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Questions tagged [efficient-energy-use]

Use the tag Efficient Energy Use in questions having to do with processes or engines or constructions where energy is spent or transferred and the efficiency thereof. Efficiency means both the measurement and the techniques and principles for its optimization.

When to Use this Tag

covers questions having to do with processes or engines or constructions where energy is spent or transferred and the efficiency thereof. Efficiency means both the measurement and the techniques and principles for its . You might hence also want to tag your question as . Usually this may be coupled with or areas related to thermodynamics (e.g ).

Other relevant areas:

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96 questions
96
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10 answers

Why bother buying efficient lights if you are already heating your house?

Assume I live in a location where at any time of day and any time of year, I need to heat my house. Assume further that I have a room with no windows. In this case, does it make sense for me to buy efficient light bulbs, considering that any…
Mathew
  • 1,153
92
votes
12 answers

What makes running so much less energy-efficient than bicycling?

Most people can ride 10 km on their bike. However, running 10 km is a lot harder to do. Why? According to the law of conservation of energy, bicycling should be more intensive because you have to move a higher mass, requiring more kinetic energy to…
Steven Roose
  • 1,007
61
votes
6 answers

Why is it so inefficient to generate electricity by absorbing heat?

When I turn on a heater, it's supposed to be roughly 100% efficient. So it converts electricity to heat with great efficiency, but why can't we do the reverse: generate electricity by absorbing heat? I have been searching the internet and from what…
Random Name
  • 621
40
votes
4 answers

Why is the efficiency of human cells less than the efficiency of an Otto engine?

I always used to think (I don’t know why!) that the efficiency of human (and animal and plant) cells should be equal to or near the efficiency of a Carnot engine or at least should be the highest efficiency among all practical engines. But I…
lucas
  • 3,199
30
votes
8 answers

Why do solar panels not have focusing mirrors?

Most of the solar panels that I have seen do not have any mirrors, etc., but usually solar cookers have mirrors. What is the reason for solar panels not having focusing mirrors?
Kartik
  • 1,162
27
votes
1 answer

Energy in bolognese reduction - lid on or off?

Generally, to let my bolognese thicken, I leave the lid off in order to "let water vapor escape." I am however distracted from enjoying the taste because I'm having doubts that my physical reasoning is sound. Given a constant power output from my…
Sarah
  • 443
17
votes
3 answers

Why is the Carnot engine the most efficient?

It seems that the only condition used in proving that the Carnot engine is the most efficient is that it is reversible. More specifically, the Carnot engine can be run in reverse as a refrigerator. Furthermore, it is asserted that all reversible…
curiousgeorge
  • 865
15
votes
4 answers

How does lowering your thermostat save energy?

Say it is winter and the outside temperature is 0 degrees f. I set my thermostat to 74 degrees. When the temperature inside my home reaches 72 degrees, the furnace will kick on and warm the house to 74. Now, if I set my thermostat to 68 degrees to…
Scottie
  • 275
14
votes
6 answers

Are neurons more energy efficient than transistors?

In terms of order of magnitude, how does a the energy consumption of a typical mammalian neuron (in the brain) compare with the state of the art MOSFET?
user1576720
  • 177
14
votes
4 answers

Do magnetic fields cause ionisation of gases?

I am doing my final year engineering project on Magnetic Field Assisted Combustion and was curious to see what people thought about it. Companies sell rare earth magnetic arrangements to be attached to fuel lines of gas burners and they are said to…
James Dawson
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13
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2 answers

Should we take the elevator instead of the stairs to save energy?

In our university there's a posted sign that encourages students to take the stairs instead of the elevator to save the university electricity during the hot NYC summers. When you climb the stairs you generate something like 8x your mechanical…
GPhys
  • 274
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9
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6 answers

Is fuel cell efficiency limited by thermodynamics?

Let's say we have a mixture of oxygen and hydrogen gas, initially at room temperature and pressure. This mixture can be used to perform work: we can burn it, using the resulting heat as a source in a Carnot cycle. However, this requires dropping…
Kotlopou
  • 433
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7
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2 answers

Is there some theoretical maximum coefficient of performance (COP) for heat pumps and chillers?

The "efficiency" for heat pumps and chillers is called coefficient of performance (COP) because there is no conversion of electrical energy to heat energy but only transportation. This COP can be way higher than $1$. A heat pump can supply more heat…
jusaca
  • 187
6
votes
4 answers

Does the Carnot efficiency apply to photoelectric conversion?

If you consider a black body as energy source and photoelectric conversion at room temperature as the energy receiver. Wouldn't it be possible to: use an ideal prism/diffraction grating to separate the incident light into its spectrum and use…
tobalt
  • 2,423
6
votes
1 answer

How does the Carnot Cycle work?

I am learning the Carnot cycle, which consists of four transformations for a fluid. In the first two transformations the volume of the fluid expands, generating work. This happens in two steps: First, we approach a hot source and the gas expands…
Álvaro Franz
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