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How Does TVA "Green" Power Benefit the Environment?

According to TVA:

by reducing (sort of) the amount of CO2 released into the atmosphere

December 24, 2002

The document below was released by TVA on December 2, 2002, under the Freedom of Information Act, in response to a request on April 7, 2002 for the following information:
Analysis, data and calculations that TVA used as a basis to state, “In fact, an investment of an additional $8 per month on your power bill buys enough Green Power Switch to equal the environmental benefits of planting an acre of trees in the Tennessee Valley.” (Reference: http://www.tva.gov/greenpowerswitch/green_mainfaq.htm#3)
The complete TVA statement at the link above, for more context, was:
How does green power benefit the environment?
The environmental effects of traditional energy sources like coal, natural gas, oil, and nuclear power can be significant. Although no source of energy is impact-free, renewable resources create less waste and pollution. In fact, an investment of an additional $8 per month on your power bill buys enough Green Power Switch to equal the environmental benefits of planting an acre of trees in the Tennessee Valley.
This claim, that purchasing $8 per month of green power provides the environmental benefits of planting an acre of trees, now appears to be a demonstrably false and misleading claim, based on the released information.

What are the benefits (documented below) that "equal the environmental benefits of planting an acre of trees," according to TVA? The statement brings to mind all the benefits of a forest - trees and associated undergrowth, grasses, flowers, and wildlife; or maybe the benefits of an orchard - fruits or nuts for food to eat. One also thinks of reforesting a barren hillside, and the benefits of restoring ground cover - reduced soil erosion, less runoff and fouling of creeks, and improved water quality. Finally, one thinks of a primary benefit of green plants and photosynthesis - consumption of CO2 and release of oxygen, which we require to breathe.

It seems almost incredible for only $8 per month to plant an acre of trees and provide all those benefits. An acre is 43,560 square feet (4047 square meters). If each tree takes about 100 square feet, then an acre will hold about 435 trees. At $0.50 per seedling for purchase and planting, the cost of 435 trees would be $218, or about 27 monthly payments of $8 per month. So, if $8 per month for a year ($96) probably cannot even support the planting an acre of trees (not even considering renting the land), then what miracle of green power allows it to provide the same benefits?

Which benefits of planting trees does TVA claim are obtained by purchasing their green power? Only one - with an odd sort of logic - consumption, or rather theoretical lack of production, of CO2. A comparison of benefits of planting trees, TVA's claimed benefit of purchasing green power, and the actual benefits are summarized in the following table.

Benefits of Planting Trees
Reference 1
Reference 2
Reference 3
TVA Claimed Benefits
of Green Power
Actual Benefits
of Green Power
Trees provide a cool, green, shady place in which to live, work, and play. n/a
One acre of healthy trees produces enough oxygen for 18 people per day. n/a n/a
Trees filter air pollution. n/a n/a
In one year, an acre of trees absorbs the amount of carbon dioxide you produce when you drive your car 26,000 miles. Purchasing 2 blocks of green power per month for a year (3,600 kilowatt-hours total) at $8 per month ($96 total) reduces CO2 emissions by about 7,300 pounds.
According to TVA's data, on average, about 80% (or more) of TVA's green power comes from burning methane gas from landfill or sewage treatment gas. In fact, this emits about as much CO2 as any other burning of fossil fuels (actually somewhat more, due to lower quality fuel); however, TVA treats this CO2 as if it does not "count" because it would have been emitted by burning the gas from the landfill or sewage treatment anyway. That's like claiming that burning natural gas in gas turbines shouldn't "count" because the gas would have been burned in furnaces or hot water heaters anyway.
Trees conserve our precious water resources by reducing water runoff, and help to prevent soil erosion. n/a n/a
Trees decrease your energy costs. Trees placed strategically around a home or building can reduce heating and cooling costs from 10-50%. n/a n/a
Trees increase property values. Building lots with trees routinely sell for 10% more than sites without trees. n/a n/a
Tree reduce noise pollution by absorbing and blocking urban noise. n/a n/a
Trees can be a haven of wildlife and plant diversity in the midst of the city. n/a n/a

Note: Horizontal lines below indicate page breaks in the original document, which was scanned and converted to HTML by mensetmanus.net. Links are given to references available on-line, and to critical comments regarding the document.
Beginning of TVA Document

