[X] My Assistant

[crabbsaline]

I'm not sure when the countdown page went up, but looks like the first peek will come on July 20:

Tesla Motors Homepage

Random thoughts:

• I wonder how similar the batteries are to those used on the MERs.
• I wonder what the replacement costs of the batteries will be.
• I wonder what the best disposal of the batteries will be.
• I wonder when they will reach a price range that I can purchase one.

As a related matter, check out the competition:

Wrightspeed Homepage

I'm glad that Doug has this chat section. This seems far enough from the subject matter of UMSF that I worried about posting it. Five degrees of separation on this topic, I suppose...UMSF : Launch Vehicles : Falcon : Elon Musk : Tesla Motors.

[jrdahlman]

Carefull... any debate over alternative energy could quickly overwhelm this forum until Doug stamps down on it!

The best comparison of current alternative energy sources is Don Lancaster's lively
Energy Fundamentals paper.

By comparing "volumetric energy density in watthours per liter and gravimetric energy density in watthours per kilogram" for gasoline, hydrogen, lithium batteries, etc, you can see what's currently efficient and what's not. While hydrogen is ideal "for deep-space aps" it has many disadvantages on Earth. Don's mostly cynical against homebrew designs--using solar cells to run an electolysis of water into hydrogen "is pretty much the same as 1:1 converting US dollars into Mexican Pesos." In fact, he's pretty cynical about silicon PV, period.

I've been raving about this to other people ever since I read it.

[helvick]

In fact, he's pretty cynical about silicon PV, period.
I've been raving about this to other people ever since I read it.

This is a wonderful piece of popular science with much more reality in it than anything else I've read on the subject - I absolutely love it. Thanks for the link it's going to provide me with tons of entertainment and material for throwing into discussions in the pub.

However even though I agree almost entirely with his assertions there are some points I'd disagree with. For example while he is perfectly correct in saying that PV is a net energy sink at the moment he says two things that are wrong. Firstly he says that PV has an inherant 30% conversion efficiency limit, that is not precisely true as 35% efficiency cells are now available and mid 40% is now believed possible. These types of cells are woefully uneconomic right now though (ie consume hundreds of gallons of old energy in order to produce one gallon of new energy) but that could be dramatically changed by creative application of semiconductor manufacturing techniques. Secondly he seems to think that diffuse sunlight is generally useless for PV generation - that is true for very low efficiency cells but as the MER's have proven repeatedly (to bring us somewhat back into the focus area for UMSF) you can convert more power from diffuse light than from direct light if you have high efficiency cells and you get the added benefits of a) that capability is available for a far higher percentage of time than direct light and PV cells that convert diffuse light effeciently do not need to be pointed at the sun. The difference is noteworthy in the following MER examples:

If you can only use direct insolation you are limited in this case (where atmospheric opacity is 0.904 which is slightly hazy by earth standards) then your maximum efficiency is limited to 30% of the theoretical maximum power potentially available if there was no atmosphere unless you have a sun tracking (ie expensive and energy hungry) mount. If (as the MER's can) your PV cells are good at converting diffuse light then your limiting efficiency rises to 76%. Now that's in terms of usable sunlight only so you still have the PV cells own conversion efficiency to deal with and storage\conversion losses but it does mean that the technology exists today (unlike all the other solutions) to power an average house in most places on earth with a 5x5m solar panel (assuming you get 0.5kWh from each 1m^2 or about half what the MER's get when clean). They are too damn expensive in terms of manufacturing to be practical today but that is a manufacturing challenge that could be met if sufficient focus was put into it. IMO at any rate.