Thursday, February 12, 2009

Energy Question

So I've been thinking a lot about the BRT report and comments on the (edited from CCT: Purple Line) in this post. The WRI study states that BRT is better for reductions in GHGs than LRT because LRT comes from dirty sources such as coal. Ok, I'll bite. Here's Greg Fuhs (from WRI) very fair comment at the end of my last post:
What we (and MTA) are saying is that by building a medium or high investment BRT system in the corridor, this would reduce GHG emissions from current levels by getting more people out of single vehicles and moving them more efficiently along the corridor than is currently the case. The significant fuel savings from this system would lead to the reduced GHG levels.

The reason light rail would increase GHG emissions over No Build is due to the electricity source, which for this region is primarily coal-fired power plants. While people would leave their cars and move more efficiently along the corridor with light rail, the coal plant emissions generated to produce the electricity required for the Purple Line would exceed the emissions savings from getting people out of their cars.
Now I understand this argument, but I have to dive in a little deeper. I'm wondering if the following thought is true. If you build an electric system, bus or rail, more electricity has to be produced during peak periods where the rail line is more efficient than the buses burning diesel. At the same time, during the off-peak, does the powerplant have to produce extra power or does that energy already exist in the grid.

I've heard ideas about the power grid benefitting from off peak power usage because the plant was going to run no matter what, but I'm wondering if the GHG's are already being produced, therefor any other emissions such as those from the bus are on top of what already existed from the power plant whether the light rail line was there or not. If this were the case, doesn't that reduce the emissions factor of the LRVs because the emissions are already out there from the coal plant? Does anyone know the answer to this or other ideas?

13 comments:

Ben Ross said...

Power grids turn plants on and off to make the produced power match the demand. You try to use the plants with the lowest operating costs the most. You also have to consider that some plant types are much easier to turn on and off than others.

No analysis I've seen distinguishes between peak and off-peak power generation. What you see are broad-brush calculations that average across the entire power grid.

There are many, many approximations in these calculations. If you wanted to put effort into improving their accuracy, I doubt that looking at peak vs off-peak power would give you the most bang for the buck.

As I read the WRI study, it boils down to a claim that burning petroleum is better for the environment than using electricity because it emits less CO2.

There is a vast literature that compares power sources in general, none of which WRI addresses in their report. They've just picked out one number that makes their favored technology looks good.

Justin said...

I noticed that in the WRI report also. The best way to debunk that argument, is that the power plant based emissions tend to be distant from populated places, compared to bus emissions, which directly impact the rider, and neighbourhoods. This is key, in my opinion. The exhaust from hundreds of buses a day has to has a significant impact.

Thelonious_Nick said...

I don't know the precise mix of electricity in the DC area, and it is true that we get a lot of coal-fired power from SW Virginia and PA (and also there is a small coal-fired plant in Alexandria). However, we also get a significant amount of nuclear from Calvert Cliffs, MD, and North Anna, VA. I'm not sure that power is really that dirty compared to other places.

Anonymous said...

another excuse for less useful transit wrapped in pseudo-techno data. If you assume that many persons will use the transit line, electric vehicles have longer component lifetimes,use less oil based lubricants etc. Secondly, electric generating sources are not static. Unless the oil/fossil fuel companies take over, we are going to expand solar, wind, and other renewables. Thus over the lifetime of the LRT system, the GHG from the electricity will be constantly decreasing.

Cavan said...

Anonymous got it right. It's just an excuse to rig the data so that it supports the conclusion that WRI already came to.

Joe Klein said...

It takes relatively few large wind generators to power traction equipment. Standard 100' rail right-of-ways can accommodate wind turbines and two tracks. An administration truly dedicated to innovative alternatives, may want to look at building wind turbines along the right-of-way. Add some superconducting magnetic energy storage (SMES) system and you can store and retrieve your power at will.

Loren said...

A further problem: what is the energy efficiency of buses vs. light rail?

