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3 answers
19 votes
5k views
Windmills in empty fields. Why no trees?
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37 votes

Trees increase the turbulence of the air that reaches the turbines. That creates all sorts of uneven, rapidly-shifting loads on the blades and structure. That increases the maintenance costs, ...

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6 answers
20 votes
12k views
How to make smoke for a small wind tunnel?
16 votes

The testing of ventilation systems and of building air-tightness is done using smoke sticks or similar - non-toxic smoke generators that produce no ash residue. One of these may be suitable for your ...

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7 answers
12 votes
5k views
What are the disadvantages of concentrated solar thermal power?
15 votes

There are no silver bullets when it comes to decarbonising the grid. That's good news: it means you can stop looking for one, and accept that every form of generation has its pros and cons. ...

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3 answers
12 votes
1k views
Thermoelectric Technology to Harvest Energy from Internal Combustions Engines
14 votes

There are good reasons why, although most of your links are from several years ago, very little has come of any of them. The economics and the engineering just aren't favourable. Part of the art of an ...

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12 answers
30 votes
40k views
What are the pros and cons of a traffic circle versus a traffic light intersection?
14 votes

There's a hierarchy of junctions, that you'll find in most standard highway design guides, such as the UK's immense Design Manual for Roads and Bridges. Different junction designs have different ...

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3 answers
18 votes
14k views
How does a traffic light sense the proximity of vehicles?
13 votes

There are two techniques commonly in use. The first is induction loops cut into the road surface. The metal in a vehicle body induces a current in the loop, as the vehicle passes over it. (public ...

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3 answers
10 votes
2k views
Harvesting thermoelectric energy from computer graphics cards
13 votes

Trevor Archibald has given you a really good answer, but I see from your comments a diffferent answer might be useful, as you still think this could be viable with the right economics. It wouldn't be. ...

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1 answers
9 votes
828 views
What kind of ship is this?
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12 votes

It's a heavy-lift vessel, carrying four identical structures as cargo. It's very likely they are jacket foundations for offshore wind turbines. The excellent 4C Offshore has a database of such ...

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2 answers
4 votes
784 views
Can solar panels absorb heat for energy?
10 votes

Yes, there are indeed combined PV-T (photovoltaic-thermal) hybrid panels that turn some of the incident light into electricity, and have a circulating fluid and heat exchanger to put some of the heat ...

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3 answers
5 votes
4k views
Relationship between wind velocity, turbine rotor diameter, and power output
9 votes

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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4 answers
3 votes
504 views
Smallest possible controlled chain reaction-based nuclear fission reactor?
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9 votes

The RM-1 Russian submarine reactor had a core of less than one cubic metre. It had about 100kg fuel load, which was 90% enriched (i.e. 90kg) Uranium 235. This was liquid-metal cooled [specifically a &...

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5 answers
6 votes
2k views
Is there a more active passive technique for removing humidity from the air besides salt blocks?
8 votes

Silica gel is the standard for most purposes. It's the desiccant you find inside those paper sachets packed with new electronic equipment. It consists of tiny beads of silicon dioxide that are ...

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2 answers
2 votes
73 views
Why are home geothermal systems usable anywhere in the U.S. but industrial geothermal plants limited in geographical use?
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7 votes

Because they're two completely different systems that have, in some circles, accidentally been given the same names. The things that are sometimes (particularly in the USA) called home geothermal ...

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1 answers
3 votes
181 views
Why is it more common to use ceiling fans instead of air pumps?
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7 votes

Mainly cost difference. And also, a fan is sufficient for the job. The problem being solved is thermal stratification. That's caused by a lack of vertical mixing; the warm air rises to the top, the ...

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3 answers
2 votes
2k views
What is the most efficient way to convert a fuel into electrical energy?
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6 votes

In theory, direct chemical to electrical energy offers the highest efficiency: it can deliver arbitrarily close to 100% efficiency. However, to date, fuel cells haven't delivered on anything close to ...

