How does Nearmap calculate the annual energy output of a proposed solar installation?
We calculate the annual energy output of a proposed solar installation using:
- User-specified panel and system parameters
- Predicted sun positions
- Local solar irradiance and temperature data
This article explains the source of each of these inputs, and how we combine them to calculate the Annual output value shown in kilowatt hours (kWh).
User-specified panel and system parameters
The number, type, location, orientation and tilt of the solar panels you place in your design will affect the annual energy output of your solar job. See the Solar installation design tutorial for basic information on setting up a solar job.
You can also specify an overall system efficiency value to account for other factors that affect the output of your proposed solar installation. This efficiency value is not calculated by Nearmap, so it must be entered accurately for the output calculations to be accurate as well.
Please see our support article on System efficiency and panel parameters for details on configuring the specifications of a solar unit, and setting the system efficiency value.
Predicted sun positions
We predict instantaneous outputs of the solar cells in a solar job, which are then integrated over the course of a year for an annual value. To predict the annual output of a given solar cell, we first need to predict the positions of the sun; we use the PSA (Plataforma Solar de Almerýa) algorithm to do this.
Local solar irradiance and temperature data
Our calculations also take into account the average solar irradiance and temperature in the location of a solar job. In both Australia and the continental USA, irradiance data comes from hourly satellite observations over a nationwide grid.
Temperature data in the USA, and irradiance data for Hawaii and Alaska, comes from ground-based weather stations.
In all cases, we average the data for each location to produce a typical year for irradiance and temperature. These values feed into our calculation of the output for a solar job in kWh.
For solar irradiance data in the continental USA, we use hourly gridded data with 0.1 degree latitude/longitude spacing from the National Renewable Energy Laboratory’s (NREL) National Solar Radiation Database (NSRDB) SUNY model. This model uses geosynchronous satellite measurements of solar irradiance taken between 1998 and 2005.
For Hawaii and Alaska, solar irradiance data is taken from the output of ground-based weather stations. These measurements were taken hourly between 1991 and 2012.
To calculate thermal derating of solar cells in the USA, we use temperature data from ground-based weather stations across the nation. These measurements were taken hourly between 1991 and 2012.
Solar irradiance and temperature data for Australia
For solar irradiance data in Australia, we use direct and diffuse historical solar irradiance data from the Australian Bureau of Meteorology. This data was sampled hourly between 1990 and 2013 over a nationwide grid with 0.05 degree latitude/longitude spacing. This grid gives approximately a 5km resolution.
To calculate thermal derating of solar cells in Australia, we use monthly maximum temperature data sampled over the same grid.