In response to a question on another thread some time ago, here is the data on energy usage of TriMet vehicles, compared to representative numbers for autos, measured in BTUs per passenger mile:
TriMet MAX646
TriMet Bus 3,792
Auto (17 mpg)6,712
SUV (14 mpg)8,150
16 responses to “Relative Energy Use of Various Modes”
Mary –
Thanks for posting this info. I’m not the guy who asked for it, but it is nice to see.
Can you tell me what assumptions were used for auto occupancy? Is it single occupancy or a regional average (1.2 or something?) to get those BTUs?
Thanks,
Bob Richardson
Cycling and walking: zero BTUs
Not quite, we cyclists and pedestrians have to eat :-)
This source puts cycling at 140 BTU/passenger mile.
Mary replied to my comment via email and said:
“Bob: We used the regional average of 1.2 persons per car.”
– Bob R.
Chris:
That assumes cyclists eat more food to fuel their cycling than they otherwise would if they drove or took the bus. It’s more likely that most cyclists just lose weight and gain fitness, or at least hope to. That’s certainly my objective.
It would also be interesting to see the same table for pollutants. My assumption is that electric MAX is “cleaner” than buses and cars. But I don’t really know how modern diesel buses compare to modern cars on a per person pollutant basis. I’m sure I could google up the info but I’m lazy.
Mary Fetsch, TriMet at 09:13 AM Relative Energy Use of Various Modes
In response to a question on another thread some time ago, here is the data on energy usage of TriMet vehicles, compared to representative numbers for autos, measured in BTUs per passenger mile:
TriMet MAX 646
TriMet Bus 3,792
Auto (17 mpg) 6,712
SUV (14 mpg) 8,150
JK: A few questions (see end for link to my reference):
1. Could you tell us how you got your Max number, because the data that you supplied to me for FY2002 works out to 838 BTU/Passenger-mile (which gives 2514 when you account for power plant losses.)
2. I assume that your 646 BTU for light rail does not include the 66% loss of energy in the power plant. When you include that loss, the consumption is 1938 BTU per passenger mile.
3. Why did your people use 17 MPG for autos, while the CAFÉ standards have been 27.5 mpg for the last 15 years and the sales weighted café has been around 29 MPG recently, per table 4.18? Table 2.12 shows a national average automobile energy consumption of 3,581 BTU/Passenger-mile. Please have you people explain this discrepancy between the U.S. Government data and yours.
4. Why did your people use 14 MPG for “SUV” (I assume you mean “light truck”), while the CAFÉ standards have been above 20 MPG for the last 20 years. This is per table 4.19. Table 2.12 shows a national average “light truck” energy consumption of 7,081 BTU/Passenger-mile. Please have your people explain this discrepancy.
Refrence: TRANSPORTATION ENERGY DATA BOOK: EDITION 24 ORNL-6973 (download from: http://cta.ornl.gov/data/download24.shtml
Thanks
JK
“I assume that your 646 BTU for light rail does not include the 66% loss of energy in the power plant. When you include that loss, the consumption is 1938 BTU per passenger mile.”
There are clearly energy losses for all fuels depending on how you want to calculate them. While I understand the desire to be wholistic in approaching energy issues, I don’t think attributing the energy loss from one mode of power generation to a transportation mode is appropriate. And if you try to do it for all modes it becomes hopelessly complex quite quickly.
You would clearly have to include the energy losses in extracting,transporting and refining oil. But would you include the btu’s lost during the refinement process? How about the BTU’s left in the ground because of inefficient extraction techniques? What about natural gas that was burned off as part of the process?
I would like to hear more details, since it appears to be an issue, about MAX energy devliery in particular.
I wouldn’t want to apply national average transmission loss figures to MAX, because light rail trains don’t suffer from as many distribution nodes on the grid as say the average home, plus they operate at higher voltages which can mean fewer step-downs from the high voltage transmission lines.
Mary –
Has anyone done run the numbers for the total BTU consumption of MAX, starting from the KW-Hours delivered to trains from outside power providers and working backward to KW-Hours input from power plants? (And then dividing that result by passenger-miles)
– Bob R.
Ross Williams Says July 20, 2005 07:32 PM: (quoting JK) “I assume that your 646 BTU for light rail does not include the 66% loss of energy in the power plant. When you include that loss, the consumption is 1938 BTU per passenger mile.”
Ross Williams Says July 20, 2005 07:32 PM: There are clearly energy losses for all fuels depending on how you want to calculate them. While I understand the desire to be wholistic in approaching energy issues, I don’t think attributing the energy loss from one mode of power generation to a transportation mode is appropriate. And if you try to do it for all modes it becomes hopelessly complex quite quickly.
Ross Williams Says July 20, 2005 07:32 PM: You would clearly have to include the energy losses in extracting,transporting and refining oil. But would you include the btu’s lost during the refinement process? How about the BTU’s left in the ground because of inefficient extraction techniques? What about natural gas that was burned off as part of the process?
