You probably know already that there are two basic types of home generators: stationary and portable. They are often called gensets because they are actually the sets comprising of an alternator and an engine.
Unfortunately, the numerous buying guides and articles available everywhere do not always emphasize all the drawbacks and the issues associated with each of these types. Before going over the details, let's start with a quick background information.
(standby) systems are permanently connected to your house and hooked up to a fuel source. Normally this would be the same source you use for the heating: natural gas, propane or diesel. An indoor
transfer panel isolates home wiring from input lines during utility power failure (see simplifed connection diagram). The wattage of the available air cooled standby systems intended for home use ranges from 6 kilowatt to 20 kW, so you can always select the right model that can supply the whole house including central a/c, sump pump, etc. In automatic mode such a system will start by itself without your involvement when it detects a power interruption. Likewise it will shut down when utility voltage is restored.
devices range from 500 W to almost 20,000 W. When you need to use a portable genset, you have to moved to the place where you want to use it, fill with fuel and start up.
Then after a short warm up period you can connect it to your equipment. There are no auto start portables. Gasoline and diesel models come with an on-board fuel tank; propane and natural gas models have to be connected to an external tank or fuel line. All the devices with an on-board tank have to be refueled several times a day if you load them to their maximum capacity.
All engine-driven units can be run only outdoors
. A stationary device always sits outside just like a central a/c. A portable one is normally stored elsewhere and connected only when you need to use it. There are detailed descriptions and reviews of different generators in our SMPS site. Here we will just discuss the basics.
PROS AND CONS OF DIFFERENT TYPES
As you realize, all types of gensets have pros and cons. Fixed systems
provide the highest level of comfort, but of course it comes with a price tag. Depending on wattage and options, complete systems with a changeover switch may sell for $2000 to $5000. You may also need to spend several thousand dollars for electrical wiring and fuel hook up. Before the installation, you will likely need to obtain permits from your utilities and pass the inspections after the work is done. All this, obviously, takes time. So, if you are looking for an emergency generator because there is a hurricane or an ice storm in tomorrow's forecast, it is too late to consider a standby type. Another issue is service. A hard-wired appliance that weights 400-500 pounds is not something you can easily disconnect and ship back or bring to a repair shop. Should you need a repair, you'll have to wait for a service technician to come to your place or for the manufacturer to send you a replacement part.
are much cheaper-- their prices start at around $120 for a 1000W model. Unlike stationary devices, they don't have to be hardwired to your house unless you choose to-- their control panel has several outlets of various types into which you can plug cables from your electric loads. This can be both an advantage and a disadvantage. On one hand, you can start using such device, so to speak, right out of the box. However, this would work only if you want to run "cord and plug" appliances, such as refrigerators and window air conditioners. You can just unplug them from the wall outlets and connect via extension cords to the generator. However, when it comes to lights, furnaces and everything else that is wired directly into your house electrical lines, you'll face problems powering them up. This is something homeowners often don't realize while dealers may neglect to mention to you. You might ask, why can't I just hook up my genset to a wall outlet? First of all, it is illegal and dangerous to connect any voltage source into any electrical wiring connected to the grid. By trying to energize your house you are also feeding voltage back into the utility lines. This may hurt line workers or your neighbors who may think the mains is down. Aside from this, unless you are the only one who lost power, you would actually be trying to power up all the neighbors houses who lost electricity. This would likely overload your generator and trip its circuit breaker. Because of all of the above, if you want to run your built-in appliances and lights from a portable backup source you still need a redundant switch. In this case it has to be a manual one though. Such a connection is the safest one, but you would still have to deal with the professional installation, permits, inspections, etc. Technically, it is possible to isolate your house wiring by flipping the main circuit breaker to OFF position. However it leaves a possibility of a human error and is not recommended (see portable generator connection
for more details and wiring diagrams).
You would also have another hurdle to overcome if you buy a portable model equipted with GFCI and grounded neutral. In such a model the GFCI will trip
when you use it with a regular transfer switch. This is something the manufacturers and retailers may not always mention you. So, if you choose a genset with GFCI, you need to buy a special 3-pole transfer switch or otherwise discounnect genset's ground wire in the transfer switch. In any case, such a setup is still cheaper than a stationary for two reasons: because portables cost less than standbys and because manual switches cost less than automatic ones. In case of emergency, if you have no choice and you really need to connect your genset into a wall outlet, first flip the "disconnect switch" on the main service panel. This would isolate your house from the outside lines. This is not a recommended method though. You also need to remember that a standard outlet is rated for 15A. So, you can't use it for more than 120x15=1800 volt-amps. If you draw a higher current you may overheat the socket and the wires, which is a fire hazard.
WHAT GENERATOR DO I NEED?
My pick for standby genset for a typical house with a central a/c:
Generac Guardian 17 kW home generator
model 5873. (An included 100A auto transfer switch is installed indoors).
Well, buying the right model for the home involves several key decisions:
How much power do you need?
How soon do you need to use it?
How often do you expect to use it and for what duration of time?
Are you able to move around a few hundred pound device?
Here is when you definitely need a standby
home generator system:
- Your house requires more than 17 kW power, or
- You want to be prepared for long-term power outages, or
- You want fully automatic operation, or
- You don't want to move around a heavy device.
Here is when you should buy a portable
- You need emergency power immediately;
- You are looking to spend less than $1,500 (maybe even a few hundred dollars).
In all other cases, either type might work for you. You just need to choose between cost and convenience.
For standby gensets, my pick is the Generac Guardian® series available in the range from 8 kW and 45 kW. For my advice on portables, see my picks
of best portable generators for home. For more buying choices also see my guide
to cheap generators.
Whatever genset you choose, remember that all engine driven devices have a common disadvantage- they all require maintenance, such as frequent oil changes. If you don't feel like getting involved into this, you may want to consider a maintenance-free battery backup solution. More details are provided in my review of different types
of power generators, which compares traditional and alternative power systems. If you are interested in "green" energy, check out the tutorials on residential wind generator
and to solar-powered