a long cycle, even greater stability of the power output can be achieved by using the technology described above in combination with technology that restricts output fluctuations by charging or discharging storage batteries.
Hitachi achieves a stable power supply by using SVCs to prevent the voltage drops that are a concern when connecting wind power generators to a power transmission and distribution networks.
In the ways described above, Hitachi is applying all its technology and expertise to wind power generation systems.
Wind Power Ibaraki Co., Ltd., Kamisu Wind Farm (started operations in spring 2010)
The Hitachi Group is utilizing its know-how in power generation systems and power transmission and conversion systems to provide total mega solar systems. The basic structure of a solar power generation system is shown in the figure below. A solar power generation system consists of components such as the mega solar power generation cells, highly efficient power conditioners, and storage batteries. This system enables power to be transmitted stably and smoothly from the solar power generation cells to the power transmission and distribution networks.
The output from the solar power generation cells is direct current, but the power in the power transmission network is alternating current. As such, a power conditioner is required that converts the current from direct current to alternating current. Also, because the output of solar power cells fluctuates according to the weather, a stable power supply is a key issue. The output fluctuations are minimized by the same storage batteries as are used in wind power systems. Excess fluctuations are absorbed by charging or discharging the storage battery.
As shown in the following figures, stable operation of the power transmission and distribution network requires that the output fluctuations be restricted to within a certain range of the required power. Because the output of solar power is affected by the weather, in particular by clouds blocking the sun, weather fluctuations can result in output outside the allowed range. When a storage battery is installed in a solar power generation system and the output is higher than the allowed range, the storage battery is charged by the excess amount. When the output is less than the allowed range, the charged power in the battery is returned to the power transmission and distribution network. In this way, output fluctuations are kept within the allowed range.
Hitachi uses the control technology that it has cultivated over the years to design systems in harmony with power transmission and distribution networks.
A rendering of the largest commercial mega solar system (13,000 kW) in Japan (scheduled to start operations in 2011); Tokyo Electric Power Company, "Ogishima Solar Power Plant (Provisional Name) (Kawasaki City, Kanagawa Prefecture)
As we have seen, the output of renewable energy fluctuates. Stable use of this energy requires a good balance between supply and demand. To achieve this, Hitachi is developing a "smart grid," the next-generation power system.
Working towards the integration of renewable energy in our everyday lives
For the next generation - The Hitachi Group is committed to helping the global environment.