Consumer Reports "The mpg gap"

energy loss for electricity occur in several places...

It takes 0.3kwh of electricity for the local electric utility to distribute/pump 1.0 kwh of electricity from my residential 120 VAC outlet.

A typical 120VAC battery charging station loses/uses 20% of power during the recharging process,
i.e. typically about .80 kwh is transferred to the battery for ever 1.0 kwh power used by a 120vac recharger.


A typical 240VAC battery charging station loses/uses 10% of power during the recharging process.
i.e. typically about .90 kwh is transferred to the battery for ever 1.0 kwh power used by a 240vac recharger.

 

Cars with stop-start idle technology normally turn off the engine will not burn gas during *idle time* unless there is a heavy passenger energy load, e.g. the Air Conditioner/Windshield defroster/cabin heat running. Do you know if the CR test loop requires that the Air condition or Windshield defroster or cabin heat is running?

 

A moron in the City crashes his car and gets 0 mpg while the mechanic runs diagnostics on the car on a lift to figure out how much damage was done .... We have plenty of morons on the road where I live - no testing is required to see them in action where I live ....

 

But do they? CR has never released anything regarding their fuel economy testing protocol that would stand up to a peer reviewed journal. They complain about the EPA test, but are unwilling to put their testing up to the same scrutiny.

While I doubt they do, and they have never said they did, let's assume they do adjust the numbers for these uncontrolled variables. Which are many. In cold temperatures, a smaller engine will lose more heat than a larger one. Is CR's hypothetical fudge factor one size fits all, or another way to phrase it, does it ignore the efficiency loss differences of different sized engines? Or do they use different adjustments based on the engine's mass?

We don't know because they don't share the details. We don't even know if the test drivers have to sweat or freeze it out, or if they use heat, AC, or open the windows. All of which have an impact on the fuel economy.

By the why, the amount of math involved in coming up with an adjustment coefficient for all the variables is on par with climate modeling.

 

...probably not if they are trying to make plug-ins look good. Sorry could not resist.

 

IMHO that is really why YMWV. We have different routes and different temperatures that we travel. These have a large impact on mpg of a car no matter how you drive. AFAIK consumer reports has taken no pains to try and have their route validated to the average american drive. If we believe the Car and Driver article, the EPA ha also not attempted to create an average american drive either, their route is one from long ago. The EPA 5 cycle test is superiour to consumer reports in many respects though. They do account for hot and cold conditions, and they do test validity against real cars and real hybrids. That is one reason the gen II prius dropped a much higher percentage than most cars on the revised 2008 test.

The 4 of the 5 epa tests also has more gentle acceleration and braking than most users experience. It seems like, but we don't know the figures, that consumer reports seems to accelerate and brake harder than american car drivers. I would give this a wash, EPA favoring hybrids, Consumer reports hurting hybrids. Neither is real world, so how can Consumer reports say they are finding fault with the EPA test? The only thing I can think of is it makes news, it sells the story whether it is true or not. There is a certain segment of the population that wants to believe hybrids are bad.

We can often not choose our commutes. Mine gives much worse fuel economy than many on this board. I don't like you cherry picking the easy loop anymore than consumer reports choosing the hard one.

Consumer Report city, highway fuel economy doesn't make sense | PriusChat

The real problem I have is not the combined figure but the city figure of 32 mpg for the prius. That just doesn't even pass the smell test of real world. Car and Driver does much better than this in there reportedly mashing the pedals. Except for the new ford hybrids C&D normally says if you drive like a hybrid driver you can get epa figures, how can consumer reports report a real world figure that is much worse than car and drivers self described fast driving bad case mileage?

 

Hi walter, I think we have gone over this a lot before, and it really is simply on the mine/sun/well to plug/pump, nothing to do with Consumer reports.

There is something very wrong with your utility if there is a 30% loss from the the utility plant to your plug. A typical figure is 7%.

