Category: Analysis

Anything that I have tested empirically, or explain with detailed calculations, or just generally bother to get all the facts straight.

Post #1789: The deadweight loss of credit card rewards

 

There are good reasons that economics is called “the dismal science.”

“The Deadweight Loss of Christmas” (Google reference for .pdf) is surely a case in point.  In that scholarly analysis, a Yale economics professor takes the time and effort to quantify the economic inefficiency of Christmas gift-giving.

The idea is simple.  If you buy something for yourself, you know exactly what you want.  By contrast, if somebody buys you a gift, they have to guess what you’d like.  And to the extent that they guess wrong — by a little or a lot —  the value of the gift, to you, may be well be below the purchase price.  And that gap between what the gift-giver paid, and what the gift-recipient would have been willing to pay — that’s the deadweight loss of Christmas.

Economists have a simple (if entirely soulless) solution:  just give money.  The gift recipient can then buy themselves exactly what they want, and the total satisfaction or “utility” of the transaction is maximized.   A gift of money eliminates the deadweight loss involved in trying to guess somebody else’s preferences.

A different deadweight loss

Which brings me to my newly-acquired, soon-to-be-cancelled Best Buy credit card.

I made a major electronics purchase a few weeks back.  The sales clerk at Best Buy talked me into getting a Best Buy credit card.  Normally, I say no to all such offers.  But the deal was that this would give me an instant 10% off the not-inconsiderable sales price.

Cash back, right?  Who would turn that down.

Only, this credit card doesn’t work like that.  What I actually got was, in effect, store credit.  I got “rewards” equal to 10% of the value of the purchase.  Rewards that could only be redeemed in Best Buy merchandise.  Worse, that’s how the card works for all purchases made on it.  There is no “cash back” feature.  All rebates are in the form of additional “rewards” that can be cashed in for Best Buy merchandise.

I guess this is a fairly good deal, if you have an ongoing need for the stuff Best Buy sells.  But I don’t.  Worse, I’m on a tear to get rid of stuff, the process of Döstädning, or Swedish death cleaning (Post #1667).  The last thing I need is yet another electronic doo-dad or small appliance.

And so, what ensued was not unlike the deadweight loss of Christmas.  I wasn’t given specific gifts, for sure.  But in order to get my money’s worth, in effect, I had to choose my gifts out of a catalog of stuff that I didn’t really need or want.

For something that was free*, it was a surprisingly grueling process.

*  As a responsible parent, and an economist, whenever my children used the f-word (free) around me, I would immediately snap “pre-paid”.  So I use the term loosely here.   The plain fact is that the cost of all such givebacks has to be worked into the original purchase prices, so that Best Buy can remain in business.  So these “rewards” aren’t free, they are merely pre-paid.

At my wife’s suggestion, I went for batteries, because those are consumables, and we’ll eventually use them up.  Once I got past about $50 worth of alkaline batteries, I was stumped.  But, gosh darn it, I was not going to leave money on the table.  So I spent hours swapping stuff into and out of my on-line shopping cart, in an attempt to get things I might use, whose prices summed to just over the total “rewards” I had been granted.

I recall buying a flashlight.  And a pocket knife (a.k.a, future contribution to the TSA).  Because you can always use another one of those.  The rest of it is a blur.

I hope I’ll be pleasantly surprised when the packages show up.  Or at least recall that I ordered it.

In any case, once I’d finally made my purchases, and burned up those rewards, I had the funny feeling that I had come across this process before.  But it took me another day to realize that what I was experiencing was the deadweight loss of Christmas.

In effect, I gave myself some gifts that I didn’t much want.

For sure, if there had been a straight-up cash-back option, I’d have taken it.  In fact, in hindsight, if they’d offered me half that dollar amount, as cash back, I’d have taken it.

Thus validating the fundamental insight of The Deadweight Loss of Christmas.

Post #1788: Recycling plastics, Part 2: My Town tells me to do the wrong thing. Does yours?

 

I am in the middle of looking at plastics recycling in my area.

Any internet search in this area feeds you a lot of pessimism about the entire concept of plastics recycling.  People say that it’s not worth doing, that it’s greenwashing, that it’s a scam, that it all ends up in the landfill, and so on.

But is that true?  It all seems to start from a figure that just 5 to  8 percent of U.S. waste plastic is recycled.

Less than an hour of internet search, and I now know that figure is totally irrelevant to the situation I’m investigating.  The often-cited 5% is for every conceivable form of plastic waste — stuff that was tossed in the trash, stuff that was tossed on the ground, plastic resins that are not recyclable, plastic items that are not inherently recyclable, plastic integrated into multi-material items, and so on.