JK: The energy efficiency is typically calculated as the energy content of the INPUT to a vehicle gas tank, or overhead wire to a desired OUTPUT, in this case passenger miles. When you consider the extraction., refining and transportation of the fuel, you are doing a systems analysis. Another subject. Now there is a big BUT here. Most electricity comes from thermal power plants which usually waste around 2/3 of the input energy. That is why they have cooling towers and why your car has a radiator. Further a lot of power plants were fired with oil and electrically powered transportation should not get a free pass on the conversion of fuel into electricity when the same process (without the generator) is going on inside you car’s engine. Remember, an electrical power plant is just a big fuel burning device with a rotary output coupled to an electrical generator. The generator makes electricity which powers the electric motors in light rail, or in your electric car (via batteries). The basic processes are similar, just re-arranged a bit.
Bob R.July 20, 2005 08:02 PM: I wouldn’t want to apply national average transmission loss figures to MAX, because light rail trains don’t suffer from as many distribution nodes on the grid as say the average home, plus they operate at higher voltages which can mean fewer step-downs from the high voltage transmission lines.
JK: See above, it is a process thing, not distribution.
Bob R.July 20, 2005 08:02 PM / Mary: Has anyone done run the numbers for the total BTU consumption of MAX, starting from the KW-Hours delivered to trains from outside power providers and working backward to KW-Hours input from power plants? (And then dividing that result by passenger-miles)
JK: > There are two common techniques applied here. Look at energy delivered to the vehicle’s input, be it a gas tank or a wire. OR, look at the whole system which is system analysis, a lot more complex than what were doing here. Electric vehicles are a special case as explained above.
Thanks
JK
Let me give a little background on energy and its usage.
1. Energy is neither created or destroyed, it is merely transformed from one form to another.
2. We routinely use several forms of energy:
A. Energy in chemical bonds – most commonly through burning things.
B. Potential energy due to height – we use this by letting something drop: Hydro power
C. Things that move – windmill captures moving air, regenerative braking
E. Energy in atoms. Fission (splitting) and fusion (combining)
F. Energy in light. Solar panels
3. There is always a loss when converting energy from one form to another, sometimes great loss.
Lets look at burning things to get electricity. We start with natural gas, coal or oil. The choice between these used to be strictly which was cheapest, now consideration is given to pollution. In a power plant, we boil water, then continue heating the steam to as hot a temperature and pressure as practical. (Hotter steam, higher pressure gives more efficiency.) This superheated steam is applied to a steam turbine which in turn drives a generator. The steps are: 1) burn fuel to 2) boil a fluid to a high temperature and pressure, 3)use this fluid to spin a turbine 4)which turns a generator. The output of the turbine is ideally water vapor at low pressure which turns to water in a condenser. This water is then reused in a continuous cycle.
This process depends on the behavior of a gas (steam) as it undergoes temperature and pressure changes: becoming hot and high pressure in the boiler then cooling and lowering the pressure as it goes through a turbine. These changes are not linear and are very lossy. The typical steam plant loses about 2/3 of the input energy in the conversion to electricity (its efficiency is around 33%). If I remember this stuff correctly, the major loss is in the steam as it cycles from cool low pressure, liquid to hot, high pressure steam and back. Other losses are the combustion gasses going up the smoke stack, the turbine’s losses in turning the temperature and pressure change into rotation energy, and loss in the generator.
There have been experiments with putting a mercury boiling cycle ahead of a standard steam plant to increase its efficiency (The hot mercury from the mercury turbine boils the water for steam to drive the steam turbine). I think I recall that this boosted the efficiency to around 50%, but was quite expensive.
To make a nuke plant, they just replace the fossil fuel fired boiler with a nuke driven boiler. The rest is the same. (This is a technical discussion, not political)
The generator’s output is used to run our modern society. Including electric rail and electric busses.
It is also possible to burn the fuel inside the rotation producing device (the engine). Here the hot combustion gasses are applied directly to the turbine (gas turbine, jet engine) or to a piston(s) to convert the pressure and temperature of hot gasses into rotational mechanical energy which can be used to turn a generator. Examples include the generator (with gas motor) you can buy at the local hardware store. Gas turbine generators can be used as power plants, as are diesel internal combustion engines.
For propelling a vehicle (the point of this whole exercise) you hook the output of the diesel generator to motors on your wheels and you have a modern diesel-electric locomotive. Use a transmission instead of the generator and motor and you have an ordinary car. You have to use an engine large enough to supply the peak power needed for rapid acceleration and hill climbing. With the electric generator and motor arrangement, you can add batteries to handle the peak loads, then you can use a smaller engine to save fuel by keeping it near its most efficient point. That is why hybrid vehicles use less energy.
Hopefully one can see the basic process beginning with the burning of fuel and ending with rotating the wheels. In the case of a car or truck these all happen in the vehicle. To calculate efficiency, you just measure the fuel used from the fuel tank and compare it to work delivered such as ton-mile of freight or passenger miles of people.
