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.

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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 ...
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Tilted bifacial solar panels vs. flat monofacials in cloudy weather

Many articles on the internet hail the bifacials for their productivity during cloudy weather. But are they really any better than a flat monofacial solar panel? FWIW, my setup is made of a 20° sloped ...
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Efficiency and capacity comparison between power grid and container ships

Both power grid and container ships can be considers as energy transmission channel. And I’m wondering which one of them is doing better in long distance setting. In a simplified example, a high ...
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Efficiency of electric heaters

I was reading this question. A person was asking what is the efficiency of an electric heater, and to sum up, people were answering "All resistive heating, can be considered to have 100% ...
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2 votes
2 answers
264 views

Why is it easier to ship goods by water than by land? [closed]

It is much, much cheaper to ship goods over water than over land. (Specifically, I'm referring to the cost per unit mass of cargo per unit distance transported. I'm also assuming the large-quantity ...
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91 votes
10 answers
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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 ...
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2 votes
2 answers
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Heat leaving a house as hot water [closed]

Most would agree that there is a current need for us to reduce energy consumption to reduce our carbon footprint. There have been a lot of articles on the news here recently about the need for ...
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14 votes
6 answers
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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?
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1 vote
1 answer
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Will fuel consumption be the same at constant speed between two engines of different power?

We have two same cars,same weights,just with two petrol engines, one has 200hp and second has 400hp.engines have same efficiency factor. In theory at same constant speed at highway of 140km/h cars ...
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Amount of wood needed to cook rice [closed]

$\def\¿{\:\mathrm}$I am trying to estimate the amount of wood fuel used by household using 3 stone stoves to cook rice. These stoves have a thermal efficiency of 10%. I first calculated the energy ...
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Will adding an electric outboard to my sailboat provide the desired benefit of added propulsion when under sail? [duplicate]

I am considering adding an engine mount to the transom of one of my catamaran's hulls so I can move the electric outboard that is on my tender and get added propulsion when trying to sail to windward (...
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0 votes
2 answers
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Trains - can aerofoils reduce friction?

Trains need energy to overcome friction at the wheel-rail interface during constant high speed speed running. Aerofoils on the roof could provide lift, reducing the friction and potentially saving ...
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Is a moving wind turbine more efficient?

To begin with, let’s get the elephant out of the room; No, I’m not asking about free energy. Now onto the question: Wind turbines have a peak efficiency at some wind speed. Say the wind speed is ...
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0 votes
5 answers
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Why is it necessary for a heat engine to work in cycles?

We can make a steam engine just by putting huge amount of water in large tank and heat it and then use the steam to run the wheel. We just have to put huge amount of water and heat then engine will ...
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0 votes
2 answers
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Cutting down on power by bypassing mechanical to electrical conversions: Why not? [closed]

The only answer to this I can think of is energy portability issues. Another modern-world insanity is converting mechanical energy to electrical, only to turn it back into mechanical. The example I ...
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2 answers
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Lighter car vs heavier car, energy efficiency

I typically assumed in vehicle energy efficiency debates, the importance always in propulsion- to reduce vehicle mass. This usually implies high energy mass density fuel, like hydrogen fuel cells, ...
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2 votes
0 answers
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PMDC Motor Characteristic Graph for Given Parameters

TL;DR Need to make a graph which showcases all parameters of a PMDC motor against the torque input. I am trying create a graph similar to as shown below. However, I am confused as to how the torque is ...
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1 answer
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Energy Utilization in Electromagnetic Actuator Vs Piezo-electric Actuator

Electromagnetic actuators are quite common in almost all industrial and household applicatons. I was wondering that the motion produced by the electromagnetic actuators are the side product of the ...
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Nuclear Reactor's Heat Engine's Thermal Efficiency

Nuclear reactor has to convert its heat into mechanical energy and to electric energy with its turbine heat engine. I learned the heat engine of a common PWR nuclear reactor is around 33%. The ...
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0 votes
1 answer
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How to find efficiency of a cycle thats not Carnot Cycle?

Here is the Full Question: A monoatomic gas is expanded adiabatically from volume $V_0$ to $2V_0$ and then is brought back to the initial state through an isothermal and isochoric process respectively....
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0 votes
2 answers
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Efficiency of engine with two isotherms one isochor and one isobar

I was creating a hypothetical engine for fun and trying to calculate the thermal efficiency. The engine which I was trying to calculate consisted of: Isothermal compression, Isobaric expansion, ...
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Does incoming light polarization and phase effect the efficiency of photovoltaic cells?

As I understand it, standard photovoltaic cells depend on both the creation of electron-hole pairs and those pairs being created in the depletion zone in a P-N junction. Is seems like the production ...
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Can regular air conditioner be used as heater? [closed]

In winter season, the normal room temperature is generally 6 to 10 degree Celsius, if the air conditioner is working at 25 degree Celsius will it be working as a heater, making the room warm (relative ...
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1 vote
2 answers
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Maximum possible fuel efficiency at a given altitude

What's the maximum physically or technically possible fuel efficiency (considering common fuels like gasoline or diesel) that can be reached for a 1 ton vehicle at sea level? Can this be calculated? ...
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1 vote
1 answer
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Heater efficiency on maintaining temperature?

I have a central heating system with natural gas (atmospheric) heater warming the water going through the closed loop to radiators. I can set the temperature of the hot water in a fairly broad range, ...
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What is the maximum theoretical efficiency of conversion of potential energy to kinetic energy and vice-versa?

