As an international reference for the solar international photovoltaics (PV) community, pv magazine is well aware of the value of forecasting for PV projects of any size. In their November 2021 edition, weather forecasting was highlighted in the article “Forecast for foresight, and prosper“. The cloud cover significantly influences power output, as do high winds, heavy snowfall, fire, and hail – and can lead to module or structural damage. Read an excerpt of the article to find out more about the value of PV production forecasts:

Forecast for foresight, and prosper

At the risk of stating the obvious, PV performance will always be inextricably linked to the weather. Cloud cover significantly influences power output and severe weather events – including high winds, heavy snowfall, fire, and hail – can lead to module or structural damage. And with climate change making extreme weather events more common, the value of forecasting and understanding the worst Mother Nature can throw at a solar array is increasing.

The list of damages that severe weather can cause at solar projects is long, and there is still much to learn about the extent of such damage. Hail can shatter glass or send shockwaves through a module, causing cell cracking, losses and degradation. High winds can contort ground-mount installations and trackers in particular, straining and warping mounting systems and hardware. And heavy rainfall, flooding or even consistently high humidity can lead to water ingress and degradation.  Knowing that each weather event presents some level of concern, predicting and preparing for these events has emerged as a lucrative business opportunity of its own, with software and monitoring providers helping solar operators avoid some of these output losses, and generate revenues as a result. With offices in the French territory of Réunion, Paris and Toulouse, Reuniwatt is a weather forecast service provider, working with a range of solar PV owner-opera-tors around the world. The company offers four main products for solar PV installations: Sky InSight™, InstaCast™, HourCast™ and DayCast™. They are demonstrating their merit at a project owned by 8minute Solar Energy’s Springbok Solar Cluster. The Springbok Cluster has a capacity of 443 MW in the Mojave Desert, in Kern County, California. Given its size, passing clouds cover can result in significant generation either ramping up or down. The Springbok Solar Cluster produces on average about 10% of the power needed for the city of Los Angeles, so ensuring maximum production, timely power delivery, minimal curtailment, and advance warnings of potential interruptions is critical. Through its sensors and digital toolkit, Reuniwatt is providing forecasts of the solar radiation and plant generation for periods ranging from a few minutes in advance, up to several days ahead. The Springbok Solar Cluster utilizes single-axis trackers and is paired w th a 1.5 MWh lithium-ion battery.

Forecasting toolkit

Marion Lafuma, a business development manager with Reuniwatt, provides some insight into how the company’s forecast toolset delivers at the Springbok project. HourCast™ uses data provided by geoststionary satellites to track cloud movements and weather patterns in order to provide intraday forecasts from 10 to 15 minutes, depending on the location and generation of the  satellite, up to six hours in advance. DayCast™ uses numerical weather prediction models developed by international weather agencies and hybridized with local weather information to improve the forecasts. It also adds additional weight onto the models which perform best on the type of location we’re looking at –there is variance in the performance of each model, dependant on differences in geography and climate. This blend enables weather forecasting anywhere from six hours ahead to up to 10 days. InstaCast™ utilizes the Sky InSight™ weather measurement system. Sky InSight™ is an infrared all-sky imager giving a temperature reading for a certain area of the sky above the solar PV plant, with the sun being the obvious constant as the hottest point. The camera can then determine any cloud’s height in the sky and its temperature. According to Lafuma, high and cold clouds usually present no issue beyond marginal production drops, whereas low and hot clouds can reduce output more significantly, along with bringing storms with them. With these offerings, Reuniwatt is able to create a global horizontal irradiance forecast, which gives site irradiance readings down to the square meter, and power production forecasts. Solar forecasts are critical to the operation of the cluster, allowing it to serve as one of the world’s first fully dispatchable utility-scale solar PV and energy storage projects, its proponents claim. Dispatchable solar power needs to be available at the request of grid operators or the plant owner to match the demands of the market. To meet these requirements, energy storage serves a huge role, providing flexibility to overcome the imbalance between periods of peak solar generation and times of peak demand. Reuniwatt claims that the high level of forecasting detail allows the operation of the battery to be optimized. It also assists in partially overcoming energy and power issues traditionally linked to solar power variability – such as generation curtailment and frequency variation, while allowing for ramp rate control and energy smoothing. Another benefit, Lafuma suggests, one she says is often overlooked, is that accurately forecasting battery discharges enables asset managers to prolong battery lifespan, because the number of annual cycles required can be reduced, facilitating the development of more large-scale battery projects. (…)”

The article by was originally published on pv magazine (Nov 2, 2021). You can read the full article on or in the November 2021 pv magazine global print edition, pp. 40-43 .

About Reuniwatt (
Reuniwatt is a major player of the solar radiation and cloud cover assessment and forecasting. Based on solid Research and Development works, the company offers reliable products and services intended for professionals of various fields, making the best out of two key facets of the meteorology: atmospheric physics and data sciences. A particular focus has been placed on solar energy forecasting, while developing cutting edge solutions to improve the short-term prediction of the solar resource.
The company has won many grants, including H2020’s SME Phase 1 programme, which makes Reuniwatt a European Champion with regard to innovation. Reuniwatt has also been selected among the national fast-growing companies to join the prestigious French Tech 120 programme in 2020, and remains a part of the selection for 2021, and the French Space Tour 2021.