DC-Based Open Energy System

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DC-Based Open Energy System

Mario Tokoro

Sony Computer Science Laboratories, Inc.

A Sustainable, Dependable, and Affordable Solution

for Next-Generation Electrical Power Infrastructures

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Power

Server Power

Server Client

Client Client

Power Packet

DC Bus Line

Table-top Experiments, 2005

in Sony CSL

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Ghana Expedition, 2010

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Okinawa, 2012 Sony CSL - OIST Joint project

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Bangladesh, 2014

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Okinawa, since Dec. 2014

Supported by Okinawa Prefecture Government

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Our Fundamental Thought Sustainable

Dependable Affordable

Do not pass on liability to next generation

Keep risk manageable

Accessible to everyone on earth

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Conventional Power Systems

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Do not pass on liability to next generation

Keep risk manageable

Accessible to everyone on earth

Renewable Energy Sources, which are

Distributed, Intermittent, and Unstable, with Batteries

Local Consumption of the Locally Produced by Self-Supporting as much, in the form of

Bottom-Up, Autonomous, and Interconnected System can start Small yet Expandable in the form of Bottom-Up, Autonomous, and

Interconnected

Our Approach Sustainable

Dependable

Affordable

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Open Energy Systems

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Conventional systems

• Distributed energy sources

• Local consumption of the locally produced

• Bottom-up and flexible configuration of distributed autonomous systems

• Stock based, asynchronous load/supply balancing

• Exchange network

• Centralized energy source

• Transmission for distant consumption

• Top-down configuration with central control

• Flow based, synchronous load/supply balancing

• Distribution network

Open Energy Systems

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How do we achieve OES?

DCOES Technologies

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Renewable Energy Sources

http://commons.wikimedia.org/wiki/File:Machikawa_power_

station_1.jpg#/media/File:Machikawa_power_station_1.jpg

©OIST

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Batteries / Energy Storage

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SONY Ferro-Phosphoric Acid Li-Ion Batteries

• Full use of capacity

• Long life under tough conditions

• Inherent safety:

no thermal runaway

• Fast Charging time:

1 hour for >90% capacity

• Eco-friendly:

no rare metals

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SONY Ferro-Phosphoric Acid Li-Ion Batteries

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How to balance the PV generation

and battery capacity?

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Batteries cannot take whole energy produced by PV

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Variety in usage pattern

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Energy Exchange Technology

Exchange energy among batteries In the form of DC

In order to maximize the use of PV panels and batteries

through complementing difference in usage patterns

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• Reactance loss of power is not negligible

• Interconnection of

networks is difficult due to sync.

• Efficient DC/DC converters are now available

• Interconnection of

networks is easy (no sync.

is necessary)

AC for transformers DC

for batteries

Phase Voltage

Frequency

Voltage

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Base Theory

Constant Voltage Source keeps

the grid voltage at 350V Constant Current Sources set desired current

One Voltage Source and n Current Sources with Durable and Flexible Distributed Control

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m-to-n Energy Exchange

DC/DC converter can have 3 modes:

• Waiting (stop)

Constant Voltage mode (CV)

DC/DC #0 #1

DC/DC #2

DC/DC #3

DC/DC #4

DC/DC #5

DC/DC

Set the Grid to 350V by CV mode (#0) Deal 1: Send energy from #1 -> #3 Deal 2: Send energy from #4 -> #2, #5

V_G=350V

CC

2A 2A

CC

I_G=2A I_G=2A

CV CC CC CC

4A

2A 2A

I_G=4A I_G=2A I_G=2A

2A 2A 2A

350V Bus line

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Energy Exchange Policies

• Baseline policy

– Capacity available for giving/receiving – Request for consumption

• Advanced policies

– Prediction based on past usage pattern

– Weather forecast for generation and consumption – Dynamic pricing reflecting demand and supply

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Scalable Architecture

Power Exchange Network

When necessary

Most exchanges happen at the lowest level!

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DCOES@OIST20 System Structure (1)

• Configuration of each house

48VDC

100VAC

Energy System Controller

Charger PV

Bi-directional DC/DC

Inverter and AC switch

350VDC

Energy Server System

Battery

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Communication Line

DCOES@OIST20 System Structure (2)

• 19 houses connected

Power Line

house 1 house 2 house 19

switch switch switch

...

350VDC

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Energy Server System

• SONY 48V Li-Ion battery modules

• 350V Grid

• Energy exchange module, DCDC

• DC to AC inverter for appliances

• AC backup by utility company

Main Controller PV Charger BMU Battery 1.2kWh Battery 1.2kWh

DC-DC Conv.

Inverter EMU

PV Charger

Battery 1.2kWh

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350V DC Power Lines (Privately Owned)

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Example Daily Operation

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Performance Evaluation

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Performance Evaluation

Distributed stand-alone

Top-down by a single entity

• Fixed in size with high initial costs

• Single failure may cause total system outage

• Efficient for a predefined users and Bottom-up by individuals

• Flexible in size and variety with incremental costs

• Failures do not cause total system outage

Centralized

vs

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DCOES: Distributed System with Energy Exchange

DCOES

• Flexible in size and variety with incremental costs

• Failures do not cause total system outages

• High efficiency and flexibility in size and variety

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Variety in usage pattern (Winter)

Q3 Median Q1 outlier

x

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Variety in usage pattern (Spring)

Q3 Median Q1 outlier

x

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Performance Result and Estimation

(Current OIST configuration with baseline policy)

Stand alone DCOES Centralized

Summer: Simulation (19 houses) 2015/7/16- 8/15

Winter: Real OIST Data (19 houses)

2015/1/1- 1/31 Spring: Real OIST Data (19 houses) 2015/4/16- 5/16

34%

60% 63%

38%

67% 71%

42%

74% 77%

0%

20%

40%

60%

80%

100%

Winter Spring Summer

Stand Alone DCOES

Centralized

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Performance Result and Estimation

(Solar x2, Battery x2 with baseline policy)

Summer: Simulation (19 houses) 2015/7/16- 8/15

Winter: Real OIST Data (19 houses)

2015/1/1- 1/31 Spring: Real OIST Data (19 houses) 2015/4/16- 5/16

57%

87% 90%

67%

94% 96%

73%

96% 99%

0%

20%

40%

60%

80%

100%

Winter Spring Summer

Stand Alone DCOES

Centralized

Self-sufficiency ratio = (Energy used - Energy bought)/ Energy used

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Next Plans

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DCOES/LV for Houses in a Community

350V DC Line PV: 3-5kWp

Batt.: 5kWh

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DCOES/MV for Larger Communities

350V DC Line PV: 3-5kWp

Batt.: 5kWh

DCOES/

LV DCOES/

DCOES/ LV LV

DCOES/ DCOES/ DCOES/

LV DCOES/

LV

DCOES/

+ 1KV Line

DCOES/MV

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DCOES/MV for Eco Campuses

1KV DC Line PV: 100kWp Batt.: 500kWh

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DCOES/HV for Cities

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DCOES

DC based Open Energy System

For sustainable mankind and development

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