Am looking at different techniques available for identifying sources of energy. As part of it, have the following question : What is the maximum theoretical efficiency of conversion of potential ...
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0 votes
1 answer
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Calculating output of a solar cell

If we are given a particular solar panel with some semiconductor tabs in it, How can I calculate the output of the Solar panel per metre square With the values of ( average hours of sun everyday, ...
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4 votes
1 answer
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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,...
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1 answer
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Sound from a rocket

I have been watching programmes commemorating the Apollo 11 mission. One obvious feature of the launch is the sound. It was mentioned that water was sprayed into the pit below the rocket not (...
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Why does intercooling improve the efficiency of a Brayton Cycle?

I've read in numerous sources that intercooling improves the efficiency of a Brayton cycle. The explanation given is that it decreases the compression work by minimizing the temperature during the ...
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2 answers
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Why a reversible engine's efficiency must be equal to that of a Carnot engine

Apparently, in order to prove that an engine must be as efficient as a Carnot engine if reversible is because apparently for its efficiency in either direction: $\eta_E \le (1-T_2/T_1)$ $\eta_R \ge (...
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Can two quasi-static adiabates intersect? [closed]

I saw a question in my physics book that I've been trying to understand lately. The question is simple: given two quasi-static adiabatic curves, could you find a point of their intersection? Also, ...
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3 votes
1 answer
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Is it possible to transform energy stored in anti-matter into coherent radiation?

In Travellers, a sci-fi show on netflix, they have 10g of some form of anti-matter floating around. A quick $mc^2$ calculation gives a quantity of $E = 10^{15} J$. For reference, Little Boy released $...
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0 votes
1 answer
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How to calculate the power required by a fountain pump?

How can I calculate the power required by a fountain pump, if just the efficiency of the pump, the height of the fountain and the diameter of the water jet is given?
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13 votes
2 answers
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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 ...
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4 votes
6 answers
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Is it more efficient to drive fast uphill?

I know that for a rocket escaping the atmosphere, it's not efficient to travel slowly because even staying stationary consumes a lot of fuel. Does the same apply to a vehicle traveling uphill? In ...
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4 votes
2 answers
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Natural gas furnace vs. power plant efficiency

In the USA, residential heaters often use a measurement called AFUE, which is supposed to be a percentage of input energy to output energy. It is typical for a two-stage natural gas furnace to achieve ...
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1 vote
3 answers
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Is the "efficiency" of car brake affected by how much force is applied by the brake?

Someone argues with me that stepping on a car's brakes for long periods of time will wear out the brakes faster than applying the brakes for short periods of time. We were talking about stepping on ...
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61 votes
6 answers
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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? ...
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-1 votes
1 answer
281 views

Efficiency of any machine

Why cant the efficiency of a machine be 100%? We always see that there is some energy that is lost, mostly in the form of heat. But why is it so? Is it impossible to create a machine with 100% ...
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0 votes
1 answer
108 views

How can I calculate the efficiency of an air-powered car?

An air-powered car is powered using high pressure compressed air stored in a tank. The pressurized tank is connected to an air-powered engine. The volume of the tank is 0.3 m3, and the initial ...
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1 vote
1 answer
46 views

would heating a stove to 400 degrees be more or less energy efficient if done more quickly?

Would heating a stove to say 400 degrees be more or less energy efficient if done over a shorter or longer period of time? say 5 vs 10 minutes. Which would cost more on the electricity bill?
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0 votes
2 answers
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Efficiency given two temperatures

Not sure what formula to use for this question? I am new to physics and the regular efficiency formula doesn't seem like the one I should be using. I was thinking the carnot efficiency, since it ...
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4 votes
1 answer
1k views

Stacking thermoelectric generators for a better efficiency

As far as I know, a thermoelectric generator has about 5-8% of efficiency. That means it uses 5% of the heat and converts them to electricity. Rest 95% is dissipated through the other side. So I can ...
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0 votes
1 answer
104 views

How can energy of petrol be compared to electricity?

When driving my car, which is powered by an electrical engine, I'm consuming between 10 and 17 kWh per 100 km (measured at the charging outlet). The car I had before consumed between 5 and 8 litres ...
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1 vote
1 answer
462 views

How much extra fuel is needed to transport a 1kg object over a distance of 10,000 miles? [closed]

I propose the scenario: a 1,300-kilogram, base weight, vehicle is carrying a 1-kilogram textbook with a 35% efficient engine over a distance of 10,000 miles. How much fuel is being burned to carry ...
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4 votes
1 answer
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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 a transportation. This COP can be ...
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How to prove that an arbitrary cycle in the PV diagram has an efficiency less or equal than Carnot's Cycle? [duplicate]

The statement is: Consider an ideal gas with constant number of particles (N is constant), and an arbitrary thermodynamic cycle (closed curve with no self-interesections) in the PV diagram. Show that ...
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1 vote
1 answer
347 views

Understanding efficiency

This is a repost of a previous question, following the advice of an experienced user. I was told that reversible processes are more efficient than irreversible ones, and that this fact is expressed ...
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4 votes
2 answers
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Understanding entropy and efficiency

A few years have passed since the last time I studied thermodynamics, and I'd like to give me a chance of asking some questions, maybe trivial, I don't know, but I want to clear matters up. Since my ...
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