It's hard for me to find numbers, but from Wikipedia on fuel efficiency in transportation, I calculate (LR) = (2/3)*(buses). And from Wikipedia on energy density, I find that the masses of coal and diesel fuel are very close, meaning that they emit roughly the same amounts of carbon.

But most alternative energy sources most efficiently produce electricity, as does nuclear, which counts in favor of light rail and electric trolleybuses.

Alon Levy said...

Loren, the Wikipedia article you link to says the opposite of what you're saying it says. It says that buses consume 8.7 liters per 100 passenger-km, the highest energy consumption of all modes of transportation. Even cars are better, at 7.2. Urban rail comes at 5.7, which means it's 50% more efficient than buses, not the other way around.

dto510 said...

This is a really complex question that would take enormous resources to answer definitively. The relative GHG output / efficiency of LRT v BRT depends on factors that haven't even been touched on here - what about impact of the more resource-dense construction of LRT? What about the extra cost-per-passenger pf LRT: are those lost dollars an opportunity cost that affects GHG (ie, the money saved from building BRT vs LRT could be put to GHG-reducing activities)?

Ultimately, any form of mass transit investment that reduces (or slows the growth of) car travel is a net gain in terms of GHG and encourages GHG-reducing land-use patterns. I favor BRT because it's much cheaper and faster to implement in my resource-strapped California city. Maybe DC has access to funding sources that can pay for LRT without jeopardizing other transit projects. But usually the opposition to BRT or LRT is because of the loss of ROW to cars, and that's something that transit activists need to work on together.

ChiefJoJo said...

I agree with anon... the assumption that we will continue to be powered by coal for the foreseeable future is wrongheaded. The ability for LRT to received power from a smart grid from clean, renewable energy sources is among it's biggest advantages... along with better ability to shape land use, lower operating costs, and widespread public preference for electric rail.

As to dto510's comments, it is a very complex question with many variables built-in. But among the most obvious assumptions external benefits of LRT would be that the extra cost per passenger (over BRT) could easily be offset by the land use benefits that would likely result. All else being equal, more people & jobs in TODs will produce lower carbon footprints vs. locating in a "conventional" development.

Bottom line for me is we need to think, plan and invest for the long term, as we used to do. If we look at high capacity transit as a multi-generational (50+ year) investment instead of a quick fix project, these issues begin to answer themselves.

anon said...

-- coal plants are "baseload" power -- very hard to turn on and off

-- commuter rail systems use more electricity at peak hours. This would be supplied by natural gas power, usually -- not baseload power.

Of course the crucial point is that we can change our source of electricity production. Changing our source of diesel is a lot harder, despite biodiesel. And if they're full, the railcars are simply more energy-efficient than the buses. Burn diesel to generate the electricity if you absolutely have to -- that eliminates any supposed "GHG increase" due to switching from diesel buses to electricity.

Definitely the electrical power system is better in terms of GHG emissions during operation, than petroleum-burning buses.

(Construction is another, more complicated matter.)

njh said...

To make buses more efficient people are talking about using an electric drive, but the problem is that you have to carry around batteries and a heavy diesel generator. Perhaps they could make buses with the diesel generators and batteries stationary, and just transmit the power via an extension lead? And of course generators become more efficient as they become larger, and you can afford to add air quality systems to them without a weight penalty.

Matt Fisher said...

Late on this, but I got somethin' to say: Good commenting. Averages are not always the most accurate way of telling a figure. It's like what would happen in Mr. Burns walked into Moe's, and Homer Simpson, Barney, Lenny, Carl, and the other regulars would see their "average" income increase, despite being skewered in favour of Mr. Burns. (I'm a Simpsons fan, and I put this in.)

To the guy named "Anonymous", brilliant point. Continued dependency on coal for electricity is not inevitable. The WRI's report is a lot like the BTI's pro BRT propaganda, and fudges the numbers to make BRT appear better than LRT.