That’s a problem, for sure.  But right now, I just want to know what happens if I properly handle a recyclable plastic object, where I live.  I want to know two simple things:

  • What plastic should go in the recycling bin, here in Vienna, VA, and
  • What fraction of (say) a clean #1 (PETE) bottle actually gets recycled?

Continue reading Post #1788: Recycling plastics, Part 2: My Town tells me to do the wrong thing. Does yours?

Post #1786: Least-effort applesauce

 

Peel, core, and quarter apples.

Way too much work.

  • Wash, peel off the plastic produce stickers.
  • Toss into a pressure cooker.  Add a cup of water.  Heat slowly to avoid scorching.  Cook for eight minutes at pressure, followed by natural release.
  • Mash the results.
  • Run that through a Foley mill.
  • Sweeten to taste.
  • If necessary, boil to reduce to the desired thickness.

The back story here is that I got a great deal on pears at my local Safeway, a few weeks back.  I thought I was buying green-skinned pears for 99 cents a pound.  What I actually bought was a bag of completely unripe yellow-skinned pears.  Which I then set aside for just a bit too long.  Hence, the need for a quick way to turn them into pear sauce.

In any case, I’m not one of those people who truly enjoys cooking.  I cook in order to have something to eat.  The less effort and less energy input, the better.

To be clear, I didn’t think this up.   My wife routinely makes apple sauce by quartering the apples, tossing them in a slow-cooker, and then running the results through a Foley mill.

My key innovations were to be too lazy to quarter my over-ripe pears, and too impatient to let them cook in a slow cooker.

Thus, pressure-cooker-Foley-mill pear sauce.  The results are a bit “rustic”, in that the occasional particle of cooked pear skin makes it into the sauce.  IMHO, it’ s not worth the effort of peeling them, to avoid that.  YMMV.

Post #1781: No comment on electric vehicles

 

The Washington Post just published one of its weekly anti-Electric-Vehicle (EV) screeds.

This thing:  https://www.washingtonpost.com/climate-environment/2023/04/15/electic-cars-biden-epa-climate/

And, God help me, I just spent a couple of hours posting comments.  I gotta stop doing that.

My wife suggest that I compile and post all my comments. Think of it as a collection of short, related essays.

Sometimes, thoughtful comments in the Post allow me to discover something new.  As in red, below.  But my main takeaway from all this is that I have to stop commenting on Washington Post articles. Continue reading Post #1781: No comment on electric vehicles

Post #1779: Approaching tax day, so it must be time to start planting

 

I paid my Federal and state income taxes yesterday, so that means it’s almost time for our last frost date.  This, in Northern Virginia, Zone 7.

This post is a bit of a potpourri regarding

  1. taxes,
  2. last frost dates,
  3. paper pots, and
  4. whatever happened to seed starting mix?

1:  The joy of tax-free vegetables, or how to misunderestimate the value of food gardening.

Source:  U.S. Bureau of Economic Analysis.

The oddest facts I can recall from my education in economics have to do with the National Income and Product Accounts.  That would be GDP accounting, to you civilians.  Back in the day, I had to memorize most of the major details of how Uncle Sam figures out the value of Gross Domestic Product.  (Back then, Gross National Product, which is a slightly different concept.)  For reasons that totally escape me, bits of that stick with me 40 years later.

Most people have a vague understanding of GDP.  It’s something like the total market value of all final (for-consumption) goods and services produced by U.S. citizens and their capital.  And, in general, things that don’t get traded via a market simply don’t get counted.

Except sometimes.

In some areas where something of value is consumed, but there’s no market transaction, Uncle Sam just kind of makes up a number.  These are the imputations in the GDP calculation.  And these imputations are legion.

So, in 2021, US GDP was $23.3 trillion.  But of that, $3.5 trillion (17%) is made up — that is, imputed.

I’m not here to dump on those imputations.  IMHO, those imputations are necessary, well-thought-out, and about as accurate as they can reasonably be expected to be.  The numbers are better with them than without them.

I just wanted to point out an historical artifact.  One of the formal, major imputations in U.S. GDP accounting is a $200M imputation for the value of food that is grown and consumed on the farm, and never makes it to market.  (That’s circled in red above.)  Without going into the details (about 2% of Americans live on a farm), I make that GDP imputation amounts to about $30 worth of farm products, per-farm-resident-capita, consumed on the farm.

