What size generator does it take to run a gas station?

November 4, 2012 3:12 PM

What size generator does it take to run a gas station?

I've found a wide range of claims from 3KW to 1000KW generators required to run a gas station in an emergency.

Can anyone speak from personal experience what the minimum power requirements would be for an average size gas station?

Specifically, it was asserted to me that you could run a gas station on a common retail generator such as you might find at Home Depot, and I'd like to know if that's true.

posted by Caviar to technology (11 answers total)

Are you talking about running just the pumps and the POS equipment, or do you want all the lights on in the shop as well?
posted by flabdablet at 3:17 PM on November 4, 2012

The minimum required to safely run the station for, say, up to two weeks. I assume that includes lights, but not necessarily if you only want to run during the day.
posted by Caviar at 3:22 PM on November 4, 2012

I am an electrician in FL. We are doing a service change at a medium size store / gas station next week. We are up-grading their power from (single-phase) 200A (amps) to a 300A service. Most homes have a 200A service. So, this gas station is working right now, with the same power that goes into 90% of the homes in America (200A). And, I am sure that most of that power in that gas station is being used for the refrigerator and freezers inside the shop, and for the AC system.

If you are just talking about running the cash reigster, the gas pumps, and a minimal amount of lights - I don't think that would require too much power. The lights and the register could be run on 20As. The gas station pumps, I don't know what they pull - but a large 1.5hp (horse-power) well pump might pull 6A. So, if you had 5 such pumps going, that would be 30A. That would be a total 50A for the reigster, lights, and pumps - and you could be up and running.

Most generators that you buy from Home Depot or Lowes can produce that kind of power. In fact, most of them come with a 50A receptacle plug built-in, which you would need for an RV camper. Every RV camper has a large enough generator on it to run the basic gas station.

The moment you turn on the freezers and the AC, the power draw will go up quick. And these days, gas stations make money on the store - not on the gas.
posted by Flood at 3:45 PM on November 4, 2012 [7 favorites]

It depends on the electrical loads of the gas station. That could vary alot depending on the scale of the petrol station (how many vehicles it can service at any time) as well as refrigeration / freezing. Also if there is a side restaurant and or attached mechanic shop including what equipment they are using (those would be variable loads depending on hours of business operation). The fridges and freezing would be 24/hr loads and therefore "base loads" i.e. the generator(s) must run all day and night to support the base loads.

I'm not sure what an average petrol station base load is, you'd need to look at the details of the utility bill to work out the exact load & pick a suitable genset size, but in short, I would assume yes you can buy a generator upto 1000kW (or 1MW) for most normal petrol stations. At 1MW that would be quite a large petrol station...

You'd want the generator to run the load at around 75% of its nameplate capacity if possible for maximum fuel efficiency, of course you need to consider if there are any peak loads as well that need accommodating, i.e. what if all of the electrical equipment was switched on all at once? You can consider a backup generator for those situations if its critical.
posted by Under the Sea at 4:04 PM on November 4, 2012

The problem is that switching from the (dead) line to a generator would require substantial rewiring of the main power box. It's not for the faint hearted.

The main has to be disconnected and the generator connected in its place. If you just connect the generator, you'd be trying to power the entire city with that generator.

In places like hospitals, which have generators for emergency power, the people who wire the place initially know there will be a generator, and the power room is wired to handle it. In that case there's a cut-off switch to isolate the hospital (or whatever) from the grid, and another to connect it to the generator.

But most homes and businesses are not wired that way.
posted by Chocolate Pickle at 5:17 PM on November 4, 2012

Caviar writes "Specifically, it was asserted to me that you could run a gas station on a common retail generator such as you might find at Home Depot, and I'd like to know if that's true."

Flood has the math right though in theory by limiting your services to daylight hours and a single pump or two you could get away with just about any of HomeDepot's generators 2KW and up. Though I imagine that most pumps aren't going to be happy though without a generator capable of generating a half decent sine wave output.

The problems extend to more than just electricity though. Most stations only have a few days supply on hand so you are at the mercy of distribution. And most stations make very little if anything on their gas sales; all the profit comes from store items and services.

And yes the work of hooking up the loads to the generator should be done by professionals; these systems won't just plug in and there are all sorts of ways to do it dangerously wrong.
posted by Mitheral at 5:40 PM on November 4, 2012

So - I found this claim that it would cost around $40k to outfit a gas station to run a pump with a generator. Any idea what that's based on?
posted by Caviar at 5:46 PM on November 4, 2012

Also, I found this thread which makes some rather bold claims that automation and safety and monitoring systems vastly increase the power draws required to have any functionality at all. Is it possible that some gas stations actually require far more power to run?
posted by Caviar at 5:55 PM on November 4, 2012

$40k is an estimate for a "whole house" generator, with an automatic transfer switch, and natural gas supply lines (a reserve tank even). With that kind of generator - power stays on seemlessly, your lights flicker when the electric grid goes out.

Most electricians want to sell these to people. Selling a system like that is very profitable to an electrician.

But there are other options. Like inter-lock kits. My company installs these kits in Florida for about $650. Being in FL, lots of people have Hurricane back-up power plans in place. With an interlock kit, if the power goes out. You have to set-up your portable generator, switch the locked position on the panel kit (to turn off the main, so you can't back-fed the system), and then work your circuits from there.

Gas station owners are relatively handy people. I have taught retired older women to operate and set-up a generator with an inter-lock kit. A gas station owner could do it. If the station had been wired from the beginning to isolate branch circuits for emergency power situations, then adding a 50A generator and an interlock kit into the design build would add maybe $1,000 to the construction cost. A fraction of the total build-out costs for a gas station.

Existing stations could be retrofitted to at least have pumps during day-light hours for maybe $1500, I bet. Because I would guess that the pumps are dedicated circuits already, which is what the interlock kit would need.

So, if you planned it out, you could have your gas station running on emergency power to dispense gas without a crazy investment.

But like I said, gas station owners don't make money on gas. If the soda cooler is out, the store (and the gas station) is closed.
posted by Flood at 6:00 PM on November 4, 2012 [1 favorite]

Caviar writes "So - I found this claim that it would cost around $40k to outfit a gas station to run a pump with a generator. Any idea what that's based on?"

That's to run the whole station not just a cash register and a pump. $40K doesn't seem out of line to run all the pumps, lighting, coolers, HVAC, water heating, registers, hot dog cooker, ATM, lottery machine etc. But it is also unnecessary in order to sell gas. The statement that control equipment needs all that power is overstated at best; it's the refrigeration that is the big power sink.

Heck a retailer determined to sell gas could get away with no electricity at all: Deal only in cash, use a hand operated rotary pump to get gas out of storage tanks, dispense into 5 gallon Jerry cans and measure by weight with a bathroom scale to handle temperature correction. Regulations probably prohibit selling gas by unit without using approved and tested measuring equipment though. I wonder if it would be legal to give it away in that manner. Petroleum companies could obviously afford that loss to garner good will and in the case where it's actually the retailer who owns the product they could reimburse the retailers.
posted by Mitheral at 7:07 PM on November 4, 2012 [1 favorite]

a retailer determined to sell gas could get away with no electricity at all: Deal only in cash, use a hand operated rotary pump to get gas out of storage tanks

M's Service (Chevron) in Makawao, HI, was like this ca. 1968. "M" Nakamura would crank the fuel into your car from a drum with a hand pump. The number of cranks * price per gallon / gallons per crank she'd calculate in her head. You paid in cash, then. No need for electricity, and "M" had big arms and a huge white smile.
posted by jet_silver at 8:49 PM on November 4, 2012