How to decide what kind of generator to install for your home, calculating power requirements for small appliances

After superstorm sandy hit we lost power for a whole week. I was able to acquire a small gasoline-powered generator and run power to our essential services. This gave us heat and some degree of normalcy. Getting gasoline was rather difficult due to fuel shortages and long lines. This was not the first time we lost power in New Jersey and it certainly will not be the last. I decided that a generator was necessary.

I started to research generators looking at what would best suit my needs and be a cost-effective solution. I have broken down the analysis into the following considerations: power level, fuel type, portable vs. permanent, type of transfer switch and connection to the house.

Power Level:
Types: low 1-5kW, medium 5-10kW, high 10-20kW

For residential use, generators come in various sizes ranging from 1,000 watts (1kw) to 20kw. Keep in mind that generators are not meant to be run at maximum capacity for extended periods of time.

Definitions:
Power is measured in watts (w) or kilowatts (kW). A kilowatt is 1,000 watts.
Voltage is measured in Volts.
Current is measured in Amps (A) or miliamps (mA). An amp is 1,000 miliamps.

Low power: Generators between 1-5kw (low power) are portable and designed to power a few outlets. They are generally not designed to patch into the home's circuit box. They can run things like lights, computers, modems, televisions, refrigerators, and other appliances, however, probably not at the same time. You plug in one or two extension cords to the generator and plug in your electric devices. It is important to calculate the power requirements for each device before plugging in so as not to overload the generator. It is best to research this before you lose power. two tools that come in very handy for this are the Kill A Watt meter and a clamp meter.

How to measure the power needed to run an electric device:
First, look on the back of the device or check the owners manual. There is often a sticker that gives the voltage, current, and wattage rating of the device. If you can't find the information you can estimate or measure it. Here are three examples:

This is from the bottom of a Blentec blender. The label is very clear, it uses 1,560 watts.

This is from the power supply from my Asus laptop. It gives information about voltage(V) and current(amperage)(A). It does not give wattage. It is easy to determine wattage from this information.
The equation is Power(P)=Current(A) x Voltage(V).
This adapter gives a range of input voltage since it is designed for a global market. In the USA, residential voltage from a standard outlet is 110-120 VAC (volts alternating current). So I would use 120 for voltage. 120 volts x 1.0 A = 120 watts. So this laptop can use 120 watts. I suspect the actual usage is much less, 50-80 watts but this is the max number.

 This is from the back of my Panasonic cordless phone. It gives the power source input requirements. I checked the wall adapter(power source) and it says 120 volts, 100mA but does not specify W (wattage). mili-amp mA is 0.001A. So from the power source the wattage is 0.100A x 120V = 12W. The phone consumes 0.500A x 6.5V = 3.25 W. As you can see, there is a discrepancy between the maximum wattage consumed by the power source and the wattage needed for the phone. I recommend always using the higher wattage or measuring the power requirements directly with a Kill A Watt meter. For small values it doesn't really matter, a 9 watt difference is not going to affect a 3,000 watt generator. A larger error like 500 or 1000 watts could cause problems.

How to use the Kill A Watt meter:

Here is the meter plugged into the wall with my Asus laptop. It is reading 39.6 watts. BTW, the power supply is rated for 120 watts max based on our calculations above. As you can see, actual usage is much less than maximum numbers printed on the power supply.