Standalone Power Generation: An Essential Part for Remote Internet Communications

M. J. Khan, mjakhan@engr.mun.caM. T. Iqbal, tariq@engr.mun.ca

Faculty of Engineering & Applied Science

International Workshop on Distributed Internet Infrastructure for Education and Research

Emerging Technologies in Power:General Discussion

Powering the Remote Internet InfrastructureService Providero Very small aperture terminal (VSAT) phones o Microwave relay stationso Television and radio transmitter/repeaters

End usero Domestic, commercial usero Stationary, mobile user

Conventional Power Generationo Thermal/Fossil Fuel Based Bulk Power

• Huge investment requirement• Greenhouse gas emission• Fuel supply

o Hydroelectric Power • Adverse environmental impact

o Grid Transmission and Distribution• System loss, slowness in expansion, lack of reliability

o Diesel Generator Based Standalone Power • Fuel supply in remote places• Emission

Alternative Power Sources: Renewable Energy Technologies (RETs)

Solar energy:

o Solar power is the simplest and most popular form of renewable energy.

o No moving parts, and need simple control mechanisms.

o Bangladesh has got favorable solar irradiation level almost all over the country

o High initial cost and low overall efficiency are the obstaclesc

Wind energy:

o Wind turbines are one of the oldest forms of renewable energy.

o Construction is simple and requires less investmento Coastal regions and North-eastern district may

possess high wind areas

Micro hydro:

o Requires source of running water o River-side locations, Hilly regions can benefit

Tidal & Wave energy

o Stream flow generators consist of a turbine (similar to a propeller) placed in a flowing river or stream.

o The water flow rotates the turbine and energy is used to generate electricity.

Biomass

o Biomass includes wood, crop residues, municipal waste, and other organic materials

o These are converted for power production and transportation fuels including ethanol and biodiesel.

Alternative Power Sources: Emerging Technologies

Fuel Cells

o Polymer membrane is sandwiched between two electrodes, containing a gas diffusion layer (GDL) and a thin catalyst layer.

o The membrane-electrode assembly (MEA) is pressed by two conductive plates containing channels to allow reactant flow.

o Highly scalable, low emission, No moving parts, higher efficiency (congeneration)

o Being considered for automobile industry mostly

o Application for portable electronics is also in view

Challenges for Fuel cell technology:o Fuel processor development

o Hydrogen storage development

o High performance material development

o Increasing Energy density

o Cost reduction

Prospects:o Fuel cell technology is expected to

revolutionize power generation scenario

o Worldwide R&D schemes would reduce its cost and increase performance, drastically

Ultracapacitors

o Ultracapacitors are capacitors with very high charge storage capacity (1F ~2000F).

o Could provide high energy-short duration pulses

o Mostly used in automobiles

Electrolyzers

o Electrolyzers convert water into hydrogen and oxygen

o Reversible fuel cell Technology is being considered

o Technology is yet to mature

o Combination of Renewable energy sources with other components to produce electricity in continuous and isolated mode.

o Mostly used in off-grid/remote applications

o Concept of distributed generation gaining popularity

Hybrid/Standalone Power Generation:

Standalone Power Generation for Telecommunication: Case Studies

o Application: Solar Installation, El Negrito-Telecom Argentina

o Location: Tucumán, Argentina

o Description: Located at an elevation of 4200 meters above sea level and approximately 140 km from the city of San Miguel.The system has a peak power output of 9,400 watts (rated 800watts) and allows more than 10 communities in the Calchaquies valley to be connected with the national communications system.

o System Components: 188 units of 50-watt solar modules 48 volts system, with 4,000 amp-hours of battery capacity. Three system controllers diesel generators were installed for auxiliary power in case of prolonged bad weather.

o Cost: $180,000-$200,000 for power system materials and installation.

o Application: Mexico's rural radio-telephony project

o Location: Serving thousands of small communities throughout Mexico

o Description: One of the largest exclusively solar powered communications systems in the world, Mexico's rural radio-telephony project has installed over 8,500 rural telephones and over 700 repeaters since 1989. The decision to use PV for all the radio and repeater stations provided the most economical and efficient implementation.

o System Components: Cellular repeater stations: Twelve to twenty 48-watt solar modules with 1,200-2,000 amp-hour (Ah) capacity battery storage systems

o Subscriber systems: Three to five 48-watt solar modules with 200-500 Ah capacity battery storage systems.

o Cost: $10,000 to $40,000 for power system materials and installation.

