About the NorthWestern Energy Net Metering Data

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This site aggregates data for hydroelectric, wind energy, and solar photovoltaic (PV) systems connected to the NorthWestern Energy’s electric distribution grid in Montana with a net meter from 2000 through 2014. The maps also indicate the distribution of renewable energy projects funded in part or in whole by Universal System Benefits (USB) grants administered by NorthWestern Energy, pursuant to Montana Code Annotated 69-8-402.



County Summary Data
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Download a CSV file of the County Summary dataset or the Yearly Summary dataset. Feel free to contact MREA with comments or corrections.

About the Calculations

NorthWestern Energy provided MREA limited data for each of the utility’s net metered accounts in Montana, as of December 31, 2014. The dataset included the following categories:

  • City
  • Zip Code
  • Building Type (irrigation, residential, commercial, school, government, non-profit)
  • Nameplate Capacity
  • Renewable Energy Type (Hydro, Wind, Solar PV)
  • USB Funded (yes or no)
  • USB Contract Year
  • Original Net Meter Ship Date
  • Renewable Energy Installer

Data that are NOT known by MREA include: address or exact location of the system, name or NorthWestern Energy account number of owner, USB grant amount, cost of the renewable energy system, height of wind turbine tower, orientation of solar panels, water resource, model of generating equipment, actual interconnection date, whether the system is still in operation, or actual amount of electricity generated.

NorthWestern Energy reported a total of 1,396 accounts that had been issued net meters as of December 31, 2014. Of those accounts, 8 were reported without data necessary for the calculations made for this project, such as energy type, nameplate capacity, location, USB contract year, net meter ship date, or the estimated interconnection date fell after December 31, 2014. For that reason, only 1,388 systems were included in this project’s maps and charts.

DATA MANAGEMENT
A “county” field was added to the database to aid in data interpretation and mapping. County affiliations were determined based on city and zip code of the account.

Interconnection dates were estimated for each system based on the net meter shipment date (which was provided in most cases). When a net meter shipment date was provided, interconnection was estimated as starting 21 days following the shipment date. This timeframe was estimated based on communications with experienced Montana renewable energy installers and NorthWestern Energy staff.

Output of Solar PV systems was estimated using a capacity factor of 14%[1] for all systems. To reflect the gradually declining efficiency of solar photovoltaics over time, a degradation factor of 0.5% per year[2] was applied to calculations of output. The annual output of a solar PV system was estimated using the following equation:

nameplate capacity (kW) x days generating x capacity factor (0.14) x 24 hours x derate factor (variable depending on years in operation) = kilowatt hours

Output of Wind energy systems was estimated using an average capacity factor of 9%.[3] An average degradation factor was NOT used for wind energy systems due to the wide variety of generator technologies. The annual output of a wind energy system was estimated using the following equation:

nameplate capacity (kW) x days generating x capacity factor (0.09) x 24 hours = kilowatt hours

Output of hydroelectric systems was estimated using an average capacity factor of 20%. The annual output of hydroelectric energy systems was estimated using the following equation:

nameplate capacity (kW) x days generating x capacity factor (0.2) x 24 hours = kilowatt hours

Based on the data available, it is not known which net meter facilities are still in operation. The end date of production used was December 31, 2014 for all calculations.

USB Funding Map
NorthWestern Energy provided the following information, which was used to assemble the Universal System Benefits (USB) Funding Map:

  • Cumulative USB grant funding dispersed per NorthWestern Energy service division, 2000-2014
  • Number of NorthWestern Energy customers per division as of 2014

[1] A capacity factor of 14% for solar PV systems was used with this project to correspond with calculations of solar PV output used by NorthWestern Energy, however actual capacity factors vary widely. Capacity factors for solar photovoltaic systems vary depending on orientation and tilt of the array, shading, efficiency of modules and inverter, solar radiation and meteorological conditions of the location. A tool developed by the U.S. Department of Energy for estimating the output of solar PV systems according to location and other system parameters can be found here.
[2] Analysis by the National Renewable Energy Laboratory of changes in the power output of solar PV systems over time showed the median degradation rate to be 0.5% annually. Source: Jordan, D. C.; Kurtz, S. R. (2013). Photovoltaic Degradation Rates – An Analytical Review. Progress in Photovoltaics: Research and Applications. Vol. 21(1), January 2013; pp. 12-29; NREL Report No. JA-5200-58443. http://dx.doi.org/10.1002/pip.1182
[3] A capacity factor of 9% for wind energy systems was used with this project to correspond with calculations of net metered wind energy output used by NorthWestern Energy, however actual capacity factors vary widely. Capacity factors for wind energy systems vary depending on tower height, efficiency of generator and inverter and local meteorological conditions. Turbines rated by the Small Wind Certification Council have capacity factors ranging from 10.6% to 20.9% in an area with average wind speeds of 5 meters per second. A map developed by the U.S. Department of Energy showing Montana’s wind energy resource can be found here.

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