Documentation of Environmental Claims Made for TVA Green Power
Ed Holt & Associates, Inc. 9 March 2000

Acres of Trees Planted

The U.S. Environmental Protection Agency estimates that planting one acre of trees on marginal land would sequester 0.6 to 1.6 metric tons of carbon annually. 1 Assuming that planting one acre of trees in the TV A region will sequester 1.0 ton of carbon (slightly less than the median of the EP A estimated range), we first convert carbon to CO2 by multiplying by 3.67. 2 Thus planting one acre of trees on marginal land will sequester (save, reduce or prevent from escape to the atmosphere) 3.67 tons of carbon dioxide, or 7,340 pound of carbon dioxide.

The amount of carbon sequestered depends on what is used for the baseline, the region of the country, the type of trees planted, the site class (relating to the height of the dominant trees at 50 years of age, and the reference or base case land use (e.g., clearcut forest, cropland, or pasture). The above example assumes that an acre of trees is being planted on marginal land. The DOE, in its guidelines for reporting greenhouse gases, provides another example that is perhaps more specific to the Southeast.3 This example analyzes the effect of planting Southern Pine in the Southeast on cropland previously used to grow soybeans. The results are reported as pounds of carbon (not carbon dioxide) per acre. The analysis estimates that planting pine trees instead of maintaining the land in crops will store carbon in the following amounts:

Year 0 0 lbs/acre
Year 5 10,000 lbs/acre
Year 10 22,000 lbs/acre
Year 20 74,000 lbs/acre

Quoting from the cited example, "These numbers measure the net effect of the project on stocks of stored carbon.  To estimate the average annual flow of carbon attributable to the project, she compared stock measures across time.  For example, the annual flow of carbon for the first five years of the project was estimated as

Average Annual Flow of Carbon = (Io -Is) / 5 = (1-10,000 lbs/acre)/(5 years) = -2000 lbs/acre/year."  [comment 1]

1 U.S. Environmental Protection Agency, Climate Change Mitigation Strategies in the Forest and Agriculture Sectors (Washington, DC, June 1995), p. ES-5.  Cited in U.S. Energy Information Administration, What Does the Kyoto Protocol Mean to U.S. Energy Markets and the U.S. Economy?  Report#:SR/OIAF/98-03.  The full report is available at http://www.eia.doe.gov/oiaf/kyoto/kyotorpt.html.
2 U.S. Department of Energy, Sector-Specific Issues and Reporting Methodologies Supporting the General Guidelines for the Voluntary Reporting o/Greenhouse Gases Under Section 1605(b) o/the Energy Policy Act O/ 1992.  DOE/PO-0028.  Volume II, Appendix D, "Conversion of Carbon to Carbon Dioxide Emissions."
3 U.S. Department of Energy, Sector-Specific Issues and Reporting Methodologies Supporting the General Guidelines/or the Voluntary Reporting o/Greenhouse Gases Under Section 1605(b) o/the Energy Policy Act O/ 1992.  DOE/PO-0028.  Volume II, page 5.24.

A similar calculation was performed for years 6-10 and 11-20 with the following results.

Period (Years) Average Carbon Flow Converted to CO2 (x 3.67)
1-5 -2,000 lbs/acre/year -7,340 lbs CO2/acre/yr
6-10 -2,400 lbs/acre/year -8,800 lbs CO2/acre/yr
11-20 -5,200 lbs/acre/year -19,084 lbs CO2/acre/yr

From this table it is clear that the carbon or CO2 reduction also varies with the age of the trees; the longer it grows and the larger it becomes, the more carbon it sequesters.  From this example, it is evident that one acre of planted trees may be conservatively assumed to sequester 7,340 Lbs of CO2, which is the same result as the first example that assumed one acre of trees sequesters one ton of carbon. [comment 1]

