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Grid tied generator info

The best grid tied generator to use is an induction motor. Induction motors are the electric motors used for long lifespan applications such as fans and pumps. If a motor has a horsepower rating, its generally an induction motor. When properly sized, an induction motor linked to a steam engine forms a grid tied generator. The generator will force electricity back into the wires, spin the electric meter backwards to credit the owner for power generated, and pass out through the AC lines to power the neighbor’s toaster. During the day, somewhere in the city a generating station consumes less fuel due to the loss of that neighbor’s toaster. At night, the owner comes home and runs his lights and computer for free, using up the credits of the power generated by day as his meter spins forwards towards where it started.

Solar power systems usually use a device called a grid tied inverter to accomplish this, an electronics box costing $1000 per kilowatt. A typical induction motor costs $120 to generate the same power. Baldor motors cost more but are more efficient, generally a better deal end to end. Use the spreadsheet tool to select the best size of induction motor for your application. Induction motors give best efficiency at their operating point. In most cases this is about 120% of the motor’s rated horsepower when operating as a generator. Normal motors run 50% efficient as a generator, Baldor motors run in the 80’s.

Generally pumps like refrigeration pumps or water pumps will use an induction motor so as to achieve long lifespan. The peak efficiency of this motor would be 50%, but to prevent damaging the motor it is actually run well off its operating point and is more like 30% efficient. The constant efficiency of the steam engine is a better match for a pump, achieve energy savings of 3x and more by driving a pump directly instead of generating power and feeding it to an electric motor later. Compatible with pool pumps and larger industrial refrigeration systems that use belt drive.

The induction motor has also been used as a grid tied generator for wind power (see page 7) ,  and it can also become a stand alone generator.

induction motorinduction tag
     Typical induction motor                                      induction motor tag.  Efficiency at its operating point is HP*745/amps/volts/PF. PF=.9