G23-006: The sunniest spot in a shady yard? Part 1, geometry.

 

This is the first of two posts on finding the sunniest spot in a yard that has shade trees on either side.  This one uses geometry.  The next one will use time-lapse photography on a sunny day.

With any luck, both approaches will tell me the same thing.

If your yard is bordered by shade trees, locate the beds so that due south (180 degrees) splits the compass bearing from your bed to each line of trees.  This gives a surprising-looking result for my back yard.  It’s not at all what you’d naively think, just looking at the trees and the yard.

Garden bed location 1:  Wrong.

I started gardening seriously during the pandemic.  Temporary raised beds were made from recycled campaign yard signs and bamboo.  I placed those in seemingly-reasonable locations in my back yard. In part, they were filling in low spots on the lawn.  But it seemed like they were located so as to get the best sun.

I’m now getting around to putting in something more permanent.  This time, I’m not going to wing it, but instead want to know what spot in my back yard gets the most sunlight.

It’s not obvious.  I have tall trees on either edge of my yard.  And, interestingly enough, what appears to be the obvious solution — locate the garden beds in the middle of the yard, away from both tree lines — isn’t even close to being right.

So, eyeball a couple of birds’-eye views of my back yard, and see if you think I put the beds in roughly the right place:

Looks pretty good, doesn’t it?  You might even say that the location doesn’t much matter, because you’re going to get the same number of hours of sunlight almost anywhere in that back yard, regardless.  What’s shaded in the morning will be sunny in the afternoon, and vice-versa.

Problem is, an hour of sun is not an hour of sun.  Sunlight is much stronger around solar noon, and is weaker the farther you are from noon.  And, because the sun is due south at noon (in the Northern hemisphere), you have to know which direction is south, in order to judge what part of the yard gets the most solar energy.

Source:  Curtonics.com

You need to figure out the locations in your yard that place due south directly between those lines of trees.  Those locations get the greatest amount of high-intensity, near-noon sunlight.

To cut to the chase, you need to calculate where your potential garden site is, relative to the obstructing trees, and to due south.  The sunniest locations in the yard will have these two properties.

  • Due south (180 degrees) bisects the angle from your location to each side of obstructing trees.  E.g., find a spot where the bearing to one set of trees is 150 degrees (180 – 30), and the bearing to the other set of trees is 210 degrees (180 + 30).  That is, you get equal hours of morning and afternoon sun.
  • The angle from your location, to the obstructing trees, is as wide as possible.  For example, the location with a 60 degree spread above will get more total sunlight than a location with a 40 degree spread.   That is, you get as many total hours of sun as possible.

So now, take a look at my back yard, oriented so that south is directly down.  Do you want to change your prior answer?  By the look of the shadows, this is about 11 AM solar time.  Note that the left edge of the yard is already in sunlight.

 


Skirting a couple of pitfalls.

Let me take a brief break to mention a couple of pitfalls that can mess up your attempts to locate your garden in the sunniest spot on the yard.

Daylight savings time.  Man I hate having to get up at 2 AM to turn all the clocks forward, as required by law.  But the upshot is that solar noon occurs around 1 PM during daylight savings time.  For example, on the hourly insolation graph above, peak insolation occurs around 13:00, or 1 PM.  That’s not a mistake, that’s just daylight savings time.  So if it’s summer, and you look to see where the shadows fall at noon, you’re screwing up.  Because noon, daylight savings time, is actually 11 AM solar time.

Above:  Compass set up for 10 degrees west magnetic declination

Magnetic declination.  Declination is the extent to which magnetic north — where the compass needle points — deviates from true north.  Because of magnetic declination, you can’t simply use the raw readings from a standard magnetic compass in order to locate your garden in the right spot.

If you have a compass made for use on land, and it’s anything but the most basic compass, chances are you can adjust the compass to account for declination.

You can find the magnetic declination for your locality at the US Geological Survey, among other places. Currently, magnetic declination at Vienna VA is about 10 degrees west.  That means that the compass needle actually points to a heading of about 350 degrees, not 360 degrees (true north).  That’s about 2.5 degrees further west than when I was a kid in the 1970s.

Magnetic declination is one of those incredibly simple topics that always manages to get an incredibly opaque explanation.  But as long as you have a compass that can be set to account for your local declination, it’s really simple.  The picture above shows a compass set up for 10 degrees west declination.  Despite the fuzziness of the photo, I think it’s obvious that the compass body has been offset 10 degrees relative to the degree ring.  When the needle points to 350 degrees (10 degrees west of true north), 360 or 0 on the degree ring shows you true north.


The sunniest spots in my back yard are directly next to the trees.

I can now take Google Earth, and start drawing in the angles between various backyard locations, and the ends of the lines of shading trees at the sides of the yard.  It’s a little crude, but the conclusion is inescapable.  I put the temporary beds too close to the middle of the yard.  For the most solar energy possible, they ought to be almost under the trees at the side of the yard.  Like so:

Which, to be honest, I would not have guessed, just eyeballing it.