Arguably, we only have that adjustment because farms were a vastly more important part of the economic landscape when GDP accounting was first developed.  That all took place in the Great Depression, at which point we still had about 20% of the U.S. population on farms or ranches.

Source:  Farm bill fairness.org

The key point here isn’t necessarily the size of the adjustment, it’s the reason they had to make an adjustment.   There’s no money transaction for food that is grown and eaten on a farm.

Not sure how accurate the underlying Federal figure is (it doesn’t matter, so I’d be surprised if a lot of effort went into it.)  I’m fairly sure that one of the reasons it’s low is that this only accounts for the products of the farm enterprise.  For a corn farmer in Iowa, it would be an estimate of the fraction of the corn crop they eat, rather than sell.

Just taking that at face value, I’m guessing that my back-yard vegetable garden produces that much.  A few hundred dollars’ worth of vegetables per year, say.

That’s a drop in the bucket, in our overall spending on food in and out of the home.

But it’s a very sweet drop, in that it’s not taxed.  If you buy groceries from the store, you’re paying with after-tax dollars.  Roughly speaking, if you earn wage income, all things considered, depending on your income and where you live, you probably need to earn around $1.50 in order to buy $1.00 worth of groceries.  That’s my rough estimate of the effect of Social Security and Medicare taxes, state and federal income taxes, and sales taxes.

I have just two points here.  If you’re working out the math of value versus expense for your vegetable garden, be sure to multiply the difference by 1.5.  Because that’s how much income you don’t have to earn, if you replace store-bought produce with your garden-raised produce.  In terms of income avoided, it’s worth more than just the prices you’d pay at the store.

Second, don’t just think of home gardening as a way to get exercise and grow fresh produce.  Think of it as a way to stick it to the tax man.  Legally.  As with all forms of D-I-Y production, there’s no money payment for the final product or service (and you are not engaged in a barter-based commercial enterprise), so there’s no tax due.

My tomatoes taste all the better for it.

2:  Last frost dates and improved weather forecasting.

This is just a quick recap of my utterly incomprehensible post G21-005.

Source:  Garden.org.

Springtime last frost dates aren’t hard numbers, they are probabilities.  Briefly, take the last 30 years or so of temperature data for your area.  Take the low temperature recorded for each day.  And, for any given day in the spring, just count how often you saw a frost on that date or later, in the past 30 years.

In my case, over a reference 30-year period, there was a frost in 10% of the years, following April 21st.  So April 21 would be my 10th percentile last frost date.  If the climate is stable, then nine years out of ten, if I plant my frost-sensitive plants on that date, they’ll survive.

But those are simple, crude averages.  They assume that you will plant on a given day, regardless of the coming forecast.  My guess is, they were developed in an era before we had reliable long-range weather forecasting.  Likely you’d get a forecast for a day or two out, but not much more than that.  So weather forecasting just didn’t figure into the picture.

But now, we have reliable five-day forecasts, reasonably reliable 7-day forecasts, and possibly even some forecasting skill in 10-day forecasts.  But the entire process of calculating last-frost dates hasn’t adjusted accordingly.

The upshot of that is that what’s labeled my 30th percentile last-frost date above is actually my 10% percentile or better.  For the simple reason that if there is frost in the forecast, I won’t plant.  But if I hit the 15th with no frost forecast for the next week, excluding major forecasting error, I’m guaranteed to make it to the 21st — my 10th percentile frost date — with no frost.

The presence of an accurate 7-day forecast converts what would have been my 30th percentile last frost date into my 10th percentile.

Either way, having paid off the tax man, it’s now time to start thinking about setting out those frost-sensitive vegetables.  Peas and potatoes went in on St. Patrick’s day.  It’s now time to get the rest of the spring garden planted out.

3.  Paper pots.

Source:  Last year’s garden.

This year I finally gave up on using peat pellets for seed starting.  Those are incredibly convenient, but seem to leave a lot of plants root-bound.  As with the comparable tomatoes grown with and without peat pellets, above.  Note the much more developed root structure on the plant without the peat pellet.

Instead, I’m doing my seed starts in paper bags.  This, as laid out in one of my Wordless Workshop posts (Post G22-012).  I figured, for 2 cents each, it was easier to use a pre-made paper bag than to go through the hassle of making my own paper pots.

But even the smallest commercially-available kraft-paper bags are a bit too large for most of my seed starts.  And potting soil costs money.

So I finally tried making paper pots out of old newspaper.  Only to find out that it’s ridiculously easy.

