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Old 04-20-2011, 01:04 AM
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Originally Posted by auroraglacialis View Post
... but generating electricity is very inefficient. Usually below 50% IIRC for the better power plants, more like 30%. Some solarthermals are at 50%, solarelectric are below 10%. Then transporting electricity (landlines) and storing it again (batteries, hydrogen) is inefficient. Overall, this is not at all more efficient really.
It depends on the type of generation. For thermal cycle generation, common efficiencies rank between 45% - 60% (for the combined thermal cycle). That's because the generator is attached to a thermal machine, and thermal machines follow Thermodynamics. If the generation is hydroelectric, the efficiencies rank from 80 - 90% (the bigger, the better). In my experience, you loss about 4 - 6% of generated power in the transmission line, add to that the transformers, typically 85% (the bigger, the better).
Let's make numbers then:
Hydroelectricity (large facilities > 5 MW)
Power available at consumer tap = Power at the turbine input x 0.90 x 0.85 x 0.95 x 0.85
= 61.77 % of power at the turbine input (that's the power that water is transferring to the machine).
Now, for thermal:
Power available at consumer tap = Thermal power at the beginning of the cycle x 0.6 x 0.85 x 0.95 x 0.85
= 41.18 % of power at the beginning of the cycle.
Storing that power in Lithium batteries is, nominally, 85% efficient. So, overall we have efficiencies of:
.67 x .85 = 56%

.41x.85 = 34%

Comparing that to the Otto cycle, electricity beats it by more than twice its efficiency, the only real competitor is the Diesel cycle. Coal powered electricity plants have efficiencies of 30%. So, it depends from where you are getting your electricity.

I think that is no reason to not do this at all. There is a very simple solution to it and that is exchangeable batteries. Just like you have several sets of batteries for your video camera or mp3-player or torchlight, you'd simply buy a full battery and return the empty one. Of course that is then not as easy as plugging the car into the wallplug at home, but the exchange could be fast and the batteries could be exchanged and recycled properly easily once their lifetime is over. It would require a standardization of battery sizes and connectors and some sort of mechanics at gas stations to replace the battery, but that is no technological problem - if anything it is one of design, regulations, standardization and acceptance. Most likely, each car manufacturer will instead produce their own batteries with own voltage and shape and connectors and at different places in the car and it sells easier if you can charge the car at home and do not need an infrastructure of refill stations that would have to be set up (though that could be combined, also - make the batteries exchangeable AND allow for homebased recharge).
That's what Tesla Motors is trying to do. To standardize the batteries, so one can exchange them easily.
The problem I see more is that using even more electricity will require massive amounts of new power plants to be built, more landlines and such. Also, the efficiency is a problem (as I said above). And to that adds the problem of getting Lithium and other materials like REEs for the huge amount of batteries and electric motors. All this has to be mined and processed and manufactured, which also costs a lot of energy and produces the usual problems with mines and mine processes. It may be a way to keep cars going, but it does not really deserve the label "green" or "clean" IMO. I think a lot more is gained if the number of cars is reduced, e.g. by easy car sharing and public transport or eliminating the need for too much transport. There is a neat project here locally that wants to put cars in the streets and you can with a membership card just rent it on the spot for a low price and leave it within the city afterwards. The organization then distributes them if they are not evenly distributed. If this is done with electric cars, at least the number of batteries would decrease.

A side fact by the way: Did you know where all the sulfur from the de-sulfurized gasoline goes to? It is dumped into the tanks of large intercontinental ships, who burn it over the open sea. So we do not have acid rain anymore on land, but the stuff just was exported to the oceans. And the 15 largest ships in the world produce as much sulfur emissions as all the land based transportation with cars together. Ugh!
As mentioned above, the bigger, the better. Efficiency is improved when the needed quantities of power are big, real big. There are ongoing projects involving Ultra High Voltage transmission lines expected to improve transmission efficiency. New materials are being developed for better transformer efficiency and the distributed generation schemes are emerging as a competitive alternative to the centralized generation (which also are expected to improve efficiency). The ideas that you mention will certainly make its way to the industry and regulatory entities. Stop using the car if there's public transportation, turn off the lights you're not using, unplug the things you don't use, etc. Many small things that most of us can do can also make the difference, globally and in our pockets.
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