Some new information on the non-US bound solar roof

But you can divide a large pack into sub-sections to do multiple tasks. It is how Hyundai is doing away with the 12-volt starter battery. A small part of the Li-ion does its job.

 

Which Hyundai? The PHEV or the EV? You mean that part of the battery is unavailable for drive? If true I'll be crossing that off my list. Seems like it would be a far easier task to install and program a DC/DC converter to take the place of the 12V.


Unsupervised!

Each battery chemistry has their strengths and weaknesses for each of the tasks assigned:

Lead acid (AKA AGM) batteries like being charged all the time and hate being left uncharged. They are best for when expecting a nearly full charge to do things like starting a car, running 12V accessories like lights (head, turn, signal, etc.), power locks and windows, the radio, etc..

NiMH batteries love being used. Charge them then discharge continuously, but not more than 60% or so. Later construction may allow a higher DoD (Depth of Discharge). They'll last forever at that task. They are a lot cheaper than Lithium based batteries.

Lithium Ion batteries also like being used all the time Just like NiMH. They just happen to hold more energy and are lighter than NiMH.

The problem then becomes making a homogenous battery. Toyota is famous for aggressively keeping the cells within their modules balanced. Far better than trying to rebalance the entire battery when some of the cells gets out balance with the others. This is the problem Honda had with their IMA system.

Also both Lithium and Nickel based batteries do not like being left charged all the time. They like being kept around 80 - 85% charged but then discharged as soon as possible.

Are there Lithium based batteries that are like Lead acid? Yes it's called Lithium Iron Phosphate (LiFePO4). In fact you probably can get a direct replacement for your car's Lead Acid. But they have some significant weaknesses.


Unsupervised!

 

with all these new technologies, it's hard to prove the superior product this early in the game. but some people like to pronounce a winner because it matches their idea of superior engineering, before one has even been produced. as always, 'wisdom is known by her children'.

 

The simple hybrid one. Hybrids and plug ins use a basic 12-volt now for safety and keeping the traction pack charge up. Simply replacing the 12-volt with a DC-DC converter(there already is one for accessories and keeping the 12-volt charged) means leaving the traction pack connected with the high voltage system energized. This will increase the self discharge rate.

I don't know if Hyundai has released the technical details, but they have a section of the pack work as the 12-volt. This gets rid of the 12-volt, while still allowing the main part of the traction pack to be physically disconnected when the car is shut down. Without details, i can't say in this subsection of battery is permanently divided for the main body, or just when the car is off.

For car applications, NiMH is no longer cheaper than lithium for most manufacturers. Best case for the NiMH is that is the same price now. Most likely Li-ion is already cheaper.

We might see improvements with the chemistry of NiMH, but there is a lot more lithium in the world than nickel.

NiMH does work much better in the cold. Your basic Li-ion cell can't be charged if it is below freezing in temperature. There some Li-ion chemistries that can handle lower temps, and work is going on for self heating cells. So it can't be said how long this will be an effective advantage for NiMH.

 

I don't know the -actual- engineering reasons for the battery layout in the Prime with solar, BUT I can give a few educated guess'.

The 12V battery in all Prius is used to "boot up" the computers and to keep them in "sleep mode" when the car is off. However, there is one more thing many on this forum forget, the 12V battery is also a "ballast" to the 12V system, keeping "spiking" to a minimum.

The "traction battery", whether the NiMH one in the "old technology" Prius or the lithium one in the new Prius and Prime -MUST- be -fully disconnected- in some easily accessed and mostly used mode. They chose "off". This is for safety. Anyone opening the hood and "messing around" in there MUST know they won't be electrocuted! Of course, for real safety we are told to use the safety disconnect whenever messing around in there.

I suspect they added the NiMH solar charge battery to keep that power out of the engine area, isolated until "ready" is achieved. And I'm betting there are warnings galore about messing with the solar panel, though I'm sure they use a DC-DC converter/charger in that system, so the dangerous HV DC would only be after the DC-DC converter/charger.
But anything can fail, so isolation is the way!

 

I'm now wondering if the traction battery placement and four seats was all about space for the solar option's components.
Is the solar only available in Japan?

 

Looked like to me from the drawings, that the NiMH buffer battery was right where the middle seat was or took up space the extra reinforcement would need to support a 5th seat. Purely conjecture on my part though.

And yes only for Japan and Europe.
Unsupervised!

 

Maybe the vast cost advantage(?) of installing a separate NiMH battery over any other proposed solution, was too much for Toyota to ignore.

 

If you leave the car 8 working hours in the sun and the car will be able to draw enough energy to go 1000 solar miles per year, maybe the solar panel is not a bad thing for someone who drives 10000 miles annually, especially in this case, where Prime makes sense to customers who drive a few miles.

 

that's 50 bucks at my high (24 cents) cost of electricity.

 

Against $3000 or so for the solar option.

 

8hrs? During early spring, late fall & winter - much if not most of the market areas where the Prius is sold - will get nowhere near 8hrs of optimum sun, due to primarily higher northerly latitudes .... & that doesn't even take into account everything between overcast to foul weather during non-summer solar season/cycles. So your 1,000 miles via the car's little output would take forever.
Plus - a thousand miles/yr is only 20miles/wk or 4 miles/day. That'd be a 2 mile one way trip. That's only an 8 minute bike ride - not even pushing it. You really gona spend > $30K on a car w/a solar panel, just to avoid an 8minute bike ride?
.

 

yup.

 

And you said it with a straight face . . . .
.

 

The solar roof doesn't make sense for me, but it certainly looks cool and adds to the car's futuristic and green image. And for some, that might be just the push necessary to make a sale.

 

I suspect many are sold due to "bundling". You can't have other options unless you get the solar roof.

 

i'm not ashamed of being a couch tater.

 

yea bundling can be an ugly thing. I'd convince a co-worker to buy a Hybrid Camry for his wife. Well his wife noticed that the vanity mirrors on the sun visors didn't have lights. Apparently that's important for women (maybe some dudes too i suppose) while looking at their self at night time in the mirror. You see, if you want those two extra light bulbs in the visor mirrors - it'll cost you an extra $1,500. That's because if you want the lighted vanity mirrors in the sun visors - you have to buy the top-of-the-line sunroof option - that they didn't want ...
Too bad for her - they already took delivery
.

 

how else do you trim your nose hair while driving?

but yes, my wife hasn't opened her sunroof in 8 years. i think one of our daughters did though, when no one was looking.