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2 answers
7 votes
223 views
When is DC power generation superior over AC power generation?
6 votes

There are cases where DC power generation is superior to AC. If it's going to be transmitted by DC, and you can generate at the transmission voltage, or you can step up the voltage to transmission ...

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3 answers
0 votes
69 views
multiplying up human compression power!
5 votes

Levers are your friends: a lever allows you to multiply up the force of your own strength. Here's a manual can crusher, demonstrating this: source Your hand moves three or four times the distance ...

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3 answers
7 votes
424 views
Why do we need to shut down power generators if we are producing more power than the grid requires?
5 votes

The electricity grid has very very little capacitance. That means that in any and every second, the energy going into it, has to come out of it too. If it doesn't come out in controlled, intended ...

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3 answers
7 votes
196 views
What development possibilities could yet exist in water desalination?
5 votes

Carnegie, through their CETO device, and others have already looked at using wave power to directly pressurise water for reverse osmosis: a wholly mechanical process rather than converting to ...

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3 answers
7 votes
567 views
Why have thorium fueled nuclear reactors not been more fully developed?
5 votes

As I wrote over on a similar question on our sister Physics site, the German THTR-300 Thorium High-Temperature Reactor operated for about 16,000 hours and the IAEA has data on it. So, a thorium-...

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2 answers
2 votes
249 views
Why can't we predict turbulence deterministically?
4 votes

We can predict and analyse turbulence, and frequently do. That's one of the things that Computational Fluid Dynamics models do, and what weather forecasting models do, and what climate models do, ... ...

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4 answers
3 votes
3k views
Is there a danger to a human that is linked to ground wire of home electrical system?
4 votes

No, the whole point of the earth in an electrical system is to provide a safe direct route away from the rest of the system. If there were any risk to someone connected to earth, there would also be ...

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1 answers
3 votes
168 views
What is the power and max flow rate required to rotate a 300 W wind turbine?
4 votes

You need to push air through the turbine at 11 m/s, or just above. That's what the rated windspeed means: it's the lowest windspeed at which the turbine hits rated power, at standard atmospheric ...

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1 answers
6 votes
1k views
What are the technical differences between flexible and rigid solar panels?
4 votes

The main high-level technical difference is that flexible panels are pretty much useless. They're an absolutely tiny part of the market. A novelty. A toy. To understand why, have a think about what ...

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2 answers
3 votes
807 views
Heat Loss in Typical House
3 votes

No, it's not meaningful to express it as a ratio. The best insulation is deep insulation everywhere. You also need to consider convection losses, and your ventilation strategy. The attic is usually ...

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1 answers
0 votes
60 views
What is the exact definition of renewable energy
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3 votes

overview: Renewable energy is one for which the input energy is renewed on human timescales. Remember, energy is always conserved. It doesn't come from nowhere. Pretty much all the energy we use on ...

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1 answers
-1 votes
91 views
Do commercial fuel cells actually exist or it is just hype?
3 votes

Fuel cells have hit the start of commercial success in Japan, where sales so far have been at least 120,000. Given they only became viable commercial products very recently, that's pretty good uptake. ...

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6 answers
3 votes
3k views
Working hours of power plant generators
3 votes

There isn't a single answer that covers large power plants around the world. There's way too much variation in generation plant, and way too much variation in the way that plant is used. Some plants ...

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1 answers
1 votes
72 views
Are there any methods to work out what appliances are running in my home from an aggregate power consumption sampled 6 times a minute?
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3 votes

The word that will unlock your searching is disaggregation - there's quite a lot of research going on right now into energy disaggregation. These generally involve some kind of learning algorithm, ...

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1 answers
0 votes
438 views
At what cold ambient air temperature will power lines fail?
3 votes

Here are some pylons in Norilsk, Northern Siberia, where temperatures get down towards -50°C (source) It's all a question of design and engineering: pylon spacing, the range of max and min ...

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