What is Energy efficiency: Definition and 25 Discussions

Energy conversion efficiency (η) is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The input, as well as the useful output may be chemical, electric power, mechanical work, light (radiation), or heat.

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  1. R

    Battery energy efficiency and Coulombic efficiency - what are they?

    I'm looking at two different batteries for home energy storage. Both batteries have a coulombic efficiency in the upper nineties, say 96%. One battery has an energy efficiency of 90%, and the other has an energy efficiency of 60%. I believe both ratings represent loses of usable energy, but I...
  2. Ranku

    I Energy efficiency of nuclear and fossil fuel

    Can anyone give a percentage comparision of efficiency of energy conversion in nuclear fuel and fossil fuels like oil and coal?
  3. T

    What is the efficiency and power loss of electric vehicle motors?

    I'm looking for a good figure out there like this to describe electrical vehicles. I know EV's are on average 60% efficient but I'm looking to discuss the losses and percentage loss at the systems in an EV. Anyone have any insight?
  4. U

    Is it more efficient to eject burnt fuel as reaction mass in rockets?

    Is it more energy efficient to throw a large object slower than a slower object faster? For example, suppose a 100kg person out in space threw a 10 kg object away from themselves at 1 m/s. that means that the 100 kg person would move in the opposite direction at .1 m/s. And this should take...
  5. izico

    Most power efficient display of single digits and color flap

    I'm redesigning a board game toy now. The first version use color flaps rotated by shaft to show color, red or blue, and it uses 7 segment LED to display a single digit of player score. I'm thinking of replacing the color flap with red and blue LED or other means to show these 2 colors. But...
  6. teslafanclub

    Energy efficiency Gain or Loss? What do you think?

    Energy efficiency related question: please help with an anwer to the following: Given a flat electrical coil of known dimentions, this coil is used as an induction coil, laid flat, on top of the cooking surface of an induction cooker. Basically, the induction cooker has a copper braided coil...
  7. D

    Energy efficiency, Transformer?

    Homework Statement A power plant produces energy at a voltage of Vi = 12693 V. Before being sent along long distance power lines this electricity is sent through a transformer with 166 turns in the primary coil and 6917 turns in the secondary coil. The voltage of the electricity sent through...
  8. L

    Energy Efficiency Assignment Help - 9th Grade

    hi everyone so i am working on an assignment to overall find the efficiency of a small electric motor. i need help with the following things: 1. Factors that can affect efficiency of a small motor (i need to talk about mass as the factor) 2. Why it is important to understand efficiency...
  9. H

    Another Energy Efficiency Equation Problem

    Homework Statement A golf club with 65 J of kinetic energy strikes a stationary golf ball with a mass of 46 g. The energy transfer is only 20% efficient. Calculate the initial speed of the golf ball. Homework Equations efficiency = E out/E in x 100% The Attempt at a Solution I...
  10. H

    Energy Efficiency: Input & Output (Work/Energy)

    Homework Statement In a race, a 54 kg athlete runs from rest to a speed of 11m/s on a flat surface. The athlete's body has an efficiency of 85% during the run. How much input energy did the athlete provide? Homework Equations efficiency = E out/E in x 100% The Attempt at a Solution...
  11. 1

    Kinetic energy efficiency question

    Homework Statement A roller coaster descends 55m from the top of the first high point to the first low point in the track. The roller coaster converts gravitational potential energy to kinetic energy with an efficiency of 50.0%. What is the velocity of the roller coaster at the bottom of the...
  12. F

    Work energy efficiency car problem

    Homework Statement Gasoline has an energy content of about 132.65 MJ/US Gallon. An average passenger car has a mass of 1500kg. The average vehicle experiences a drag force F(drag) = (0.176 kg/m)v^2, regardless of road conditions. A uniform and level road surface provides a 'rolling...
  13. G

    Energy Efficiency and Transfer

    Hello, First of all this is a fun sidetrack thing. I'm looking for the safest and most efficient molecule that could be split or combined or some way to produce force.Could it be put in a motor-type device and therefore be used as a motor?BTW, this is for like a car.Could Salt Water produce...
  14. N

    What Are Some Hot Topics in Energy Efficiency?

    I need to research something on energy efficiency, but I have no idea what I should do. I've looked at laundry systems, dehumidification in hospitals, textile production. Energy efficiency in residential or commercial settings is paradox because engineers worked to make every component more...
  15. L

    Which Door Type Uses Less Energy: Hinged or Sliding?

    To understand, in a specific case, which motion spends less energy - angular or linear - I want to ask an unusual question. Which kind of door - hinged or sliding door - needs less energy to change its state from closed to fully opened, in a specific interval of time "t"? If I want to close...
  16. JJBladester

    Energy efficiency - purchasing the right furnace

    Homework Statement Consider a homeowner who is replacing his 25-year-old natural gas furnace that has an efficiency of 55 percent. The homeowner is considering a conventional furnace that has an efficiency of 82 percent and costs $1600 and a high-efficiency furnace that has an efficiency of...
  17. S

    Comparing Energy Efficiency of New vs Recycled Paper

    How i am going to compare energy efficiency between new paper and recycle paper ? in order to compare them, i have to convert all the energy require in those process into the same unit right ? By using Joule ? or ?
  18. L

    Energy efficiency of torsion Catapult

    Homework Statement How would you find the energy efficiency of a torsion catapult ? (one i built for project) I have the Force at which I am pulling the arm. F = 20N also the angle from origin to the point of release ( or when the ball leaves the arm) Theta = 50 degrees...
  19. T

    How much is the energy efficiency of the process of photosynthesis?

    Homework Statement During photosynthesis found that a plant is necessary to absorb 8 photons of red light with wavelength 6850 Å to produce an O2 molecule. The average energy storage during photosynthesis is 112 kcal per mole O2. Calculate the energy efficiency of the process of...
  20. A

    Energy efficiency and home insulation

    I live in a very hot climate. I have upgraded my windows to double pane thermal with some some success in cooling my home. I have been considering both additional fiberglass insulation and a radiant heat barrier for my attic as the air conditioning bill is still horrific and rates keep rising...
  21. G

    Can Tracking Degree Days Help Improve Energy Efficiency for HVAC Systems?

    As I fine tune our VAV HVAC system (506,000 sq.ft. facility), we'd like to determine the effectiveness of our adjustments over time. As we both heat and cool portions of the building at the same time (electric VAV reheat), we need to apply degree days to the analysis. How is that done...
  22. P

    Medical Super Humans: Exploring the Potential of 100% Energy Efficiency

    My science teacher told me the human body is only 38% efficient at converting energy, if we were able to to convert energy at 100% efficency we would be "Super Humans"? As in heightened senses, amazing endurance, incredible speed or we would just die or something?
  23. D

    Thermodynamics energy efficiency

    Homework Statement Each second, a nuclear power plant generates 2000 MJ of thermal energy from nuclear reactions in the reactors core. This energy is used to boil water and produce high pressure steam at 573 Kelvins, the steam spins a turbine, which produces 700 MJ of electric power, then the...
  24. Loren Booda

    Your practical tips for energy efficiency

    What habits and technology can we adopt to reduce personal energy consumption?