Tesla Motors: Another Elon Musk enterprise, Another of the SpaceX founder's investments Options

[Guest_Richard Trigaux_*]

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.

There is no theoretical limit about the efficiency of a solar cell. It is not like a thermal engine, which has a maximum allowed efficiency (Carnot theorem) given the temperatures of heat source and heat sink. Nothing such for solar cells, which can theoretically reach 100%. The much poorer practical efficiency is due to a number of factors which are difficult to overcome, so that nobody can say if we will really have one day a near 100% efficiency.

About the cost in energy to produce solar cells (the energy required to manufacture them, versus the energy they produce during their lifetime) I don't think it is so bad. Anyway the worse case is for high efficiency solar cells like those used in space. Cheaper solar cells have a much lower efficiency (5 to 10%) but they are energy positive, not energy sinks. To give an idea, paving a railway with such cheap solar cells would allow to circulate several high speed trains per day. This is just too costy for today solar cells.

The main energy cost for solar cells is the purification of silicium, which requires several cycles of melting and solidifying. Such ovens were intended for producing integrated circuits, where energy is a little part of the total cost. To produce solar cells for energy purposes would use more economic ovens (with heat recycling) and less cycles.


Anyway the smartest way to use solar energy on earth would rather be large solar ovens used to dissociate water and produce hydrogen. This is possible at 950°C with a catalytic cycle using sulphuric acid. This temp is of easy reach for solar ovens. After the hydrogen could be associated with CO2 to produce methane or gazoline, without the need to change anything to our industrial habits.

At a pinch, a smaller version of this could be used on space stations to produce energy. It would be perhaps more efficient than solar cells.

[djellison]

Get this - on a trip to Coniston a few weeks back...we went in a Solar-Diesel hybrid boat. The boat ran on an electric motor, and for about half the trip ( in fairly good sun ) it ran purely on the batterys, with the solar arrays topping them up and the diesel augmenting it when appropriate.

Doug

[jamescanvin]

In Sydney we can go one better.

Solar powered ferry whose movable 'wings' can also also be used as wind 'sails' - looks cool too.

http://www.solarnavigator.net/solar_sailor.htm

[Guest_DonPMitchell_*]

In Sydney we can go one better.

Solar powered ferry whose movable 'wings' can also also be used as wind 'sails' - looks cool too.

http://www.solarnavigator.net/solar_sailor.htm

Very interesting. Does it have to charge up for a while, or can it generate enough power on the fly to run continuously?

[jamescanvin]

Very interesting. Does it have to charge up for a while, or can it generate enough power on the fly to run continuously?

Here's a better web link - http://www.solarsailor.com

From the technology FAQ:

For example a 50 tonne 149 pax hybrid/electric ferry requires 660 kw to achieve speed of 20 knots for commuter services - so power has to come from stored fuel. However for tourism, the max solar power of 20hp will drive the vessel at 6 knots and the average solar power of 10hp will drive the boat at approx 4.5 knots.

[crabbsaline]

The car was unveiled at Midnight, California time:

Tesla Motors

The car looks great . The website design is nice too. Lots of info.

...just no price, yet.

[Guest_Richard Trigaux_*]

Hmmm...

Yes, nice car for car lovers.

The problem I see in several other recent instances of electric cars, is that they are luxury cars or sport cars. perhaps this is the best market niche for cars which are anyway still expensive, by lack of mass production.

But, I think, electric cars will really take up when there will be family cars, small economic cars to go to work, and other models of common use.

We don't really need cars able to run at high speed (the speed limits are here and they are here to stay) and even not very nervous cars, which may be dangerous in town. And unused powelful motors add weight. Not to speak of eight wheels in place of four, as a recent japanese model has.

Cheap cars for everybody. Cheap at buying, cheap to use. (By the way 1 cent per mile is not bad).


In a general way, electricity is not an energy source. So that electricity simply offsets the nuisances, costs and problems of producing energy. In a general way, we gain on this (provided that electricity transportation and storage is efficient) but the silence and absence of exhaust must not hide heavy problems which may occur at the energy source.

By the way, solar cells on a car a far not enough to run it, but they could add some help, especially on small individual cars. Imagine a small car loading its batteries all day long on a parking, for someone just doing a short run to go to work.