Over the coming weekend, I’ll set up a stop-motion camera to film my back yard for one sunny day.  With that, I should be able to validate that the area that gets the most solar energy is the one outlined.  And I should be able to determine just how much energy I lose if I move away from that optimum spot.

Post G23-005: Wacky weather? No, just seems that way.

 

With last night’s frost, and this afternoon’s snowstorm, I’m trying to think back to the last time we had an 80 degree (F) day. 

Oh, yeah — day before yesterday.

Which got me to asking whether this most-recent temperature swing was unusual.  At Dulles Airport, they went from a high of 80F on Thursday afternoon, to a low of 27F on Friday night.   Or just over 50F swing over the course of two days.

As it turns out, that’s perfectly normal.  Below I’ve plotted the biggest two-day temperature swing, by year, at Dulles, through 2022.

Source:  Analysis of NOAA data, downloaded via https://www.ncdc.noaa.gov/cdo-web/

As you can plainly see, at least one event of this size seems to happen more-or-less every year.  The upshot is that in this part of the country, going from shorts one day to winter coat the next (or vice-versa) does not count as a particularly unusual weather event.

Post #1714: Ah, crap, another 80 MPG trip.

 

I am presently recovering from a severe shoulder sprain.

It was self-inflicted, the result of patting myself on the back too hard.

The problem starts with my wife’s Prius Prime.  It has more-than-met our expectations in every respect.  In particular, as-driven, it typically exceeds the EPA mileage rating, either on gas or electricity.

Lately, I’ve been trying a few techniques to try to squeeze some extra gas mileage out of the car.  Just some around-town trips, driving it to try to keep the gas engine in its most efficient zone.  Which, per Post #1711,  boiled down to fast starts on gasoline, followed by coasting on electricity.  Below, that’s an attempt to stay on the top of the green efficiency “hill”, followed by keeping the gas engine off while driving in the aqua “EV carve out” zone.  (The labels on the contour lines are “efficiency”, the percent of the energy in the gasoline that is convert to motion.)

Results were encouraging.  A couple of test trials showed mid-70-MPG for a series of trips and test runs, entirely on gasoline (using no grid electricity).  Given that the car has an EPA rating of 55 MPG for city driving, I figured I was doing something right.

But at some point, it dawned on me that

  1. the current EPA mileage test is based on the typical U.S. driver (i.e., somebody who drives like a bat out of hell, whenever possible), and
  2. I have no idea what my “typical” city mileage is, because I almost never drive the car, around town, on gasoline.

In short, I made a classic mistake of trying to do an experiment without a control.  I had no baseline to which I could compare my results.  I literally didn’t know what mileage the car would get if I wasn’t fooling around with the accelerator pedal.

I decided to find out.  Yesterday we took a trip out to my sister-in-law’s and back.  About 15 miles, mostly on 35 MPH suburban roads, rolling hills, no traffic to speak of.  Gas only.  Didn’t need the AC or the heat.  Relatively few stop lights.  Driving normally.  (But acknowledging that I’m a light-footed driver by nature, and that monitoring the car via a Scangauge 3 has done nothing but increase that tendency.)

In short, reasonably close to ideal conditions for a trip.

Results:  The odometer clicked over to 80 MPG for the trip, just as we were returning to our driveway.

I am reminded of the following medical advice:  If untreated, the common cold will last a week.  But with proper medical attention, you can expect a full recovery in just seven days.

Thus it would appear, for urban hypermiling in a Prius Prime.  As-driven, 80 MPG, for my suburban area.  No fancy footwork required.

Post #1713: Norfolk Southern Accident History

 

As we all know by now, the cause for the recent Ohio train derailment was traced to an overheated, failed wheel bearing, per the National Transportation Safety Board.

Sounds like a random equipment failure that, in this case, had some bad consequences.

But isn’t that just part of a much larger pattern of neglect, leading to an ever-increasing rate of train derailments?

No.  And that’s easy to say, because, of course the Feds track this.  Of course you can access it.  You just need to bother to look.

From the Federal Railroad Administration, Office of Safety Analysis, Ten-year query form.  Data for 2022 are preliminary through November.

Norfolk Southern’s rate of derailments has been more-or-less the same over the past two decades.  Same for accidents involving hazardous materials.

Obviously, facts cannot possibly compete with the angertainment-fest that has become our national news reporting.  As evidenced by the comments sections on newspaper articles.

But on the off chance that you might have been wondering about this, the answer is no.  For Norfolk Southern, the rate of accidents of this type is about what it has been for the past twenty years.

Post #1712: The Balkanization of EV battery recycling

 

Background:  I can’t get rid of the damned thing.

My wife and I have been believers in electrically-powered transport for some time now.

In 2008, we bought an aftermarket battery pack to convert my wife’s 2005 Prius into a plug-in hybrid electric vehicle.  At the time, the manufacturer (A123 systems) assured us that the battery pack would be fully recyclable, and that they had partnered with Toxco, Inc. to guarantee that.

