Off-Grid
Hybrid Power Systems
Components and Architectures
E. Ian Baring-Gould
Session Overview
• Provide an overview of renewable based
power systems for rural areas.
• Describe renewable power penetration and
the basic design of wind/diesel power
systems
• Provide examples of power systems that
have been installed.
• Review common power system components
and their purpose
Session Goals
Provide a basic understanding of
renewable based hybrid power systems
so that attendees will be able to
understand these power system options
Key Messages
Hybrid power systems are an economic
reality that can be used to limit or
reduce the dependence on diesel fuel
and may provide power to remote
communities at a lower life cycle cost
that other traditional alternatives.
Stages of Remote Power Systems
Renewable power system can be used to
cover a wide range of needs.
These include:
– Dedicated use: Water pumping/ice
making.
– House systems: Power systems for
individual buildings, dispersed generation.
– Community Power Systems: Power
provided to a large community with large
loads
– Wind/Diesel Systems: Large communities
with large loads
Direct connect Water Pumping
Agricultural Water Pumping
• Livestock watering at the Bledsoe Ranch Colorado,
USA
• PV, Mechanical
wind and diesel
backup solves
problems with
seasonal
variations in
resource
NEOS Corporation
Direct Water
Pumping
• Ranch near
Wheeler, Texas
• Water-pumping for
120 head of cattle
• Whisper 1000 wind
turbine,
1 kW, 9-ft rotor, 30-ft
tower
Small Power Systems
• Systems do not have a dispatchable backup
generator like most hybrids
• Very simple architecture:
– Turbine, PV, Disconnects, Batteries
– DC Loads or AC power through an inverter
• Primarily PV dominated for small loads, wind
has potential at larger loads.
• In many instances a combination of PV and
wind make most sense
• Can vary in size, power output
Single Source System Architecture
0.2
Wind
0.15
Load
0.1
0.05
Solar
21
21
23
19
19
17
15
13
11
9
7
5
3
0
1
Power sources and sinks,
kW
Energy Flow for a Small Hybrid
100
50
Hour of day
23
17
15
13
11
9
7
5
3
0
1
Battery SOC, %
Hour of the day
Solar Home System
• Provide entry level
of service
– Lighting, radio
– DC service
• Expandable in size,
>20W
• Cost ~$700 for
small unit
• Developed market
Wind/PV Home Systems
• Provide more
energy
• AC Power
• Higher output
• Lower $/kW
Inner Mongolian wind/PV system
Village Scale Power Systems
• Larger, village scale power systems use
centrally located power plants and distribute
AC power to the connected homes.
• Single point of service and maintenance
• Usually use larger or multiple generation units
to improve operation performance and benefit
from quantities of scale benefits
• Act very much like small power utilities
• Provide “grid” style power
Village System Architecture (DC)
Wind Turbine
Guyed Lattice Tower
Turbine Disconnect
PV Charge
Controller
Turbine Controller
PV Array
DC Source Center
Generator
Battery Bank
DC Loads
AC Loads
Inverter or
bi-directional converter
Micro-grid System Architecture (AC)
Wind Turbine
Guyed Lattice Tower
Turbine Disconnect
Turbine Inverter
and Controller
PV Inverter
and Controler
Generator
PV Array
AC Loads
Battery Bank
Bi-directional Converter
and System Controler
Micro-Grid Power Systems
• Supply communities with demands from
~100kWh/day load (15 kW peak load) up to
~700 kWh/day (75 kW Peak load)
• Components of wind, PV, biomass, batteries
and conventional generators
• Generally provide AC
• Use of batteries to store renewable energy for
use at night or low renewable times
• Generator used as backup power supply
• Mature market
Parallel System
20
•Morocco
Wind
Diesel
14
•Algeria
12
10
•Jordan
8
Load
•Ghana
6
4
•Egypt
2
•Southern
Africa Region
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
•(Nigeria,
Mozambique)
Hour of day
18
100%
50%
Hour of Day
23
21
19
17
15
13
11
9
7
5
3
0%
1
Battery SOC, %
Power, kW
16
Both diesel
and
inverter
needed to
cover the
maximum
load.
Both units
run
together.
