Off-GridHybrid 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

NEOS Corporation

• PV, Mechanical wind and diesel backup solves problems with seasonal variations in resource

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

Energy Flow for a Small Hybrid

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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)

D C Loads

Turbine Disconnect

Guyed Lattice Tower

Inverter or bi-directional converter

Turbine Controller

D C Source C enter

Battery Bank

P V C harge Controller

W ind Turbine

G enerator

AC Loads

PV Array

Micro-grid System Architecture (AC)

W ind Turb ine

G uyed Lattice Tow er

Turb ine D isconnect

G enerator

Turb ine Inverter and C ontro ller

PV Inverterand C ontro ler

PV A rray

B i-d irectional C onverterand System C ontro ler

Battery Bank

AC Loads

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

•Morocco•Algeria•Jordan•Ghana•Egypt•Southern Africa Region•(Nigeria, Mozambique)0

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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 VACsingle 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

Instantaneous Penetration:

– Voltage and frequency control – Reactive power

Average Penetration: (generally a month or a year)

– Total energy savings– Loading on the diesel engines– Spinning reserve losses/efficiencies

(kW) Load ElectricalPrimary

(kW)Output Power WindnPenetratio ousInstantane

(kWh) DemandEnergy Primary

(kWh) ProducedEnergy Wind n Penetratio Average

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

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

These are really three different systems which all should be considered differently

Note: People play loose with the definitions

Low Medium High

Peak Instantaneous

<50% 50 – 100% 100 – 400%

Annual Average

<20 20 – 50% 50 – 150 %

Commercial status

Fully utilized

Well proven Fully commercial Multiple use

System prototype Operating

Examples Denmark, Greece

San Clemente, CA Kotzebue, Ak Coyaique, Chile

St. Paul Wales Ak

Diesel Only Power System

Po w

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Diesel Gensets

Village Load

System Controller

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Multiple Diesel Plants with ControlIn 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

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Load, kW Dsl #1Power Dsl #2 Power

Potential use of a 500 and 1000 kW diesels

Low Penetration wind/diesel system

Diesel Gensets

Wind Turbine

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System Controller-20

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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

AC Wind Turbines

AC Bus

Community load

System Control

Diesel Engines

C ontro lD um pLoad

San Clemente Island, California

Plant Details• Four generators

• 3 NEG-Micon 225 kW turbines

Yearly impact -• $97,000 fuel savings• 871,785 Ton CO2

avoided

• U.S. Navy island off San Diego• Diesel powered grid• 850-950 kW avg; 1,400 kW peak

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

AC Bus

C ontro lSystem

SynchronousC ondenser

C ontro lD um pLoad

D ispatchedLoads

Wind Diesel without Storage

When the wind power is larger than the

load by some margin - Diesel is shut off.

• Frequency controlled by dump load

• Voltage controlled by condenser

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Red = DieselBlue = LoadGreen = Windpower

High Penetration W/D Schematic

AC W ind Turbines

AC BusD C

R otary C onverter

Battery

D C Bus

C ontro lSystem

C ontro ledD um pLoad

AC

AC D iesels

D ispatchedLoad

Wind/Diesel with Short Term Storage

• 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

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Diesel p

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St. Paul Alaska, USAIsland in the middle of the Bering SeaPeak load of 160kWCost of Power, + $0.21/kWhWaste energy used for heatingTDX 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

• 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

Northwind 19/100

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 facilityat remote ranch

UEK 50kW flow turbine

Hybrid System Power Converters• 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

Trace Tech 100 kW

converter

Wales AK 156 kW rotary

converter

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

Flywheel

Low Load Diesel

75 kW Synchronous Condenser

Grid Conditioner

Controlled Dump load

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 used2. The load3. 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

Turb ine D isconnect

G uyed Lattice Tower

Inverter (b i-d irectional optional)

Turb ine Contro ller

D C Source Center

Battery Bank DC Loads AC Loads

PV C harge C ontro ller

W ind Turbine

G enerator

PV Array

Power system schematic

W T G (B W C E xce l R 7kW )1 2 0 V , 3 P , 3 W

G

Turb ine 1.8 D ow n-Tow erD isconnect

40A

1.5" EM T3-1/C #61-1/C #8 G ND.3-1/C #6 Arm ored, Jacketed Cable

S ite 1 .8 O ne-L ine E lectrica l D iagram for BW C Insta lla tion(C hile R eplica tion P ro ject)

G N D . R O D

1-1/C #2 G N D.

G

Turb ine 1.8 C ontro l Room

D isconnect40A

1.5" R T C om p EM T3-1/C #61-1/C #8 G ND.

30 K VA: 36 .1A P rim ary

480V /208V

110A

G

1.5" R T C om p EM T3-1/C #11-1/C #6 G ND.

P os. FusedS olid Neg.300A

2-1/C 1 /0 W eld

2-1/C 1 /0 W eld

2-1/C 4/0 1-1 /C #4

Inverter5 .5 kV A, 1P4 8 V D C - 1 2 0 V AC

Kohler Generator5 kV A, 1P

1 2 0 V AC

50 AG

.5" EM T2-1/C #8 1-1 /C #8

GN

G

G N D . R O D

D C B us

G

G

Trojan T105 Battery Bank4 8 V , 5 2 k W h

W TG C ontro ller

R ectifier/V oltage R egulator

L igh tn ing Arrestor

LP 1.8

To Load To Load

P os. FusedS olid Neg.250A

P os. FusedS olid Neg.150A

G

G

G G round B ar (or equ iva lent)

G

.5" EM T2-1/C #8 1-1 /C #8

.5" EM T2-1/C #8 1-1 /C #8

1-1/C #8

1-1/C #8

continuous1-1/C #8

1-1/C #8

(DC)

Neg

Neg

Neu

Neu

50A or less

1-1/C #4 G nd

N o N egative /G round C onnection

N o N eutra l/G roundB onding Jum per

1-1/C #4 G nd

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

2.2

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2.22

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Energy Sys tem

Wind T urbine/T ow er

E lec tric al/E lec tronic Equipment

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 DangerousThe 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.orghttp://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 bio-fuels, 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 havea place in rural development