“Smart” Micro-Grids for
Developing Regions
Achintya Madduri, Javier Rosa, Matt Podolsky,
Daniel Soto*, Eric Brewer, Seth Sanders
(*) In Collaboration with: Matt Bassinger, John Sarik, and Vijay Modi of the Earth Institute,
Columbia University
Outline
• How we fit into LoCal.
• Need for electrifying rural developing regions.
• Work done so far by Columbia University in
Africa: usage statistics, methodology, etc.
• DC microgrid description and features.
• Future plans.
How Does this fit into LoCal?
• Do more with less.
• Build a grid from ground up to achieve
maximal energy efficiency.
• Test-bed for LoCal grid-tied ideas: IPS, thermal
slack, demand-response, etc.
Need for Rural Electrification
• Displace fossil fuels for night-time lighting.
Source
Cost/Hour
Lumens
Kerosene
$0.04
8-82
10W LED@
$0.67/kWH
$0.0067
400
• Low power required per household, but
individual generation or fixed monthly cost
not practical.
Millennium Village Project
• The Modi Group at Columbia University has
implemented a community generation project:
Shared Solar in 20 sites in Africa.
• Goal: Was to build a framework to effectively
collect tariff.
– Existing overhead (administrative) costs are high
– Non-payment rates for post-paid plans at 40%
• Collected fine-grain data on usage and losses.
Shared Solar Overview
• Central generation station using a single large
source (ex. 2.5 kW Solar Panel)
• 220 V-AC transmission & distribution
• Centralized metering, switching, and SMS
communications.
• 100 m radius for transmission.
• 20 households with usage of ~200 W-hrs/day
Uganda, 7% Electricity Penetration
Shared Solar Installation & Gateway
Problems Encountered
• Off the shelf metering hardware inefficient,
expensive, prone-to-failure, and no longer
available.
– Solution: Custom Hardware that we have
developed and tested.
• Bigger problem: System losses due to
inverters and multiple AC-DC/DC-AC
conversions while using mostly DC appliances.
DC Micro-Grid
• DC generation, distribution, and appliances.
• Soft-transmission-voltage control scheme to
ensure effective power sharing (ex. 280-320
VDC).
• Real-time switching and metering for each
household in a tree architecture.
• Grid-controlled distributed storage.
• Communications over power lines.
AC vs. DC Comparison
Factors
AC micro-grid system with
centralized storage
DC micro-grid system with
distributed storage
Sizing Issues
Inverter losses can dominate
with mismatch to load.
Lack of inverter/centralstorage makes it easy to
incrementally add more
generation.
DC-AC/DC-DC
conversion losses
20%4 : due to central battery
bank + inverter.
15% daytime, 23% nighttime:
due to 3 DC-DC conversion
steps4,9
Component losses due
to internal rectification
and conversion
> 25%7
0% for DC and >25% for AC
loads8
End-to-end Efficiency
< 60%
85-77% for DC loads,
< 63% for AC loads
Overview of Architecture
Power Sharing Architecture
Power Source
ex. Solar Panel (1 KW)
MPPT with DC/DC
Converter
DC line voltage that
is variable depending
on the load state.
Ex. 280-320 VDC
Housholds: (~100 W)
DC-DC convertor with
Storage (100-200 Whrs)
…
…
Power Sharing Controls
Distributed Storage
• Storage should be sufficient for night-time
usage.
• Distributed storage minimizes losses of stored
electricity.
• Allows for incremental growth of high-cost
components.
Communications Over Power Lines
• Low cost communications using a TDMA
scheme over power lines.
• Allows to close loop for power sharing.
• Low bitrate communications:
– Charge state of household
– Credits
– Usage
Future Plans
• Deploy AC-grid custom metering hardware in
Haiti with Columbia University.
• Finish framework for DC grid for both power
and communications.
• Simulate with sample DC-DC convertors and
loads with usage patterns obtained from AC
grid deployments.
Thank You
• Acknowledgements:
– Modi Group, Columbia University
– Alex McEachern, Power Standards Lab
– Paul G. Allen Foundation
• Questions?
Summary
• Target a market that is high need but has low
usage.
• Efficiency is essential to making a solution
sustainable.
• Re-make the grid to provide the desired utility
without the existing constraints.