Selection, sizing, installation and maintenance of these units can impact your energy efforts.
In many facilities, the process of selecting a standby generator can either go relatively quickly or painfully slow.How you approach the specification, purchase, installation and maintenance issues will ultimately influence the speed and agony factors of your new genset.
Why would you need a generator for backup power?
What happens in your facility when the power goes off? Do the employees simply go home to wait out the event? What do you have to do to start the facility or get the process back up? Are there machines that need to run off the excess material in order to start anew? Does some equipment need to be cleaned out in order to be restarted? How much material did you consume in waste or scrap because the process wasn't completed in time? How long does it take to get started again–and do you know what the resulting costs are? Is it possible that lives could be at risk when power goes away and people are stuck in elevators or automatic access areas?
If you have answers to these questions– or if you are asking even more probing questions–then you probably need a backup power source for your facility.
Backup power could bring elevators full of people to safety, keep your cash registers ringing, the phones in your call center up and available and your worldwide computer network operating.Or, it could simply help ensure that a site is getting the most out of its operators and machinery, even when a storm hits or the power company blips. These are just a few of the things that backup power can do for you.
How many generator choices do you have?
The short answer is a lot! But, like most systems you deal with every day, when you break your selection process into pieces, your decision-making task becomes easier. Before you specify a standby generator system, or genset, for your operations, you'll need to make sure you know want you're going to be doing with it. You have quite a number of questions to answer.
When are you expecting to run your genset?
In an emergency…during a storm…when the power company lets you down or doesn't want to supply all your usage during high-demand periods? Are you trying to save energy costs by running when utility costs are high, or do you have free fuel to use up from another part of your operations? Do you want to power your entire facility or just the part of it that is costly to live without when the power goes away? Are you expecting the genset to supply power for future facility expansion(s)?
What does it cost to operate a generator?
How much maintenance will you need to supply on an ongoing basis? Are there any permits required before placeing the genset in service? Are there any environmental impacts of locating a genset on site?
Which fuel is right for you?
The answers to some basic questions will lead you to some reasonable cost analyses of using engine-driven gensets and the associated fuel consumption and delivery charges. Whoa! "Hold on there," you say, "while I'm expecting to burn some fuel, what's that ‘delivery charge' stuff all about?"
There are three major types of fuel used for standby generators: diesel, liquid propane (LP) and natural gas. (Fig. 2 reflects estimated installation and operating costs of a typical standby rated dieselpowered unit. )
Diesel and LP are certainly the most popular choices if you're trying to operate independently of the fuel supplier in times of disaster or emergency. In both cases, you already have the fuel in a holding tank, ready to run. Diesel is probably the most preferred option, since, unlike LP, you can store it unpressurized. In some locations, such as hospitals or nursing homes, pressurized storage may not be acceptable or preferable.
If you select natural gas as your fuel, you'll typically be dependent on your local gas company in time of disaster. And, there's usually no holding tank to supply the fuel if the gas company can't pump it to you. If, however, during a disaster you aren't expected to power your facility, natural gas is probably the most convenient fuel to use with a backup power system, especially if the pipe from the gas company comes close to your location. Once the natural gas fuel connection is made, there's no reason to call the diesel or LP truck to come fill up the tank!
By the way, what size tank did you specify for your diesel or LP genset? Can you imagine what would happen if a big storm were to blow in and the fuel truck couldn't get to your facility to refill the tank for a couple of days?
Should you have contracted with your fuel supplier to be one of its high-priority customers in times of disaster? Or, were you just planning to call the supplier when you needed fuel? Oops…
How big a generator do you need?
There's a short answer to this question: that depends…on what electrical loads you want to power and how you sequence the load applications. Are you planning to power only lights, industrial machinery that uses electric motors, heating or air conditioning, water pumps or emergency equipment?
Lighting, for example, is a somewhat linear load. You need little more power to turn on the lights than to operate them continuously. Be aware, though, that some lights may have increased starting characteristics. Check with your lighting supplier just to make sure–before you get too far along in your genset selection process.
Machinery that uses electrical motors with inductive style loads typically will have an increased starting power requirement as compared to the continuous power required for normal running. (Note, the word "typically" is used here because if the motors utilize motor controls (drives) or soft starts, starting power requirements will be somewhat reduced as compared to flipping a switch for acrossthe- power-line starting.)