To be honest, that retrofit never worked very well.  It wasn’t the battery’s fault.  The main limitation was that a Prius of that generation wasn’t really built to function as an electric vehicle.  That placed a lot of limitations in driving in all-electric (“EV”) mode.  Gasoline savings were modest, at best.

Fast-forward to 2012.  A123 had gone bankrupt.  Toxco was no longer in the battery recycling business.  We had a problem with the charger on that battery pack, and decided to have it fixed, in large part because, at that time, there was no way to get rid of the damned thing.  Far less hassle to fix it and keep using it.

At that time, the word was that infrastructure for EV battery recycling was just around the corner.  But from a practical perspective, here in Virginia, we couldn’t find someone to take that off our hands and recycle it.

Fast forward to 2018, and the original nickel-metal-hydride traction battery in that Prius died.  We thought about scrapping the car at that point (177K miles), but everything else was fine, we dreaded the thought of buying a new car.  So we we paid to have the dealer install a new Toyota nickel-metal-hydride (NiMH) traction battery.  (Toyota recycles the dead NiMH batteries recovered through their dealerships.)   But, in part, the decision to keep the car was driven by that A123 battery pack.  We looked around for recyclers, but there was still no way to get rid of the damned thing.

Apparently, EV battery recycling was still just around the corner.

Jump to 2023.  It now looks like that 15-year-old A123 pack has finally given up the ghost.  It will no longer charge.  And at this point, we have no interest in trying to get it fixed, even if we could.  Any money spent on that would be better invested in getting a new purpose-built PHEV, such as a Prius Prime.

I’m sure you’ve guessed the punchline.   I just looked around for recyclers, and yet again, there is even still no way to get rid of the damned thing.

Now, that’s not 100% true.  There’s an on-line ad for a company that, if I give them all my information, might be willing to offer me a quote on how much they’ll charge to recycle my particular battery.  There might be a shop as close as North Carolina that might take it, if I could prepare it properly.  I haven’t bothered to inquire.  My wife’s going to call the dealer who installed it originally, after this three-day weekend, and see if they’ll remove it and dispose of it for us.  (Last time we asked, that wasn’t an option.)

My point is there’s no place within, say, 200 miles, that I can just call up, make and appointment, and drop off the battery for recycling.  It’s all either a custom, one-off service, or requires crating and shipping the battery, or required driving at least hundreds of miles, round-trip, if I can find a place that will take it.

On the plus side, I’m in no hurry.  A fully-discharged lithium-ion battery isn’t a fire hazard.  I’ve checked several sources on that, and that’s the overwhelming consensus.  A completely discharged lithium-ion battery is just dead weight, not a death trap.  You definitely don’t want to try to recharge one and power it up, once it has been over-discharged, as it can easily form internal short-circuits in an over-discharged state.  That can lead to a big problem in a short amount of time.  (And chargers in general will not allow you to try to charge a lithium-ion battery with excessively low starting voltage, for exactly this reason.)  But as long as you don’t do anything stupid — don’t bypass the charger, don’t puncture it, don’t roast it — it’ll remain intert.

On the minus side, it looks like the U.S. EV battery recycling industry is in no hurry, either.  I sure don’t perceive a lot of forward motion since the last time I looked at this.  Worse, what seems to be happening is that the industry is going to get split up along manufacturer lines.  Tesla will recycle Tesla batteries, Toyota will recycle Toyota batteries.  And if you fall into the cracks — with some off-brand battery — there will still be no way to get rid of the damned thing.


My impressions of the EV battery recycling market

I’ve been tracking this market for more than a decade now.  With the personal stake described above.  I thought I might take a minute to offer my observations.  In an unscientific way, without citation as to source.

First, it doesn’t pay to recycle these.  At least, not yet.  That was surely true a decade ago, and my reading of is that it’s still true.  So you’ll see people talk about the tons of materials saved, for ongoing operations.  But I don’t think you’ll hear anybody say what a cash cow lithium battery recycling is.

Second, EV battery recyclers start up and fail at an astonishing rate.  Near as I can tell, none of the companies involved in it, when I looked back in 2012, are still in that business.  I just looked up a current list of companies that cooperate with GM dealers for EV battery recycling, and all the names were new to me.  This “churning” of the industry has been fairly widely noted by industry observers.

Third, we’re still just around that damned corner.  The Biden infrastructure bill appears to have about a third of a billion dollars earmarked for development of EV battery recycling (source).

But surely you realize what that means.  See “First” above.  The fact that the Feds have to subsidize EV battery recycling is pretty much proof that it just doesn’t pay to recycle these big lithium-ion EV batteries.  At least not yet.

Finally, car markers are developing their own captive recyclers, for their own batteries.  Tesla has its own systems.  GM has contracts with a limited number of vendors, plausibly to serve GM dealerships.  Toyota has its own system, for batteries recovered by its dealerships.

That last move makes perfect sense.  Because recycling is a net cost, and yet a significant consumer concern, manufacturers are pledging to take care of their batteries, if they are recycled via their dealers.  But, so far, I’m not seeing any generic recycling capability for (say) any hybrid or EV showing up at a junkyard.  Let alone for my oddball A123 batteries.

