Due to our complete dependence on electricity and because of frequent blackouts,
power backup has become a necessity. Before discussing various types of generators for home use, let's briefly review how electricity is produced and what causes power outages. Technically speaking, electric energy is a secondary energy source because for practical use it is derived from other sources (called primary). It is often casually called
electricity. An
electrical generator by definition is a device that produces electricity from mechanical energy. The mechanical energy for electric generators in turn is produced from primary forms of energy by using various methods.
Currently, the dominating method of electricity generation employed in power plants is the one that uses steam
turbines. The turbines burn fossil-based fuels or split atoms of nuclear fuel to heat water and make highly pressurized steam. The steam's pressure spins the blades on a turbine's shaft. The spinning shafts turns the generator's electromagnets inside electromagnetic coils. This creates an alternating magnetic field in the coils, which induces AC voltage. This voltage is then stepped up in transformers and is applied to the network of cables of the power transmission grids. The reason electricity is transmitted at high voltages (230-765 kV in US) is that at a higher voltage you need a lower current to deliver the same amount of power. Lower currents result in higher efficiency due to reduced copper losses in transmission lines. The AC form of voltage is preferred because it is easy to change from one level to another with the transformers. Nevertheless, there are some high-voltage DC transmission lines too. The transmission lines carry the currents across long distances to substations. Substations use step down transformers that reduce the AC voltage to medium-high level (typically 2.2 - 34.5 kV). From there, distribution lines go to the transformers on utility poles or on the ground. These transformers reduce the voltage to the level suitable for conventional household devices.
In the US, all power generator stations are interconnected in the systems called
grids. In the continental US, there are three main grids (interconnected systems): Eastern, Western and Texas. Within each grid, all electric generators are synchronized and share the load in order to provide redundant power to all users. As a result, any changes in electricity
generation or consumption at any point in the grid will change the loads on power generators and transmission lines at every other point.
Local power outages can be caused by many things such as storms, earthquakes, falling trees, lightning, various accidents, high demand, or equipment failure. If for whatever reason one plant fails or disconnects from the grid, the remaining plants have to pick up an extra load. If they are all operating near their maximum capacity and cannot handle the extra load, they may automatically disconnect from the grid as well. This may cause a cascading effect resulting in a wide-spread blackout. During blackouts, private
emergency backup systems can supply electricity to critical circuits or the whole house. These systems typically include either an AC genset or a battery-based system with
DC-AC inverters.
Electric generators for homes or commercial use are normally driven by small engines that produce the mechanical energy from burning fuel. The alternator and the engine are mounted together to form a single unit, which is called an
engine-generator set or a
genset. This combined device is casually simply referred to as a
generator.
This site is a practical consumer buying guide to electric back up power generators for home or business use. You may want to start with our guide on
choosing electric generators for the home, which includes a review of the basic types and detailed selection recommendations. You will also find in this site an overview of various types of back up power systems, principles of their operation, selection guides, comparisons,
reviews and ratings of portable and permanently connected (standby) gensets.
