Generators

With the winter season approaching, and the possibility of downed trees and power outages picking up, getting an emergency generator is a very good idea.

Before you rush out and buy an el-cheapo from the local big box store, there are a few questions you should answer to help make an informed decision.

Do I want a permanent standby generator or a portable generator?
What are my output wattage requirements?
What fuel do I want to use?
Do I want a cutover switch installed, and if so, a manual or automatic one?

Standby vs Portable

A permanent standby generator is exactly what it sounds like.  It’s designed to be hardwired into your house’s electrical system, remaining on standby to provide electrical power when the public grid fails.  Those designed for residential use will typically be a fully enclosed metal box roughly the size of a central air conditioning unit.  Most are connected to your house’s electrical system with an automatic cutover switch that detects power outage conditions and quickly switches your house to generator power in such an event.  Most are powered by natural gas (a potential concern should your natural gas utility service be interrupted), although some are powered by diesel.

A portable generator consists of an engine and generator set bolted inside of a tubular frame, often with a pair of wheels at one end.  It offers the benefit of being able to provide power anywhere you take it.  It can be connected directly to your house via either a manual or automatic cutover swith; alternatively, it will have receptacles into which you can directly plug appliances via extension cords.  Most are either gasoline powered or diesel powered, although the gasoline powered models can easily be converted into tri-fuel capability (gasoline/propane/natural gas) and some companies sell tri-fuel models as a turn key package.

The decision between a permanent standby generator and a portable one is driven by a number of factors.  Once installed, a permanent standby generator with an automatic cutover switch is much more convenient.  You literally don’t need to do anything in the event of an outage, the system will automatically switch you from grid power to generator power and back again when the grid comes back up.  If you have frequent power outages or a medical condition that makes you dependent upon equipment that requires electricity, this would be a good choice.  A portable generator requires you to go outside, start the generator (some offer optional remote starters), and then either throw a manual cutover switch or plugg your appliances directly into the generator.  On the flipside, should you need to evacuate, you can take it with you and have power wherever you go.

Wattage Requirements

There are a number of websites, run by both generator manufacturers and dealers, that have calculators to help determine the appropiate size generator for your needs.  Since this information is widely available, I won’t duplicate it here.  Instead, I’ll offer some key points and guidelines to keep in mind when sizing a generator.

Any appliance that has an electric motor will have two different requirements - a running requirement and a starting requirement.  This is because electric motors require additional current to start, often times the additional current alone is more than the the running requirement for the appliance.

Most generators have two ratings - a load rating and a peak rating.  The peak rating is intended to address the starting requirements of motors above.  Many manufacturers are a little liberal with their peak rating and for the most part you should ignore it and focus on the average or load rating.

While you have to account for the starting requirements of motor driven devices, not all of your appliances are going to start at the same time, so you really just need to be able to account for the starting requirement of the largest one.

Any estimates of requirements for various appliances and devices you find online should be treated as ballpark estimates.  A much more accurate estimate will be found on the sticker on the device itself or in its owners manual.  You should probably add 10% to even that number, just to be safe.

If, as I recommend, you only use the generator for intermittently powering your primary refrigerator/freezer, a chest freezer, sump/well pump, and a radio and laptop computer, you should be fine with a 5000 watt generator.  If you’re extra careful, and only run a couple of devices at a time, you could probably get away with a 3500 watt generator.  If, on the other hand, you want to be able to run all of the above devices simultaneously, then you should look into a 6000-7000 watt system.  Anything beyond that, and you’re starting to get beyond the sweet spot of portable generators and should start looking at permanent standby generators.  The really big consumers of electricity are things like central A/C (2500-5000 watts running, 3000-6000 additional starting), furnaces (500-750 running, 750-1500 starting), washing machine (750 running, 2300 starting), gas clothes dryer (700 running , 1800 starting), electric clothes dryer (5700 running, 1800 starting), electric range (2000 running), dishwasher (1400 running, 1400 starting).  While you could run any of these in isolation with a large portable generator, running them in combination will quickly exceed the limits of most portable, particularly if central A/C is involved.  Potential ways around these problems include keeping a window A/C unit handy for power outages and using it instead of central A/C when power is out, using space heaters in the winter, cooking on a natural gas range or liquid fuel camping stove, air drying clothes, and hand washing dishes.

Fuel Selection

Virtually all generators start life with either diesel engines or gasoline engines.  The ones with gasoline engines can be further converted to run either natural gas or to be tri-fuel and able to run on gasoline, propane, and natural gas.