Per this article, it currently costs Tesla more than $4 per pound to recycle its lithium-ion batteries.  At that cost, you can see why they might be willing to deal with their own, but they’re sure not going to take anybody else’s batteries for recycling.  It’s not clear that other processes — with less complete recycling of all the materials — are as costly as Tesla’s.  As of 2021, at least one company was in the business of simply warehousing used EV batteries on behalf of vehicle manufacturers, handing batteries replaced under warranty.   The theory is that right now, it’s cheaper to store them and hope for lower recycling costs down the road (reference).

I’m sure that big junkyards and scrap yards have some way of dealing with these, at some cost.  Surely plenty of the (e.g.) Generation 3 Toyota Prius hybrids with lithium-ion batteries have now been scrapped.  I don’t know if they can recycle via Toyota’s internal system, or if … well, I just don’t know.


Conclusion

All I know, at present, is that if I can recycle that totally dead 5 KWH A123 lithium-ion battery pack, it’s going to be either a hassle or a major expense or both.  As long as I can get it recycled, I will.

But, the fact is, until that 2005 Prius actually dies, I won’t have to face up to it.

And, in a nutshell, that characterizes the American market for lithium-ion EV battery recycling.

I’ve decided just to let that dead battery be, and let the 2005 Prius continue to haul around that 300 extra pounds of dead weight.

Because, as we all know, readily-available EV battery recycling is just around the corner.

Post #1711: State-of-charge hypermiling and a generalized theory of pulse-and-glide

Why pulse-and-glide saves gas.

Gasoline engines run most efficiently when under a fairly heavy load.  Load them too lightly, or too heavily, and their efficiency drops.

Below is the “efficiency contour” of a hypothetical 2 liter Atkinson cycle engine. Engine RPM is on the X-axis.  Engine load (output) is on the Y-axis.  The labels on contour lines are percents, and show the fraction of the energy in the gasoline that is converted into motion by the engine.  Those contour lines define a sort of hill, with the peak of the hill — maximum efficiency — occurring when this engine is running around 2500 RPM, putting out about 100 horsepower. And converts just shy of 39% of the energy in the gas into usable power.

Source:  Kargul, John & Stuhldreher, Mark & Barba, Daniel & Schenk, Charles & Bohac, Stanislav & McDonald, Joseph & Dekraker, Paul & Alden, Josh. (2019). Benchmarking a 2018 Toyota Camry 2.5-Liter Atkinson Cycle Engine with Cooled-EGR. SAE International journal of advances and current practices in mobility. 1. 10.4271/2019-01-0249. Accessible though this link.

The engine modeled above is a 2.0 liter Atkinson-cycle engine.  That’s just a bit bigger than the 1.8 liter engine that’s actually in the Prius Prime.  But it’s close enough.

Below, there’s the crux of the problem.  Much of the time, the engine is inefficiently lightly loaded.  I’ve marked the power required to cruise on level ground at a steady 55 MPH in a Prius.  The car only needs about 12 HP.  (I infer this from the ~12 KW of power drawn to keep the car at that speed in electric (EV) mode.   That power, less about a 20% loss in the electric motors, is the energy required at the wheels to keep the car moving forward at that speed.

And so, if you cruise along at a steady 55 MPH on the gas engine, even though the car won’t be burning a huge amount of gas, what little it burns will be burned inefficiently.

Instead of running that engine steadily at 12 HP output, you could alternatively run it hard — run it briefly at 100 HP — then shut it off.  And repeat as necessary.  That’s pulse-and-glide.

And that’s why pulse-and-glide saves gas.  You extract energy from gasoline as efficiently as possible, by running the engine under heavy load.  And then you match the engine output, to the average power required by the car, by cycling the engine on and off as needed.

Traditional pulse-and-glide makes you a rolling hazard.

With traditional (or kinetic-energy) pulse and glide, you first run the gas engine and speed up.  Then switch it off, coast, and slow down.  And repeat.

Practically speaking, this is of almost no value on the public highways, because this makes you a nuisance to other drivers.  It makes you into a rolling traffic hazard.

Potential energy pulse-and-glide requires the right terrain.

Speeding up, however, is not the only way to store the output of the car’s engine.  Going up a hill works just as well.  You store that excess output in the form of potential energy (height) instead of kinetic energy (speed).  Apply gas on the uphills, coast with engine off on the downhills.

I can attest that this most definitely works.  This is how I achieved my last two 80-MPG all-gasoline (no energy from the grid) road trips.

Needless to say, this only works where you have significant hills.  Ideally, hills large enough that the car will maintain the posted speed limit on the downhill with no or minimal energy input from the drive train.

A new/old concept:  State-of-charge pulse-and-glide.