The EPA includes charging losses in mpge calculations, but they often will use the L2 charger, a L1 charger may have greater charging losses. In your example you seem to think L1 is only 90% as efficient as L2, if that is correct, and I have no idea, multiply mpge by 90% if using L1.

The thing that makes mpge well/mine/sun to wheel so difficult is we don't do this at all in mpg, and never have. At least in mine or well to pump the losses in conversion are tight, probabbly ranging from 65%-86% efficient averaging 84% in the continental US, while for electricity to wall, if we assume 100% efficient for solar off grid charging (no fuel) range from 20%-100%. This makes any national number difficult to determine.

 

You are way off on grid losses. See link: Electric power transmission - Wikipedia, the free encyclopedia
It is about 6 or 7%, not 30%.

I've measured L2 charging losses at about 9-10%. I've measured L1 charging losses at about 12%.
When you take the energy back out of the battery, through the motor(s) and to the wheels there are additional losses (maybe 10%-15%)...but then gas cars have huge losses from the gas tank to the wheels as well (typically 75%).

Mike

 

Mike

My local grid - Pepco charges me .33 kwh for every 1.00 kwh I purchase for Clean Current.
So for every 1.00 kwh that comes out of my 120vac Pepco actually charges me for 1.33 kwh
maybe its all a scam but it is a scam that been going on for the +20 years I've been paying
electric bills for my home. After the 1.00 kwh of electricity leaves the outlet - a 120 vac
transformer for low current levels loses about 5 to 8 percent - losses can be higher for
heavy current loads if a smaller wire gauge is use ... the quality of the charging system
matters.

Walter

 

First let me say, thank you for buying wind electricity.

Wind and nuclear incur greater transmission line losses as the sites are longer from the turbines/power plant to customers. IIRC my losses from west texas for the wind I buy is around 15%, but they are upgrading the grid to decrease these losses. It is not likely that your losses are 1/4, but.... that doesn't mean the utility is ripping you off. I get billed for the electricity at the meter, and the utility calculates how much wind plus a margin for error. Your utility seems to do the opposite and buys RECs at the source, instead of use at the meter. They do some kind of calculation, that I don't understand, but it likely isn't all losses.

 

That is profit, accounting or whatever. It has nothing to do with the actual energy losses, except maybe it is some multiple of it, for example.

Mike

 

Maybe my circumstances are out of the ordinary?
As they say - The Devil is in the details.
Seeing that more detail is necessary ....
I understand if you stop reading right now(*)...

My regional electric company, Pepco, charges about the 8 cents per kilowatt for residential electricity but they also charge separately for the energy used for electricity transmission. On my last bill, my electric transmission energy cost was 3.6 cents per kwh transmitted (45% energy loss) - which is higher than normal because I am using an alternative electricity provider ( thanks in part to Maryland's deregulation of electricity) . If had bought electricity directly from Pepco my electric distribution charges would drop to .00605 cents per kwh ( closer to 8% energy loss overhead) --- about 3 cents less per kwh transmitted. My alternative electricity provider, Clean Current, which is a reseller-consolidator of Wind Turbine Farm generated electricity charges 10 cents per kwh. As of this moment, Clean Current is using wind farms in Iowa, Nebraska, Texas, and Pennsylvania - which are pretty distant locations. The reason I had not selected to buy electricity from Pepco is because Pepco generates electricity mostly from fossil fuels ( coal, gas, oil) and nuclear power. This choice does not come without a cost to me .... not only does clean electricity cost 2 cents more per kilowatt but it cost 3 cent more per kwh to buy it. This suggest to me that unless clean energy is available locally - transmission/distribution cost can make distant clean energy sources economically uncompetitive with locally available dirty energy sources.

Below is my energy distribution charge on my last electric bill from Pepco...

Energy Charge 319 kwh x 0.0363949= 11.61

Pepco also does charge a variety of accounting fees and
there are also some taxes too...