Woodstock, Minnesota
• Wind farm maintenance shop and office
• Electric loads include lighting, PC, and shop tools
• Passive solar day-lighting, corn used for space heat
• Installed cost $6,800 in
2001 (grid extension
alternative: $7,500)
• 1200 ft2 shop, 900 ft2 office
• Whisper H40 wind turbine,
900 W, 35-ft tower
• PV panels, 500 W
• 24 VDC battery, 750 Ah
• 4-kW inverter, 120 VAC
single phase
Santa Cruz Island, California, USA
• Remote Telecommunications station
• Power System
– PV array
– Two wind
turbines
– No Backup
generator
• Vary costly
access/site visits
• Remote operation
and monitoring of
system
Northern Power Systems
Mt. Newall, Antarctica
• Science
Foundation
Station project
• Repeater and
Seismic
monitoring station
• Power System
– 3.3 kW PV array
– Diesel generator
– HR3 wind turbine
Northern Power Systems
Isla Tac, Chile
• Island community
with Health post,
school and 82
homes
• Power System:
• 2x7 kW wind
turbine s
• Flooded batteries
• 2 x 4.5 kW
inverter
• 16 kWA backup
gas generator
Subax, Xinjiang, China
• Small community of
60 homes in very
remote part of
Western China
• Power System
– 2 BWC excel (8kW)
turbines
– 2 15 kVA Inverters
– 4 kW PV
– Low Maintenance
battery bank
– 30kVA diesel
generator
Dangling Rope Marina, Utah, USA
• Remote National
Park Center
• 160 kW PV /
Propane generator
hybrid system
San Juanico, Mexico
Remote fishing
community of
400 people
with tourism
Power System
• 17 kW PV
• 70 kW wind
• 80 kW diesel
generator
• 100 kW power converter/controller
Advanced monitoring system
Wind-Diesel Power Systems
• Larger systems with demands over ~ 100 kW
peak load us to many MW
• Based on an AC bus configurations
• Batteries, if used, store power to cover short
lulls in wind power
• Both small and large renewable penetration
designs available
• Large potential mature with fewer examples
• Due to cost - PV generally not used
Penetration
There are many different potential configurations for Wind –
Diesel power systems, one of the critical design factors is how
much energy is coming from the wind – called wind penetration
Instantaneous Penetration:
Wind Power Output (kW)
Instantane ous Penetratio n 
Primary Electrical Load (kW)
– Voltage and frequency control
– Reactive power
Average Penetration: (generally a month or a year)
Wind Energy Produced (kWh)
Average Penetratio n 
Primary Energy Demand (kWh)
– Total energy savings
– Loading on the diesel engines
– Spinning reserve losses/efficiencies
AC Based Hybrid System
• Low penetration systems - Wind acts as a
negative load, very little control or integration of wind
turbines into the power system is needed .
• Mid penetration systems - Wind becomes a
major part of the power system. Additional
components and limited automated control is
required to insure that power quality is maintained.
Little operational control required though may be
used.
• High penetration systems - Completely
integrated power system with advanced control.
Limited operational control of system by plant staff
System Penetration
Low
Medium
High
Peak
Instantaneous
<50%
50 – 100%
100 – 400%
Annual
Average
<20
20 – 50%
50 – 150 %
Commercial
status
Fully
utilized
Examples
Well proven
Fully commercial
Multiple use
Denmark, San Clemente, CA
Greece
Kotzebue, Ak
Coyaique, Chile
System
prototype
Operating
St. Paul
Wales Ak
These are really three different systems which all
should be considered differently
Note: People play loose with the definitions
Diesel Only Power System
System Controller
100
80
Diesel Gensets
60
40
20
0
0
6
12
-20
Time
Village Load
18
24
Multiple Diesel Plants with Control
1500
1000
500
23
21
19
17
15
13
11
9
7
5
3
0
1
Power Sinks Power Sources
In multiple diesel
systems the
diesels may be
dispatched to
take advantage
of size and load.
Generally
requires
automatic diesel
control.
