PVWatts

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PVWatts is an online calculation tool used for estimating the energy production and cost savings grid connected PV systems at locations around the world. PVWatts is used by a full-spectrum of people, including those wanting to get an initial, high-level understanding of PV potential to those wanting to generate an hourly output for a site. Two versions of PVWatts are available. Version 1 allows a user to select a location from a map or text list of pre-determined locations throughout the world. Version 2 allows users to select any location in the United States.



 



Overview

PVWatts is an online calculation tool used for estimating the energy production and cost savings grid connected PV systems at locations around the world. PVWatts is used by a full-spectrum of people, including those wanting to get an initial, high-level understanding of PV potential to those wanting to generate an hourly output for a site. Two versions of PVWatts are available. Version 1 allows a user to select a location from a map or text list of pre-determined locations throughout the world. Version 2 allows users to select any location in the United States.

The PVWatts Viewer is an interactive map providing access to multiple data sets which link directly to their corresponding PVWatts Calculators, allowing the user to determine energy production and cost savings of grid-connected solar photovoltaic (PV) systems. Both calculators are accessible through the viewer by querying their corresponding data layers, which feature weather data in the form of specific locations (239 TMY2 sites in the United States and 76 international) as well as a 40km x 40km grid which covers the United States.

The PVWatts Viewer provides easy access to both datasets. This application, built on ESRI Flex Viewer, utilizes an interactive web mapping interface that allows you to query both data sets simultaneously for any specified location. The screenshot below illustrates the various data sets as they are displayed in the PVWatts Viewer. Station locations are indicated by a black cross with a yellow center and a 40km solar resource grid (yellow to red squares) is overlaid on top of a street map of the United States.

Inputs and Outputs

Inputs include:

  1. The user first selects a location from a map or text list of pre-determined locations throughout the world (for Version 1) or from any location in the US (for Version 2).
  2. The user then inputs the following data for the location and system being considered:
    • DC rating (in kW)
    • DC to AC derate factor
    • Array type (fixed tilt, 1- or 2- axis tracking)
    • Array tilt (in degrees)
    • Array azimuth (in degrees)
    • Cost of electricity (in cents/kWh)
  3. Default values are provided for all of these inputs, should the user need to use those.[1][2]
Outputs include:

The tool outputs the following location-specific information:

  • latitude
  • longitude
  • elevation

It outputs the following PV system information on a monthly basis:

  • Average solar radiation (kWh/m2/day)
  • AC energy (kWh/month)
  • Energy value ($/month)

Annual numbers are also provided for three outputs:

  • Average solar radiation (kWh/m2/day)
  • AC energy (kWh/year)
  • energy value ($/year))

The user is also able to output hourly performance data (AC power (W)) for many typical meteorogical year (TMY) datasets.

Highlights

PVWatts is one of the most commonly-used tools for estimating the potential electrical output associated with a PV system. It is very straight-forward to use and it also enables the user to procure hourly output data, which could be useful in a more detailed analysis of solar PV potential.

Notes

PVWatts is a web-based tool that calculates electrical energy production and cost savings of grid-connected photovoltaic (PV) systems. Researchers at the National Renewable Energy Laboratory developed PVWatts to permit non-experts to quickly obtain performance estimates for grid-connected PV systems.

PVWatts estimates the hourly performance of a photovoltaic system using a single derating factor to convert solar radiation data from an hourly weather file to hourly AC output estimates. The model applies a temperature correction factor to these estimates using temperature data from the weather file to account for the effects of temperature on system performance.

To run the model, the user selects a weather file by either clicking on a map or selecting a location from a list, enter values for five variables describing the PV array's DC capacity, DC to AC derating factor, and tracking and orientation. To calculate the value of cost savings through avoided electricity purchases, the user must enter an electricity cost. The results display information about the weather station from which the weather data was developed and monthly averages of the solar resource, specifications of the PV system based on the user-specified inputs, and monthly estimates of AC electrical output with the value of energy saved based on the user-specified cost of purchasing electricity.

The PVWatts calculator is available in two versions. Version 1 allows users to select a location from a map or text list of pre-determined locations throughout the world. Version 2 allows users to select any location in the United States.[1]

Resources

PVWatts Version 1
PVWatts Version 2
The National Solar Radiation Data Base is used by the tool for several of the calculations and can be used for finding local inputs. [2]

References

  1. 1.0 1.1 1.2  "PVWatts PVWatts"
  2. 2.0 2.1 2.2  "National Solar Radiation Data Base"