After reading about a dozen sets of contradictory instructions, and looking at various gizmos for making paper pots, I decided to wing it.  Picked up some some tabloid-style papers that I had on hand, plus a skinny wine bottle, and some sopping-wet potting soil.

There’s no need to wet the paper, no need to use a device, and so on.  Just realize two things.

  1. Until you fill the pot, the only thing holding it together is your hand.
  2. Once you fill it with sopping-wet potting soil, and set it down, it’s nice and solid.

So, in order, and without illustrations, assuming you are right-handed:

  • Rip a tabloid newspaper sheet along the center fold.
  • Fold the resulting half-sheet once, to make a long thin strip.
  • Wrap that long strip around the bottom of a skinny wine bottle, letting the paper extend beyond the end of the bottle, by almost the diameter of the bottle.
  • Fold that extended paper over in three of four places to form the bottom.
  • Briefly mash the bottom against the table top to set the creases.
  • Pull the paper pot off the wine bottle, cradling the bottom of the pot in the palm of your left hand,  and fold down a 1″ “cuff” around the top of the pot with your right hand.  The point of the cuff is to lock in the seam where the paper strip ends.
  • At this point, the pot is still quite fragile and will fall apart if you take it out of your hand.
  • Fill with very wet potting soil, still cradling the bottom in your left hand.
  • Set it down carefully in a tray.

Any idiot can do it.  No device needed.

4:  Woke potting soil?

A final oddity in this whole process is that the “soil” I’m using for seed starts this year is completely different from what I used last year.  Compared to what I used last year, it’s nasty stuff.  Coarse, full of little sticks, and quite clumpy.

I’m pretty sure it’s the same brand I used last year.

And it absorbs water right out of the bag.  The old stuff, I used to have to coax it to get wet.  Pour water into the bag of potting mix and knead it for minutes to get it uniformly damp.  This stuff, I just use the watering can and it’s instantly wet.

It finally dawned on me what has changed.

Best guess, they’ve taken the peat out of the potting soil.  The stuff I got in the past looked so nice — and absorbed water so poorly at first — because it was a peat-based potting soil mix.

Peat — peat moss — is now officially Frowned Upon as being unsustainable.  At least in some circles.  But this is, of course, disputed in other circles.  I haven’t cared enough to try to form an educated opinion.  I guess when it comes to Canadian imports and the environment, I’m far more worried about the Alberta tar sands. (Or whatever they are called these days.)

That said, just by buying a cubic foot of peat-based potting soil each year, I’d have been a typical U.S. consumer of it.  The most recent figure I could find showed that the U.S. imported 420,000 tons of peat moss from Canada in 2022.  That’s down from about 480,000 in 2000.  (That info courtesy of the U.S.G.S.)  That’s (420,000 x 2000 / 360,000,000 = ) 2.3 pounds of peat per capita per year, on average.

In any case, it’s probably just an odd coincidence.  The year I finally swear off peat pellets for seed starting, my potting soil supplier appears to have switched away from peat-based potting soil.

I’m not so attached to the old mix that I’ll even bother to try to hunt some down.  It was just unsettling to find that a product I’d bought for years was now something almost completely different, in the same old bag.

Post #1776: Gas versus electric mowing, Part 6: Why I’m not buying a battery-powered mower

Weird, eh?  I’m happy to rely on a (mostly) battery-powered car.  But I don’t want a battery-powered lawn mower. Even though I used a plug-in electric mower for years.

I swore off battery-driven power tools years ago.  So, for me, it’s not as if this is some new stance.

In this post, I explain why.  Why I’m not going for a battery-powered mower.  And why I no longer buy any power tools that run on batteries.

Let me emphasize that my decision isn’t due to ignorance.  If anything, it’s because I’ve had too much experience with big lithium-ion batteries.

A few things about lithium-ion batteries.

Practically speaking, your sole option for a walk-behind battery-powered mower is lithium-ion batteries.  There have been some riding lawn mowers powered by lead-acid batteries.  But I don’t think there’s anything on the market today not powered by lithium-ion batteries.

Point 1:  Maybe you can recycle them.

Almost no lithium-ion batteries are recycled in the U.S.

I’m acutely aware of this because a) I bought a 200-pound lithium-ion add-on battery pack for my wife’s Prius in 2008, and b) recycling of those big lithium-ion batteries has been just around the corner for the past 15 years.  I think my most recent post on that was Post #1715.

Still don’t believe that lithium-ion is rarely recycled? Here’s a handful of relatively recent references.

