Photovoltaic output can be hugely impacted by weather conditions. Incident solar energy can be significantly altered by even intermittent cloud cover, whilst other factors like wind direction and speed, air temperature, humidity, precipitation and air pressure can all influence the output efficiency of solar cells.
Image Credit: OTT HydroMet - Solar Energy
It is, therefore, crucial to accurately monitor weather conditions to better understand variations in PV plant performance.
Why is it Important to Monitor Weather Parameters?
Variations in weather conditions are of critical importance for commercial and industrial PV systems, despite the fact that they may only be of minor concern to the average domestic PV user.
Even trivial relative fluctuations in performance can make a huge difference for large installations in terms of overall productivity, and, as such, it is important to closely monitor any source of output variation to ensure that the overall system is performing optimally.
Meteorological monitoring is essential in such cases so that it can be determined whether any marked variations in output are indicative of a serious hardware degradation or malfunction or simply due to weather conditions.
When it comes to understanding PV system health and scheduling maintenance on time, weather monitoring is an essential factor. Seasonal trends can be uncovered via the analysis of historical data – on precipitation and wind conditions, for instance, which in turn can be used to optimize seasonal maintenance and cleaning schedules.
When it Comes to Solar PV, Which Weather Parameters are Important?
When it comes to determining the efficiency of a solar plant, measurements of solar irradiance are crucial.
Typically, this is expressed in terms of PR, the performance radio: the true yield of the plant (the amount of energy the plant produces in a given time period) expressed as a percentage of its theoretical yield (assuming the panels were able to convert the incident light into energy at their nominal efficiency, the amount of energy it could produce in that time period).
Performance Ratio = Actual Yield / Theoretical Yield x 100
Calculation of the theoretical yield of a plant is only possible when using measurements of different components of solar irradiation. Therefore, these measurements are essential when it comes to calculating the performance ratio, which is itself a key indicator for PV asset owners – but it’s certainly not the only parameter of interest.
To gain a complete picture of plant performance, it is important to monitor other weather parameters that directly impact solar cells.
Module and Ambient Air Temperatures
Temperature significantly impacts photovoltaic efficiency. The efficiency of a typical PV module drops by around 0.5% for every degree centigrade the temperature rises over 25, as a general rule of thumb.
The calculation of a temperature-corrected performance ratio is facilitated by measuring both the temperature of ambient air and the modules themselves, which gives PV plant operators a more accurate picture of the plant’s performance.
Wind Direction and Speed
Wind can also have a dramatic effect on PV module temperature: wind cools down PV surface temperatures, which are typically hotter than ambient air, which therefore increases their output and efficiency in warmer environments.
Knowledge of wind conditions can play an important role in soiling monitoring, as wind also has a significant effect on soiling.
Monitoring wind speed and direction is often important for determining safe locations for equipment, and, since high wind speeds can damage PV installations, this can affect insurance payments.
PV plants can be affected, both positively and negatively, by different kinds of precipitation.
While heavy rainfall can significantly ease soiling by washing off dirt, light rainfall can actually increase panel soiling.3 Hailstorms can also cause serious damage to equipment and panels.4
Air Pressure, Dew Point and Humidity
The occurrence of snow, frost and condensation on panels can be affected by air pressure, humidity and dew point, which can have an effect on soiling as well as decreasing energy output. In particular, air humidity can also generate spectral changes, which has an impact on the productivity of PV modules.
Creating an Effective Meteorological Station for Solar PV
Assembling a meteorological station capable of providing complete and accurate information can be daunting due to the number of parameters of interest coupled with the sheer volume of different sensors available today.
The process of mixing-and-matching sensors from different vendors can often mean battling with multiple data formats and software interfaces, as well as grappling with multifaceted mounting configurations and long cable runs. OTT HydroMet provides a complete range of meteorological sensing solutions to overcome these challenges and offer a simplified and integrated experience.
Schematic environmental monitoring setup by OTT HydroMet tailored for solar PV plants. Image Credit: OTT HydroMet - Solar Energy
OTT HydroMet and Meteorological Sensors
Meteorological sensors from OTT HydroMet are perfectly designed for commercial and industrial solar PV installations.
The Lufft WS line boasts a range of powerful instruments, each of which has various combinations of sensors for measuring atmospheric parameters. The Lufft WS600 is recommended for solar PV applications: perfectly designed for its purpose, it measures wind speed and direction, air temperature, air pressure, relative humidity and precipitation.
Purpose-built to deliver best-in-class accuracy and long-term reliability, Lufft WS all-in-one sensors come with active ventilation and integrated heating, providing industrial and commercial PV facilities with unparalleled insight into plant performance.
As a result of its simple modular design, the WS600 can easily be integrated into existing data acquisition systems through a single Modbus connection. HydroMet’s Smart Hub facilitates easy integration with other OTT HydroMet solutions: the Hub enables simple connection of soiling monitoring systems, pyranometers and weather sensors to be connected.
OTT HydroMet’s complete environmental monitoring system means that all relevant weather parameters can be accurately, easily and reliably monitored with verified instruments from its brands, including Lufft and Kipp & Zonen.
For Solar PV plants, the recommended selected setup is as follows:
Users may also wish to consider the new Kipp & Zonen SMP12 Class A pyranometer: this equipment features both integrated heating and additional components which combine to maintain the highest measurement accuracy, e.g., sensitive sensors which can measure the humidity and tilt angle inside the housing.
To find out more about meteorological solutions for solar PV applications, contact OTT HYdroMet today and a member of the team will be happy to answer any questions.
This information has been sourced, reviewed and adapted from materials provided by OTT HydroMet - Solar Energy.
For more information on this source, please visit OTT HydroMet - Solar Energy.