Your math doesn't add up. The installer doesn't pay back the $3500, the tax break does, so the installer gets $4k not $500. And the consumer only gets back $3500 if they owe that much in taxes on top of all the tax deductions they're already getting.

<div class='quotetop'>QUOTE(MikeSF @ May 2 2007, 07:18 PM) [snapback]434364[/snapback]</div>

Consumer pays $4,000 to have the conversion done.
$3,500 goes for the complete kit.
$500 goes to the installer

Finally the consumer gets $3,500 back on their taxes.

Net consumer expense is $500

<div class='quotetop'>QUOTE(Cheap! @ May 2 2007, 08:45 PM) [snapback]434414[/snapback]</div>

Don't count your credits before they are itemized. Quite a few people got an unpleasant shock last year when they discovered after the fact that they did not qualify for the hybrid credit. If memory serves, the plug in credit is in the same section of the 1040 as the hybrid credit.

Yea, I know but it just makes me so mad when a bill it pushed through say oh yes you can get a tax break but only if company x does the work. If you do your own or if A123 does it, or if Altairnano does it, or if Duracell does it, or if you do it yourself you should be able to qualify for the tax credit if you pass the 100mpg emission tests.

I'm not falling for that tax credit thing again! Is it a full $3500 credit or like the $3150 Prius credit that very few people received the full amount?

<div class='quotetop'>QUOTE(Cheap! @ May 2 2007, 10:40 PM) [snapback]434494[/snapback]</div>

IMO legislation is always written for the special interests, sometimes some public good comes of it. Remember the Golden Rule. He who has the gold makes the rules. Would it be a coincidence if company x or its trade association were found to be big campaign contributors?

I was not aware that the Do It Yourself Plug in Prius was in the $4000 price range. I may need to buy a kit, who assembles the kits?

Let's make the math as simple as possible:

Assume your Prius gets 40mpg after upgrade: the $10K battery only is used for the first 40 miles every morning.

Assume you can recharge during the day for your ride home.

Assume the cost of electricity is $0.90 / gal, which I have seen computed elsewhere.

Assume you pay $3/ gal for gasoline.

Ignore the interest you forfeit by spending the $10K

Then you save (3-.9)*2= $4.20/day

Assume you drive to work 300 days a year.

Then you save $1260 per year, or $6500 in 5.15 years.

Reducing carbon emissions by half and giving terrorist the middle finger instead of cash = Priceless

<div class='quotetop'>QUOTE(fan-atic @ May 4 2007, 08:51 AM) [snapback]435369[/snapback]</div>

That's a reasonable calculation, but might be optimistic for a couple of reasons. Kind of a best case scenario, from my standpoint. For me, the way I drive, I think the Hymotion pack is not even close to cost effective. But I'm going to buy one anyway.

I think that calculation assumes two full discharges per day, 300 days a year, or 24,000 electric miles per year. I don't drive anywhere near that so I'm not going to save that. Well, of course.

What's not obvious is that, contrary to the way Hymotion describes this, I don't think you'll ever be able to get all-electric miles out of it. So you can't figure on driving a bunch of 90-cent-a-gallon (all electric) miles. That's based on some discussion in a thread here about a year ago, although the Hymotion site appears to contradict that.

Anyway, Hymotion says you'd use no gasoline below 55 kph. But my understanding is that the Prius conversions still do all the things a Prius would do -- they just kind of make the Prius think the battery is overfull. So the ICE will still have to run some. Why? Because you still need to have the ICE ready for hard acceleration -- the motors alone won't cut it. In that case, the PHEV Prius would still do all the things the Prius does to keep the ICE in a state of readiness -- warmup at startup, probably runs it to maintain some minimum temp in the winter. And you certainly need to run it in winter if you're one of those wimps who actually uses the heat in the car in the winter. And run the ICE when you want hard acceleration, even at city-driving speeds. And run the ICE at highway speeds.

So, where Hymotion describes this as if you'd never turn on the ICE in city driving, well, I think that's a bit of an approximation. And everyone says the ICE has to run at highway speeds.

On that thread a year back, somebody ventured that you'd get no more than 80% electric in city driving, less on the highway. I don't know if that was data-driven or just a guess. So, on net, you'd never get those 90 cent-a-gallon miles. At best, you'd get $1.32-a-gallon miles (that's 80/20 electric gas), and if you did a lot of (e.g.) high-speed highway, youre cost per mile would likely be higher still.

Still, the point is that you can't just tap a bunch of 90-cent-a-gallon miles. At best you get some mix of gas and electric miles, so your average cost is higher.