That last reference is particularly illuminating.  Read down to the part where the Federal government is still at the point of offering cash prizes for anybody who can figure out how to do it cost-effectively.  Its not merely that lithium-ion batteries aren’t recycled, it’s really that there’s not even one good, standardized, agreed-upon process for doing it, let alone doing it cost-effectively.

Post #1712 has the details, but the reason for the lack of recycling is obvious.  It costs money.  Reportedly, Tesla currently pays $4/pound to recycle is lithium-ion batteries.  Even with that, the cost of post-recycled lithium is higher than that of virgin lithium, making it an uneconomic source for production of new batteries.

Still, some stores — around here, notably Home Depot — have boxes where you can drop off old batteries weighing under 11 pounds.  That should cover most lawn tool batteries.

That’s free to you because Home Depot covers the cost of processing those via call2recycle.  This is an organization whose funding comes from battery- and battery-powered device manufacturers, or from organizations willing to pay to recycle those batteries.   For example, their board of directors has representatives from Panasonic, Sony, Energizer, and Duracell, among others, based on their 2021 annual report.

You can see examples of their retail pricing on this page.  It looks like they charge about $2.50 a pound to take boxes of mixed rechargeable batteries off your hands.  So Home Depot is paying on-order-of $12 to allow you to dispose of a 5-pound lithium-ion lawn mower battery.

What happens after that is a bit unclear to me.  For sure, the value of the materials recovered appears trivial.  Here’s their 2021 Annual Report, showing revenue sources.  Less than five percent of their revenues comes from the materials recovered from those batteries.

Source:  call2recycle 2021 annual report.

They do not break out their collection and recycling costs separately.  Combined, those account for the bulk of their costs.

At any rate, they are clearly at least paying to have those batteries disposed of properly.  What fraction of the materials actually ends up in new products — is actually recycled — is not possible to determine from their annual report.

Interestingly enough, when I look up their lithium-battery recycling partners, the only U.S. partner appears to be a 2021 startup.  Which again seems to emphasize just how iffy lithium battery recycling remains, at this time.

Fifteen years.  For fifteen years, I’ve been living with a 200 pound LiFePO battery pack.   And for fifteen years, large-scale lithium-ion battery recycling has been just around the corner.  Which is right where it is today.

Point 2:  Batteries trade lower fuel cost for higher capital consumption cost.

Which is a fancy way of saying, if you want to keep using the tool, you have to keep buying batteries.

We replaced the nickel-metal-hydride traction battery in my wife’s (now son’s) 2005 Prius somewhere around 178,000 miles.  Doing the math, the cost of that new battery ate up roughly half of the total lifetime savings in gasoline costs, from driving that efficient hybrid compared to a similarly-sized non-hybrid 2005 vehicle.

But it’s not just the dollar cost.  It takes quite a bit of energy to manufacture batteries, something that contributes to the multi-year “payback period” of a Prius relative to a non-hybrid automobile.  For the first couple of years that you drive a hybrid, from a carbon-footprint standpoint, all you are doing with your lower fuel use is paying back the higher energy cost of the vehicle’s manufacturing.

In particular, worst-case (made-in-China, meaning, made using coal-fired electricity), large-format lithium ion batteries result in the release of roughly 200 kilograms of C02 per KWH of battery capacity (calculated from this MIT reference, 16 metric tons per 80 KWH battery pack).

And so, creating a typical lawn-mower battery — 0.3 KW (72 volt, 4 amp-hour)  would result in (200 KG/KW x 0.3 KW * 2.2 lbs/KG = ) 132 pounds of C02 released into the atmosphere.

I use 2 gallons of gas a year to mow my lawn.  That generates about 40 pounds C02 per year.  The upshot is that even if my electricity were carbon-free, I’d spend the first three years of battery-powered lawn mowing merely paying back that initial 132-pounds-of-C02 debt, for the manufacture of that disposable battery.

That’s not a huge surprise, to those of us who have been using big battery-powered objects.  It was an estimated two year payback period for a 2005-era Prius, where the battery and motors didn’t really power the entire car.  So, a three-year payback period for a small tool that’s entirely battery-powered?  To me, based on my experience with the Prius, that seems entirely plausible.

As for the energy cost of the rest of it, I’ll just point to the high energy cost of smelting copper.  Electric motors require quite a bit of that, which is another reason hybrids require more manufacturing energy than non-hybrid cars.  Plausibly, depending on expected lifespan, there may be no manufacturing energy savings in the non-disposable portions of the devices.

