Power consumption by electric pumpjack

[ggunn]

My management is asking me to estimate the power consumption of a 50 HP motor on an oilfield pumpjack for a possible PV (solar) application. In a journal article about pumpjacks, the authors use the formula for Annual Electrical Cost as AEC = HP X 0.746 X 8760 X kWh rate. The 8760 is hours per year, and that's OK (the pumps run continuously), but the .746 is just the conversion factor between horsepower and kilowatts, and it seems to me that it cannot possibly be that simple.

My question is this, though: is using that formula going to be way optimistic, way pessimistic, or "close enough"? Better yet, can anyone point me to a good source of information on the subject of power consumption of electrical oilfield pumpjack motors in the field?

 

[iwire]

The 746 watts assumes 100% efficiency.

I would go out and take an actual load reading from a running unit. If not that I would use FLA rating of the motor but that will end up with more then you need.

Will this be a grid tied PV system or a stand alone system.

 

[ggunn]

The 746 watts assumes 100% efficiency.

I would go out and take an actual load reading from a running unit. If not that I would use FLA rating of the motor but that will end up with more then you need.

Will this be a grid tied PV system or a stand alone system.

Yes, I know it assumes 100% efficiency, but it also assumes a full load on the motor. Going out to a unit in the field is not an option right now; they are all very far away and this is a "blue sky" feasibility question. It would be a grid tied system for utility offset.

Using the formula in the article yields an energy usage of over 325,000 kWh in a year, and 100% offset would require a 200+ kW system - over 1,000 200W modules. For a single pumpjack that sounds just a bit excessive.

 

[winnie]

Added to the efficiency issue mentioned above, you have the huge unknown that having a 50 hp motor does mean that your load consumes 50 hp of mechanical power, or 50 hp on a continuous basis. You need to size your system for the actual consumption, not the rating of the motor.

I have been told that pumpjacks have wildly variable mechanical loads, and that they often regenerate for part of the pumping cycle. Thus designing this system will require careful integration of both the power supply and the motor control.

-Jon

 

[winnie]

Okay, I see from your second post that I misunderstood your question; you are already aware of the potential issues and just wanted confirmation....yes, you are correct, the equation given is oversimplified.

Since this is a 'blue sky' question, you might ask your customer if they have any flammable gas coming off the well, along with the desired oil. Do they capture this gas?

-Jon

 

[ggunn]

Added to the efficiency issue mentioned above, you have the huge unknown that having a 50 hp motor does mean that your load consumes 50 hp of mechanical power, or 50 hp on a continuous basis. You need to size your system for the actual consumption, not the rating of the motor.

I have been told that pumpjacks have wildly variable mechanical loads, and that they often regenerate for part of the pumping cycle. Thus designing this system will require careful integration of both the power supply and the motor control.

-Jon

At this point I am just looking for some order of magnitude numbers to figure out if it's even worth chasing. If I could get hold of a utility bill for a candidate wellhead, that would simplify things considerably, but I haven't figured out who to contact to ask for that information.

 

[winnie]

For what its worth, a google search for "pump jack well utility bill" gets lots of hits from companies that sell internal combustion engines for powering pumps. They are trying to compete with the electric power based systems, by claiming much lower operating costs that offset the initial installation costs and maintenance costs. Several of the worksheets used a conversion of 0.75 * motor hp to get continuous average hp.

Doesn't help you much, but its a start.

-Jon

 

[iwire]

Using the formula in the article yields an energy usage of over 325,000 kWh in a year, and 100% offset would require a 200+ kW system - over 1,000 200W modules. For a single pumpjack that sounds just a bit excessive.

As soon as you said 50HP I assumed the PV array would be excessive.:grin:

 

[ggunn]

For what its worth, a google search for "pump jack well utility bill" gets lots of hits from companies that sell internal combustion engines for powering pumps. They are trying to compete with the electric power based systems, by claiming much lower operating costs that offset the initial installation costs and maintenance costs. Several of the worksheets used a conversion of 0.75 * motor hp to get continuous average hp.

Doesn't help you much, but its a start.

-Jon

Yeah, I've been there. I'm looking for information that hasn't been posted by companies trying to unseat electric pumpjacks; it's in their interest to quote the largest numbers they can.

 

[bob]

In a journal article about pumpjacks, the authors use the formula for Annual Electrical Cost as AEC = HP X 0.746 X 8760 X kWh rate. The 8760 is hours per year, and that's OK (the pumps run continuously), but the .746 is just the conversion factor between horsepower and kilowatts, and it seems to me that it cannot possibly be that simple.

I found this chart for motor efficiency that shows a 50 HP to be about 92% efficient when it is loaded at 75% to 100%. So you can use the Annual Electrical Cost as AEC = HP X 0.746 X 8760 X kWh rate / efficiency and it should give you an estimated cost. One question is do you have to include a monthly KW demand charge in addition to the KWH charge?

 

[dbuckley]

Problem with solar is I would guess you want your pump to run 24/7 not just during sunlight hours and if thats the case then you either need dual fuel or storage and tripple size arrays.

 

[ggunn]

Problem with solar is I would guess you want your pump to run 24/7 not just during sunlight hours and if thats the case then you either need dual fuel or storage and tripple size arrays.

We are looking at doing grid-tied systems to offset the utility charges on existing pumps. Assuming 100% offset, such a system would overproduce during periods of sunlight and push power onto the grid, and then draw it back out at night. So far, though, it looks like the array footprint would be prohibitively large.