Empirically, Calcars claims 85 mpg equivalent for theirs, but those are more like prototypes and I am sure they don't have 40 mile packs. Still, that's a far cry from the 150+ mpg equiv you'd get from all electric -- so it clearly implies a much lower share of electric than you'd think would be reasonable. If I did the math correctly, the Calcars 85 mpg-equiv statement implies an average 50/50 mix of gas and electric miles. So, with their PHEV, in effect, only half the miles are electric, in effect, on average. It's not clear how relevant that is to the Hymotion conversion but it is a published benchmark.

What kind of cost-per-mile you'll actually get does not seem to be posted anywhere on the Hymotion site, which is kind of a pain given that they've had a bunch of these out in fleets. So they surely must know. In fact, that Hymotion site needs to be updated in a lot of ways. Not only do they not give any empirical data on actual observed fuel cost per mile, they still say they guarantee the batteries just two years. At two years, that's a nonstarter for me. If they want my business, they need to post the actual observed cost per mile and the actual warranty they plan to offer me. Given that the seem to want my $10K starting 7 months from now, it would not be too soon to start posting the correct relevant data on their website.

Anyway, I tend to be a bit conservative, so I'm working from the Calcars 85 mpg equivalent number until Hymotion posts something to the contrary. Between fewer miles and much higher estimated cost per mile, I think the savings for me are going to be a lot lower. I don't think this comes close to paying for itself, for me. But I'm still going to buy one, as long as Hymotion will say it'll last something like 10 years.

It seems like this needs to be done on a case by case basis. If you have a really short commute that you can do on surface streets, you might be able to do most if not all EV driving a lot of the time. Those quick trips to the store would also be covered. By putting the car in EV mode you'd skip the warm-up cycle and thus, would get all electric miles.

However, for most people it'd be like you said, really good mileage still burning gas, just some amount less (maybe 30% less?).

<div class='quotetop'>QUOTE(tripp @ May 6 2007, 01:02 PM) [snapback]436393[/snapback]</div>

Well, that's the crux of it right there. Blow off my comments about winter heat and such. Will that conversion let me put it directly into EV mode? My wife and I discussed this, as we have the EV mod. If so, I take back some (but not all) of what I said. As long as I keep the acceleration below what'll kick it out of EV mode, then I can toodle around town as an EV. Now that would be worth the price of admission right there.

OK, I'm a dummy. Found a discussion of a purchse of one of these by the Fairfax Co VA gov't, a poster said exactly that: it uses the native EV code to prevent ICE startup below 34 mph. What I ought to do is track down the right guy in Fairfax County and ask what combined mpg-equiv mileage the car has gotten for them.

I just did the rational thing -- I emailed the guy in the Fairfax County gov't who is driving the Hymotion Prius, see if he'll share some mpg numbers with us. Maybe the deal with hymotion prevents that, but ... we'll see. If he tells me, I'll post it here.

lovely mate. Hopefully he can give us some real world numbers.

<div class='quotetop'>QUOTE(chogan @ May 6 2007, 02:24 PM) [snapback]436437[/snapback]</div>

Got a very nice response back from Mr. Duval. The car was put into fleet use five months ago and it's not clear that got a clean test of the mileage. For whatever reason, Hymotion puts a battery cutoff switch on the dash, Mr. Duval found it in the off position a couple of times. So their average mileage was low, but it's not clear that all or even most of that was actually PHEV. On his last trip (Fairfax to DC and back), Mr. Duval got 97 miles per gal of gasoline, over 47 miles driven. That seems more in line with how the car ought to perform.

He pointed me to some materials from Argonne labs. There, they quote Hymotion as expected only 100 MPG-equivalent (gas + electric) in routine use. So, that's modestly better than the observed 85 out of the CalCars conversions, consistent with the slightly larger battery pack. Argoone has a draft paper (I could not find) showing higher mileages, but I think those were theoretical optima, not observed -- not sure, could not track it down.

http://www.transportation.anl.gov/pdfs/HV/393.pdf


I also found out from the Argonne materials that the "50 km" rating is for mixed mode driving -- it's not 50 KM on the battery pack, its an average 50 km (31 mi.) of mixed gas/electric before the pack depletes. That matched Mr. Duval's observation -- that the pack typically clicked anywhere from 24 to 33 miles.

Anyway, my take on this is about where I started. Between the actuals on the Fairfax car and the materials are reported in the Argonne presentation, I'd be expecting maybe a bit better than the 85 mpg equivalent that the Carcars PHEV is getting.

