Our innovative and patented sky cameras were developed by Reuniwatt for the continuous tracking and forecasting of the cloud cover. What are they offering and how can they be useful for solar power plants and other applications?

 

Discover Sky InSight™ and Sky Cam Vision™ 

The variability of clouds above a site is a challenge for power plant operations and meteorological purposes alike. Sky cameras can be installed on-site and give information about the cloud cover, provide forecasts of the solar irradiance and the generated PV energy every 30 seconds, with a resolution of up to 1 data point per minute for the next 15 minutes.

For power plant operators, all-sky imagers allow the prediction of steep changes in irradiation (“ramps”) with very high accuracy. Once they have been detected by the system, controls can be adjusted accordingly, to counteract a production drop by activating and relying on other power sources or avoiding curtailment of available PV energy in case of a sudden increase in power production, through regulating the power generation from other sources. This is especially relevant for off-grid hybrid installations that combine solar with thermal or other renewable energies, but also to comply with grid operator rules and to ensure grid stability. In case of installed battery energy storage, the piloting rules need to comply with the charging and discharging rates enabled by the system. Knowing the expected production from renewable sites very accurately is important to obtain certain target load conditions and again, to optimize operations. In time of day tariff power purchase agreements, the value of the energy varies over the course of the day and the year. In direct marketing operations the energy value changes within a 15-minute time frame. Knowing future generation allows to operate the plant in a grid-supporting mode, which at the same time means to generate additional revenue.

For universities and meteorological researchers, the images provided by the sky imagers are a useful tool for cloud-related studies, and can be used in combination with measurements from other instruments, such as GHI or liquid water path. Other applications include air traffic controls, which rely on real-time sky images from all around the facility to improves safety and be aware of potentially hazardous weather conditions before they occur. The cameras’ cloud data also makes sure that air controllers are aware of sudden changes in the visibility.

In the measurement process, the camera acquires images of the entire sky vault every 30 seconds. The embedded computers process these images for further analysis and provide the output data in a convenient format (standardly .jpg or .csv). Coupled with Reuniwatt’s InstaCast™ software for the intra-hour forecasting of the cloud cover, it provides short term forecasting of up to 30 minutes in advance and anticipates local events. Probabilistic forecasts can also be provided here, and can be relevant to cover the risk even for unlikely cloud events.
 

Sky InSight™ provides highly accurate short-term irradiation forecasts


Our innovative and patented infrared sky camera Sky InSight™ was developed by Reuniwatt for the continuous tracking and forecasting of the cloud cover 24/7. Sky InSight™ uses infrared vision technology, which enables an unprecedented accuracy in cloud detection and allows cloud observation day and night with a constant accuracy. Another perk of the infrared vision is that is not blinded by the sun’s glare – which is particularly useful for solar forecasting, since the most interesting region to forecast the solar radiation in the next minutes is the circumsolar area.

The high-performance instrument enabling all these functions is Sky InSight™’s infrared camera, which takes a picture down to every 30 seconds, and provides a 360°x180° images of the cloud ceiling thanks to a hemispherical mirror. The images are acquired on the embedded computer and transmitted through a usual protocol (FTP, SFTP, HTTP, Modbus, Email). A range of software applications have been developed to extract various cloud features from this brightness temperature images of the sky, such as cloud fraction, cloud-base height or even cloud classification. The housing is designed to resist strong environmental conditions. It is rated IP 65, and highly resistant to corrosion, dust and liquid ingress, and operates from -40°C to +60°C. Its solid, reliable hardware results in almost no maintenance costs. The equipment has been installed and operated successfully within various climates, including rainforest/mooand desertic zones. Sky InSight™ was the first and is the highest quality all-sky imager using the infrared thermal spectrum, and ensures you are always up-to-date with your local cloud and irradiance levels.
 

Sky Cam Vision – an automatic all-sky imager for many applications


Sky Cam Vision™ is an industrial-grade sky camera system operating in the visible spectral range with a fish-eye lens. Sky Cam Vision™ contains an embedded computer for image processing and cloud cover estimation and forecasting. The imager’s onboard mini-PC together with a data storage device perform a local processing of the images and a global horizontal irradiance (GHI) sensor, used for verification of the forecasted data. Continuous cloud information and the system status will be forwarded to the power plant operator. Using a CMOS sensor, it has a a 360°x180° field of view obtained thanks to a fish-eye lens, and delivers images with 4.2 Mpx resolution. The equipment is suitable even for harsh climatic conditions and withstands temperatures from -20°C to +50°C.

Just as Sky InSight™, some software services specifically developed to get the most of the Sky Cam Vision™’s cloud imaging capability are offered, for cloud studies or solar forecasting applications. The irradiance forecasts are provided through InstaCast™ service, which combines image processing with machine learning techniques to guarantee the best adaption to the site’s specific conditions. The forecasts can be computed locally and sent to the SCADA or power plant controller via Modbus, for integration into the plant’s control scheme – completely offline, if necessary, to serve even the most remote projects.
 

Sky cameras help optimize hybrid plant control mechanisms

PV-Diesel(-Storage) hybrid plants have been established as a price competitive choice for the electrification of isolated and remote communities and as off-grid plants for C&I applications. Using an all-sky imager in combination with our forecasting tool InstaCast™ for an up to 30-minute forecast, enables plant operators to predict upcoming GHI time series for the given location within a 306°x180° field of view / 2 km radius and optimize power plant controls according to upcoming changes in solar production. Installing PV overall reduces the operational costs, while diesel compensates the PV variability risk. But clouds passing over a PV installation can lead to serious production drops and even cause a blackout in seconds, if unprepared. This is a serious issue for off-grid projects and one of the applications for Reuniwatt’s sky imagers. Reuniwatt’s local and highly accurate forecasts delivered by Sky InSight™ and Sky Cam Vision™ can be considered to bring higher cost-efficiency to renewable hybrid plants. All-sky imagers make it possible to adapt plant operations and bring the generators online right on time for absorbing strong production changes caused by GHI variability, avoid blackouts and reduce related costs, and overall optimize power plant controls and provide the plant owners with an additional fuel saving potential. In other words, the locally installed all-sky imager implies higher return-on-investment benefits and a safer PV ramp control due to the anticipation of large PV production drops.
 

From sky observation to sustainability

Reuniwatt has focused on developing the best skills in cloud observation through investing in research and development in order to deliver the best-in-class irradiance reconstruction and forecasting model. Given its island origin, Reuniwatt was founded at a time where solutions were needed to ensure grid stability on Reunion Island with the increasing share of PV energy. Reunion is an island with tropical climate and more than 200 micro-climates. For this island with abundant solar irradiance and ambitious renewable energy goals, the issue of the changing cloud cover and its impact on grid stability needed to be tackled, therefore Reuniwatt has been a specialist in solar energy forecasting since the founding of the company in 2010, and since successfully installed sky imagers all around the world in over 50 different locations, from Brazil to New Caledonia. Reuniwatt’s sky imagers have been developed with the ambition to deliver the best quality input data for irradiance forecasting, and our forecasts provide you with highly accurate results thanks to many years of ongoing research and field experience.

About Reuniwatt (www.reuniwatt.com)
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.