Approximately how much does it cost to operate a 10-horsepower (hp) motor continuously for a year?
Every professional working in a plant should be actively involved in the profitability of the plant and, as such, should know how much money will be saved by simply turning off a piece of equipment that is simply not needed at the time. With that in mind, any plant professional should be able to answer this question in 10 seconds or less — even if it is not within his or her area of expertise.
Let’s assume that a motor is 90 percent efficient and operates for 8,760 hours per year. Further, the incremental cost of electricity is $0.07 per kilowatt-hour (kWh). Using these assumptions (they could be different in your location), the energy that a fully loaded 1-hp motor in continuous operation will consume is approximately (0.746 kW/hp / 0.90) * ($0.07 / kWh) * 8,760 hours/year, or $508/year.
Therefore, a fully loaded 10-hp motor would cost approximately $5,080 per year to operate continuously. Answer B is the best answer using the above assumptions. Another answer might better apply in your location.
Additional complicating factors
Plants are typically subject to time-of-day billing, demand charges, hatchet clauses, ratchet clauses and other tariffs that can make this calculation quite complex. You might consider having one person perform this calculation for your plant and subsequently publicize the results throughout the plant to increase awareness of how energy conservation can dramatically affect the bottom line.