# Power consumption by electric pumpjack

Solar Expert Posts: 1,973 ✭✭✭
My management is asking me to estimate the power consumption of a 50 HP motor on an oilfield pumpjack for possible PV applications. 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 0.746 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?

• Solar Expert Posts: 9,571 ✭✭✭✭✭
Re: Power consumption by electric pumpjack

746 watts = 1 HP

In real life, there are resistance losses, and bearing losses, so we figure about 1,000W (1Kw) for 1 HP delivered. Or 50Kw in the case of your 50hp motor. (per hour)

Starting loads are often much larger, but this scale of motor, is way beyond my 1Hp seat-of-pants experience.

But if you are not loading the 50HP motor to full load, it won't pull the entire wattage, only what it needs, so you need a better guess as to it's actual load/work requirement.
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Re: Power consumption by electric pumpjack

You did not say anything about if this was to be an off-grid or grid tied system...

You can use the PV Watts program to estimate your available sunlight (by month/season). For grid tied system (solar panels + grid tied inverter + utility power) is the best investment per dollar if you have an electric utility and they are willing to do "net metering". We typically use a derating factor (solar panel to useful AC power) of 0.77 to do this.

If you are looking an an off grid system, you are looking at a derating factor of 0.52 (or less) to account for battery and extra conversion losses.

Picking Austin Tx, 0.52 and fixed mount grid tied system per 1,000 watts (1 kW) of solar panels:
"Station Identification"
"City:","Austin"
"State:","Texas"
"Lat (deg N):", 30.30
"Long (deg W):", 97.70
"Elev (m): ", 189
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 0.8 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 30.3"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 9.7 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (\$)"
1, 4.32, 99, 9.60
2, 4.96, 101, 9.80
3, 5.47, 122, 11.83
4, 5.52, 116, 11.25
5, 5.54, 118, 11.45
6, 5.93, 121, 11.74
7, 6.21, 129, 12.51
8, 6.22, 129, 12.51
9, 5.77, 119, 11.54
10, 5.65, 121, 11.74
11, 4.60, 98, 9.51
12, 3.96, 90, 8.73
"Year", 5.35, 1362, 132.11
This system would generate around 1,362 kWHrs per year per 1kW of solar panels--for your system:
• 50 HP * 1 KW watts/HP * 24 hours * 365 days per year * 1/1,362 kWH per year per 1,000 watts of panels = 322,000 watts of solar panels [fixed equation]
For an off grid system, you can do the same thing--but now you have to look at output by season (less sun in winter).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Re: Power consumption by electric pumpjack

Sorry--fixed the above equation--Had too many distractions when I typed up the post and I mixed 1,000 watts and 1 KW in the same equation.

The actual number is 320,000 watts of Grid Tied solar panels to drive a 50 HP motor 24x7 in Austin Texas--assuming 1 year net metering plan.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 1,973 ✭✭✭
Re: Power consumption by electric pumpjack
BB. wrote: »
Sorry--fixed the above equation--Had too many distractions when I typed up the post and I mixed 1,000 watts and 1 KW in the same equation.

The actual number is 320,000 watts of Grid Tied solar panels to drive a 50 HP motor 24x7 in Austin Texas--assuming 1 year net metering plan.

-Bill

We are looking at offsetting the electric bill at a grid tied system. I used PVWATTS, too, and for a 50HP motor, using 746 Watts per HP, and Midland, TX (Permian Basin oil patch), I got about a 210kW system result.

The differences between what you got and what I got are due to the derating you used assuming off-grid (batteries, etc.) and the HP to Watts ratio you used. 746 W/HP is of course assuming two things: 100% efficiency and 100% loading on the motor. The first is too high and the second is too low. What made you settle on 1000 W/HP?

At any rate, this is looking less and less feasible, at least at 100% offset, unless something in my assumptions is off in a very large way. The footprint of a 200+kW PV array would be prohibitively large.
Re: Power consumption by electric pumpjack

I picked 1,000 watts per HP as just a round number to estimate for losses---As you say, the exact measurements will give you a more accurate number to start with.

