Hot answers tagged renewable-energy
19
More blades give you more cost, but very little increase in efficiency.
Three blades turns out to be the optimum.
With four or more blades, costs are higher, with insufficient extra efficiency to compensate. Edit: prompted by a comment, here's some elucidation - this is more expensive per unit electricity generated, if you go for more, but shorter, blades: ...
12
There are quite a few novel energy technologies coming through. I guess that without quantification, "breakthrough" is a subjective term. Below, I've tried to list all the energy technologies that I know of, that are not yet at commercialisation, but could be within 50 years, and that could offer at least tens of gigawatts of power. They are, in descending ...
10
In principle, yes, the ultimate source of energy for a tidal power plant is Earth's rotational energy, so these plants are slowing down the Earth's rotation. By conservation of angular momentum, that means they are pushing the Moon further away as well, although I wouldn't phrase it as being due to "waves in the gravitational field," as that expression ...
9
The energy needed to remove an electron from a solid is called the work function. For most metals you would need UV photons (300 nm for Aluminium) that rarely reach the Earth's surface. Visible light can eject electrons from alkali metals, but the quantum yield (the probability of electron emission per incident photon) for pure metals is low (probably less ...
8
The next serious advance that is not an speculative/fringe idea is most likely to be fusion power. Harnessing the power of nuclear fusion has long been a goal for energy production since the first hydrogen bomb was created in the 1950s. Creating controlled fusion, rather than the chaotic variety has proven a rather challenging task here on Earth however. ...
8
Starting in the fifties, there was a lot of work (see RDD-8, V.C.1.g) trying to build a pure fusion weapon for mainly two reasons: they promised to be cleaner than conventional thermonuclear devices (important for peaceful uses and some of the not-so-peaceful ones) and they wouldn't need relatively scarce fissionable materials. As you can use staging to ...
8
Yes, the claims in the video are totally absurd from the viewpoint of science. It's enough to listen for roughly 70 seconds to be sure that the narrator doesn't have the slightest clue about physics and the remaining 302 seconds make this fact even more self-evident. I won't try to answer the question whether the authors of the video realize that what they ...
6
First kind of principles is 'How the linear motion is transferred into revolutionary':
There are horizontal- and vertical-axis windmills, horizontal are more common, vertical ones doesn't care about the wind direction.
Second way how to sort windmills is by the principle of transfer energy conserved in axial flow into momentum. Easier way is based on ...
6
Although I am no big friend of the solar panels today - because they are subsidized - I think it is correct to say that from a theoretical point of view, we are already "there".
Solar panels are typically guaranteed to work for 10 years at their 90% capacity and/or for 25 years at their 80% capacity.
The price of a piece of solar panel producing 1 Watt ...
6
The simple answer is price. Solar panels are still highly cost inefficient (particularly in low-sunlight regions) compared to conventional methods of energy production.
To be fair, there is really very little physics to be said about this. Efficiency, while far from 100%, is still pretty decent (typically from 10% to 30%). One interesting area just ...
6
First, let's do some back-of-the-envelope calculations. The word for the average amount of Solar energy reaching the Earth's surface over the course of a year is "insolation." According to this page, insolation in populated areas ranges from $2.27\,\mathrm{kWh/day/m^2}$ in Norway to $5.26\,\mathrm{kWh/day/m^2}$ in Miami, Florida. In slightly different units ...
6
To essentially quote http://en.wikipedia.org/wiki/Tide:
Energy of the Earth is not conserved while energy of the Earth-Moon system must exist. Energy from bodies of water are diminished (by about 3.75 TeraWatts) where about 98% of this energy loss is due to marine tidal movement.
Because energy is lost in the water, this imposes a torque on the Earth ...
5
An engineering answer:
Note that it's not just about water vs air. It depends on a lot of things: the density & compressibility of the fluid, and tradeoffs between torque, efficiency, cost, materials, maintenance needs, fouling hazards, and so on. Below is a water turbine blade, the SeaGen, that's not much different from a wind turbine blade, because ...
5
As an ex-physicist who now works as a quant in power markets I think it's safe to say the physics of the matter will be swamped by the economics in commodities and how power markets work. Two things to note:
power prices are set by markets and not by the viability of the technology (prime mover)
solar is hard to make money with w/o a long term Power ...
5
I find the idea of a breakthrough technology presented by the other answers to be extremely modest. I'm almost positive that I'll get downvoted and flamed for my answer, but I have a strong desire to impress the potential for, and the implications of, a truly breakthrough energy technology.