Favorable in
power systems
with renewables
-500
-1000
-1500
Hour of Day
Load, kW
Dsl #1Power
Dsl #2 Power
Potential use of a 500 and 1000 kW diesels
Low Penetration wind/diesel
system
Wind Turbine
100
Diesel Gensets
80
60
40
20
0
0
System Controller
6
12
-20
Time
Village Load
18
24
Kotzebue, Alaska
• 11 MW remote diesel
power station in Northern
Alaska
• 2 MW peak load with
700kW minimum load
• Installation of 10 AOC
15/50, 50 kW wind
turbines and 1 NW 100,
100kW wind turbine
• KEA, Island
Technologies, AOC
Coyaique, Chile
• Large regional
distribution system
• 3x 660 kW wind turbines
• 4.6 MW of mixed hydro
• 16.9 MW of diesel
• Manually operated through
local control center
• Currently runs as a
wind/hydro facility
Medium Penetration W/D
Schematic
System Control
AC Wind Turbines
Community load
Diesel Engines
AC Bus
Control
Dump
Load
San Clemente Island,
California
• U.S. Navy island off San Diego
• Diesel powered grid
• 850-950 kW avg; 1,400 kW peak
Plant Details
• Four generators
• 3 NEG-Micon 225 kW
turbines
Yearly impact • $97,000 fuel savings
• 871,785 Ton CO2
avoided
Ascension Island
• U.S. Air Force installation in the Atlantic ocean.
• Prime diesel generation with rotary interconnect to
British 50 hertz system
• Four NEG-Micon 225 kW turbines.
• Operating since 1996
• Average penetration 14-24%
Expansion in 2005
• 2 MICON 900 kW turbines
• Synchronous Condensers
and 2 electric boilers for
fresh water
Impacts
• 650,000 gal/yr fuel saved
Selawik, Alaska
• Small Alaska Village
Electric Cooperation
community in
northern Alaska
• Installation of 4 e15,
50 kW wind turbines
and dump loads
• Part of a diesel plant
retrofit project
AVEC, Entegrity, Sustainable
Automation
Toksook Bay, Alaska
• Small community in western Alaska
• Installation of 3 NW100kW turbines and dump
loads
• Part of a diesel plant retrofit project
• Installed winter of 2006
AVEC, NPS
High Penetration w/out storage
Control
System
Dispatched
Loads
AC Bus
Synchronous
Condenser
Control
Dump
Load
Wind Diesel without Storage
When the wind
power is larger
than the load by
some margin Diesel is shut off.
100
80
60
40
20
• Frequency
controlled by dump
load
• Voltage controlled
by condenser
0
0
6
12
-20
Red = Diesel
Blue = Load
Green = Windpower
18
24
High Penetration W/D Schematic
Control
System
AC Wind Turbines
DC Bus
DC
AC
AC Bus
Rotary Converter
AC Diesels
Battery
Controled
Dump
Load
Dispatched
Load
Wind/Diesel with Short Term Storage
300
250
Wind
200
Load
100
50
193
181
169
157
145
133
121
109
97
85
73
61
49
37
25
-50
13
0
1
Power, kW
150
-100
-150
Battery power (Charging is negative)
-200
-250
Time, minutes
250
150
100
50
Time , minute s
193
181
169
157
145
133
121
109
97
85
73
61
49
37
25
13
0
1
Diesel power, kW
200
• Diesel used to
provide power
to system when
the wind can
not cover load.
• Battery used to
fill short gaps in
or to start
diesel
St. Paul Alaska, USA
Island in the middle of the Bering Sea
Peak load of 160kW
Cost of Power, + $0.21/kWh
Waste energy used for heating
TDX and Northern Power Systems
Wales, Alaska
• Remote community in
Northern Alaska
• 80kW average load with 2
AOC 15/50 wind turbines
• Short term battery storage
with rotary converter
• Resistive loads used for
heating and hot water
• Operation with all diesels
turned off
• Problems with maintenance
and operation
• AVAC, KEA and NREL
Systems and Components
• Hybrid power systems are made up of
separate pieces of equipment that are
brought together to form a cohesive power
system
• Configuration and component size depend on
the load and resource available at site
• Controlling the power systems is a
complicated question, both logically and
technically.
• Must understand the components
Dispatchable Generators
• Generators that can be
turned on with short
notice.
– Diesel, Gas, Natural
Gas, Bio-gas
• Usually require a lot of
maintenance
• Role depends on
system design.