For an extremely-long-lived battery, such as one used in a car, that payback period usually isn’t much of a consideration.  You’re saving a ton of fuel, and the battery will typically last well over a decade.  Overall, it’s a winner, even if you fully acknowledge the energy cost of producing the battery.

Here’s the kicker:  How long do those lawn-mower batteries last?  Every website I visit seems to give the same answer of three-to-five years.  So they might last long enough to pay back that initial carbon-footprint debt.

The upshot is that a lithium-ion powered lawn mower is a fine way to reduce local air pollution.  It may not be such a winner from the standpoint of reducing your carbon footprint.  And since global warming/carbon footprint is my main concern, I’m not hugely attracted to those devices from an environmental standpoint.

In addition, knowing what I now know about lithium-ion batteries, I’d bet on the lower end of that three-to-five-year range.  My wife’s new Prius — a Prius Prime — arguably contains a $12,000 lithium battery pack.  With no warranty to speak of.  So I got kind of serious about not trashing that.  And that’s when I learned the rules for lithium-ion batteries.  See Post #1703.

The rules, in brief:  Lithium-ion batteries don’t like heat.  They don’t like to be fast-charged.  They don’t like rapid rates of discharge, either.  And they really don’t like being worked from fully charged to fully dead.  They much prefer shallow charge-discharge cycles.

And yet, every manufacturer seems intent on using them in all the wrong ways, in mowers.  These will see highest use in the heat of summer, and typically be stored in a non-climate-controlled space.  Everybody seems to charge their lawn-mower batteries at a “1 C” rate of charge or higher — from dead to fully charged in one hour.  (Presumably, that’s to all ow you to swap batteries continuously and mow very large lawns.)  I’m pretty sure manufacturers allow the full capacity of the battery to be used, unlike cars that reserve the top and bottom 10 to 15 percent as a buffer against over– and under-charging.  (That’s why a 72-volt battery pack can be advertised as 80 volts, because once you’ve absolutely fully charged it, that’s what it’ll read, despite the fact that charging it to that degree is bad for battery life.)

Point 3:  If you love buying name-brand inkjet cartridges, you’ll enjoy purchasing batteries for your lawn mower.

Here, I’ll just refer to the highest-rated 21″ walk-behind battery powered mower on Amazon.  This is the Greenworks Pro 80V 21″ model, with 4.0 Ah battery.

On Amazon, the complete mower, with battery and charger, is $425.  But the replacement 4.0 Ah battery, by itself, costs almost $300.

In short, your cost of the replacement battery is 70% of the total cost of the functioning lawn mower.  And, as with power tools of all sort, manufacturers go way out of their way to make sure that only their batteries will fit their tools.

This, more than anything else, is why I swore off battery-powered shop tools.  It’s the monopoly-exploitation aspect of the battery replacement.  Once you’ve bought into a particular manufacturer’s line, they’ve got you.  And as far as I was ever able to tell, generic batteries manufactured to fit those tools are all completely dreadful.  So if you want a battery that works, for that name-brand tool, you pay that name-brand price.

Once I bought my third $45 battery pack, for my $60 drill, I did eventually figure out that a battery-powered drill is an expensive way to make holes in stuff.   That drill eventually got to the point where battery packs were no longer available.  (Which, if you own one long enough, will happen.)   At that point, it too became just another particle in our great national solid waste stream.  And was replaced by a corded drill.

Point 4:  Caginess about power.

This is more of an irritation than a point of substance.  But take any battery-powered lawn mower on the market, and try to find out the peak power of the electric motor, expressed either as kilowatts or as horsepower.  Nobody will tell you that basic information.

At some level, the average power output is just basic physics.  The mower above has a 72-volt, 4 amp-hour battery, and claims to be able to run for an hour on that.  That should be sufficient to cut my half-acre lawn.

But do the math.  How much energy is at your disposal, for that hour of mowing?  Well, 72 volts x 4 amps = ~300 watts of average instantaneous output.  Or, over the course of an hour, you have 0.3 KWH of power available to you, to accomplish your hour of mowing.  For sure, your peak power output will be much higher than that.  But if that battery is going to last an hour, it can’t put out more than an average of 300 watts, over that hour.

One horsepower is about 750 watts.  So the average available power output is less than half a horsepower, if you’re going to get your hour of mowing out of that battery.  Again, peak output will clearly be many multiples of that.  But that’s what you have, to get through your lawn, on average, over the course of an hour.

