One important issue often overlooked when selecting and installing generators is their power ratings and how that power output is distributed at 115 / 230 volts. The first point to consider is surge power. Generators are sold at their surge rating in watts. If you buy a 4,000 watt generator it will put out 4 K (a K is a kilowatt, which is equal to 1,000 watts) at most, it has no surge above that. It's continuous power rating will actually be 500 watts lower, or, 3.5 K. Compare this to most inverters which are sold at their continuous power ratings and will surge more than twice their rating to start motors.

The second point is difficult to follow for most non-electron nerds but it bears mentioning. Most independent home systems are set up to use only one leg of 115 volt generator output and most generators do not put out full power on only one leg (they will put out full power using two separate legs of 115 volt and full power line to line at 230 volts). So what does this mean to you? Remember the example of the 4 K generator that is in reality a 3.5 K unit? Well now take half of that away (because you are probably not set up to use both legs of 115 volts) and you now have only 1,750 watts to use from your 4 K generators. And you are probably mistreating the generator because you are only using one half of the generator's windings. There are some ways around this issue such as using both the 115 v legs, or putting 230 volts through a step down transformer to yield 115 v full power, or buy a generator set up to give you full power at 115 volts. Kohlers can be set up this way, as can some Onans. Honda presently does not make (to my knowledge) a generator over 3.5 K that truly has full power available at 115 volt single leg (single line).

The last point I can think now that should be mentioned on the complicated subject of generators is voltage regulation. Inexpensive generators have bad, or no, voltage regulation which is fine if you are just running the normal tools used to build your house. Saw and drill motors are not too fussy about voltage surges, dips and spikes. But modern electronics are quite a bit more picky when it comes to bad voltage. I have heard of $3,400 Trace sine wave inverters being smoked because the generator connected to it for battery charging spiked and fried some electronic components on the Trace's power board. Fortunately there is a new type of generator on the market that has its own inverter on board. The inverter accepts the raw power coming from the alternator and reforms it to the precisely regulated conditions that modern electronics are designed to accept. These inverter generators are particularly good at maximizing the output current of renewable energy system battery chargers. Invest in a generator with good voltage regulation.

Power inverters take the DC electricity stored in your batteries and invert it to 115 volts AC (we can set it up to make 230 Vac, but this is less common) for use in powering your household loads. There are a number of types of inverters based on the quality of the power that they produce. Square wave inverters are an outdated technology and should no longer be used due to the harm that they can do to the loads they are driving. Modified sine wave inverters (Trace DR Series) are very efficient, have large surge power capabilities and are less expensive than sine wave inverters. The down side is that they have from 30 to 45% THD which can cause a buzzing noise on telephones and stereos and cause interference on televisions. Also some loads such as most laser printers will not run on MSW. Motors run hotter and less efficiently. Electronic battery chargers such as the type used for some portable power tools can be ruined by plugging into MSW. AC water pumps require an old style relay type control box to run on MSW inverters because the new pump control boxes have electronics that are not compatible with modified sine wave power. Stepped sine wave inverters (Trace SW and PS Series) output a good approximation of utility power by stepping from 34 to 52 times per cycle. They have 3 to 7% total harmonic distortion (THD) and run 99.9% of all loads. Sine wave inverters (Exeltech, Studer, Outback) output a true sine wave with THD of about 2%. In many locations such as those that experience frequent brown-outs the output quality of these inverters often exceeds that of utility power. Sine wave inverters run loads the way they were designed to be powered and the loads will run better as a result.

Inverters often come with on board battery chargers that automatically charge your battery bank whenever your generator is running. The more sophisticated  models can even be programmed to start and stop your generator. This feature requires the correct type of generator to accomplish this.