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 ...
- 1,603
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 ...
7
votes
Accepted
Size of wood lot required for cooking/heating (US west coast)?
OK, one possible setup (and assuming both my math and memory are right, neither of which is certain):
Planting Douglas Fir, which is fairly fast growing (one to two feet a year) and a good wood for ...
- 186
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 ...
- 11.8k
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 ...
- 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 ...
- 323
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 ...
- 141
4
votes
Accepted
How efficient are tiny cars compared to others?
In the USA the Daimler/Mercedes "Smart" Fortwo car is the obvious choice, rated at 41mpg on the highway. Those look silly but are quite safe and very fuel efficient, as well and being ridiculously ...
- 3,875
4
votes
Size of wood lot required for cooking/heating (US west coast)?
I've done this calc for my farm here in Alberta.
I know that it takes 5 cords a year to heat my house.
The average lifespan of trembling aspen is about 40 years. At that point it's about 40 feet ...
- 7,207
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 ...
- 1,897
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 ...
- 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 ...
- 3,690
3
votes
Fuel efficiency when decelerating on a hill
Generally a driver doesn't know the exact angle of the hill at any point in time, nor do they generally know the exact combination of gear and gas-pedal that will be the most efficient.
Maybe some ...
- 8,755
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 ...
- 2,116
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 ...
- 3,690
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
...
- 14.5k
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....
- 587
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 ...
- 4,786
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 ...
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 ...
- 667
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 ...
- 11.8k
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 ...
- 31
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 ...
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 ...
- 21
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 ... ...
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 ...
- 11.8k
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 ...
- 2,804
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 ...
- 11.8k
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 ...
- 11
1
vote
Is it possible to calculate energy efficiency of a flat by knowing how much energy was consumed for heating?
No, because with this limited data you cannot separately estimate the three components that make up a building's energy signature:
the base load
the base temperature
the energy efficiency
Even if we ...
- 501
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