Both methods described above can be done by a standard gas car.  No electric motors are required.  In fact, in a Prius, you achieve maximum efficiency under either method if you never use your electric motors.  (Using the gas engine to charge the battery, then run the motors, wastes about 30% of the power produced.)  Champion Prius hypermilers actually shift the car into neutral on the “coast” phase, specifically to avoid moving electric current into or out of the battery via the motor/generators.

But a plug-in hybrid electric vehicle (PHEV) like the Prius Prime has yet a third option, which I’m going to call state-of-charge pulse and glide.

To be clear, what I’m about to describe is something that the car does, on its own, anyway.  The only question is whether you can modify your driving behavior to take exceptional advantage of it.

If you use the gas engine to charge the battery, then run the electric motors, that wastes about 30% of the energy produced by the gas engine.  So, at first blush, it seems like you’d want to avoid using those electric motors.

But, if you charge that battery at the peak of the gas-engine efficiency curve, that means the electric motors are using up your gas with somewhere around (0.7*38% = ) 27% efficiency.

This leads to the section that I’ve labeled “EV carve out” above.  Roughly speaking, if the driving situation requires less than about 25 KW of power, it’s more efficient to run in EV (electric-only) mode, as long as you can later recharge the battery at relatively high engine load.  (So that the recharge happens near peak gas engine efficiency.)

In the Prius Prime, assuming this engine chart is a reasonable proxy for the actual Prime 1.8 L engine, that has the following practical implication for running the car in hybrid-vehicle (no-grid-power-used) mode.  If you can, you should run on electricity-only up to a current draw of about 90 amps.  That’s the point at which the electric motors, less their inherent 20% loss, are producing about 25 KW of power. That’s the point where switching to gas propulsion is more efficient.

But the closer you get to that 90 amp limit, the less advantage electricity has over gas, and the less gas you are saving.  So, from a battery wear-and-tear perspective, it’s probably best not to push it that far.  You will likely get the bulk of your savings with a more conservative limit of (say) 50 amps, or roughly a “2 C” discharge rate.  (The rate at which the entire EV battery would be dead in half an hour.)  Assuming the car will let you do that, in hybrid mode.

So, a conservative rule-of-thumb is that a power output of somewhere around 17.5 KW (25 HP) is where you should try to flip the car from gas to electric and back.

To be clear, the car does something like this on its own.  At low power demands, it shuts off the gas engine and used the electric motors.

What I have noticed, however, is that there’s considerable hysteresis in the car’s decision.  In particular, once the gas engine is on, it tends to stay on until power demand gets quite low.

So I believe that driver intervention can improve mileage, using (e.g.) terrain anticipation.  If you’re coming to a stretch of road with likely low power demands — cresting a hill, starting a slow deceleration, or just coming up to a level stretch — you may be able to beat the Prius’ internal algorithms.  Conversely, when you see a high-power-demand situation coming up — a hill, say — you can flip the car into gas mode before it begins to bog down in electric mode.

My simple initial rule-of-thumb will be a 50-amp cutoff.  When in hybrid mode, drive the car on the electric motors up to 50 amps current or low state-of-charge cutoff, whichever comes first.  Anything over 50 amps, nudge the accelerator to kick the car into gas mode.

Edit:  I decided to do a little acid test of the concept.  As every driver knows, the worst trips for a gas engine are short, around-town jaunts.  I decided to do a little run to a couple of stores, in hybrid vehicle mode, total trip of about 8 miles, divide into three legs with stops in-between.  After the mandatory gas-engine warm-up period, whenever the gas engine came on/power was needed, I loaded the gas engine heavily.  I gave it enough throttle to bring it immediately to the “power” zone on the dashboard.  But, once up to speed, I let off the accelerator to shut the gas engine off, and drove for as long as feasible on electricity only, respecting a maximum draw of 50 amps.

Results:  71 MPG.  And it was clear that if I’d had a longer distance between stops, that would have increased. 

One short trip does not prove the concept.  And the Prius chastised me soundly for those hard accelerations, basically giving me a flunking score on the eco-meter.  Nevertheless, I consider this first test to be encouraging.

By the book, and by the dashboard readouts, I was doing everything wrong. And yet, it’s hard to argue with the MPG.

Edit 2, 2/19/2023.  Not so fast.  Building on the above, I went to a local disused office building and circled the parking lot.  Roughly a 1.3 mile circuit, 25 hour speed limit, three full stops per loop.  On one set of loops, I tried this hypermiling approach.  On another set, I drove gently, then used the “charge” function to bring the battery state-of-charge back to its original level. 

Results:  In both cases, I got about 75 MPG.  Which, in hindsight, may simply be what the Prius Prime gets, driven in hybrid (gas-using) mode, around 25 MPH.

I think the moral of the story is that I’ve done so little around-town driving in hybrid (gas-using) mode that I’m not sure sure what sort of gas mileage I should expect as a baseline.

Conclusion

Anyone who has ever used the Prius cruise control in hilly country knows that it’s quite “reactive”.  It doesn’t anticipate the hills, but instead holds speed steady, then pushes the car far out onto the power curve in an attempt to maintain speed on the uphill.  For that reason alone, I don’t use the cruise control on hilly roads, as I feel that I can drive the car more efficiently in manual mode, making some modest adjustments in speed on the downhills and uphills.

