Green Power Equivalency Calculator - Calculations and References
This page describes the calculations used to convert green power electricity (kilowatt-hours) into various types of equivalencies.
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Number of American Homes’ Electricity Use for One Year
According to the U.S. Energy Information Administration (EIA), the average annual electricity consumption for an American household in 2016 was 10,766 kWh, an average of 897 kWh per month (EIA 2017). The number of American homes is determined by dividing the annual amount of green power procured in kilowatt-hours (kWh) by 10,766 kWh.
The conversion factor for this equivalency statement is [your annual green power purchase in kWh]/[10,766 kWh/American home/year].
- EIA (2017). How much electricity does an American home use?
Wind Turbines Running for One Year
In 2016, the average nameplate capacity of wind turbines installed in the United States was 2.15 megawatts (MW) (DOE 2017). The average wind capacity factor in the U.S. in 2017 was 36.7 percent (EIA 2018). Electricity generation from an average wind turbine is determined by multiplying the average nameplate capacity of a wind turbine in the United States (2.15 MW) by the average U.S. wind capacity factor (0.367) and by the number of hours per year (8,760 hours).
[2.15 MW average nameplate capacity] x [0.367] x [8,760 hours/year] x [1,000 kWh/MWh] = 6,912,078 kWh generated annually from one wind turbine.
The conversion factor for this equivalency statement is [your annual green power purchase in kWh]/[6,912,078 kWh/average turbine/year].
- DOE (2017). 2016 Wind Technologies Market Report (PDF) (94 pp, 2.4MB) U.S. Department of Energy, Energy Efficiency and Renewable Energy Division.
- EIA (2018). Capacity Factors for Utility Scale Generators Not Primarily Using Fossil Fuels.
Number of Football Fields of Solar Powered for One Year
The number of American football fields covered with solar panels is determined by dividing the annual amount of green power procured in kilowatt-hours (kWh) by 1,129,242 kWh, which is the estimated annual electricity output of one football field (including end zones) covered by PV solar panels.
Calculating annual PV solar system output is a function of the equation E = A * r * H * PR, in which:
- A = Total solar panel Area (m2)
- r = Solar panel efficiency (%)
- H = Annual average solar radiation on tilted panels (shadings not included)
- PR = Performance ratio, coefficient for losses (range between 0.5 and 0.9)
- E = Energy (kWh)
The factors for this equation were determined in consultation with experts at the National Renewable Energy Laboratory (NREL) based upon conservative best estimates and utilization of NREL's Annual Technology Baseline (ATB) tool and PVWatts Calculator. Based on these resources, NREL recommends these factors:
- A = 5,353.36 m2 (109.7 m x 48.8 m = area of American football field, including end zones)
- r = 15% solar panel efficiency of PV module (NREL 2017, Annual Technology Baseline, Solar Distributed Commercial PV: capacity factor for an average mid-resource location, Kansas City, MO)
- H = 1,635.2 kWh/m2/year annual average solar radiation for the U.S. (4.48 kWh/m2/day x 365 days) (NREL 2018, PVWatts Calculator)
- PR = 86% performance ratio (NREL 2018, PVWatts Calculator: 14% system losses)
Note: Due to rounding, performing the calculations given in the equation below may not return the exact results shown.
[5,353.36 m2] x [0.15] x [1635.2 kWh/m2.yr] x [0.86] = 1,129,242 kWh estimated annual electricity generated by one football field covered with solar PV.
The conversion factor for this equivalency statement is [your annual green power purchase in kWh]/[ 1,129,242 kWh/football field of solar/year].
- NREL (2017). 2017 Annual Technology Baseline. Golden, CO: National Renewable Energy Laboratory. http://www.nrel.gov/analysis/data_tech_baseline.html.
- NREL (2018). PVWatts® Calculator. Golden, CO: National Renewable Energy Laboratory. http://pvwatts.nrel.gov.
- Correspondence with Nate Blair, National Renewable Energy Laboratory (NREL) on 1/27/17.
Miles Driven by an Electric Vehicle
Based upon a review of DOE's fueleconomy.gov (DOE 2018) and conservative best estimates, an average of recorded efficiencies (kWh/100 miles) among fully electric vehicles (Model Year 2011-2019) is determined to be 34 kWh/100 miles. The number of miles driven by an electric vehicle is estimated by multiplying the annual amount of green power procured in kilowatt-hours (kWh) by [100 miles/34 kWh].
The conversion factor for this equivalency statement is [ [your annual green power purchase in kWh]*[100 miles]/[34 kWh] ].
- DOE (2018). http://www.fueleconomy.gov/feg/powerSearch.jsp.