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Solar Electricity Interchanged for Peak Cut Adjustment


Solar Electricity Interchanged for Peak Cut AdjustmentMitsui Fudosan Co Ltd opened "Gate Square," the core facility of "Kashiwanoha Smart City," which the company is developing in Kashiwa City, Chiba Prefecture, Japan, July 8, 2014.


Kashiwanoha Smart City is a project for developing the area surrounding Kashiwanoha Campus Station on the Tsukuba Express Line by building high-rise condominiums, commercial facilities, office buildings, etc. In Gate Square, there are specialty shops, offices and hotels in addition to "Kashiwanoha Smart Center," which controls "Kashiwanoha AEMS (area energy management system)." Kashiwanoha AEMS optimizes energy supply for the entire urban area.

On the roof of Gate Square, there is a solar power generation system whose output capacity is about 220kW. Also, in an "energy building" adjacent to Gate Square, there is a lithium-ion storage battery system (output: 500kW, capacity: 3,800kWh). "Lalaport Kashiwanoha," which is located across a public road, has a solar power generation system with an output capacity of about 500kW on its roof and a NaS battery system (output: 1,800kW, capacity: 11,850kWh).

In normal situations, electricity generated with the solar power generation systems is stored in the rechargeable batteries. And when the demand peaks, it is discharged and supplied to reduce the amount of electricity received from Tokyo Electric Power Co Inc (TEPCO), which is a power company.

On holidays, when the power demand of Lalaport Kashiwanoha is large, electricity stored in Gate Square's battery is transmitted to Lalaport via Mitsui Fudosan's own power transmission lines. On weekdays, when the power demand of Gate Square, where there are many offices, is large, electricity stored in Lalaport's battery is transmitted to Gate Square via the power transmission lines. As a result, the amount of electricity received from TEPCO can be reduced by up to 26%.

Because both Gate Square and Lalaport are run by Mitsui Fudosan, it is permitted to transmit electricity across the public road based on the "power interchange" scheme. However, only the generated electricity can be interchanged. Because electricity stored in the batteries include electricity from TEPCO (in case of emergency), only the amount of electricity generated with the solar power generation systems can be used for power interchange (for peak cut adjustment).

Each of the two buildings has two power receiving points for the power interchange. Due to rules set by the power company, multiple power receptions in the same area are not permitted. Therefore, for the power interchange, alternating-current (AC) electricity is converted to direct-current (DC) electricity via a "power interchange unit," and, then, it is reconverted to AC electricity.

The additional investment for the power interchange (e.g. the construction of the power transmission lines and the power interchange unit) can be made up for in less than 10 years by the reduction of the amount of electricity purchased from the power company, Mitsui Fudosan said.

Also, when the electricity from the power grid is cut off in a time of emergency, a gas engine generator with an output of about 2,000kW will start operations in Gate Square, enabling to continuously supply about 60% of the normal amount of electricity for three days.

Furthermore, in the multi-family building located in an urban area across the public road, Mitsui Fudosan installed a system that can be supplied with electricity via the power transmission lines to power emergency elevators and lamps in shared areas. The scheme of providing electricity across the public road is permitted by applying the "partial supply scheme" of the "specific power supply" system.

Mitsui Fudosan plans to further expand the development area of Kashiwanoha Smart City in the future by installing solar power generation systems. The company is considering storing the electricity generated by the additional solar systems in rechargeable batteries and supplying it to adjacent areas by using the power transmission lines, increasing the amount of electricity that can be used for peak cut adjustment.
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