Answers:

1. Answer = D. Because 1 REC = 1 MWh produced from a renewable source, the 1,000,000 kWh are only equivalent to 1,000 MWh and thus only 1,000 RECs. Thus, the cumulative value is:

=($8/REC)(1,000 RECs)

=$8,000

2. To determine the savings, we need to compare the emissions before and after the retrofit.

Look up the CO_{2} emission factor for residual fuel oil #6:

CO_{2}: 75.1 kg of CO_{2} emissions per MMBtu (from emissions tables)

Before the retrofit, if the boiler is only 50% efficient, then the fuel supplied to the boiler will be more than the 10,000 MMBtu needed for the process. Thus, the fuel input will be 10,000/.5 = 20,000 MMBtu. So, if we are burning 20,000 MMBtu of fuel, the emissions would be:

= (20,000 MMBTU)( 75.1 kg/MMBtu)

= 1,502,000 kg of CO_{2} emissions, which we should convert to metric tons:

= (1,502,000 kg) (1 metric ton/1,000 kg)

= 1,502 metric tons of CO_{2} emissions

After the retrofit, we are using a different fuel, so we must look up the CO_{2} emission factor for natural gas:

CO_{2}: 53.02 kg/MMBtu (from emissions tables)

After the retrofit, the new boiler is 80% efficient and the fuel input will be 10,000/.8 = 12,500 MMBtu. So, if we are consuming 12,500 MMBtu of fuel, the emissions would be:

= (12,500 MMBTU)( 53.02 kg/MMBtu)

= 662,750 kg of CO_{2} Emissions, which we should convert to metric tons:

= (662,750 kg) (1 metric ton/1,000 kg)

= 662.75 metric tons of CO_{2} emissions

The CO_{2 }emissions savings would be:

= 1,502 – 662.75

= 839.25 metric tons of CO_{2 }emissions

3. To determine the savings, we need to compare the emissions before and after the retrofit to B20, which by volume is 20% pure biogenic origin and 80% regular fossil fuel diesel.

Look up the CO_{2} emission factor for regular diesel:

CO_{2}: 10.21 kg of CO_{2} emissions per gallon of regular diesel fuel (from emissions tables)

Before the retrofit, if we are consuming 50,000 gallons, then the CO_{2} emissions are

= (50,000 gallons)(10.21 kg/gallon)

= 510,500 kg of CO_{2} emissions, which we should convert to metric tons:

= (510,500 kg of CO_{2} emissions) (1 metric ton/1,000 kg)

= 510.5 metric tons of CO_{2} emissions

After the retrofit, we would only be consuming about 80% of the previous volume of fossil fuel diesel, and the remaining 20% would be biogenic content (which is reported separately from fossil fuel emissions). Therefore, the fossil-fuel diesel emissions would be:

= (50,000 gallons)(10.21 kg/gallon) (.8)

= 408,400 kg of CO_{2} emissions, which we should convert to metric tons:

= (408,400 kg of CO_{2} emissions) (1 metric ton/1,000 kg)

= 408.4 metric tons of CO_{2} emissions

The fossil fuel emissions savings would be:

510.5 – 408.4

= 102.1 metric tons of CO_{2} emissions

Note that you would report the biogenic CO_{2} emissions separately, and they would be calculated as follows:

Look up the CO_{2} emission factor for B100 fuel (100% pure biogenic material):

CO_{2}: 9.45 kg of CO_{2} emissions per gallon of B100 fuel (from emissions tables)

After the retrofit, 20% of the fuel volume will be “pure” biogenic (B100), so the biogenic CO_{2} emissions would be:

= (50,000 gallons)(9.45 kg/gallon)(.2)

= 94,500 kg of Biogenic CO_{2} emissions, which we should convert to metric tons:

= (94,500 kg of Biogenic CO_{2} emissions) (1 metric ton/1,000 kg)

= 94.5 metric tons of Biogenic CO_{2 }emissions

4. Look up the CO_{2} emission factor for Florida:

CO_{2}: 1,176.61 lbs/MWh (from emissions tables)

If we are consuming 1,000,000 kWh, then that is 1,000 MWh, and the CO_{2} emissions are

= (1,000 MWh)(1,176.61 lbs/MWh)

= 1,176,610 lbs of CO_{2} emissions, which we should convert to metric tons:

= (1,176,610 lbs) (1 metric ton/2,204.62 lbs)

= 533.7 metric tons of CO_{2} Emissions

5. To compare the economics, we need to get the options expressed in terms of $/mt of CO_{2}e. To do that, we must convert the RECs into $/mt. Look up the CO_{2} emission factor for Oklahoma (for a quick comparison, we can ignore the impact of the methane and nitrous oxide trace gases as they are a miniscule contribution to the CO_{2}e emissions value):

CO_{2}: 1,599.02 lbs/MWh (from emissions tables)

Because 1 REC = 1 MWh produced from a renewable source, then that means that 1 MWh would not have been produced from the OK grid, thereby saving 1,599.02 lbs CO_{2}, which we can convert to metric tons by dividing by 2,204.62 lbs/mt, which yields 0.7253 metric tons.

Thus, the value of the OK REC in terms of metric tons of CO_{2}:

= ($10/REC)(1 RECs/0.7253 metric tons)

= $13.787 per metric ton of CO_{2}

Therefore, the Answer is B. On a cost per metric ton basis, the RECs would be less expensive than buying the CERs.

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**Eric A. Woodroof, Ph.D.,** is the Chairman of the Board for the Certified Carbon Reduction Manager (CRM) program and he has been a board member of the Certified Energy Manager (CEM) Program since 1999. His clients include government agencies, airports, utilities, cities, universities and foreign governments. Private clients include IBM, Pepsi, GM, Verizon, Hertz, Visteon, JP Morgan-Chase, and Lockheed Martin.