'DC Microgrid' Installed for Efficient Energy Use in Island

2014/04/09 18:48
Kenji Kaneko, Nikkei BP CleanTech Institute

An industry-university research group started an operation test of a "system that supplies direct-current (DC) electricity using natural energy" in Nushima (island), Minamiawaji City, Hyogo Prefecture, Japan, in April 2014.

The group consists of researchers from Kobe University, the Hyogo Prefectural Institute of Technology, etc.

For the system, the group installed a DC microgrid (small-scale power grid) in a facility by using solar power generation and storage battery systems. It will try to reduce power demand through visualization of power being consumed at general households and demand response.

The solar power generation and storage battery systems were installed on three sites in Nushima. The output capacity of a solar power generation system and the capacity of a storage battery system are 18kW and 46kWh at Nushima Elementary School, 10kW and 23kWh at Nushima Sogo Center and 8kW and 23kWh at an apartment building for teachers.

DC electricity generated by the solar power generation system is stored in the storage battery system as it is and used for LED lamps, air conditioners, TVs and personal computers that can be powered by DC electricity. Alternating-current (AC) grid electricity is converted to DC electricity and used as auxiliary power.

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Depending on facility, DC and AC distribution boards are installed to be used for different electric appliances. At Nushima Elementary School, three units of a 20kWh mobile storage battery were deployed to be used for hybrid boats capable of running on electricity, electric carts, etc. By using DC solar electricity in house without converting it to AC electricity, conversion loss of the entire energy system is reduced.

Moreover, the research group installed a smart meter at about 50 residential houses in the island and gave out a tablet computer to each house to test demand response. Data on power consumption stored in the smart meter is displayed on the screen of the tablet in the aim of raising awareness of energy saving. Also, with pseudo TOU (time-of-use) rates using points, the group will try to reduce demand and adjust demand-and-supply balance.

The project was selected as the "Technology Development/Verification Research Project for Global Warming Prevention" of Japan's Ministry of the Environment in March 2012. It will end in January 2015. The cost of the project is expected to be about ¥550 million (approx US$5.39 million).

In addition to Kobe University and the Hyogo Prefectural Institute of Technology, the project is participated by Ritsumeikan University, Osaka City University, Sanyo Electric Co Ltd, Nakanishi Metal Works Co Ltd, Kei Communication Technology Inc, Sansha Electric Manufacturing Co Ltd and Fuji Electric Co Ltd.