A couple things--You might check with the local electric utility--perhaps a joint project (centralized array, perhaps even on power company property, etc.). A little green marketing by both companies.

Also, at those power levels, you may look at Time of Use billing and how that will affect your array sizing...

For example, my rate plan has \$0.30+ per kWhr for summer rates between noon and 6 pm and we have \$0.09 for off peak rates the rest of the year (peak winter rates are \$0.12 per kWhr--but is it more complex, because we have tiered ratings--the more power I use, the higher rates I pay).

We get almost 3x the money for noon-6pm summer generation and use that extra money to purchase off-peak power... Makes our array look "larger" by 3x for summer peak generation (we turn off most of our power during peak summer rates).

Depending on your spread sheet (cost of power, cost of solar, can you shut down a well pump during high power costs, what the power company could do to work with you guys, etc.)--it can be a very interesting engineering/MBA cost benefit study.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 5,436 ✭✭✭✭
Re: Power consumption by electric pumpjack

Does this have to pump 24/7 or can it run only when the conditions permit? Sort of makes a big difference.

Tony
• Banned Posts: 17,615 ✭✭
Re: Power consumption by electric pumpjack

50 HP electric motor is going to be 3 phase. That brings up the whole issue of "utility grid tie-in on how many legs?"

Since it's going to be grid-tie, you're really looking at building up some sort of system to off-set power costs. So the question is, will it really save any money?

Or have I completely got the wrong end of the stick here?
• Solar Expert Posts: 1,973 ✭✭✭
Re: Power consumption by electric pumpjack
50 HP electric motor is going to be 3 phase. That brings up the whole issue of "utility grid tie-in on how many legs?"

Since it's going to be grid-tie, you're really looking at building up some sort of system to off-set power costs. So the question is, will it really save any money?

Well, of course that is the question at the root of my inquiry. Is such a PV system economically sensible?

It would be a three phase tie in.
Re: Power consumption by electric pumpjack

You can use your MBA skills to do the present value / future worth calculations... But you can make some starting assumptions. Assume a system costs around \$7,000 per 1,000 watts of solar array for a Grid Tied system.

In Austin TX, a 1,000 watt array will generate around 1,362 kWHrs per year. Assume no costs over twenty years:
• \$7,000 per 1kW of panels / (1,362 kWH per year * 20 years per 1kW of panels) = \$0.26 per kWH over 20 years
Subtract 30% federal energy tax credit (if available for large commercial systems). Add property taxes for system over 20 years. Subtract depreciation over XX years. Add maintenance (new inverters every 15 years?). Add cost of funds over 20 years, etc...

But, as you can see--the costs currently may not make a lot of sense for you if it costs \$0.26 per kWhr to run your system vs \$0.10 per kWhr in charges from the utility.

In California, we have "Reservation Charges" which means, roughly, that 1/2 of a commercial power bill is for the infrastructure (wires, poles, transformers, etc.) and the other have is the cost of power generation (generators, fuel, etc.).

A school district found that reservation charges went higher (peak solar output 15 minute period per 1 year is higher than the peak power consumed by the school) and the money offset for generation costs was much less than they counted on in their economic model.

In any case, to properly figure out the cost/benefit ratio of solar GT vs Utility Power on a large system--there are many factors that need to be taken into account--including the politics of power (both state and corporate)--that make this a pretty sophisticated project to cost out.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: Power consumption by electric pumpjack
ggunn wrote: »
Well, of course that is the question at the root of my inquiry. Is such a PV system economically sensible?

It would be a three phase tie in.

I always think of PV systems as being economically insensible!
• Solar Expert Posts: 1,973 ✭✭✭
Re: Power consumption by electric pumpjack
I always think of PV systems as being economically insensible!
Cue the Beatles - "It's getting better all the ti-i-ime..." :roll: