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13 votes

Are fuel cell electricity generators a sustainable way of making electricity?

No. There is no readily available supply of net-positive-energy hydrogen on Earth, where most human power usage takes place. Hydrogen fuel cells may be a useful component of a total energy system ...
Jean-Paul Calderone's user avatar
7 votes
Accepted

Is flying more sustainable than taking the train?

I am not able to find any studies comparing the energy consumption. But if we look at a paper investigating emissions directly, which one could argue is an even better proxy for sustainability than ...
Uli Alskelung Von Hornbol's user avatar
6 votes

Efficiency of delivery services vs individuals travelling to purchase items?

The Umweltbundesamt (sort of German EPA, I figure) recently released a new study on the "Ecologisation of online shopping" - which obviously is in German. Anyway, core findings are that ...
Erik's user avatar
  • 587
6 votes

To what extent do CO2 emissions from motor vehicles vary?

CO2 is produced by burning the carbon in the fuel, so if your driving style causes you to use twice as much fuel, you will produce twice as much CO2. Driving aggressively can have a big impact on ...
Mark's user avatar
  • 333
6 votes
Accepted

Does putting an automatic car in neutral when stopped help save petrol?

According to this answer over on mechanics.SE, below a certain engine RPM, your vehicle automatically disengages the torque converter. That is to say, when stopped, there isn't a fundamental ...
LShaver's user avatar
  • 11.9k
4 votes
Accepted

How to choose a more sustainable vacation option?

The issue here is using the word "sustainable" as something like "healthy" - the more the better - when it actually refers to a balance between, say, resources used and resources generated. If I buy a ...
Kate Gregory's user avatar
  • 1,955
4 votes

Carbon emissions from Ethanol car fuel

There are a ton of different factors to take into consideration here. Lets make sure we keep net GHGe and tailpipe GHGe separate here. Net GHGe Net GHGe: Since 2015, satellite observation as well as ...
ChemE mang's user avatar
3 votes
Accepted

How feasible is a city with no cars and no streets?

This is simply a fancily designed chain of cities based on the about 40 years old idea of the "compact city". The idea is to reduce urban sprawl, reduce traffic and improve living conditions....
Erik's user avatar
  • 587
3 votes

Why are new cars being built in the UK / europe without Start-Stop technology when it seems it can lower pollution?

The simple answer is because any feature costs money, so car makers won't include it unless they're forced to. On some models it's available as an option for extra cost - which relies on the purchaser ...
Chris H's user avatar
  • 2,126
3 votes
Accepted

EU Real Driving Emissions testing (RDE) - does it factor in real driver behaviour and the inefficient driving habits they often exhibit?

Under RDE [Real Driving Emissions test], a car is driven on public roads and over a wide range of different conditions..... Conditions include: Low and high altitudes Year-round temperatures ...
THelper's user avatar
  • 14.5k
3 votes

Is it better to use propane or natural gas as a heating fuel?

Depending on where you are, the natural gas may be mostly propane ;-) The answer from Russel McMahon gives an excellent summary of the chemistry. However, I suspect that the differences there will ...
Flyto's user avatar
  • 3,712
3 votes

Is flying more sustainable than taking the train?

That's an interesting paper that you've linked. From a non-expert skim, three things spring to mind: Firstly, that it doesn't compare like with like. Air travel is compared with commuter rail, and ...
Flyto's user avatar
  • 3,712
3 votes

How to choose a more sustainable vacation option?

Instead of comparing the impact of each travelling modality with 1 traveller, you want to compare modalities per passenger-kilometer or passenger-mile with average load. This means that you divide the ...
THelper's user avatar
  • 14.5k
3 votes

Why are EVs tagged as green when they consume so much?

The faster they are, the more they consume, right? No. In conventional vehicles, especially those powered by a gasoline engine, this is true. Gasoline engines are very inefficient at part-load. So ...
juhist's user avatar
  • 5,099
2 votes

Can alloy wheels (for a car) pay for themselves through fuel savings?

Wheel price is low If you buy for fuel economy, then scuffed wheels from a scrapyard search service or classified ads are OK. "$600 for a set of alloy wheels. Given the costs I saw at Tiretown ... ...
veg-buildlog.blogspot.co.uk's user avatar
2 votes

How effective is turning a car's engine off while standing at a traffic light?

Nobody who turns off their engine ever mentions the fact that restarting their engine causes a slight delay in getting away and must result in increased congestion. This will increase the fuel ...
John Heaton's user avatar
2 votes

Are electric cars as environmentally friendly as we think they are?

The answer to this depends on your assumed alternative. Electric vehicles are better than some traditional gas-fueled cars, but hybrids can have an even larger footprint than efficient combustion ...
Jennifer Rae Pierce's user avatar
2 votes

How effective is turning a car's engine off while standing at a traffic light?

My 95 Accord MT went from ~28.5mpg to ~32mpg easily from mostly shutting off at stoplights, even as little as 7sec or more. About 10%-12% increase in mpg. I also use engine breaking and conserve ...
Richard's user avatar
  • 21
2 votes
Accepted

Does a short-term shut down of a coal plant cause more CO2 emissions than keeping it running?

TL;DR: No -- due to the length of time it takes a coal plant to return to full output after shutting down, it will not produce more emissions during startup than a fully-loaded plant over the same ...
LShaver's user avatar
  • 11.9k
2 votes
Accepted

Water heater vs stovetop: most efficient way to heat water using natural gas?

Stovetop vs water heater efficiency A gas stove-top is about 44% efficient (source), and a modern natural gas water heater with a tank is up to 67% efficient (source (pdf)). Basic formula From this ...
LShaver's user avatar
  • 11.9k
2 votes

Why are new cars being built in the UK / europe without Start-Stop technology when it seems it can lower pollution?

There is another possible reason, just a theory mind. Small cars may pass emissions testing without the need for the technology whereas large cars must have it to pass. In other words, it is not ...
atreeon's user avatar
  • 667
2 votes

Are fuel cell electricity generators a sustainable way of making electricity?

So, are fuel cell generators sustainable? Yes. The hydrogen will be generated using spare electricity when wind and/or sunshine are plentiful. It will be stored, and used later to create electricity ...
juhist's user avatar
  • 5,099
2 votes

Are fuel cell electricity generators a sustainable way of making electricity?

The focus on electricity is probably secondary: Any energy source can be converted into electric energy. The focus on fuel cells is probably secondary, too: Hydrogen can simply drive combustion ...
Peter - Reinstate Monica's user avatar
2 votes

How feasible is a city with no cars and no streets?

A "city" implies people. Lots of people. Those people need to eat. Food generally is purchased at (super)markets and grocery stores. It usually is delivered by trucks. No roads means no ...
Tim's user avatar
  • 2,844
1 vote

For Electric vehicles, HOW are miles per gallon equivalent (or L/100 Km) calculated, accounting for different sources of energy in the grid?

None of any "equivalent" figures make any sense. Electricity and amount of liquid fuel have no relation to each other. Any relation "estimated" would be totally and completely ...
juhist's user avatar
  • 5,099
1 vote
Accepted

How efficiently do different vehicles convert stored energy to kinetic energy?

The Department of Energy has an equivalent infographic for electric cars here. The bottom line is 60% to 73% efficient, not counting the benefit of regenerative braking, compared with 12% to 30% ...
Mark's user avatar
  • 333
1 vote

Efficiency of delivery services vs individuals travelling to purchase items?

According to this article in Environmental Science & Technology (2020) the least GHG intensive process would be online shopping with fulfillment via physical store delivery: We found that ...
sba222's user avatar
  • 383
1 vote

Carbon footprint of CNG vs. Diesel as a vehicle fuel

TL;DR: At the tailpipe, a diesel vehicle and a CNG vehicle have roughly equal greenhouse gas emissions. But taking into account leaks in the natural gas production systems, the diesel vehicle is ...
LShaver's user avatar
  • 11.9k
1 vote

Water heater vs stovetop: most efficient way to heat water using natural gas?

Any water heater built in the last 10 years will be significantly more energy efficient than your stove. At the same time you might want to consider a number of other variables if you are really into ...
Noel's user avatar
  • 11
1 vote

Can chip tuning make a car more fuel-effective?

I would say that the OEM engine tune is sufficiently developed to be as lean as possible relative to the fuel octane. And so improve fuel economy by increasing the tire pressure. Also, shorter ...
S Spring's user avatar
  • 302

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