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Course Title
100 Home
101 Introduction
102 FAQ Page
103 Course Catalog
104 Green World
105 Demand & Supply
106 Conservation Careers
107 Solar Careers
108 Wind Turbine Careers
109 Entrepreneurs
110 Employee or Employer?
200 Demand Management
201 Summary
202 Residential Energy Profile
203 Ten Conservation Rules
204 HVAC System
205 Kitchen Appliances
206 Water Heater
207 Lighting
208 Laundry Appliances
209 Calculating Savings
300 Renewable Technology
301 Solar Energy
302 Solar Collectors
303 Solar Water Heating
304 Stirling Engines
305 Basic AC-DC Electronics
306 Silicon Solar Panels
307 Thin Film Solar Panels
308 Wind Turbines
309 Inverters
310 Grid Tied and Off Grid
311 Solar Site Survey
312 Solar Site Diagram
313 Sun Path Chart
314 Site Survey Worksheet
315 Wind Turbine Site Survey
316 Wind Turbine Worksheet
400 Solar Thermal Design
401 Solar Heat Overview
402 System Configuration
403 Site Survey
404 SRCC Compliance
405 System Specification
406 Bill of Materials
407 System Installation
408 Solar Heat Incentives
409 Document Package
410 Future Products
500 Solar PV Design
501 Solar PV Overview
502 System Configuration
503 Site Survey
504 Grid Tied & Off Grid
505 System Specification
506 Bill of Materials
507 System Installation
508 Solar PV Incentives
509 Document Package
510 Future Products
600 Wind Turbine Design
601 Wind Turbine Overview
602 System Configuration
603 Site Survey
604 Grid Tied and Off Grid
605 System Specification
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Green Collar Careers AC - DC Electronics

When people think of solar or wind power the image that comes to mind is a solar panel or a windmill.  Electricity generated by those systems isn't quite ready to connect to your electrical panel needing first to be converted to "commercial grade AC" power.  Conversion is done by an inverter, usually a drab gray little box that few ever see or pay attention to.

Solar cells and most windmills produce a Direct Current (DC) output, and usually at a voltage different then needed.  Some windmills may produce an Alternating Current (AC) output but usually the wrong voltage and the frequency of alternation is determined by the speed of the turbine blade.

To understand a little more about the inverter and how it works, some basics about electricity are all you need to know.  In Module 201 we reviewed Volts, Amperes and Watts the units of electrical power measurement.  DC power is fairly straight forward, one wire is a steady negative voltage, where the other wire is a positive voltage.   Connect something like a battery to a speaker and all you'll hear is one click when its connected, and another click when its disconnected.

Alternating Current is different.  Commercial AC oscillates at 60 Hertz (Hz) or 60 times a second.  Connect a 60 Hz signal to a speaker and it makes a low frequency sound equal to that of the "A" string of a bass guitar.  Shown on an oscilloscope commercial AC oscillates almost identical in shape to the A-string in a waveform known as a sine wave.

Now imagine you have two guitars with perfectly tuned strings - pluck them both at exactly the same time and the sine waves "resonate".  Pluck them just off a little bit from each other and they have a slight muting effect.

Commercial AC is like those guitar strings in the shape of the electricity - add a second source of electricity and the waves have to be synchronized.  Connecting your home to the power grid requires use of an inverter system that the electrical company will first want to qualify, otherwise its possible that a loss of synchronization could affect the operation of your appliances - or even your neighbor's appliances.

The inverter will take "dirty power" and tidy it up into a proper voltage and waveform that will synchronize to the commercial AC power.  It does this in the following order:

  1. Line monitors Commercial AC voltage frequency and compares that with a built in clock.
  2. Converts AC power to DC - only for AC windmills.
  3. Creates a pulsed DC output with semiconductor switching transistors.  The frequency is synchronized to the commercial AC when present, otherwise the clock sets the 60Hz timer.
  4. Pulsed power is fed into a transformer to convert the voltage to the proper level.
  5. Steady DC voltage is maintained at the output of the transformer using a large capacitor.
  6. A series of "stepped switching" transistors build a sine wave;  the shape is more like a series of 8 steps up and 8 steps down, but that's good enough.

Inverter specifications requires only the basic electrical understanding:

  • Input Voltage
  • Input Amperage
  • AC or DC Input
  • Output Voltage (240VAC in America)
  • Output Watt
  • Cycles per Second (Hz)
  • Grid compliant - usually requires a UL1741 rating and IEEE 1547 compliance to be acceptable to most utilities

And you thought this would be a hard lesson.