To estimate the number of acres planted/kWh of green power purchased:
(1) TVA CO2 average emissions across all of its coal-fired power plants is 2.1 lbs ofCO2/kWh. 4
(2) TVA CO2 emissions from a new simple cycle gas turbine is 1.36 Lbs of CO2/kWh. 5
(3) Weighting these resources at 95% coal and 5% natural gas, as suggested by TVA, results in a
weighted average emissions of2.063 lbs of CO2 /kWh. [comment 2]
(4) 2.063 lbs CO2/kWh divided by 7340 Lbs CO2/acre = 0.000281 acres/kWh.
(5) 0.000281 acres/kWh * 150 kWh/block/month = 0.04215 acres/block/month
(6) 0.04215 acres/block/month * 12 months/year = .5058 acres/block/year [comment 3]

It is assumed that combustion of landfill gas produces no net CO2 emissions because similar emissions result from flaring of methane gas in the absence of electricity generation. 6 [comment 4]

Purchases of green power blocks, therefore, will have the environmental effects shown in the table below.

Number of Blocks Green kWh/month Acres/block/year Acres of Trees Planted*
1 150 .5058 0.5058
5 750 .5058 2.529
25 3,750 .5058 12.645
100 15,000 .5058 50.58
250 37,500 .5058 126.45
375 56,250 .5058 189.675

*Based on purchasing the specified number of blocks for one year.

4    See memo from Mark K. Hill to Susan H. Ross, March 9, 2000, attached to the end of this memo.
5    Ibid.
6    U.S. Environmental Protection Agency, Emissions & Generation Resource Integrated Database for 1996.

CO2 Emission Factors

Sent: Thursday, March 09, 2000 3:27 PM
To: Ross, Susan H.
Subject: RE: Help with data for environmental claims

Average Coal Unit CO2 emission rate:

Average Heat Rate * CO2 Fuel Emissions Factor = CO2/KWH

10229 BTU/KWH * 205 lb CO2/million BTU = 2.10 Lbs/KWH

1999 Average Heat Rate from 1999 TVA annual Report, page 44.
Coal Emissions Factor from General Guidelines Voluntary Reporting Of Greenhouse Gases under Section 1605(b) of the Energy Policy Act Of 1992, Appendix B.

New Natural Gas Fueled Simple Cycle Combustion Turbine (CT) CO2 emission rate:

Heat Rate * CO2 Fuel Emissions Factor = lb CO2/KWH
11728 BTU/KWH * 116 lb CO2/million BTU = 1.36 lb CO2/KWH

CT Heat Rate for new GE 7EA CTs.
Natural Gas Emissions Factor from General Guidelines Voluntary Reporting Of Greenhouse Gases under Section 1605(b) of the Energy Policy Act Of 1992, Appendix B.

Mark K. Hill
Tennessee Valley Authority
1101 Market Street, LP 5D-C Chattanooga, TN 37402

End of TVA Document

  1. According to the referenced data, the carbon taken up by newly planted trees would be at a lower rate; however, the trees continue growing, and the rate increases to considerably more than 2000 pounds per acre, which is the simple average based on the total after 5 years. In other words, the assumption of a linear average between year 0 and year 5 is not conservative as claimed. A conservative rate might be at the higher end of the first range (0.6-1.6) given, or about 60% more than the assumed rate.
  2. There is no guarantee that TVA would reduce coal or gas turbine power to compensate for generation by "green" power sources. They might simply produce as much power as possible, and sell any excess, which would result in an increase, not decrease, in CO2 emissions. They might alternatively reduce nuclear or hydro power, which would also result in an increase, not decrease, in CO2 emissions from burning the methane gas. Also, according to TVA's "electricity label," the average CO2 emissions used for comparisons should be about 1.35 pounds CO2/KWH. This average value is about 65% of the assumed value.
  3. Assuming 1.6 metric ton of carbon per acre of trees, and 1.35 pounds per KWH, the result becomes 0.188 acres per block for a year, or 0.376 acres for two blocks for a year, which is about 38% of the "benefit" claimed by TVA. This is accepting the dubious assumption regarding zero CO2 emissions from burning landfill and sewage methane gas.
  4. Burning methane is burning methane. CO2 is released. The same argument could be applied to conventional natural gas. If one rejects the dubious substitution logic, then the only green power sources that may be truly without CO2 emissions (after construction) are solar and wind. Since these provide only about 10 to 20% of the green power energy production, then the "tree equivalent" CO2 benefits are reduced to 10 or 20% of the claimed amount on that basis alone.

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