Tag Info

Hot answers tagged

5

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 ...


5

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 ...


3

I think EnergyNumbers's Answer is an excellent one, but could leave some people a bit mystified by what exactly a "direct ray" is and what exactly its relevance is. The essential idea here is that a Fresnel lens is an imaging machine: it puts a curvature on a low aberration wavefront so that that wavefront converges. Its working depends on there being ...


3

I don't think that the fact that they are connected to the grid has anything to do with that. In fact, the generator part of the turbine is one of the most expensive parts, so it is protected against impacts from the outside. The reason is simple: the turbine blades are being charged as a result of rubbing against the humid air. As a result we can observe ...


3

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.


2

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 ...


2

Let's suppose the light from the Sun was perfectly coherent. In that case you would get interference, however the optics used in the sort of solar tower you show are manufactured to nowhere near single wavelength of light precision. That means the phase of the light arriving at the collector would vary wildly with position across the collector, and the ...


2

Short answer: On something operating with non-coherent light on the scale of a solar power collector, there is no net effect from interference. The increase in light intensity is not additive interference at all, but is simply that the light falling on a wide area is collected and focussed on a small area. However, I'm guessing that there is some confusion ...


2

Ballpark estimate, I'm not a geoscientist so I don't kn ow if the whole idea even makes sense: This abstract of a paywalled articel states $4*10^{10} W$ Energy release and a mass flux of $3 * 10^4 kg s^{-1}$. So we are talking roundabout $1.3*10^6 J kg^{-1}$. A supervolcano eruption is typically defined as yielding more than $450 km^3$ magma. Assuming a ...


2

The basic energy requirements of homes, industries etc are measured in watts. It may be sometimes seen how much energy each sector utilizes over a span of time, but generally we see how many watts are used in homes, industries then further in colonies, cities etc. Atleast here in India (and I think it would be similar everywhere) we get our home supplies ...


2

Some PV modules are indeed one single large area: thin-film modules and polycrystalline silicon modules can be done as one single large area, or as arrays of rectangular cells. The design in this case is driven by economics. Monorystalline silicon modules always consist of an array of connected cells: and the reason for that is primarily about the science, ...


2

The energy is converted to heat. The friction of the water with the river bed, and with itself, converts the energy to heat.


1

First off, I would be cautious about interpreting the parameter that press releases focus on as being the "most important" - it's just as likely to be the one that a press officer happened to pick because it seemed like a Nice Big Number, or possibly the one that they understood. Think yourself lucky if the units actually made sense! However, there is a ...


1

The system you describe, a water tower with pumps and turbines, is a version of a pumped hydro storage system. The amount of energy stored in a pumped hydro storage system is defined by the elevation, i.e. the height that the water is lifted; multiplied by the volume of water that is lifted (assuming that the height the water will fall, is the same as the ...


1

Rare earth elements aren't really used much in PV at all. The market is dominated by silicon cells (~95% of the market). The next big player is Cadmium Telluride (~5% of the market). The rest are pretty insignificant. Also, note that rare-earth elements are (with the exception of Promethium) not particularly rare.


1

Light gets "trapped" in an optical fiber when the light travels such that the angle of incidence when hitting the surface is low enough that the optical index change causes the light to "bend" back into the fiber. This is known as total internal reflection. Basically with larger fibers you'll get light bleeding out. Thin fibers work over long distance ...


1

You'll usually find these data in the Supplementary Information of relevant papers. If you find a paper where they've made such measurements, but don't give them in supplementary information, you can email the contact author, with a couple of paragraphs explaining what data you're after, and what use you'll put it to. For example, here's the Supplementary ...


1

From Sze (chapter 14 in the second edition): "As the temperature increases, the diffusion lengths in Si and GaAs will increase, because the diffusion constant stays the same or increases with temperature, and the minority lifetime increases with temperature. The increase in minority-carrier diffusion length causes an increase in J_L. However, Voc will ...



Only top voted, non community-wiki answers of a minimum length are eligible