DAY 43_MPG vs GPM (GARBAGE TRUCK ENERGY)

26 September 2010

How much energy is used to take out the trash?

I decided not to create any waste for this project mostly to see if it was possible, but have recently been looking into just how much energy it takes for a garbage truck to haul your trash away once a week.  A little background on Minneapolis (Hennepin County's) waste system from the city website(http://www.ci.minneapolis.mn.us/solid-waste/garbage.asp):

"None of your garbage goes into a landfill. City of Minneapolis garbage goes to the Hennepin Energy Resource Co. (HERC).
Located in downtown Minneapolis, the HERC facility uses mass burn technology to convert 365,000 tons of garbage a year into electricity that is sold to Xcel Energy, Inc."

This waste-to-energy facility is located in downtown Minneapolis, just 2.1 miles from my house.  While it may seem strange that Minneapolis burns all its waste near the most densely populated area of the city, this is a convenient location for the facility because it can more efficiently distribute the steam (heat energy) which is being created by HERC.  While the facility is extremely close to where I live, the main problem lies in how garbage gets there -garbage trucks.  As this article outlines (http://www.informinc.org/pr_ggt.php), garbage trucks have some serious fuel efficiency issues:

"The study found that garbage trucks are among the oldest, least fuel-efficient, and most polluting fleet vehicles in the United States:

• There are more than twice as many garbage trucks in the US (179,000) as there are urban transit buses (82,600). The garbage truck fleet includes refuse and recycling collection vehicles as well as transfer trucks.
• Forty-one percent of garbage trucks in use are more than 10 years old, nearing the end of their lifetime (12 to14 years), and performing at reduced efficiencies.
• Garbage trucks use more fuel than any other type of vehicle – averaging 8,600 gallons per year – except for tractor-trailers and transit buses (which use 11,500 gallons and 10,800 gallons on average per year, respectively).
• Garbage trucks in the US consume approximately 1 billion gallons of diesel fuel annually and get the lowest fuel efficiency (2.8 miles per gallon) of any vehicle type. Transit buses, single-unit heavy-duty trucks, and tractor-trailers get 2.9, 7.0, and 6.1 miles per gallon, respectively.
• Diesel garbage trucks are a major source of air pollution, including smog-forming compounds, particulate matter, and toxic chemical constituents. While heavy-duty diesel-powered vehicles, including garbage trucks, make up only 7 percent of vehicles on the road, they contribute 69 percent of on-road fine particulate pollution and 40 percent of nitrogen oxide emissions.
• Diesel garbage trucks are notoriously loud, generating noise levels of up to 100 decibels, which can cause serious hearing damage. Garbage truck operators, as well as those living along garbage truck routes, are affected by this noise.

Trying to crunch some numbers to get the # of gallons used to get from my house to the facility I realized that 2.8 miles per gallon = 2.8 gallons per mile.  Wait, why don't we use GPM instead of MPG?  Wouldn't it be interesting to be able to calculate exactly how many gallons of gas you use for each trip you take (or on a long vacation?).  It turns out, that the term MPG is an easy way to confuse consumers. according to this article (http://www.mpgillusion.com/2009/02/overveiw-of-gpm.html):

"MPG tricks people's perceptions. Replacing a car that gets 14 MPG with a car that gets 17 MPG saves as much gas for a given distance as replacing a car that gets 33 MPG with a car that gets 50 MPG (about 1 gallon per hundred miles--see this table). MPG obscures the value of removing the most inefficient cars. As the GPM table shows, a 14 to 20 MPG improvement saves twice as much gas as a 33 to 50 MPG improvement:"

MPG = miles per gallon
GPHM = gallons per hundred miles

MPG	GPHM
10	10
11	9
12.5	8
14	7
16.5	6
20	5
25	4
33	3
50	2
100	1

More information on this at http://www.mpgillusion.com/"

A few conversions from wikipedia:

1 barrel of crude oil (42 gallons) makes 19.5 gallons of gasoline (other products are made from the barrel as well)

1 gallon of gasoline = 132 MJ = 36.6 kWh

Garbage trucks = 2.8 MPG = GPM
2.8 GPM x 2.1 (miles from my house to the HERC) = 5.88 gallons of gas

Multiplying 5.88 gallons of gas x 36.6 (kWh in a gallon of gasoline) I found that 215.2 kWh of energy are used in the garbage truck's 2.1 mile trip from my house to the waste facility. Whoala. A few comparisons, our house uses about 140 kWh of energy a month (that's 3 people).  Check your energy bill, this is probably pretty close to the amount of energy most small homes use in a whole month!  Granted, the truck makes many stops, so it isn't just MY garbage that is being picked up on the truck. For example, if the truck was on a 10 mile round-trip route which served 50 houses, the energy use per house would be 20.49 kWh (((2.8 MPG x10 miles)/50 houses) x 36.6 kWh)). I have had trouble finding data about garbage routes and number of homes served by each truck.  Updates on these numbers as I find more data...

But just for a moment I would like to consider how much energy would have to be dedicated for garbage hauling each day if I were to be using this service.  215.2 kWh divided by 7 days (garbage picked up once a week) = 30.7 kWh per day.  My energy budget is 5kWh/day.  (Again this number comes from my 'share' of the average solar energy that lands on my roof each day). This means that if I were to consider having garbage trucks haul my garbage away, and dedicated my ENTIRE energy budget towards it, I would only have enough energy to have garbage hauled every 43 days (215.2 kWh per load/5 kWh energy budget per day).  While there is no way I could dedicate my entire energy budget to garbage hauling, picking up garbage once a month doesn't actually seem that unreasonable.  As mentioned in earlier posts, while it is almost impossible to not accumulate ANY waste, it is certainly possible to minimize waste dramatically.  There are only a few items that I continually collect (milk lids, glass wine bottles, twisty ties).  Most of these things are actually recyclable (but I'm not recycling in this project due to energy requirements as well).  I won't have any problem collecting waste in the 14 gallon (2.5'x2'x2') plastic tub I am using now over the 100 days.  This means that I would really only need garbage to be picked up every 3 months or so. 

Below is a graphic describing the garbage energy use and flows (click to enlarge in a new window):

waste energy flows (click to enlarge)