• Wide range of old and
new technology
• Wide range of control
40 kW Diesel Generator
10 kW Diesel
Generator w/
Fuel tank
Wind Turbines for Hybrids
Northwind 19/100
• Range in size from
300W to 750kW
• Large AC turbines for
diesel plants
• Small turbines
designed for remote
applications,
generally DC but also
AC being developed
• Self erecting or tilt up
towers common
• Installed cost $3-6/W
with production from
$0.10-0.20/kWh
Entegrety e15
Bergey XL10
Photovoltaics
• Applicable for small,
remote applications
• Installation cost of
~$10/W, LCC of
$0.22/kWh
• Low maintenance
requirements
• Quite accepted
internationally
• Not used commonly in
large applications but
there are some
examples
PV on Active Tracker
Micro and Run of River Hydro
• Applicable for areas
with a dependable
resource.
• Lower head systems
available
• Run of river up to 50kW
pre-commercial
• Generally larger
infrastructure cost
Micro Hydro
facility
at remote ranch
UEK 50kW
flow turbine
Hybrid System Power Converters
Trace Tech
100 kW
converter
Wales AK 156
kW rotary
converter
• Convert energy from DC to AC
and back
• Some units contain power system
control
• Solid state or rotary systems
• Solid state range in size from 1kW
to 300kW
• Rotary systems built to size
depending on needs
• Combined with batteries for
storage
Xantrax 4kW
converter
Batteries
• Many types
– Lead Acid (deep cycle
and shallow cycle)
– NiCad
• Two uses/sizing:
– Store energy to cover
long periods
– Store power to cover
short periods
• Requires periodic
replacement
• Sensitive to environment
• Life dependent on use
and the environment
Other Power Control Devices for Large
Power Systems
75 kW Synchronous
Condenser
Flywheel
Low Load Diesel
Controlled
Dump load
Grid
Conditioner
System Controllers
Monitoring and
Remote Access
• Remote access allows
oversight of system
performance
• Enables real time
system interrogation
and troubleshooting
even when off site
• With expert analysis
system reduces
maintenance and
down time
• Small incremental cost
That looks simple – doesn't it?
The design and implementation of power
systems is a complex matter and although the
models (and initial presentations) make it look
simple, it is never that easy.
Every power system is complicated, some
much less than others but you do need to
think about the design and how it will be
implemented.
The Complication is with
Uncontrolled Generation
By their nature renewable generation are
stochastic (uncontrolled) and vary with the
resource.
The amount of variation and thus the amount of
system control to handle the variation
depends on the
1. Renewable resource being used
2. The load
3. Power system design
Two basic types
• DC based systems that feed AC loads
– Relatively simple in nature
– System control provided by the battery bank
based on battery voltage
– Issues associated with component efficiency and
power factor of the loads
• AC based systems
– More complex in nature
– System control needs to be considered carefully
since it many cases it must be done actively
– Issues of power quality and system stability
DC Based Small System Architecture
Wind Turbine
Guyed Lattice Tower
Turbine Disconnect
PV Charge
Controller
PV Array
Turbine Controller
DC Source Center
Generator
Battery Bank
DC Loads AC Loads
Inverter (bi-directional optional)
Power system schematic
Site 1.8 One-Line Electrical Diagram for BWC Installation
(Chile Replication Project)
1-1/C #8
.5" EMT
2-1/C #8
1-1/C #8
Lightning Arrestor
G
Ground Bar (or equivalent)
G
50 A
Kohler Generator
5 kVA, 1P
120 VAC
Inverter
5.5 kVA, 1P
48VDC - 120VAC
Neu
G
Neu
No Neutral/Ground
Bonding Jumper
2-1/C 4/0
1-1/C #4
GND. ROD
N eg
G
G
50A or less
G
Turbine 1.8
Control Room
Disconnect
40A
N
(DC)
.5" EMT
2-1/C #8
1-1/C #8
Turbine 1.8
Down-Tower
Disconnect
40A
1-1/C #8
continuous
1-1/C #8
.5" EMT
2-1/C #8
1-1/C #8
Pos. Fused
Solid Neg.
150A
To Load
To Load
30 KVA:
36.1A Primary
480V/208V
LP 1.8
1-1/C #4 Gnd
G
G
G
G
G
WTG (BWC Excel R 7kW)
120V, 3P, 3W
G
DC Bus
110A
1.5" EMT
3-1/C #6
1-1/C #8 GND.
