Will more electricity be generated by using a lens to focus sunlight onto solar cells?

I have been wondering about this question for quite some time. Assuming an ideal case, the energy from photons hitting solar cells is converted into electric energy as described by the equation: $RI^2t=W\equiv E=\hbar\nu$ where $\nu$ is the frequency of photons. Using a lens won't increase the frequency of photons, thus no extra electricity is generated. Am I correct in thinking that no extra electricity will be generated by solar cells when a lens is used to focus light onto them?

electrical-engineering optics photovoltaics solar-energy

Your equation is partly correct. You've calculated the energy per photon ($\hbar \nu$), but you've neglected the number of photons. That's why the units don't match (power is energy per unit time, while you've only got energy for each photon). The ideal power (energy per unit time) depends on the area of the solar panel, $A_p$, the number of photons striking it per unit time ($\Phi$) and the energy of each photon, $E$, such that $W_{Ideal} =A_p \cdot \Phi \cdot E$. A lens or mirror can focus light (a flux of photons) onto a small area. Under really ideal conditions,...

As others stated before, induction loops are the primary - most reliable method: the coils (usually just several loops of wire) embedded in the road; fed given frequency from a generator, in presence of metal the frequency of the LC circuit changes and the sensor circuitry detects the change of frequency, producing a presence signal. In some cases these may fail to detect bicycles, but they are by far most common as they aren't affected by weather (or more precisely, the detection circuit tunes in to slow changes of frequency caused by weather) and are immune to accidental false positives....

On this processor, the register that holds the conversion result is 16 bits wide. A right-justified result means that bits [( N -1):0] (where N is the number of bits of precision) of the register contain the ADC value and the most-significant bits of the register are set to zero. A left-justified result means that bits [15:(16- N )] of the register hold the result, and bits [(15- N ):0] are set to zero. For example, if your actual conversion result is 0x123, it would be read as 0x0123 if the register was right-justified, and as 0x1230 if it was...


How long does it take for dust to settle out of the air?

In order to make this a manageable question, let's add a few simplifications. The dust particles can be well described as uniform spheres of radius $R$ and density $\rho$. The space is enclosed and there is no bulk flow, i.e the air is still in a macroscopic sense. The air is at the standard temperature and pressure (STP) ; $T=20\ ^\circ\mathrm{C}$ and $P=1\ \mathrm{atm}$. Under these conditions, what is the settling time for dust particles? At what size/density does Brownian motion of the air become important?

Please note : I'm not a building designer by trade, but I have had to investigate related questions for other reasons. I'll let you in on a dirty secret about sanitation lines within buildings - The biggest concern is not about how fast things are flying, it's about maintaining air pressure and providing adequate ventilation. This guide presents a bit of a historical background to tall building design with respect to sanitation system design. This presentation provides some more recent perspective and goes into some of the research that is refining current building standards. The traditional viewpoint is that waste...

Solid particle settling time in air depends mainly on the size of the particle. Different forces become significant depending on what size range you're talking about, so it's hard to give an answer that's both concise and accurate. I'll do my best to synthesize the important points rather than parrot a reference; that said, where practical applications in the field of air quality are concerned, the text I recommend is Air Pollution Control by Cooper & Alley . In particular, I'm going to pull many of the details for this answer from Section 3.3: Particulate Behavior in Fluids. Gravitational Settling...

Electricity production optimization is a very complex subject. It is also affected by many parameters , which I will try to outline below. TL;DR: Demand is constantly monitored and supply is constantly adjusted TL;DR 2: Lshaver's excellent post is a suggested reading after reading this, because it expands and explains what happens at timescales ranging from the micro-second to minutes timescales. Changes in energy demand during the day First of all, the energy demand during the day, week, month of year can change quite a lot. Below is a typical day in New England. Fluctuation in power energy consumption a...

The picture, below, of the exaggerated long section of the Channel Tunnel was taken from Wikipedia . Full-sized image here . Some of the limiting factors for the Channel Tunnel are: Railways don't like steep gradients The tunnels comprising the Channel Tunnel were excavated using tunnel boring machines (TBMs). Like railways, they cannot tolerate steep gradients. The tunnel was excavated in chalk marl (green coloured material in the picture). This was due to its depth (not being too shallow and not being too deep) and its ability to be easily dug but also it would cause major support issues for...