# Tag Info

15

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) ...

9

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

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 ...

4

To harness the energy of the Earth's rotation, you need something with different angular velocity (just like harnessing thermal energy requires two things at different temperature). Everything on Earth is rotating with the same speed, and so has the same angular velocity; the closest thing with a different angular velocity is the Moon. This is in fact what ...

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 ...

4

Fresnel lenses are not used, but fresnel reflectors may be soon. There are two main ways in which electricity is generated from sunlight: Photovoltaics: These (what are commonly thought of as "solar panels") are generally used without optics. The reason is that they will accept light from nearly any direction, and the power generated is directly ...

3

Boden & Bagnall (pdf) looked at this question of reflection, in their paper Bio-Mimetic Subwavelength Surfaces for Near-Zero Reflection Sunrise to Sunset. Their estimate of the proportion of photons reflected, from sunrise to sunset, in a fixed PV system is 20%, rather than your estimate of one-third. The proposed etalon is not an efficient or ...

2

I'll answer the current version of the answer and a bit of a previous. The math is extremely basic. If the power production grows 2.3% a year and the initial power production is $2 \cdot 10^{13} \, \text W$ then in 1400 years your energy production would be: $$P_{1400} = 1.023^{1400} \cdot 2 \cdot 10^{13} \approx 0.13 \cdot 10^{28} \, \text{W}$$ Now, ...

2

There are a few important points to make before I attempt an answer. The first is just a point about terminology: you have to be careful to distinguish between energy and (angular) momentum. They are not the same thing - they have different units - and so it doesn't strictly make sense to talk about "draining energy from Earth's angular momentum", since it's ...

2

If you want to know more beyond the physics concepts, please do ask over on the new Sustainability Stack Exchange, where we can cover the physics, economics and engineering of such a question. Here I'll deal with the physics (and only touch on the other aspects in passing) Technical feasibility Each of the bits of the system you propose happen in real ...

2

Yes you can use the falling water to make electricity - that's how hydroelectric dams work. But if you are using power to pump water back up then you will always use more energy to pump it up than you get back from falling down. Otherwise you have a perpetual motion machine The only way it makes sense is if you need to pump the water up for other reasons ...

2

The trouble with an etalon is getting the light into it in the first place. Bearing in mind we want normal inidence to maximise the light intensity our solar panel looks something like: But solar panels aren't transparent (obviously since they reflect two thirds of the incident light) so if you wanted to use a second panel you'd need something like: ...

1

A typical bifacial module will transmit energy that passes through the silicon as well as the energy that passes around the edges of the cells which would otherwise be absorbed in a typical monofacial module design, around 3% of the total. Using the 20% energy transmission value quoted above, a bifacial solar module will absorb ~23% less energy than a ...

1

Contrary to what we might want to believe, any kind of perpetual motion device would violate the known laws of physics. No system can create energy out of nothing, and even if an engine were 100% efficient and didn't lose anything to friction, gravity, etc, it might run forever as long as there was no draw of energy out (ie. to do useful work). As nice as it ...

1

There are many ideas analogous to the water tower/turbine/pump system (minus the solar panels). One common example is a water electrolysis system which passes an electric current through water to split water molecules into hydrogen and oxygen, which is then used as a fuel in either an engine or fuel cell to produce electric power to feed the electrolysis ...

1

You're absolutely right that annual mean power is by no means a useful guide to the peak power a panel might generate. You can find places on Earth where annual mean insolation is well below $100~W/m^2$, and places where it's higher than $250~W/m^2$: but at both those places, there will be times when peak insolation is $1000~W/m^2$ or more. And so all PV is ...

1

Let's look at the amount of energy (in Joules) in one second - i.e. in SI units of power, Watts: that way, you can directly compare between them, and scale up the times as you choose. So, for Wh, kWh, MWh, etc - it's each of the activities below, for one hour 2 W average power used in charging a mobile (cell) phone 20 W laptop power consumption, at low ...

1

Credibility Your source is at first not really credible to me as a physicist and how should air be made conductive? This can only be done at very high pressure, i.e. we do not talk about ideal gases as in the atmosphere anymore. The particles which would be ionized still have a very high velocity such that such a path is unrealistic. The distance of 2 km ...

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