3-1/C #6 Armored, Jacketed Cable
Rectifier/
Voltage Regulator
1.5" RT Comp EMT
3-1/C #6
1-1/C #8 GND.
1.5" RT Comp EMT
3-1/C #1
1-1/C #6 GND.
Pos. Fused
Solid Neg.
250A
2-1/C 1/0 Weld
1-1/C #4 Gnd
N eg
GND. ROD
Pos. Fused
Solid Neg.
300A
WTG Controller
No Negative/Ground
Connection
1-1/C #2 GND.
2-1/C 1/0 Weld
1-1/C #8
Trojan T105 Battery Bank
48V, 52kWh
System Drawings and
Documentation
All systems should have simple one line
drawing that shows the location and
size of all of the fuses and circuit
breakers in the system. This should be
posted in the building and will help
people find problems.
Things to worry about in DC based
systems
• True availability of your battery (due to
control and temperature)
• Yearly variation in resources and loads
• Starting currents on large loads
• Space requirements for components
• Maintenance and service infrastructure
• Venting of battery bank
Wire Losses
• Lower voltages
mean higher
currents
• Higher currents
mean larger
wires (or higher
losses)
(increased
cost)
Basic Electrical
• Everything should be
fused with the ability
to disconnect specific
components if that is
needed.
• Good junction boxes
that are properly
installed
• Cables are well
protected and buried
Grounding
Wind Turbine/Tower
Electrical/Electronic
Equipment
Energy System
2
2 .
.
2
2
.
2
.
2
2
.
2
2
2
2
.
2
2
.
2
.
.
2
2
2
2
4
1
3
2
5
5
3
7
6
Grounding Details
• Solid ground for towers or PV arrays further than 15m
from main junction
• Lightning arrestors to protect towers
• Lightning arrestors to protect the electrical/electronic
equipment
• Transient voltage surge suppressors (TVSS) for the
most sensitive electronic equipment
• Solid ground for all metallic housings of equipment
• Grounded metal conduit for buried power leads
• Low impedance connection to earth potential
• Tied earth planes to eliminate potential differences
The right way
The wrong way
But this is
OK for
towers
Facilities
• Water proof with
overhang
• Separate rooms
for major
components
• Safe diesel
storage
• Ventilation
• Good lighting
and security
• Work
environment
Site Issues
• Access issues - need to be sure
you can get to the site when it is
needed
• Strong Fences - Keep animals
from damaging equipment,
gives the sense of importance
to the site
• Good and plentiful signs Keeps people safe and off
equipment
Things to Worry About
• Power factor of installed loads
• Temperature (for batteries)
• Environment – Corrosion,
humidity - protective coatings
• Vandals, animals, insects...
Lead Acid Batteries
… the known evil
But there is nothing else that is
really available, especially in
remote areas, that can
compete based on simplicity,
cost and availability
Battery explosion
at a school
system in Chile
Batteries Can Be Dangerous
The use of batteries has to be considered carefully and
appropriately.. This starts from proper system design
Wireless Energy, Chile
General Battery Types
• Starting Batteries
– Automotive applications
– Unsuitable for renewable
energy storage (but are
commonly used due to
availability)
• Deep Cycle Batteries (traction
or stationary batteries)
– Robust construction designed
for repeated, deep discharge
– Highly suited (even optimized)
for renewable energy storage
Considerations for Batteries
• The deeper the discharge, the fewer the cycles
• One bad battery can bring down the whole string and
can even affect parallel strings (practice due vigilance)
• Ensure a reliable supply of
distilled water
• Avoid leaving batteries at a
low state of charge for long
periods
• Extractable capacity dependent
on a number of factors
http://www.benchmarking.eu.org
http://www.ecn.nl/resdas/
Conclusions
• There are a lot of options / configuration of hybrid
systems - Depend on load, resource, and costs.
• Many configurations for small DC-based power
systems for smaller communities or individual loads
• Options for larger communities are also available –
Advanced diesels and control, locally derived biofuels, wind/diesel applications
• Renewable based rural power systems can help
supply energy to rural needs in a clean, inexpensive
way that does not burden the national economy
• Configuration depends on many factors
• Social issues dominate over technical issues
• Its never as easy as it seems
Renewable power systems have
a place in rural development