DC-based autonomous Microgrid for community (DCOES)

The DC-based Open Energy System (DCOES) proposes a whole new type of bottom up grid. It is an alternative way of exchanging energy in-between energy subsystems in order to manage energy fluctuations within the community. Supply and demand are balanced autonomously without impacting the utility grid and thus energy autonomy is increased with minimal infrastructure costs. The concept and feasibility of OES have been demonstrated in a decentralized, peer-to-peer system in Okinawa.

DCOES Implementation

How to implement it?

Each house is equipped with an in-house microgrid system, including batteries that are connected to a dedicated, shared DC power bus as well as a communication line. The goal of OES is to allow energy flows between independent microgrid systems within a community, allowing neighbors to share their energy, similar to a peer-to-peer network.

Figure 1 :Main architecture of DC Open Energy Systems

OES is based on independent DC microgrids that are interconnected from the bottom-up to share distributed power. It is called open because the connections can vary freely and energy can be exchanged among subsystems. A distributed control software managed the energy exchanges between houses according to various scenarios,.  Also, the community size may reduce or expand as new microgrids are being plugged into it. This provides an unprecedented flexibility for electricity grids that is unimaginable with the current grid infrastructure.

Figure 2: Autonomous power exchange can be controlled depending on a variety of usage patterns

We are developing a grid system from bottom up, which means we are free to choose radically different technologies than the mainstream. One of the different approaches we chose was to use direct current (DC) everywhere. Alternative current (AC) has been used until now for over a century and contrary to DC, AC makes transforming voltages trivial but makes energy merging hard. Batteries, most home appliances and solar panels all use DC internally. Since DC voltage conversion has improved over the last decade thanks to efficient DCDC converters, we decided to use DC both for the microgrid as well as for the exchange.

OES platform in Okinawa

We are testing DCOES concepts and implementation at our platform in Okinawa where 19 inhabited houses are equipped with individual microgrids and interconnected using DC power bus. On 2-3 February 2015 we held The 2nd International Symposium of Open Energy System we first demonstrated the autonomous power exchange on the full scale system. A visualization for monitoring the power flows and the power exchanges in real time has been implemented. 

Figure 3: Ongoing feasibility study of Open Energy Systems in Okinawa

Figure 4: Visualization of current system

DCOES-OIST20 Autonomous Energy Exchange Visualization

Acknowledgement:
This project is supported by the “Subtropical and Island Energy Infrastructure Technology Research Subsidy Program,” Okinawa Prefectural Government. (March 2013 – March 2015)
Also, the test is being held in collaboration with Okinawa Institute of Science and Technology Graduate University (OIST),  Okisokou、Ltd., and Sony Business Operations,Inc.