Due to our complete dependence on electricity and because of frequent blackouts, power backup has become a necessity. Before discussing various types of generators suitable for home use, let's briefly review how electricity is produced and what causes massive power outages. Technically speaking, electric energy (which is often casually called electricity) is a secondary energy source. For practical use it is derived from other sources (called primary), which can be stored and transported. This conversion may go through several steps. For example, in an electrical generator electricity is produced from mechanical energy, which in turned is extracted from various primary forms of energy.

Currently, the dominating method of electricity generation employed in power plants is the one that uses steam turbines. These turbines burn fossil-based fuels or split atoms of nuclear material to heat water and make highly pressurized steam. The steam's pressure spins the blades on the turbine's shaft. The spinning shafts turns the generator's electromagnets inside electric coils. This creates an alternating magnetic field in the coils, which induces AC voltage. This voltage is then amplified and applied to the network of cables of the power grids. From there, distribution lines go to the transformers on utility poles or on the ground. They 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. There are three main grids in the continental US: Eastern, Western and Texas. Within each grid, all electric generators are interconnected and synchronized. They are sharing the entire load in order to provide redundant power to all users. As a result, any changes in electricity generation or consumption at any point will change the loads on power generators and transmission lines at every other point.

Local power outages can be caused by many different 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 include either a home generator or a battery-based system with DC-AC inverters.

Electric generators for homes or for commercial use are normally driven by small engines that produce the rotational 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. Even though this combined device contains an engine, it is casually simply referred to as a generator.

This site is a practical consumer guide to electric back up power generators. You may want to start with our guide to home generators, which includes a review of the basic types and detailed selection recommendations. In this site you will also find 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.