<div class='quotetop'>QUOTE(JimN @ May 2 2007, 08:20 PM) [snapback]434484[/snapback]</div>

I'm not aware of many people claiming the credit and not benefitting from it. Two obvious exceptions would those who didn't really owe a lot of tax to begin with, and those who are subject to the AMT. People who fall into those camps would have difficulty benefitting from most any tax credit. Were there additional quirks about the hybrid credit that made it difficult to claim?

EDIT:

OK, looked at the other 3 page thread about the credit. Damn, the IRS didn't make it easy to claim that. A lot of people were subject to AMT, too.

One more point about the Hymotion conversion that was reported as being said by Argonne, though I could not find the original Argonne report.

The Hymotion PHEV puts out more total unburnt hydrocarbon and more N0x than the stock Prius. That's because the engine is not warmed up and kept warm, so it burns less efficiently and the catalytic converter operates less well. (Recall that in other thread some knowledgeable poster noted that the lack of EV mode in America was due to EPA requirements, not battery warranty issues. EV mode will also prevent the Prius from doing the warmups required to keep emissions down).

This may or may not be an issue depending on whether the EPA wants to make it one. The issue being that you're not supposed to tinker with a "rated" car in a way that raises emissions. One of the other PHEV conversion offerers has a "California" mode where the car will warm the engine and keep it warm to comply with the rated emissions level - and uses more gas accordingly. I have to believe that even with the dirtier exhaust, the car is still pretty clean in an absolute sense. Nevertheless, Argonne is reported saying that the Hymotion PHEV will run dirtier than a stock Prius.

The way the system works is you can have all EV. No emissions.
or
You have EV assist at highway speeds where the engine runs and warms up.

The only way you would have a problem is if you drive below 40 mph for a while and then at 45 for a moment while the engine warms up and again at 40 mph for a long time so the engine cools way down again. By that time you would have used up all your second pack, and gone back into normal hybrid mode again.

Cheap!,

I have doubts you are correct.

As I understand the Prius, the hybrid will exit EV mode if the absolute speed is over ~ 35 mph, or if power demands exceed about 20 kW. Once the ICE turns on, it will stay on until it has gone through the four or so stages of warm-up, including bringing the Cat to spec operating temperature.

IMO, the practical consequence of this is that I can expect to go through ICE warm up every start-up, unless the system is still hot from a very recent drive. I'd love to see numbers of how many Kwh this takes in freezing, cold, warm, and hot conditions. Just from daily driving I'd guess 2 - 5 miles.

Perfect for me, btw. A 5 mile drive is bicycle distance, while most of my jaunts into the 'city' are around 20 miles. This upgrade will not fit everybody, but I suspect many, particularly if the owners are a bit flexible in modifying their transport patterns to make the most of it.

<div class='quotetop'>QUOTE(EricGo @ May 16 2007, 02:01 PM) [snapback]443511[/snapback]</div>

That's my understanding as well. If you drive it below 34 mph and accelerate slowly enough (and I guess, don't use the cabin heat) you stay in EV mode. Otherwise you run the engine, hence the Argonne observation of more of some pollutants from the Hymotion PHEV Prius than a stock Prius.

Another thing that is not clear until you read the Argonne materials is that the Hymotion conversion apparently does not allow the ICE to charge the batttery as long as you are in PHEV mode (until the PHEV pack depletes). That means the ICE runs less efficiently than in the stock Prius -- if the car can' load the ICE by charging the battery, then the ICE spends more time at inefficient load levels.

I think all of that goes a long way toward explaining the relatively modest gains in efficiency from the aftermarket PHEV Prius conversions -- compared to what you might possibly get based on a calculation of total electric miles that are available.

For Argonne, the context of their research was some speculation on what the optimum approach to PHEV should be, for the typical driving cycle, for a parallel hybrid. I get the impression that 1) the fact that Hymotion and (many) others can do this at all is pretty cool, but 2) the aftermarket conversions that piggyback on the stock Prius electronics result in a car that isn't optimized for PHEV use. You get a PHEV Prius but not an optimized PHEV Prius -- I think that was the gist of what Argonne was after.

I think this makes a serial hybrid look somewhat better, at least in this context. Not starting the ICE at all would be a plus. If the next generation is going to have built-in PHEV capabilities, that might shift the balance in favor of a serial hybrid. The Volt could be a real winner as an urban commuter car.

But none of this deters me. A whole lot of (my wife's) Prius miles are below 35 mph and require only modest acceleration. I think an inverter and a small space heater would solve the cabin heat issue. If Hymotion offers it in 2008 with a decent warranty on the battery, I'll buy it.