[crabbsaline]

Richard,

I've thought about solar panels. This car comes with an optional hard top. Understanding that the overall design of the car has omitted solar, it would be nice if they made a solar hardtop for this. I'm wondering how much further than 250 miles you could get then? How much more would this weigh, than the normal hardtop option? What would the longevity of the cells be, as compared to the overall longevity of the car?

Also, cheap electric vehicles would be a good thing. But I think much of public opinion is led by popular fashion. By making a sports car, I wonder how much more popular EV's will be to those who normally would not purchase it for frugal, environmental, or political reasons. I'm not fond of "keeping up with the Jones" motivation. But if this type of car becomes a status symbol, then an untapped section of society supports this technology. And that would be a step toward mass production, which would bring the price of this down further. "Keeping up with the Jones" worked with SUV's (yes, there were practical reasons too, but my opinion is that SUV's were partially status oriented"), maybe it can work here.

[Guest_Richard Trigaux_*]

Richard,

I've thought about solar panels. This car comes with an optional hard top. Understanding that the overall design of the car has omitted solar, it would be nice if they made a solar hardtop for this. I'm wondering how much further than 250 miles you could get then? How much more would this weigh, than the normal hardtop option? What would the longevity of the cells be, as compared to the overall longevity of the car?

perhaps solar cells are not very interesting on cars, because a car is small but with a power much larger than the one it receives from the sun. But perhaps it would be interesting in some cases, or with better cells than available today. Anyway the cells must be sedigned to fit an aerodynamical shape, not just add a solar panel of the top of the car.

Also, cheap electric vehicles would be a good thing. But I think much of public opinion is led by popular fashion....

Alas...

Worse than than, it may be that some still think that electric cars are things for hippies.

[djellison]

It might make sense if you could have an intelligent charging system using the solar arrays.

A 30 minute drive to work...

The car sits in the carpark for 6hrs+..at the best time of the day for charging...and then 30 minute drive home.

Allowing for inefficiency in the system - if you could have an array that chucked out power at say, 1/6th of that during driving, you could drive to work - park up, and then when you were ready to leave, your car would already be fully charged again.

Doug

[helvick]

Allowing for inefficiency in the system - if you could have an array that chucked out power at say, 1/6th of that during driving, you could drive to work - park up, and then when you were ready to leave, your car would already be fully charged again.
Doug

OK say you have 3m^2 of surface area to put cells on, live in a reasonably sunny climate and get ~4 hours of peak sun every day (ie 5 kw hours of insolation per m^2 which is close the the continental US annual average) and have pretty good commercial grade solar cells (~12% conversion efficiency), then you get ~2kw hours of energy from a full days charge. That's about 50cents worth of juice give or take. Also bear in mind that the 3m^2 panel will set you back somewhere between $4 and $12K.

The motor(s) in this beauty are listed as having a 185kw peak (~250hp) so you'd only get about 30 seconds of driving at full welly on a days solar charging.

However they do also say that the electrical cost per mile can be as low as 1-2c and that presumably factors in normal driving and the benefits of regenerative braking etc. This site that I found through their links indicates that an AC powered system could require as little as 0.174-0.288 kwhr per mile. Let's assume that we're getting the 0.174 number here and that our entire system loss is around 25% betwen initial conversion, storage and reconversion back to AC.

Your 2kw hours would then be good for about 9 miles.

And the panel would take somewhere between 8 and 24 years to pay itself back.

[djellison]

I didn't say it made financial sense

Doug

[helvick]

I didn't say it made financial sense

It doesn't yet but it's interesting that even now PV is within an order of magnitude or so of being worthwhile.

If 0.174kwhr per mile is realistic (I don't know if it is to be honest) then 50mph cruising would should require about 9kw/hr per hour generating capacity for a system that could charge a car fully on the go.

To get to that you could:
Triple the effective cell area - use the sides of the car and all of the surface area available on a ~3x2x1m car. should be straightforward enough.

Quadruple the cell efficiency - 50% efficient cells would be expensive but should be possible. Not quite impossible but pretty close.

Move far enough South (or North) and get 100% more total solar energy on an average day (say 9 kwhr/day/m^2).

Now instead of generating 2kwhr in a day you would be able to generate 48kwhr per day, with more than 9kwhr/hr for a few hours around midday.

The only real problem is that some bright spark has to come up with a cheap PV technology that gets >=50% conversion efficiency.

[crabbsaline]

Looks like cost will be around $100,000:

CBS Evening News Article

Now I'm curious about what kind of family car they will release in three years. Anybody got a spare 100 grand laying around?