In my case, there are parts of the lawn, at times of the year, that nearly stall the Honda 3.3 KW gas engine that runs my mower.   I would love to know that some prospective battery-powered mower has a peak power output that meets or exceeds that 3.3 KW instantaneous power output.

But here, I bring up the last thing I know about lithium-ion batteries.  If that battery could, in fact, produce 3.3 KW of instantaneous power, it would be discharging at more than a “10 C” rate.  (That is, at that rate, the battery would be dead in less than one-tenth of an hour.)  Discharges at rates like that are unambiguously bad for battery life, for traditional cylindrical-design lithium-ion cells.  So even if it could match the peak power of my current mower, I’m not sure I’d want it to.

In other words, just as was true for my old corded Black-and-Decker, I’m pretty sure that the mower will get through my lawn.  But I’m also pretty sure that I’m going to have to “baby” it when the going gets really tough. 

But short of buying one and using it, there’s no way for me to tell, because manufacturers do not disclose peak power output of these mowers.  And so, how well will some battery-powered mower cut through stands of uber-thick Zoysia grass?

Instead of providing me with the concrete information that would allow me to judge that, manufactures require that I take a guess.  And when I see something like that, I assume it’s because their product would appear in an unfavorable light, if that information were disclosed.

Let me put it this way:  If those battery-powered lawn mowers had peak power that exceeded that of a typical gas mower, you can bet that manufacturers would crow about it.  So I think the absolute silence regarding peak power output tells me more-or-less all I need to know.

Point 5:  Summary

For the time being, I’ve decided to continue using a gas-powered lawn mower.  It’s a modern overhead-valve design, and (best guess, see prior post) mowing produces as much smog-forming pollution per hour as driving a mid-2010s-era sedan for an hour.  That’s clearly a downside, compared to battery-powered mowing, but not an extreme one.  For good measure, I’ve tossing my antiquated gas can in an effort to keep my gas-powered mowing as clean as possible.

My main environmental concern is global warming, and it’s not clear that a battery-powered mower offers much advantage there, compared to gas.  That’s due to the carbon-intensive nature of lithium-ion battery production and the relatively short expected lifetime of those batteries in fairly harsh use conditions.

Otherwise, not switching to battery-powered mowing is mostly a question of avoiding annoyances.  No mower maker will bother to tell me peak power.  So I suspect that will be lacking.  Each mower maker uses proprietary batteries.  So I expect to pay an outrageous amount for them.

And the whole lithium-ion battery-recycling thing is one big question mark.  Yes, you can drop your dead lawn mower batteries off at Home Depot, and Home Depot will cover the cost of getting them recycled, to some degree.  The degree to which the material in these batteries is actually re-used is far from clear.

So that’s it.  I saw a compelling reason and significant gains from switching car transportation to electricity.  There, at issue was a considerable amount of gasoline burned per year, batteries with an extremely long projected life-span, and some guarantee of responsible end-of-life recycling via Toyota.  Maybe. And the driving experience is better under electricity than with gas.  For mowing the lawn, by contrast, at issue is just two gallons of gas a year, there’s no clear benefit in terms of carbon footprint, and I’m betting that it’s harder to mow with a battery-powered mower than with a modern gas mower.

So this is one area where I’m not going to electrify the task.

Post #1775: Gas versus electric mowing, Part 5: Finally, a sensible estimate

To cut to the chase:  I use a 21″ push mower with a modern Honda overhead-valve engine.  Starting from EPA data on emissions for engines of that type, I calculated two simple rules of thumb, for the pollution generated by my lawn mowing.

If the standard of comparison is the typical car on the road — call it a mid-2010s full-sized sedan — then gas lawn mowers are 100 times dirtier than gas cars, per horsepower.  And an hour of mowing generates about as much pollution as an hour of driving.

That’s just the mower.  That doesn’t include emissions from your gas can, as outlined in the just-prior post.

Also see Post #1776, explaining why, despite this level of pollution, I’m not going to switch to an electric mower any time soon.  This, even though I drive an electric car (Post #1924, et seq.) Continue reading Post #1775: Gas versus electric mowing, Part 5: Finally, a sensible estimate

Post #1774: Gas vs. electric mowing, part 4: A correction on vapor recovery, and why you’re not supposed to top off your car’s gas tank.

 

In my just-prior post, I was about a decade out-of-date in my understanding of the gas vapor recovery systems installed on U.S. gas pumps.  I’m going to correct that here.

