Prius software cuts possible electric only range by 80 percent
I went to the PHEV Symposium in Washington we mentioned yesterday. I talked to Bob Bruninga about his solar powered Prius. Bob's pitch is solar power is perfect for electric cars and hybrids because that's where you get the payback. Solar power for your house makes less sense says Bob because your house has easy access to cheaper electricity. You can watch Bob talk about the logic of using solar power on electric cars below the fold.
I asked Bob how much of an improvement he got in the electric-only range of the solar Prius. Bob said the batteries are doubled but he gets more than a double in electric-only range. How? You would not know this unless you looked at your Prius battery indicator constantly but: The Prius battery never goes below about 60 percent charge. At some point around 80 percent charge, the Prius software starts to do things to make sure the battery never goes dead.
So if you increase the capacity of the battery, you could get larger than expected improvements in electric-only range because the point at which the Prius pretends the battery is dead is much higher. Logically, Bob should get four miles on electric power only but Bob says he can get 6. Before you run off to hack your Prius software to increase your mileage and save a lot of money on gas, remember that Toyota has set the software to increase the life of the battery.
Reader Comments (Page 1 of 1)
Luis E. Julia 4:58PM (2/04/2008)
I just purchased a 2008 Prius. I am getting the advertized "new" EPA MPG results from the vehicle.
However, I am very upset at the under-utilization
of battery power. Toyota won't tweak, discharge and recharge rates in order to extend the life of the battery.(Forever?)
I ran across a us company who claims to have a simple kit that would allow battery only under certain circumstances.
The name of the Co. is Coastal Electronic Technologies at www.coastaletech.com Are they for real?
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bob Bruninga 12:19PM (2/14/2008)
I stand by the math. Please see the web page:
http://www.ew.usna.edu/~bruninga/APRS-SPHEV.html
The premise is not that this is a good investment for a Prius. The premis is that if your house is ON-GRID but you want to invest X$ in solar panels for back-up power, then it is more cost effective to put them on the roof of your car than permanently stuck on the roof of your house where you dont need them 99.99% of the time.
On the Car, I can take solar power where I need it in the field. And when I dont need it anywhere else, the Prius is happy to use it too. (Offsets about 25 cents per KWH gas cost on the roof of the prius compared to 10 cents per KWH on my house.
Each hour in full sun (200 Whrs) equals about one mile of Prius driving (200 Whrs).
Bob
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wayne 1:14PM (9/20/2007)
I've attended Toyota events where their engineers explained that the Synergy hybrid system is programmed to keep the battery between 20 and 70 percent charge. They don't want it to be fully drained nor fully charged, as that will reduce the life of the battery. Keeping it between that 20 and 70 percent mark makes the batteries last for the life of the car.
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Lascelles Linton 1:30PM (9/20/2007)
I think Toyota should let you drain the battery and get better mileage if you like or at least sync it up with the mileage. I bet there are plenty of people out there now that drive more than average, i.e will have short car life, that are really missing out. The software starting to do something about 70 percent charge also seems a bit much, no? I would really like to see their number on how much it actually extends the life of the car.
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rgseidl 5:28PM (9/20/2007)
California ZEV legislation lets manufacturers claim credits toward compliance if they sell HEVs and/or other qualifying ultra-clean vehicles. The catch is that once you claim credits, the technology is considered an emissions reduction strategy and must therefore last 150,000 miles.
That means mollycoddling the batteries to make sure they last. The alternative is to allow deeper discharges and bake the cost for the expected warranty repair into the purchase price up front. However, replacing the batteries after ~75,000 miles is expensive relative to the dollar amount saved by more aggressive hybridization - unless you're willing to bet the replacement pack will be cheaper to produce because it uses more modern technology.
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RockStoneSteel 8:42PM (9/21/2007)
This guys math is way off base. His justification for using solar on a vehicle as opposed to a house is totally whacked. Any electricity gleaned from the tiny panels on a vehicle is quite insignificant. That electricity probably can't even overcome the additional drag on the drivetrain posed by the aerodynamic inefficiencies of the panels themselves, not to mention the added dead weight.
While the logic of piggybacking the battery makes sense in the video, again his math is quite off base.
I suspect this guy is simply playing on the guilt ridden consciences of tree huggers ...attempting to part the greenies from their greenbacks!
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