Notes

Outline

DC-Bus Hybrid Power Systems

Battery and Hybrid Systems

Battery Charging Stations Carting Batteries to Town for Charging is a Common Practice in Developing Countries Offering Wind/Diesel Powered Battery Charging Services at the Village Appears to be Very Cost Effective Cost Of Service, Including Lights and Battery Delivery Service, Ranges From $2.50 - $5.00 Per Month Profitable Public or Private Sector Electrification, Even Serving The Very Poor, Is Possible With This Technology

Diesel Liabilities Systems Operate Inefficiently Due To Low Load Factors Power Is Not Available 24 Hours ... Limits Economic Development (e.g.,Daytime Productive Uses) and Some Valuable Applications (e.g., Refrigeration) Manual Controls and Dispatch - High Labor Costs Major Overhauls And Extended Downtime Are Common ... Total Abandonment Of Equipment Not Uncommon Continuing Headache of Fuel Supply Governments Often Have Goal Of Reducing Fuel Use And Expenditures

Hybrid Systems Characteristic Wind Diesel Capital Cost High Low Operating Cost Low High Maintenance Requirements Low High Available On-Demand No Yes

Hybrid Systems The New Way to Electrify Villages

Advantages of Hybrid Power Systems Provide Dependable, Utility-Grade 24 Hour AC or DC Power Not Dependent On Single Source Of Energy Flexible, Expandable, Able To Meet Changing Loads Simple, Quick, Low Cost Installation Low Operating Costs (O&M and Diesel Fuel) Simple Operation, Low Maintenance & Service Requirements User Not Required To Operate, Maintain, or Repair Lower Life-Cycle Cost Of Electricity For Remote Applications

Disadvantages of Hybrid Power Systems High Capital Cost Compared To Diesel Generators Diesel And Hybrids Have Very Different Cost Components More Complex Than Stand-Alone Power Systems ... Requires Battery Storage And Power Conditioning Not Yet In Full Commercial (High Volume) Production ... Few Suppliers

Hybrid System Configurations Very Small Systems (< 2 kWp Total) Usually Do Not Use Back-up Generators And Have Relatively Larger Battery Banks (And Usually Solar Modules) Larger Systems Usually Are Hybrid Systems With A Diesel Generator (And Sometimes Solar Modules) New System Architectures:  Rotary Converters And “AC Bus” Systems Are Emerging for Larger Systems

Advanced Inverter Systems

DC Bus Architecture

Static Inverters Inverter Is Often the Critical Component Inverter Technology Has Improved Greatly in Last 5 Years ... Reliability  is Now Quite Good Features:  Charging, Low Battery Cut Off, Diesel Synchronization (Load Sharing) Small Units Still Mostly Modified Square Wave Output ... Okay, But Can Cause Noise in Light Ballast's and in Communications Equipment Units Above 3 kW Now Mostly Sinewave Output; THD < 5% Efficiencies Run 80-94%; Average is ~90% Costs are Typically $0.60-1.00/W 50 kW+, 3Ø Units Now Common For Village Power, Leading Suppliers are Trace Engineering (U.S.) and Advanced Energy Systems (Australia)

Batteries I Flooded Lead-Acid Batteries Still the Technology of Choice Deep-Cycle Batteries Required - Vehicle Starting Batteries Last Only 1-2 Years in Deep Cycle Service Sealed Batteries Cost ~50% More ...  Too Expensive for Most Village Power Situations Typical Efficiency is ~75%, But Only 40-70% of Generation Goes to Storage - Batteries Only Take Net Power After Load Battery Costs are Typically $55 - 150/kWh Best Costs on Smaller Systems Achieved in Using High-Volume Golf-Cart Batteries (eg., Trojan T-105:  ~$45/kWh)

Batteries II Batteries Should Not be Discharged Below 80% ... Usable Capacity is ~80% of Total Capacity Batteries Should be Equalized Approximately Monthly Batteries are Connected in Series to Build Voltage and in Parallel to Build Capacity Batteries Can be Paralleled Up to 5 Strings Without Problems Battery Strings Should be Fused or Breakered to Protect for Short Circuits Battery Acid Is a Serious Health Hazard Hydrogen Gas is Generated, Particularly During Equalization The Variable Nature of Battery Charging with Wind Power Seems to Have a Positive Effect of Operating Life

DC Source Centers DC Source Centers Eliminate the Bad Practice of Attaching Sources and Loads Directly to the Battery Terminals Common Connection Point for All DC Sources, Loads, and Storage  Incorporates Fuses or Circuit Breakers for Major Components ... Providing Short Circuit Protection Often Constructed Around Multi-pole Switch, Providing Main System Disconnect Usually the Inverter is the Primary Load Costs are $400 (1 kW) - $1,800 (20 kW), Costs Primarily Determined by Current Levels Some Suppliers Offer Nice Power Metering Package Options DC Bus Provides Easy Method for Paralleling Multiple Wind Turbines and/or PV Arrays

Controls Typical Hybrid System Control Functions: •  Battery Overvoltage ... Wind & PV Regulators •  Battery Undervoltage (Load Shedding) ... Inverter •  Battery Equalization ... Wind & PV Regulators •  Back-up Generator Start / Stop ... Inverter or DC Source Center Centralized Controller Which Monitors All Sources and Loads is Not Necessary Most Controls Triggered by DC Bus Voltage (Battery Bank Voltage) State-of-Charge Monitors or Energy Counting (e.g., Net Ampere-Hours) Controls Don’t Work as Well Some People Prefer to have Manual Back-up Power, Controlled by Local Operator