Future of Renewable Energy

Average Annual Growth Rates of Wind, Solar PV, Natural Gas, Oil, Coal and Nuclear, 1998-2002

Projected Growth of Wind, Solar and Nuclear Power (GW), 2002-2030

© Worldwatch Institute

Sizing, Optimization & Economics

Sizing:

o Resource assessmento Cost estimationo Energy consumption

analysis

Optimization (Software tools):

o HOMER: http://www.nrel.gov/homer/default.asp

o Hybrid2

http://www.ecs.umass.edu/mie/labs/rerl/

o RETScreen:

http://www.retscreen.net/

An Example:Dynamic Modeling and Simulation of a Wind Fuel

Cell Hybrid Energy System

Components of the proposed system

o Primary power: Wind turbine (Southwest Windpower’s AIR403)

o Backup power: PEM fuel cell (Independence 500 of Avista Lab Ltd.)

o Hydrogen production: Electrolyzer (FPM20 of Idatech Ltd.)

o Transient power: Ultra-capacitors Four 435F, 14V units (BMOD 0117 by Maxwell Technologies)

o DC/AC conversion: Single phase 120V 60Hz inverter (TSi power’s Inv 48v VDC series)

Layout of the schemeo Main system specifications : 500watt, 120V, 60Hzo Wind turbine produces electricity depending on availability of windo Excess power is used for hydrogen production by the electrolyzero Hydrogen is kept in the storage tank

o Any deficit in power demand is met by the fuel cell stack

o Sudden changes in the load demand is offset by the ultra-capacitor units

o The inverter converter 48V dc into 120V, 60Hz ac

o A controller controls power flow to and from the components

Small wind turbine

Modeling:Y(s)/X(s)=0.25/(S2+0.7S+0.25)

X(t), Captured powerY(t), Electrical power

Southwest Windpower’s Air 403 specifications:o Rotor Diameter: 1.14 meterso Weight: 6 kgo Start up wind speed: 3 m/so Voltage: 12, 24 and 48 voltso Output: 400 watts at 12.5 m/so Alternator: PM Generator

Fuel cell system basicsBasics:o A Fuel cell generates electricity by electrochemically

reacting hydrogen (H2) and oxygen (O2) and producing water (H2O).

H2+O2 => H2O + Heato A cell contains an anode, cathode and electrolyte. o Several cells are connected to form a stack to deliver

sufficient power

PEM fuel cell systemso Among various types of fuel cells, such as, Alkaline (AFC), Phosphoric

Acid (PAFC), Molten Carbonate (MCFC), Solid Oxide (SOFC), ProtonExchange Membrane fuel cells (PEMFC) are the most promising

o PEM fuel cells are favored for low temperature (~80oC)- low pressure (~3atm) operation, high power density and good transient capability

o A PEM fuel cell system contains auxiliary components such as:o Fuel processoro Compressoro Pumps, Blower, Cooling fanso Filters, Sensorso Power conditioner, Controller etc.

PEM fuel cell modelingThe thermodynamic potential:E=1.229 – 0.85x10-3 (T - 298.15) + 4.3085x10-5 .T. (lnPH2 + 0.5 lnPO2)The concentration of dissolved oxygen:cO2 = PO2 /(5.08x106 exp(-498/T))Activation voltage drop:ηact = -0.9514 + 0.00312 T – 0.000187 T ln (i) +7.4x10-5 T ln (cO2)Internal resistance: Rint = 0.01605 – 3.5 x 10 -5 T + 8x10-5 i

Activation resistance: Ra = -ηact/iCell voltage: V = E -vact + ηohmicVoltage transients: dvact/dt=i/C – vact/Ra/COhmic voltage loss: ηohmic = - i RintStack voltage: Vstack = 65 Vcell

Auxiliary components modelingElectrolyzer:nH2 = nF.nc.ie/(2F)nF = 96.5exp(0.09/ie –75.5/ie

2)

Ultra-capacitor:One R-C branch with R=16mohms and C=108.75F

Inverter:PSB model Single phase full bridge inverter for 120V-60Hz output

Controller:PID controller as given by : Gr(s) = Kp(s + Td s2+ 1/Ti)/sO2 flow controller : Kp=2.17, Ti=0.5, Td= 0H2 flow controller : Kp=5.0, Ti=0.5, Td=0

Matlab/Simulink® modeling

Inverter

Electrolyzer

Power flow controller

Reactant flow controllerUltra-capacitor

Fuel cell stack

Wind turbine

Results

Distribution of load demand current among fuel cell stack and wind turbine

DC voltage output with and without ultra-capacitor

Change in wind speed and wind turbine’s power output

Reactant pressures within the fuel cell stack

Conclusions

o Availability of electricity is a precondition for remote Internet & Communication Infrastructure

o Alternative energy solutions and specially renewable technologies should be explored

o Assessment of wind, solar, bio and hydro resources should be done

o An example of wind/fuel cell system is introduced

o Government, private sector and researchers should come forward

Acknowledgemento Dr. T. Iqbal,

Faculty of Engineering & Applied Science, MUNo School of Graduate Studies, MUN & NSERCo Faculty of Engineering & Applied Science, MUNo IICT and BUET

o Danish Wind Industry Association: http://www.windpower.orgo Fuel Cells 2000: http://www.fuelcells.orgo National Renewable Energy Laboratory: http://www.nrel.govo Shakti: http://shakti.hypermart.net

Further Reading