Practical Photovoltaic Applications

Solar electric technology has come far enough that powering your house is now within the realm of practical photovoltaic applications.

| July/August 1981

  • 070 photovoltaic applications 2 power inverter
    A power inverter can change 12-volt DC current into 110-volt AC power. 
    T.J. BYERS AND MOTHER EARTH NEWS STAFF
  • 070 photovoltaic applications 3 electric rototiller
    Richard Pratt uses a 12-volt Sears electric rototiller (unfortunately, this model has been discontinued) when he cultivates his garden.
    T.J. BYERS AND MOTHER EARTH NEWS STAFF
  • 070 photovoltaic applications 4 chainsaw
    A solar-powered chain saw quietly cut all the Pratts' firewood last winter.
    T.J. BYERS AND MOTHER EARTH NEWS STAFF
  • 070 photovoltaic applications 1 solar panel
    Photovoltaic applications can including supplying electricity to a house, as this panel of cells from ARCO Solar is doing at the home of Richard and Maureen Pratt.
    PHOTO: T.J. BYERS AND MOTHER EARTH NEWS STAFF
  • 070 photovoltaic applications - diagram 1
    In a basic setup the solar collector and motor are connected directly.
    MOTHER EARTH NEWS STAFF
  • 070 photovoltaic applications - diagram 2
    When a single panel can't meet the current needs of a motor, several panels have to be wired together in parallel.
    MOTHER EARTH NEWS STAFF
  • 070 photovoltaic applications 5 teel water pump
    The Pratts irrigate their vegetable patch with the help of this sun-energized Teel water pump.
    T.J. BYERS AND MOTHER EARTH NEWS STAFF
  • 070 photovoltaic applications - diagram 3
    Hooking panels up in series boosts the system's total voltage.
    MOTHER EARTH NEWS STAFF
  • 070 photovoltaic applications - diagram 5
    As long as they match the voltage of the system, any number of batteries may be connected in parallel. When wired in series, the batteries again need to match the panel voltage.
    MOTHER EARTH NEWS STAFF
  • 070 photovoltaic applications - diagram 4
    Groups of panels wired in series to match the voltage of a device can then be wired in parallel to increase the available current, as long as they're added in increments of the total voltage .
    MOTHER EARTH NEWS STAFF
  • 070 photovoltaic applications - diagram 6
    A small inverter can work with a 12-volt input current, but larger inverters need higher voltages to compensate for internal power loses.
    MOTHER EARTH NEWS STAFF
  • 070 photovoltaic applications - diagram 7
    Diagram shows a method of connecting photovoltaic panels to complement an existing wind generator system.
    MOTHER EARTH NEWS STAFF

  • 070 photovoltaic applications 2 power inverter
  • 070 photovoltaic applications 3 electric rototiller
  • 070 photovoltaic applications 4 chainsaw
  • 070 photovoltaic applications 1 solar panel
  • 070 photovoltaic applications - diagram 1
  • 070 photovoltaic applications - diagram 2
  • 070 photovoltaic applications 5 teel water pump
  • 070 photovoltaic applications - diagram 3
  • 070 photovoltaic applications - diagram 5
  • 070 photovoltaic applications - diagram 4
  • 070 photovoltaic applications - diagram 6
  • 070 photovoltaic applications - diagram 7

A short while ago, most North Americans thought solar energy too exotic to be put to any practical use. In the past few years our worsening energy situation has changed the picture considerably. Sun power is now becoming a standard means of heating homes and domestic water, and its popularity is no doubt due—at least in part—to the feelings of self-sufficiency and wellbeing that an "independent" energy source can provide. In fact, harnessing the sun has become so widely accepted that a number of regional governments (California's San Diego County, for example) now require that solar features be incorporated in all new construction.

However, when someone mentions producing electricity from sunlight, most of us are probably still inclined to be skeptical. We assume the technology isn't ready and photovoltaic applications are better left to the latest Buck Rogers episode. "Not so!" I say. For many people, practical solar electric power is here today and at affordable prices! And how, you may ask, do I know? Well, for one thing, a bank of solar cells provides all the electricity used in my family's home!

How It's Done

Changing sunlight (photons) into electricity (electrons)—the process called photovoltaic conversion—was pioneered by Bell Laboratories in the mid-fifties. And the silicon solar cells that Bell first developed for the space program are still the workhorses of the industry.

The cells are sliced from a cylinder of ultra-pure silicon crystal, which is nothing more than ( highly ) refined sand. Every wafer is then chemically treated and processed to form a semiconductor junction (the technique is similar to that used in the fabrication of common transistors). It's within this thin semiconductor junction that electricity is generated.



And just how is the power produced? Well, photons strike the junction, liberating electrons (the action involves a mechanism that can be fully explained only by an excursion into quantum physics that I'd rather not make). The freed electrons are then collected by a conductive grid placed over the face of the cell. When a wire is connected from the front grid to the back of the cell, current flows.

Each cell generates about 1/2 volt of DC electricity, while the amount of current (amperage) depends upon the number of free electrons—which is proportional to light intensity and the size of the cell.






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