A typical motor starting across the line can draw as much as five or six times the normal running power in kVA. If the typical genset will supply about three times its rating for a short amount of time, it's easy to see that it will start a motor across the line that's about one-third the size of the generator rating. You might want to consider using a modern motor controller that may cause the motor to only draw 1.5 times the normal running kVA or less during starting. You might also want to consider staggering the start sequences of motor loads as seen by the generator, to give the generator a chance to recover from a motor start before another motor is connected. Otherwise a genset as big as the normal power grid supplied to your facility would need to be considered. Whew. . . that would be a darn big generator!
Don't let all this sizing stuff worry you too much. Most genset manufacturers have a sizing program available to help you understand electrical loads and select what size generator you need for your facility. Before you start the sizing program, you might want to survey your facility and write down the nameplate data for all the loads you expect the generator to run. Also, think how you might sequence the loads if necessary to get the genset to be a little smaller or to provide additional overhead for future expansion.
Speaking of overhead, when you drive your car, do you floor it all the time going down the interstate? Probably not! So, when you size your generator, you probably don't want to size it to be floored all the time, either.
Sizing for 80% of the capability of the genset usually provides a reasonable margin and additional overhead, unless you're thinking of expanding your facility.
Besides, the additional overhead may be needed when the filters clog a little, or the fuel is a little stale, or the oil is a little dirty, or Murphy shows up one hot, dry day. Electric motors usually power heating, air conditioning and pumps somewhere in a system.Make sure you take all of these components into consideration when sizing a genset. If any comfort or safety systems are considered to be "emergency," in nature, special operating considerations may apply when powered from a genset. It's best to check with the local authority having jurisdiction over these types of systems to make sure you meet any emergency requirements for your location.
Are all my worries over, once it's installed?
Yes, absolutely! But…if…as long as…you may want to…Few things are ever really that simple, are they?
Your power worries may be over. And the resulting difficulties from a power outage in your facility also may be over! But, can you be sure your standby generator is going to run when you need it?
How about when you need it really, really bad? Naw, come on, they always work. . . my car never, ever really left me stranded. Even when the oil was low and really dirty–even when that neighbor kid put sugar in the tank! On the other hand, there was that one time that I forgot to fill up the tank…
Maintenance? You'll need some! Poor maintenance—or, even worse, no maintenance— could turn all your hard work (to properly select, size and install a genset) into a wasted effort if the unit doesn't power up when you need it.Most stationary generators are used with automatic transfer switches that monitor the utility power and automatically start the genset if the utility power goes away. The transfer switch also contains the high power contacts to disconnect the utility from the building and connect the genset to the building when needed. Slightly more sophisticated transfer switches also can be set up with a built-in timer to automatically start up the genset on a regular time schedule in order to verify that the unit is operational. If it doesn't start up and run, an alarm usually goes off to warn you of the failure. If the genset were not going to run properly, when would you rather find out about it…during the scheduled equipment exercise period, or during a power outage?
So, plan on some exercising of your genset.Yes, you're going to burn some fuel, and, yes, you're going to use up some life of the engine consumables (i.e., oil, coolant, filters, etc.). But, it will be worth it to have confidence the genset will run when requested.
You probably need to make sure that you plan for scheduled exercising and maintenance of your genset in your maintenance budget.How much? It depends… The bigger the genset, the bigger the engine and expense for operation and consumables.
Most genset manufacturers recommend exercising these units for about half an hour of run time, once a week. The schedule is up to you and any local codes that may affect operation and yearly run time of the equipment.What you're shooting for is to ensure that your standby generator starts and runs long enough to heat up all of its components.
So, what's the most important question?
It was estimated that in the aftermath of the 2005 hurricanes along the U.S. Gulf Coast that as many as one-third of the backup generators in the region didn't start and operate when needed. Most of those units reportedly had undergone little or no maintenance since being installed. Perhaps their owners had considered the cost of regular maintenance to be too high.
Rather than ask how much a genset "costs," a better question is what the cost would be to your operations if you didn't have such a unit when you needed it–and if you did have one, what would happen if it didn't work when you expected it to…