  1. Gasoline vapors are a major contributor to photochemical smog, and, in particular, to the creation of ground-level ozone.
  2. Once upon a time, the U.S. EPA required that gas pumps in some urban areas have vapor-recovery nozzles.  These were designed to collect the gasoline vapors that would otherwise just pour out of your car’s gas tank as you refilled it.
  3. By and large, these were only mandated in areas that could not meet federal air pollution standards for ground-level ozone.
  4. But by 2006, virtually all new cars and trucks were equipped with on-board vapor recovery systems.  They collected their own gasoline vapors during refueling, stored them, and burned them
  5. In 2012, the EPA dropped its requirement for vapor-recovery nozzles (reference).  At that point, so many cars had the new on-board systems that the vapor-recovery nozzles no longer offered sufficient benefit to justify their cost.
  6. Whether or not gas stations were required to keep up those vapor recovery systems was left up to the states.  For example, Virginia chose to decommission all those vapor recovery systems in 2017 (reference).

The upshot is that gas pumps in my area haven’t had those vapor-recovery nozzles for more than half a decade.  They still have some sort of rubber cup on the fuel nozzle, but I guess that’s just to prevent splashback or possibly to aid the car’s own on-board recovery system.

Some implications

With this, a lot of things now click into place.

Vehicle fuel tank filler necks now have an elastic seal in them.  I’m sure that older cars did not have those.  That seal is required on a modern car because the on-board vapor recovery system needs a tight seal against the gas nozzle.  That’s the only way to make sure that the gas vapors in the tank end up in the on-board charcoal canister.

The standard advice of “Don’t top off your tank” now has a new rationale.  In the ancient past, that was the advice because gas expands as it warms, and if you topped off your tank in summer, you’d end up spilling gas out the fuel filler as you drove down the road.  Now, that advice is there to protect your on-board vapor recovery system.  If you top off you tank, you can end up shoving liquid gasoline into your vapor recovery system, something it was not designed for.

My old two-gallon gas can produced four gallons of gasoline vapors before I even considered spills, venting, and the gasoline-permeability of the plastic.  Every time I filled that at the gas pump (since 2017), that displaced the two gallons of vapors, in the gas can, into the atmosphere.  And then, as I repeatedly filled the tank on the mower, that sums up to another two gallons of gasoline vapor displaced into the atmosphere.

How does that compare to gasoline vapor emissions from cars?

The EPA estimates that these on-board vapor recovery systems capture about 98% of gasoline vapors, at least according to this presentation.  The same source shows that the EPA estimates an average of 0.32 grams of gasoline spilled per gallon dispensed at a typical gas station.

The U.S. averages about 650 gallons of gasoline consumed per licensed driver.  Based on that, a year’s worth of fill-ups, for the typical licensed driver in the U.S., would generate:

  • 13 gallons of gas vapor spilled directly into the atmosphere (2% of that 650 gallons).
  • Another 12 gallons of gas vapor due to the average 208 grams of fuel spilled (0.32 g/ gallon).

In other words, the average driver with properly-functioning vapor recovery equipment and average diligence about spilling gasoline will generate about 25 gallons of gasoline vapors annually.

In that context, the 4+ gallons of gas vapor directly emitted by my old gas can seems quite material.  Particularly because my wife and I now exclusively drive her Prius Prime.  We seem to use on-order-of 40 gallons of gas a year, with the rest of our travel being electric.  From that 40 gallons, based on those EPA averages, we’d only be emitting about 1.5 gallons of gasoline vapor per year.  So that, in our household, the lawn mower and old gas can were responsible for far more gas vapor emissions than our car was.

That said, it’s worth noting that the lawn mower — even with the old gas can — is nowhere as bad as the average American passenger vehicle, in terms of venting gas vapor to the atmosphere as a result of refueling.  That’s not because the lawn equipment is clean — it’s not.  That because the average driver uses such a vast quantity of gasoline.  Even those small fractional losses during refueling add up to far more gasoline vapor than the lawn mower / old gas can emit in a season.

But that’s only for refueling-related gasoline vapor losses.  That does not include any gasoline vapor losses by the mower during operation.  For example, losses through the charcoal-filled gas cap, losses from the vented carb bowl after engine shutoff, and so on.  I still need to track those down.

The new gas can ought to eliminate half of those “displacement” gas vapor emissions.  The new can vents through the end of the pouring spout, so it’s “inhaling” the gas fumes out of the tank as it puts new gas into the tank.

The only gas vapor that will be directly emitted as a result of displacing vapor during refueling will be from refilling the gas can, at the local gas pump.  That, because our gas pumps no longer have vapor-recovery nozzles.  And apparently haven’t had them since 2017.