Diesel generators tend to be very heavy duty and very reliable and can stand to run uninterrupted for long periods of time.  For this reason, they are a favorite amongst commercial and industrial users.  The main downside is the need to store significant quantites of diesel fuel in order to run them.  Diesel, like gasoline, begins to break down after a couple of months of storage and also can attract water and algae.  Fuel stabilizer treatments can reduce this tendency and extend storage life, but nowhere near indefinitely.

Gasoline generators make up the largest segment of consumer grade portables.  While not quite as heavy duty as diesels, they are more than adequate for emergency backup use in the typical residential environment.  However, the same fuel storage problem that arises with diesels also arises with gasoline.  You would need to store a significant amount of fuel, and in addition to degrading quickly, gasoline presents significant fire/explosion dangers unlike diesel.

With most permanent standby generators designed for residential use being natural gas fired, there is not much choice to make there.  The real choice comes into play with selecting a fuel for a portable generator.  For most situations, it is my opinion that a tri-fuel generator is the best choice.  It certainly provides the most flexibility.

There are a couple of companies that sell tri-fuel conversion kits that consist of a plate that fits either over or underneath the carburetor, to meter the propane or natural gas to the engine in place of gasoline.  It’s generally a straightforward installation.  Be aware that some of the kits (and even some of the turn key models) offer a fuel shutoff solenoid as an option.  It really isn’t an option, it’s a necessity - without one, there’s no way of turning off the generator while running on Propane/NG short of turning off the valve on the propane cylinder or natural gas line manually.  Be sure to pick up a solenoid.  Be aware that some tri-fuel models require you to always START the generator on gasoline power before switching to run on propane or natural gas.  Also be aware that a given generator will generally produce about 10% less output on propane than on gasoline and will see a further 10% power decline going from propane to natural gas.

Cutover Switches

A cutover switch is used to connect your generator to your house main power supply.  In the absence of a cutover switch, you will need to connect appliances directly to your generator with heavy duty extension cords.  In additon to connecting your generator to your house electrical system, a cutover switch also disconnects your house from the public grid.  This is important in order to prevent feeding electricity back into the public grid, which poses an electrocution hazard for utility workers who think they’re working on dead lines.  There are two basic types of cutover switches - automatic and manual.  Automatic cutover switches detect a power outage condition and automatically and quickly switch the house over to generator power.  They also tend to be hardwired directly to the generator.  Manual cutover switches require throwing a switch after firing up the generator to switch the house to generator power.  While they can be hardwired to the generator, more often they are not.  If not hard wired, they require a special extension cord with a male plug on both ends.  Any cutover switch should be installed by a professional electrician.

Miscellaneous

Depending on the sort of exhaust system utilized, noise levels can vary widely between generators.  A noisy generator will annoy you, annoy your neighbors, and also attract unwarranted attention.  It’s worthwhile to spend a little extra and get a quieter model.  Generator thefts have unfortunately become fairly common, so also look to spend a little money and effort anchoring your generator down.  Anecdotal evidence seems to indicate that Honda engines tend to be much more reliable than others, though it comes with a cost.  Since other manufacturers often use Honda engines in their generators, you may be able to get the best of both worlds - modest cost and reliability.  Also, avoid brush-style generators and get a brushless model, again for reasons of reliability.  Since most consumer grade generators only run at one speed, buying too big of a generator will waste fuel.

Final Thoughts

For most people, a portable tri-fuel makes the most sense, though there are circumstances where a permanent standby generator is a better choice.  In a protracted emergency situation, where fuel supply is likely to be limited, the generator should really only be used sporadically to maintain temperatures in your refrigerator/freezer, to operate sump pumps and well pumps as needed, and to power electronics/communications gear on a limited basis.  Cooking and heating are more efficiently carried out using fuel-burning stoves and space heaters (which will both be the subject of future blog entries).  Wattage requirements should be carefully calculated when selecting a generator.  The choice of a cutover switch is largely a matter of individual preference.

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2 Comments

  1. Posted May 15, 2011 at 11:39 pm | Permalink

    With regard to a portable tri-fuel, do you have fuel cost comparisons? I have difficulty finding this info online.

    Also, I wonder if different fuel are more or less hard on the machinery?

    Thanks.

  2. Posted September 30, 2011 at 10:42 pm | Permalink

    While winter storms usually occur frequently and uprooted trees. This led to frequent power outages. So, I need a generator to help overcome them. Incidentally, I’m looking for information about the generators is suitable for my home. Looks like I need a portable generator. By the way, can you recommend me a quality portable generator?

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