Similarly, I’m betting I can squeeze a little extra mileage out of the car, in hybrid mode, by manually selecting the point of switch-over between gas and electric propulsion, and pushing the gas engine at high load to maximize efficient use of gasoline.  Then, once at speed, or over the crest of a hill, lifting my foot off the gas briefly to shut the gas engine down, and continuing in electric-only mode as feasible.

You need an extra bit of instrumentation to be able to do that well.  I’m using a Scangauge 3, which will show me quantities such as battery current, engine RPM, and engine output.

What makes this work, as a form of pulse-and-glide, is, of course, the traction battery.  That’s where the excess power production of the gas engine is stored if not needed.  So the right way to view this is state-of-charge pulse-and-glide.  Instead of letting the speed vary (kinetic energy), or the height vary (potential energy), you let the battery state-of-charge vary (electrical energy).

Same concept either way, you just choose a different place to store the excess power output of well-loaded gas engine.  With different implications for how usable pulse-and-glide is, in actual highway traffic, for a given terrain.

Finally, I note that there have been recent patents issued for systems that would automatically pulse-and-glide large trucks, based on a system that anticipates changes in terrain.  They seem to be characterized as a more fuel-efficient form of cruise control.  With everything in modern cars being controlled by a computer, it doesn’t seem too far-fetched to think that some form of automated pulse-and-glide — a fuel-saving cruise-control mode — might eventually become a standard option on vehicles capable of doing it.

With that point of view, driving a gas engine at a constant, low engine load is something of a relic of the past.  It dates to the era when there was literally a metal cable connecting your gas pedal to the throttle body on the carburetor.  With everything computer-controlled these days — and carburetors a thing of the far distant past, for cars — it doesn’t seem like a stretch to ask your computer to do your energy-saving pulse-and-glide for you. As long as you have some safe way to store that excess gas-engine output.

Post #1710: The best thing that ever happened to all my friends’ gas mileage.

My wife bought her first Prius in 2005.  We tend to forget, but there was a lot of hatred expressed toward that car, at that time.  Which sounds hilarious now, but is true.  There was also disinformation spread about that car, similar to the disinformation you’ll hear these days regarding electric vehicles.  E.g., that the Prius had single-handedly ruined Sudbury, Ontario due to the need for nickel for the battery.

There was also a lot of just-plain-ordinary denial.  That car got an EPA-rated 46 MPG, which, for the time, and the size of the car, was absolutely outstanding.  This was a time when you could not find a traditional gas car with similar interior volume that broke 30 MPG.

It was, as I have noted before, alone in its level of efficiency.  That’s expressed below by an index combining gas mileage and interior volume.  (This is my calculation, from EPA mileage data.)

At that time, if you were willing to drive a small car, and required that it get at least a whopping 35 MPG overall, your choices were:

  • Honda Insight (basically, a tiny 2-seater).
  • Honda Civic Hybrid (as shown on the chart above).
  • Three small VW models with 35 MPG turbo-diesels.

This per the federal website fueleconomy.gov.

And yet, I used to joke that my wife’s Prius single-handedly improved the gas mileage of the U.S. automobile fleet.  Because, every time we mentioned 46 MPG, the universal response was, “Big deal, I get almost that good of a mileage in my fill-in-the-blank.”  That Prius was the best thing that ever happened to the gas mileage of all of our friends’ cars.

The first year we owned that car, we heard about all kinds of mythical non-hybrid vehicles that easily got over 40 MPG.  Easily.  All the time.  Without all that fancy hybrid nonsense.

In reality, none of these folks had a clue what they were talking about.  None had actually carefully tracked mileage.  Most had some impression of some road trip they once took where they think they got great mileage.  Nobody was talking about city mileage.  And so on.

But they all knew that hybrids were just so much hype.

As I continue to learn how to drive my wife’s 2021 Prius Prime for greatest fuel economy, I keep setting new personal bests.  Most recently, we drove out to a local scenic byway (the Snickersville Turnpike) and back.  Door-to-door, using “hybrid mode” (no energy from the grid), we managed to get 82.4 MPG over the course of the 80-mile round trip.

That was a mix of 55+ MPH urban arterial highways, country roads, and then small-town streets.  So, no high-speed interstate driving.

Back in the day, people could fool themselves into thinking that their non-hybrid vehicle was just about as efficient as a Prius.  Even though the U.S. EPA clearly said otherwise.

But this most recent generation of Prius, when driven with an eye toward best mileage (Post #1624), gets such eye-popping numbers that I don’t think you can kid yourself any more.  This is now my second trip where I’ve ended around 80 MPG, driving the car in hybrid mode (i.e., not using energy from the grid.)  Even our interstate trips now routinely yield high-60’s MPGs (admittedly, without the extreme speed limits present on Western interstates.)

