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37 votes
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Why does it take so long to restart a nuclear power plant?

When a reactor is shut down the core produces much less heat, but they do still produce heat through a mechanism known as decay heat. The fact that the core is producing less heat means that the ...
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36 votes
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How does turning off electric appliances save energy

Electricity production optimization is a very complex subject. It is also affected by many parameters , which I will try to outline below. TL;DR: Demand is constantly monitored and supply is ...
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19 votes

Why do hydroelectric plants use turbines instead of an efficient 'water wheel' configuration?

Actually the turbine method is very efficient. The Turgo turbine is up to 90% efficient at extracting the energy from the water. Large-scale hydro plants using Francis Turbines can be as high as 95% ...
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19 votes

How does turning off electric appliances save energy

Timescales on the grid Power demand fluctations can be broken into timescales from micro-seconds to decades. On the "decades" end of the scale, the power industry and utility regulators work ...
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14 votes

Why do hydroelectric plants use turbines instead of an efficient 'water wheel' configuration?

There are two different ways for the water flow to transmit energy. One is the pressure difference between the water entering and leaving the turbine. The other the kinetic energy change of fast ...
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13 votes

Why does it take so long to restart a nuclear power plant?

Xenon is a result of the nuclear reaction and a neutron poison. If you don't wait for the xenon to decay, it eats up too many neutrons and you can't go critical. They always say "there are not ...
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10 votes
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Does a transformer use power when output isn't under load?

Does the DC load somehow feedback and lower the resistance of the primary coil so that more power can be drawn? Yes. It would be simpler to analyze an AC load though. The diodes are not central to ...
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10 votes

How does turning off electric appliances save energy

Yes, they monitor demand and due to differences in how different power stations are controlled they can increase or reduce output to match demand. Some power plants like nuclear run at full output as ...
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9 votes

Relationship between wind velocity, turbine rotor diameter, and power output

It's not a simple relationship. First let's deal with the kinetic energy of the wind passing through the rotor. The mass of air passing through it in one second, $m$, is equal to the the density of ...
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8 votes

How much power does it take to supply a laser which delivers 100 watts?

The total electrical to optical power efficiency of a laser system is sometimes termed wall-plug efficiency. It is the ratio of $$\eta = \frac{\text{optical output power}}{\text{consumed electrical ...
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7 votes

Why does it take so long to restart a nuclear power plant?

The answer really boils down to two factors: safety and testing. I'm going to give a generic summary of these two things below, but the real answer is quite complicated. The crux of nuclear plant ...
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7 votes

Alcohol as a working fluid?

Yes - for certain applications. Low-energy, low-temperature, small installations, possibly 'accessory' power where providing a bit of weak rotary power to some point of machinery would be difficult ...
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6 votes
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What is the difference between shaft power and brake power?

The short answer is these terms are defined by standards organizations based on specific test methods. These methods specify the engine condition, environmental factors, fuel chemistry, inlet and ...
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6 votes

How does turning off electric appliances save energy

Peak Demand One of the biggest issues in the electricity business is managing peak demand. This is the maximum amount of electricity needed at any one time. Typically this will be the middle of the ...
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5 votes
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How can I calculate the temperature rise of a circuit board for a given power dissipation and area?

Assumptions: The copper side with the traces is modeled as a sheet of copper rather than traces. The body is thin enough that thermal conductivity within the body is unimportant, and the entire ...
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5 votes

Generating power from fruit

You seem to be asking about using fruit juice as the electrolyte of a battery. Yes, that's possible, but you don't get a lot of power that way. The power also doesn't just come from the fruit juice. ...
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4 votes
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Why there is no piston style pedal bicycle?

The biggest problem with a "two cylinder" crankshaft is that there is a dead spot in the torque curve whenever either "piston" is at TDC or BDC. When you have your feet directly on the pedals of a ...
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4 votes

Why is electricity used for powering our device?

Electricity is a convenient way to generate power centrally and distribute it to where it is needed according to demand. Central power generation by technologies like steam and gas turbines means that ...
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4 votes

How can I calculate the temperature rise of a circuit board for a given power dissipation and area?

Base on a quick calculation using online max current calculator for trace width properties, I believe your traces are undersized for 20A of current. Strip line current calculations (Internal Traces) ...
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4 votes

Does a transformer use power when output isn't under load?

A transformer offers resistance to AC current flow due to the magnetic field produced by the current flow. This "AC resistance" is termed "impedance" and is a function of number of turns, core ...
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4 votes
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What needs to be considered when configuring the clock system for a MSP430F5xxx micro-controller?

It depends a bit on the quality you expect from some of the peripherals and what their qualities are at given clock speeds. Will you want a very high speed SPI interface and can this specific chip ...
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4 votes
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Having three heaters on single PCB

Increasing the insulation between the heat sources there is quite difficult. Instead, you can sink the heat away: Add a full copper fill on the backside of the PCB and connect that into a heat sink ...
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4 votes
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Third Rail vs Overhead Cable: which is more efficient in terms of electricity consumption?

Your "Bonus question" holds the answer here. Assuming that the two trains are perfectly identical, and that the power consumption is identical (which, if you have the same weight, motor, and size, it ...
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4 votes

substituting power supplies safe?

If you get lucky, the power supply will either shut down because it is overloaded, or deliver a very reduced voltage. Either way, the keyboard won't work properly, or won't work at all. If you get ...
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4 votes

What is the difference between Bluetooth Low Energy and Bluetooth BR/EDR in Park mode?

There are many factors that make BLE low power, and I have attempted to address as many of them as possible. In order to better understand the power consumption differences between Bluetooth classic ...
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4 votes

How to calculate hydropower in kW without water head

If you have horizontal water flow (no head) you are extracting its kinetic energy (from its velocity) not its potential energy (from its head). So you need to know the velocity of that flow as well ...
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4 votes
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Intuitive explanation for why doubling max speed is proportional to eightfold power

Think of it as the volume of water you're displacing per second - the area multiplied by the distance moved. So intuitive I hope I can get away without an equation, but there's some good stuff in the ...
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4 votes

Intuitive explanation for why doubling max speed is proportional to eightfold power

It's a pretty rough approximation, and only holds where skin friction is the dominant source of drag throughout the speed range considered. Skin friction increases about as speed ^2. So for double ...
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