# Tag Info

34

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. This is more expensive per unit electricity generated, if you go for more, but shorter, blades: if you have 4 shorter blades (rather than three longer ...

18

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 ...

18

This is mainly an engineering & economics question; and we can deal with those aspects of it over on the Sustainability Stack Exchange, if you want. And there is one conceptual physics aspect too. No, fresnel lenses are not widely used for solar power. Occasionally, but rarely. Concentrated solar power (CSP), including concentrated photovoltiacs (CPV) ...

15

where does that electricity go? The photons from the sun have energy and momentum, but not "electricity". Essentially, a photon (solar or otherwise) striking the solar panel can create an electron-hole pair (EHP) and, if the EHP is within or near the depletion zone, the pair will be separated by the built-in electric field. This results in a ...

12

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 ...

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 ...

11

Any high slew rate (fast rate of change of power) stresses the grid. Lots of things cause high slew rates. People getting ready for work in the morning, having showers, turning lights and appliances on. Factories starting up at the same time. Faults on major international HVDC transmission lines. Safety shutdowns at nuclear reactors. Lots of people turning ...

10

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 ...

10

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 ...

9

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. ...

7

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 ...

7

There are several ways to design the circuit. If it's a Smart system, then when there's surplus power, additional devices will get turned on, to use it: dishwashers, washing machines, or immersion heaters in hot-water storage tanks. If there's still surplus after that, then it's as below. If it's grid-connected, with an inverter, then it's usually designed ...

7

Photosynthesis is less efficient than solar panels. According to the Wikipedia page on photosynthetic efficiency, typical plants have a radiant energy to chemical energy conversion efficiency between 0.1% and 2%. Most commercially available solar panels have more than 10 times this efficiency.

7

Rather than considering quantum efficiencies or such details it's instructive to step back and take a broader view. One of the main fuel crops grown in the UK is miscanthus. There are various figures around for the yield produced by miscanthus, but these people estimate it as about 14 tonnes per hectare per year. The energy content is 19GJ/tonne, so that's ...

6

Betz' limit arises from the fact that if the turbine tries to take too much energy out of the flow, the wind will divert and go around the turbine instead of through it. With a hydrothermal system the water is typically behind a dam, so the water has nowhere else to go. The turbines effectively convert gravitational potential energy into work, which can be ...

6

The principle of conservation of energy is your friend. The wind turbine generates electricity. That energy has to come from somewhere. The other energy in the system is the kinetic energy of the wind. Therefore, the wind turbines convert the kinetic energy of the wind into electricity, and the kinetic energy of the air downwind of the rotor is less than ...

6

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 ...

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 ...

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

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 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

(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 ...

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

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 ...

5

Wind turbines use induction generators, and most commonly, the jargon of doubly-fed induction generators applies. Now, the terminology I've seen most often in textbooks identifies motors and generators to be the same thing, just operating in different "directions", and both are called machines. The next major item to cover is the fact that a wind turbine ...

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

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 ...

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