Creating Power From Wasted Heat 186
Roland Piquepaille writes "Today, about 90 percent of the world's electricity is created through an indirect and inefficient conversion of heat. It is estimated that two thirds of the heat used by thermoelectric converters are wasted and released. But now, researchers from the University of California at Berkeley have found a new way to convert this wasted heat into electricity by trapping organic molecules between metal nanoparticles. So far, this method of creating electricity creation is in its very early stage, but if it can scale up to mass production it may lead to a new and inexpensive source of energy."
Not by trapping molecules actually... (Score:5, Informative)
Re:New source of power ? (Score:2, Informative)
Just look at at this previous SlashDot article: http://hardware.slashdot.org/article.pl?sid=07/02
Um hello. Not new. (Score:3, Informative)
Invented almost 200 years ago. I have a huge box full of Peltier "chips" sitting in my store room..
Re:2nd Law? Try the 3rd law (Score:3, Informative)
The 2nd law just basically states that any energy conversion process cannot be 100% efficient, AKA "entropy".
In effect, this is adding a secondary process to the first (or possibly list of processes), of which we already know some amount of energy will escape due the 2nd law.
This additional process just makes the overall process more efficient, and does not really add to it above the original process's input energy. However, the 3rd law just states you can't achieve 0 entropy in a process with a finite number of steps. Basically, you can never have a process that is 100% energy conversion efficient.
Probably the more important question is does the increase of enthalopy merit the proposed decrease in entropy? AKA, does the cost of implementing this solution outway the benefit.
Re:Not by trapping molecules actually... (Score:5, Informative)
But fundamental to thermodynamics is that you can not have a cycle more efficient than the Carnot Cycle http://en.wikipedia.org/wiki/Thermodynamic_cycle [wikipedia.org]. This give a max efficiency = 1-(TEMPlow/TEMPhigh), so you always want that low temp to be as low as possible - for a car engine that would be the ambient air. If you have your device, then the hot side is on the engine, and the low side is in the air. But the device itself will get hot, an you will have to blow a lot of air on the cold side to keep it cold. It you let the whole device rise to the same temperature you get no conversion.
Re:Way to save energy.. (Score:3, Informative)
Large thermoelectric plants are ~40% efficient. A burner heats water, the steam passes over a turbine (connected to a generator), the steam is then condensed (where all the energy is lost) and pumped back into the water tank so it can be heated again.
My suggested idea would, most likely, use an internal combustion engine at ~25% efficiency. But even at a lower efficiency it is still more efficient then just burning gas at 0%. (Note that the efficiency ratings are for electricity production.)
Willy
Not a big deal (Score:4, Informative)
Firstly, there is a theoretical limit (Carnot Cycle [wikipedia.org]) to the efficiency of any pure heat engine based on the Second Law of Thermodynamics.
If a quantity of heat Q is taken from a high-temperature reservoir at temperature T2, partially converted into useful work W, and the remainder (Q - W) is deposited into a low-temperature reservoir at temperature T1, then the net increase in entropy is at least
\delta S = (Q-W)/T1 - Q/T2 >= 0.
So the efficiency (useful work generated per unit energy input)
e = W/Q < (T2 - T1)/T2
The waste heat is ultimately deposited into the environment, so T1 can't be much smaller than say 300K.
In a steam engine T2 has to be greater than the boiling point of water (at whatever pressure it is operated), but it is limited by what the materials of which it is composed can withstand. Temperatures of order 1000K are typical. That gives a maximum theoretical efficiency of around 70%. The best steam engines barely reach about half that efficiency.
However, modern power plants (which are not pure heat engines) use a Combined Cycle [wikipedia.org] that can do better by first generating electricity from their fuel with a combustion turbine and then using the waste heat from the combustion turbine to make steam to generate additional electricity via a steam turbine. Their efficiency can reach about 60% of the net calorific value of the fuel.
So you can see that one might be able to shave a few more percentage points off the waste, but it will not at all be the godsend we really need...
IMHO only nuclear power can fulfill that role today.
"Wasted" heat is not available for this device. (Score:5, Informative)
Re:generation vs consumption (Score:3, Informative)
White LEDs, 30-45 lumens per watt off the shelf, 131 in the lab. And way more expensive.
http://www.netl.doe.gov/ssl/faqs.htm [doe.gov]
http://www.cree.com/press/press_detail.asp?i=1150
http://members.misty.com/don/lede.html [misty.com]
Right now the reason to use LEDs is if the environment is harsh (vibrations, impacts, etc.) or if you really, really don't want to change the light often (traffic lights, or that %^#@!! bulb over my stairs). LEDs also scale down better than anything else.
Re:2nd Law? Try the 3rd law (Score:3, Informative)
If you cool the radiator to gain energy using this device, then you'll decrease the efficiency of the primary device.
e.g. if you connect this to the radiator at the back of your fridge, then your fridge will be less efficient.
I don't know whether the net gain is positive or negative though.
The real story here... (Score:3, Informative)