I want to begin calling attention to Jevons Paradox, as well as ...
5
We can. But they don't scale well: to get grid-level storage, you need to be able to scale to gigawatts of power, and gigawatt-hours of energy. And to be able to cycle hundreds, or thousands, of times.
To date, we have one technology which will do that, which is pumped storage hydro, which typically has a round-trip efficiency of 75%. So even though that's ...
5
It will vary a lot by site, and on the particular PV technology being proposed.
So, you need to know:
is it monocrystalline silicon, is it CdTe thin-film, or something else?
what's the efficiency of the inverter?
what's the guarantee on the kit (5 years, 10 years, 20 years)?
Using @Martin Beckett's figure of 2000kWh/y, that means, roughly, that your ...
5
Progress in Photovoltaics: Research and Applications publishes a biannual review of PV efficiency records, under the name Solar cell efficiency tables. The 2013 January review gave a record efficiency under standard test conditions for an organic PV cell of $10.7\pm0.3\%$. For an organic PV sub-module, the record is $6.8\pm0.2\%$
Cells have higher ...
5
Making ammonia is an absolute bugger because nitrogen is so unreactive. The normal route is the Haber process, http://en.wikipedia.org/wiki/Haber-Bosch, but this requires high pressures and temperatures.
Hydrogen is easy to produce from electricity, and I guess that's why it's the first choice for storage of energy generated by unreliable sources like wind ...
5
(I tried to post this response with chart and links, but I'm new here, so the system won't let me include images or more than two links. Please cut and paste the other links to view them in your browser.)
This diagram from the NH3 Fuel Association (taken from www.nh3fuelassociation.org/about-us--why-nh3) (scroll down the page) may answer part of your ...
5
Typically, yes, the water does need to be pumped up.
Because if it released energy by rising, it would already have risen to the surface.
OTEC depends on a high-enough temperature difference between the lower-depth water intake and the higher-depth one, for that temperature difference to do enough work to provide some surplus power, in addition to the ...
5
Storing electricity as electricity is currently possible only in capacitors. A lot of fuss is made about the potential of super-capacitors and ultra-capacitors to scale up, but little has happened yet at the grid level.
Almost everything else involves converting electricity to a different kind of energy; and then converting it back to electricity when ...
5
As I understand it, there are two versions of this idea. The first is kind of interesting and might work - the idea is that you heat the air at the bottom using a power station, and allow the vortex to carry the air into the upper troposphere. The vortex acts like a chimney, drawing the hot air out of the unit, causing a pressure difference that allows you ...
4
The amount of energy we can capture as geothermal is only a very tiny fraction of the amount that leaks naturally through the earth's crust. In addition, the distance from the earth's surface to the generator is so very long that the time constant for heat movement at one end to cause heat change at the other is very long.
To get an idea of the calculation ...
4
In order to slow down the rotation of a body angular momentum must transferred off that body. In the case of Earth and the moon this occurs from the difference in gravity across the Earth, or tidal force. A tidal power generating system simply converts a tiny fraction of energy in the tidal bulge of the Earth, mostly in the oceans, as it moves around the ...
4
Wind is caused by differences in air pressure, where air flows from high pressure areas to low pressure ones. To "consume" all the wind would require air pressure to reach equilibrium, something that won't happen since the effects of solar heating and cooling from bodies of water constantly introduces differences.
The only effect you might observe if you ...
4
From the point of view of aerodynamics, a smaller number of longer blades is preferred. From the point of view of engineering strength, a larger number of shorter blades is better. What is actually chosen is a trade-off.
It should be obvious why shorter blades are stronger. Longer and thinner blades are more efficient aerodynamically for the same reason ...
4
This question of the week article describes the tradeoffs of aircraft propeller blades - number, angle, shape, length etc.
The final paragraph gives a good summary and relate directly to your question about why the blades do not cover the entire circle. It turns out that they do cover as much as is needed for a given engine to transfer the available energy ...
4
What you propose is a version of concentrated PV.
Concentrated PV has been in development for some time.
The big issue with PV, is lifetime cost per unit energy. There are no other constraints really - there are plenty of alternative commercial panels that material shortages aren't an issue; we know we can manage their exogenously variable power ...
4
Yes, many things rob Earth's angular momentum and slow it down.
For example, when a rocket lands on Earth, it gains/loses speed due to the Earth's rotation. Other than that, when a rocket leaves Earth, they use the fact that the Earth rotates in order to gain kinetic energy from the Earth's rotation. In other words, the rocket robs the Earth's energy.
NASA ...
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