And, separately, more than 70% of our miles are run purely on electricity from the grid.  Which means the 65-to-80 MPG observed in hybrid mode is our version of gas-guzzling.  In “EV mode”, using the battery and not the gas engine, we manage somewhere around what the EPA would term 150 MPGe.

This isn’t by way of bragging.  It’s by way of setting the record straight about what’s routinely and reliably available these days.  For not much money, as new car prices go.

I continue to read articles about how hard it is to move to electric transport, what a huge expense it entails, and so on.  And, yeah, you can make it hard, and you can make it expensive, and inconvenient.

But none of that has to be true.  Buy a quality plug-in hybrid electric vehicle (PHEV).  If you’re like us, you’ll get most of the benefits of electrical transport and none of the drawbacks.  Sure, you have to have some faith in the technology.  You need to learn the do’s and don’t of taking care of that big battery.  In a few areas,  electricity is currently a more expensive fuel than gas, by a modest amount.  But as far as I can tell, hybrids started out pretty good, and they just keep getting better.

I’m no longer satisfied when I only get 80 MPG, driving my wife’s hybrid.  And I find that absolutely mind-blowing.

Post #1707: Nobody offers a warranty on the electric range of their plug-in hybrid vehicles?

 

Edit 2/11/2023:  I grossly underestimate the replacement cost for a Prius Prime lithium-ion battery.  Per this thread on Priuschat, the cost of new Prius Prime battery, from the dealer, is $12,595.  Others suggested the dealer took some markup, as the list price from Toyota is just under $10,000.  I say, potato, potahto.

In round numbers, the cost of a new replacement battery is 43% of the cost of a brand-new Prius Prime, base model, current MSRP $28,770.  As a footnote, literally none were available in North America, and the battery has to be shipped directly from Japan.

I should put in the usual EV-weasel-wording:  By the time the battery dies, there will be plenty of good-used batteries in junkyards, from wrecks.  That did, in fact, happen with the original Prius NiMH hybrid battery.  Plus, there may be much cheaper aftermarket replacements at some point.  And so on.  But right here, right now, what I cited are the hard numbers for battery replacement cost.

Original post follows.

Only Volvo offers any warranty on your plug-in hybrid electric range, near as I can tell.

And I think I have finally nailed down why that is.

A typical battery guarantee for a fully electric vehicle (EV) is that a car will lose no more than 25% of range in 8 years/100,000 miles.

Based on research shown below, using actual driving behavior, for a Prius-Prime-like plug-in hybrid electric vehicle (PHEV), you would expect about 5% of batteries to fail, under that 8-year, no-more-than-25% loss definition.  Just from normal wear-and-tear, as-typically-driven.

So, my guess is that PHEVs don’t get those guarantees because manufacturers would end up replacing too many batteries.

All the more reason to treat your battery gently.


Background

Last week, I found out that my wife’s Prius Prime had no warranty on its electrical range.  Currently, as we drive it, we get mid-30-miles on a charge.  But if that drops to zero, tough.  As long as the car will still run as a hybrid, they battery has not “failed” under Toyota’s 10-year/150,000 mile warranty.

So I got curious.  I already have a list of all 2022 plug-in hybrid electric vehicles (PHEVs), from a just-prior post.   I decided to look up the warranty information for as many manufacturers as I could find.

Here’s the results.

Volvo offers a 30% loss-of-range warranty.  If you lose more than that, during the eight-year warranty period, they’ll fix it.

Near as I can tell, none of these other manufacturers offer any warranty whatsoever, on the electrical range of their PHEVs.

Toyota
Kia
Porsche
MINI
Ford
Chrysler
Mitsubishi
Jeep
Hyundai (I think)
BMW (but maybe they decide case-by-case?)

The Hyundai warranty covers EVs, PHEVs, and hybrids, and in separate places says that it definitely covers loss of range, and that it definitely does not cover loss of range.  Your guess is as good as mine, but I’m guessing they cover range for EVs (as required by law) but not for PHEVs.

Originally, I could not understand why Toyota offered no PHEV range warranty.  That situation has now improved.  I’m now baffled why almost nobody offers a PHEV range warranty.

Unfortunately, I think that “no PHEV range warranty” is the industry norm  for precisely the reason stated in the Toyota warranty documents:

 

I’m an economist by training, and I find it this interesting, I guess. When there’s a de-facto industry standard, there’s usually a reason for that.

And I think I understand why no-PHEV-range-warranty is the industry standard.


How many would “fail” under normal driving conditions?

I’ve been searching for an answer for this for the better part of a week.  I posted my thoughts on preserving battery capacity on a chat side dedicted to the Prius (PriusChat), and with a few exceptions, got met with derision.  For sure, nobody there had ever heard of a Prime or the prior version (Plug-in Prius) showing any signs of premature loss of range.  Almost nobody thought that any sort of battery-protecting behavior was necessary.

I finally came across what I believe is a realistic projection of the fraction of Prius-Prime-like vehicles that would fail under the typical EV warranty of no more than 25% range loss in eight years/100,000 miles.