Distribution services Customer Charge 6.78
Franchise Tax 0.0006200 per Kwh = 0.20
MD Environmental Surcharge 0.00001500 per kwh = 0.05
EmPower MD Charge Res 0.0018130 per kwh= 0.58
Gross Receipts Tax at 2.040800% = 0.40
Montgomery Cty Energy Tax 0.0119037 per kwh = 4.08
Administrative credit res 0.0002912 per kwh = -0.09
----------------------------------------------------------------
Total Electric Delivery Charges = 23.98

Clean Current electricity charge
319 kwh x 0.10100/kwh = 32.22
=======================================
Total electric bill = $56.20


If your decisions are solely based on cost - buying dirty electricity from the local
electric company to power your BEV or Plugin is the least expensive route.
However, even with the tax breaks - a BEV and Plugin cost more overall than a
cheaper hybrid or a conventional gas economy car - well at least
from where I am looking from...

(*) Angels fear to tread where fools will follow..

 

I interpret your bill differently.

Pepco is charged 10 cents a kWh for the energy, and in turn charges you 11.6 cents (8 + 3.6). Pepco is adding a 16% surcharge, or $5.21 to your bill for the clean energy. OTOH, the assorted fees and stuff are nasty.

It would also be instructive to simply ask: how much more expensive is 321 kWh of clean energy compared to dirty energy ?

Dirty:
8.6 cents/kWh * 321 kWh = $27.606
Fees = $23.98
---
Total:$51.58

addendum: I'm not sure why the total clean energy bill came out differently than what you posted. The 2 kWh error explains little.


Clean:
11.6 cents/kWh * 321 kWh = $37.236
Fees = $23.98
-----
Total: $61.21

 

My natural gas company bases its distribution fees on the btus or therms supplied. I know it's not a direct comparison, but it sounds like your electric company is just using kWh as the metric to calculate their charge. It might actually reflect some of the transmission losses, but I think it is actually be their distribution energy costs with multiplier.

Transmission lost is from the resistance of the power line, which is lower in high voltage, long distance lines. It is generally measured from the difference between what the company produced and what the customer got. 8% is actually high for this. 6.5% was the estimate for the US in 2007. Distribution losses are the energy used for transformers and the like. Pepco is most likely just charging you for those distribution power uses. Plus for their lights, the coffee maker in the break room, a rental fee for using their aluminum and copper, and something for good measure, because they lost the income of supplying power to you.

 

The EPA figure does account for air drag, other wise we would have lots of cars in 60+ mpg range for hwy mpg. The EPA testing is a little more sophisticated than what you are giving them credit.

 

The EPA figure does account for air drag, other wise we would have lots of cars in 60+ mpg range for hwy mpg. The EPA testing is a little more sophisticated than what you are giving them credit.

 

Here's what I wrote to CR in their comments section for the article: Hopefully CR will allow the comment:

In the interests of giving consumers the best information on why Consumer Report's city mpg are normally lower than EPA city mpg Consumer Reports needs, in the interest of full transparency, to publish the specifics of its City Fuel Economy Test Driving Cycle, specifically showing the acceleration and deceleration profiles it follows. I have always questioned if Consumer Reports follows such a profile consistently for all vehicle models it tests. One of the biggest factors that affect city mpg is the amount and intensity of the braking applications. Put simply, braking is to compensate for the excessive acceleration one did just prior to braking.

I hope Consumer Reports accelerates and decelerate all vehicles (regardless of performance specs.) at the same rates in the city cycle testing that they perform. If so they should have no issues about publishing the details of their City Fuel Economy Test Driving Cycle like the EPA and European do.

If the acceleration and deceleration rates are not consistent for all models than an apples to apples comparison cannot be made between the CR published city mpg values for each vehicle.

It would be relatively easy for one to make a video of vehicles being tested on their test city loop and derive if their deceleration/acceleration rates are consistent. If not one would have evidence that either CR city mpg testing is inconsistent or if consistent it would give us some information why their mpg estimate is poorer than EPA value (likely rapid braking).