Here is the rub: in electrically powered transportation, the fuel is burned elsewhere. Is it valid to ignore the loss in burning the fuel because it was burned somewhere besides in the vehicle that uses the energy from that fuel? This is why we include the power plant losses in calculating the efficiency of electrically powered transport.
My understanding is that the losses in the electrical transmission system are fairly small – the major losses are in the power plant. I have seen specs for electric motors (to power automobiles) where they are running around 85-90% efficiency over a fairly wide range of power output. Transformers are also quite efficient, probably 95-98% for utility scale. I don’t recall seeing numbers for the actual wires. One other real world gotcha: combine a few high efficiency devices, say two 95% efficient transformers and a 90% efficient motor and you get: 0.95 x 0.95 x 0.90 = 0.81. So just a few 90%+ devices and you are at 81%.
Batteries also have a loss during the charge – discharge cycle which works against electric vehicles and hybrids. There are claims, from credible sources, that electric cars actually use more energy than their non-electric counterparts, especially hybrids. (I have not run through the numbers, nor do I intend to.)
Key points: There is no known device that will make energy, only convert it form one form into another. All conversions involve loss. Energy conversions involving gas cycles are very inefficient. Electric devices are frequently very efficient.( My definition of very efficient is that they only loses 1-10% of the energy.) Generators don’t generate electricity, they convert rotation into electricity (and they loose a little energy doing it.) Many energy related decisions are made on the basis of cost – we use a particular fuel because it is the cheapest way to accomplish the task. Efficiency must always be considered – including cost.
Hopefully this will help some people who have not been exposed to the technical side of transportation energy. I believe that everything mentioned here is mainstream thinking and can be easily verified by any highschool science teacher (or on the internet if you stick to major college and university sites). Some of my numbers may be off a bit, but not enough to negate the principles.
Thanks
JK
Yes, Jim, I am aware of generation losses. I would like to know _actual_ numbers for those, too — Generation efficiencies for the mix of power sources typically found in our region. On top of that, transmission losses, which is what I was talking about, are significant — there is no such thing as a 100% efficient transformer. All stages of the electrical grid waste energy in the form of heat from resistance and transformer stages.
– Bob R.
PS to JK – I was a bit terse in my previous comment. I do appreciate your participation thus far in this thread.
– Bob R.
Here is the actual generation sources for PGE’s basic rates.
Hydro 46.1 percent
Coal 39.7 percent
Natural Gas 11.2 percent
Nuclear 1.7 percent
Waste 0.5 percent
Wind 0.4 percent
Geothermal 0.0 percent
Other 0.5 percent
So why would we include the energy inefficiencies in a hydroelectic plant as an energy input to light rail?
Ross –
Thanks for posting those generating source breakdowns… that’s along the lines I was looking for.
Indeed, how should we categorize/evaluate hydropower as part of this equation? Obviously hydropower has its own unique qualities and impacts (positive and negative) that differ from fossil fuels.
Any thoughts on this from JK?
– Bob R.
Bob R. July 21, 2005 02:19 PM:
Ross –
Thanks for posting those generating source breakdowns… that’s along the lines I was looking for.
Indeed, how should we categorize/evaluate hydropower as part of this equation? Obviously hydropower has its own unique qualities and impacts (positive and negative) that differ from fossil fuels.
Any thoughts on this from JK?
JK: Well, we aren’t building any more hydro. Haven’t for years, so all new demand comes from the other categories. Mainly coal, gas and nuke with a smidgin of renewable. On the other side, Tirmet will tell you that they purchase renewable power, but admit that the green electrons are all mixed up with then black ones (in the wires) and cannot be separated because they are exactly the same electrons. The fact does remain that TriMet says that they pay for renewables. The question is wether on not this results in added renewal capacity. I don’t know the answer, but since wind energy is now economically competitive, I doubt that the extra $$ is causing capacity to be built that wouldn’t other wise be built. Maybe it is built a little sooner?? I don’t know.
However I do know that when there is no wind, they have to use something else. Which of course is the problem with both wind and solar – you still have to have enough conventional generation capacity to carry the entire load, it is just that you can shut down some of those plants when the wind is blowing. Of course efficiency is best when the plant is running all of the time at its best point – something that might reduce the savings from alternative energy.
End JK – who has no income from anything discussed here.
What I would like to know is whether the btu/passenger calculations for either MAX or a Tri-Met bus are based upon a “fully-occupied vehicle” or what? I see many MAX trains running at about 15 or 20 % capacity. This must represent a reduction in energy efficiency. How much more energy-efficient are they during the times when hardly anyone is using them? I am certainly not against rail for commuter use but we need to get realistic about exactly how much these systems are costing the public. Some critics are charging that rail transit represents an unfairly subsidized extravagance: I don’t agree but I think a legitimate issue has been raised. Perhaps streetcars, operating at nearly full capacity, would be better.