That’s:  Comparison of Plug-In Hybrid Electric Vehicle Battery Life Across Geographies and Drive Cycles, 2012-01-0666, Published 04/16/2012, Kandler Smith, Matthew Earleywine, Eric Wood, Jeremy Neubauer and Ahmad Pesaran
National Renewable Energy Laboratory, doi:10.4271/2012-01-0666

They used actual driving data from about 800 trips taken by Texans in PHEVs.  The then extrapolated that to eight years of driving behavior.  Their model is not quite perfect, as the modeled vehicle only provides a 10% “buffer” at maximum allowable charge, while the Prius Prime provides 15%.  On the other hand, for the key chart, they did not include (e.g.) the effects of high temperatures on battery life.  (So, no parking your car in the sun in this model, so to speak).

Here’s the key graph, where the most Prius-Prime-like vehicles is the PHEV40.

Source:  Cited above.

In a nutshell, only counting the wear-and-tear from normal driving and charging, they expect the average user to lose 20% of range by the end of the eighth year.  And about 5% of users would experience in-the-neighborhood-of 25% range loss.

If they were to throw in the effects of variation in climate (hot climates kill batteries quicker), and variation in practices regarding storing the car fully charged (which also kills batteries quicker), I might guess that around 10% of drivers might exceed that 25% loss threshold within an eight-year warranty window.

To put that in perspective, car manufacturers as a whole spend about 2.5% of their total revenues on warranty repairs (reference).  A ten percent failure rate of this part, replaced at new-battery cost shown above, would by itself account for (roughly) 4 percent of Toyota revenues from Prius Prime sales.

As far as I’m concerned, this solves the mystery of the missing warranty.  (Almost) nobody offers anything like the standard EV warranty, because if they did, they’d have to replace an unacceptably large fraction of batteries under warranty.  And that would lead to an unacceptably high warranty cost.

All the more reason to avoid unnecessary wear-and-tear on a PHEV battery.

Post #1706: When is electricity the cheaper home heating fuel?

 

Today the Washington Post had an article on electric heat pumps displacing oil and propane in Maine.  Not only do modern heat pumps work reasonably well in that cold climate, but they were reported to save a lot of money, compared to oil or propane furnaces.

I had a hard time believing that they were big money-savers, as electricity rates in New England are pretty high.  So I decided to check the math, using reasonably current prices and some reasonable guesses for technical performance of each type of heating.

The answer is yes.  If you replace on old, inefficient oil stove with a heat pump, you should expect to cut your heating bill in half.  Probably more interestingly, not even a modern high-efficiency oil furnace can compete with a heat pump, at Maine’s prices.

But I note one fact that makes Maine’s situation different from that of Virginia, where I live.  I don’t think you can get natural gas most place in Maine.  It would be slightly cheaper to heat with natural gas, at national average prices, if you used a 95% efficient natural gas furnace.  In Maine.  Given Maine’s high electricity prices.

As a final footnote, near as I can tell, the interesting thing about these new generation heat pumps is that they will work in extreme cold.  Near as I can tell, they are not hugely more efficient that the prior generation, as long as temperatures are moderate.


But what about electricity versus natural gas, in Virginia?

Source:  Clipart Library.com

My home heating system was designed by the internally-renowned HVAC engineer Rube Goldberg.  The original 1950s gas-fired hot water baseboard heat is now the secondary heating system.  That’s run by a 95%-efficient gas furnace, which also provides domestic hot water.  Layered over that is the new primary heat source, consisting of two elderly ground-source heat pumps, fed by just over a mile of plastic pipe buried in the back yard.

I have pipes, wires, and ducts running every which-away.  In the house, throughout the yard.  In the attic.  Under the slab.  Up the outside of the house and over the roof (no joke).

It works.  Except when it doesn’t.  As was the case this week, when the super-efficient gas hot water heater failed.  That finally got fixed today.  Which is what got me thinking about this.

From the standpoint of carbon footprint, after I put that high-efficiency gas furnace in ten years ago, I was more-or-less indifferent between electricity and natural gas as the fuel source. Pretty much the same C02 per unit of heat, either way.

But as the Virginia grid has more than halved its carbon footprint over the past two decades, electricity has become by far the lower-carbon option.  (Underlying source of data for both graphs is the U.S. EIA).

Every once in a while I revisit the issue of cost, mostly because natural gas prices fluctuate all over the place.  Using the same framework as above, here’s the current match-up between my ground source heat pumps (with assumed coefficient of performance of 3.3), and my 95% efficient gas furnace.

Turns out, at current prices, and with my setup, electricity now beats the pants off natural gas, cost-wise.  Not hugely different from the situation for oil in Maine.  I didn’t expect that, and I’m pretty sure that’s a consequence of currently high natural gas prices.

In any case, it’s nice when you can do well by by your bank balance by doing right by the environment.

My only real takeaway is that I should minimize my use of gas-fired secondary heating, within reason.  I figure if the citizens of Maine can get by with nothing but heat pumps, I should be able to do that as well, in the much milder climate of Virginia.