Many residential PV system Web portals can access weather data from a local public weather station—keeping costs lower by reducing the number of monitoring components and sensors. If using your own weather station, be sure that the monitoring system is compatible with the station’s sensors. Consider the following components for your weather station:
Pyranometers measure solar irradiance, and are usually mounted in the same plane as the array to measure the actual direct and diffuse irradiance received by the PV modules. This is called plane of array (POA) irradiance. A second pyranometer can be mounted horizontally (a flat plane) to measure global horizontal irradiance (GHI). GHI is the component of historical meteorological satellite data that is mathematically modeled at different tilts to estimate PV system energy production resulting from POA direct and diffuse irradiance.
Temperature sensors measure cell temperature from the back of PV modules, while an ambient air temperature sensor is in free air. Cell temperature can be used with POA irradiance values to calculate whether a specific size PV array is producing the expected amount of power. Performance ratio can be calculated by dividing monitored production by expected production. The closer to “1” the ratio is, the better the array’s performance. The performance ratio is often prominently displayed on a Web portal, as it provides quick insight on whether a system is performing properly. The performance ratio can be calculated as an instantaneous value based on 15-minute interval power data.
Anemometers measure wind speed, and usually have a vane to measure direction. While wind can help cool PV modules, this data is not necessary for PV monitoring or to calculate a performance ratio. The equipment is normally provided in home weather kits and people who like PV data often have a similar affinity for wind and other weather data.
A pyranometer, which measures solar irradiance, can be helpful for verifying PV system performance in varying weather conditions.