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Comment Moore's Law != Performance (Score 1) 239

DNA sequencing is becoming faster and cheaper at a pace far outstripping Moore's law.

Moore's law, or rather Moore's observation, has absolutely nothing to do with performance and everything to do with the number of transistors. For the love of deity of your choice, will they stop using it regarding performance? Simply mentioning something computer related doesn't make the writer look smarter. Yes, an increase in the number of transistors can see an increase in performance but it isn't guranteed. Eg. Bulldozer

Comment Re:Numbers please... (Score 1) 182

Since accelerating the mass of the batteries raises the cost even further, batteries are even less efficient for urban transportation when you accelerate and decelerate a lot. We would need to bring back trolleys or another way not to have to transport the energy source for our cars to have something efficient.

Um, what?

Top of the line Lithium Ion batteries (they'll soon trickle down to automotive) are at about 240 Wh/kg, or 0.864 MJ/kg. Now, here's the cool thing about electric cars, you can get ~70%+ efficiency from battery to tire patch (aka, 70% of the power is used to move the car), and 80%+ fairly easily. Gasoline engines top out at around 25-35% efficient (Carnot efficiencies). Assuming a gasoline efficiency of 35% and electric car efficiency of 70%, you need half as much energy per kg storage capacity for electric cars.

The second cool thing about electric cars, regenerative breaking. You can recover around 70% of the energy from stopping as electricity and put it back into your battery. It is easily more efficient to use batteries/electric drive trains than gasoline in urban transportation. Why do you think hybrids get such great city mileage? This further reduces the storage density needed. Hybrid buses are awesome at city transportation, serial hybrids at any type of transportation are just epic. Electric drive train to maximize drive train efficiency, gasoline or other generator for range running at most efficient gearing.

Comment Re:I think its entirely reasonable to say... (Score 2, Informative) 439

You touch on another of the ideas that people are working on alongside efforts to make a high efficiency cell. While concentrator systems up cell efficiencies, the convertible spectrum is still limited by the cell. Some researchers, such as those at MIT as published last year, are working with dyes and other materials to re-emit the sunlight at a more cell friendly frequency, although this method too has major losses.

A second method not often mentioned here is called thermophotovoltaics. The idea is that you use concentrated light to heat up an element that then emits light at a different spectrum. To me, the cool idea about this is that if you can emit at the right range and get really high efficiency cells, somewhere down the line you might be able to replace the steam part of current power plants. Although that goes outside my realm of knowledge.

The issue with most cells' spectrum is that you need to shift the light up in frequency, not down, which is harder/more expensive. However, it could be useful if you could target the frequency at which the cell is most efficient.

Comment Re:I think its entirely reasonable to say... (Score 2, Informative) 439

I don't know exactly what the absorption and conversion rates are with the 40% efficient cells, but its safe to say it's very high. One of the biggest hurdles with solar cells is simply getting the charge out, getting the electrons and holes that are knocked out out of the semiconductor. It plays a very large part as to why current efficiencies are so low.

To hit 25+% efficient cells, in essence 3 cells were combined to create a multijunction cell that has 3 layers in series. To get to 30+%, refined deposition methods and clever semiconductor tricks were used. To get to 40+%, you need concentrated light and, in some cells, more layers of different materials.

The journal paper describes a simulated cell with a 14.5% efficiency and that it will compete with crystalline silicon cells - the middle of the pack for silicon efficiency and cost. The big advantage here is that the amount of semiconductor used is very low, which could make these cells very cheap. Another thing to keep in mind is that this method can potentially be applied to other, more efficient technologies, although there will be a few more hurdles should they go that route.

I very much like the idea of cheap solar cells, but it needs to be clear that this is not an efficiency breakthrough. But let me tell you, as a solar car alum, the idea of even a 40+% efficient non-concentrator cell gets me excited, even though this is not that.

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