The DLR Institute of Solar Research has developed jointly with Black Photon Instruments (BPI), a spin-off of the Fraunhofer ISE, a new optical sensor to measure circumsolar radiation. It enables the operators of solar thermal plants to measure the circumsolar radiation on site.
The new technology is now applied for the first time in a commercial solar thermal steam plant in Southern Oman that was built by GlassPoint Solar for Petroleum Development Oman (PDO). The new sensor BPI CSR460 has been developed for the use in solar thermal plants in challenging desert environments, prone to extreme heat and high levels of airborne dust, dirt and sand.
What is the measurement of the circumsolar radiation?
Understanding the circumsolar radiation at a specific site enables solar thermal project developers and operators to improve the accuracy of their plant performance.
In solar thermal power plants, mirrors concentrate the direct solar radiation onto a receiver. The receiver contains a heat transfer fluid such as water, which is heated by the concentrated solar radiation and used to generate steam, electricity or to heat, cool or purify water.
Solar radiation deflection is caused by clouds and aerosol particles, such as desert sand in the air. If a portion of the radiation comes not directly from the sun center, but from the circumsolar field—for example, 2° off from the sun center—the radiation is not focused properly on the receiver and does not contribute to the heat generation.
The circumsolar radiation impacts the efficiency of the solar collectors. With the knowledge of the circumsolar radiation, project developers can design the solar thermal plant according to the expected efficiency (more mirrors) or adopt its components to capture more of the available energy (e.g. better mirrors, larger receiver tubes).
Advantages of the new sensor
Compared to the SFERA measurement system that is used at DLR for research purposes, the new sensor needs less maintenance, is easier to use and is less expensive. Like the SFERA system, the new sensor withstands the extreme weather conditions, which often prevail at the sites of solar thermal power plants.
Another special feature is the self-cleaning function of the sensor, developed by BPI.
The “AirShield” technology consists of an air- supply unit that provides compressed filtered air and a distribution system integrated into the sensor that guides the compressed air via 4 nozzles to the entry window to keep it free from dirt and dust. This feature increases the accuracy of the measurements and reduces maintenance costs.
New sensor is first used by GlassPoint in a steam generation plant in Oman
GlassPoint develops and manufactures solar steam generators built specifically for harsh desert environments. Its enclosed trough technology seals large parabolic mirrors inside a glasshouse to protect the solar collectors from wind, dust and sand, common throughout the Middle East region.
In 2013, GlassPoint commissioned a 7MWth project with Petroleum Development Oman (PDO) at PDO’s Amal West oilfield in South Oman. The facility generates steam for heavy oil extraction, a process called solar enhanced oil recovery (solar EOR), which reduces the amount of natural gas typically burned for steam generation.
For this project, GlassPoint used the BPI CSR460 sensor to determine the influence of circumsolar radiation on plant performance. GlassPoint is the first company to use this sensor technology to measure circumsolar radiation in demanding real-world operating conditions, applying the data to enhance performance.
"GlassPoint built the enclosed trough from the ground up to overcome high winds and dust common throughout the Gulf region," said Ben Bierman, GlassPoint Chief Operating Officer. “The CSR460 gives us greater insights into the value of the energy we can capture from sunlight as the sunshape changes over the course of the day. As a result, we are able to better model and design our system to ensure the enclosed trough operates economically at the highest efficiency.”
GlassPoint, DLR and Black Photon Instruments strive to continue their close cooperation to develop innovative solutions for the use of solar energy and the required measurement technology in desert regions with strong solar radiation and high dust content.
Development was carried out as a joint project of DLR and BPI
Scientists of the DLR and the Fraunhofer spin-off BPI have been working for several years on the technology for measuring the circumsolar radiation. BPI has licensed the sensor technology from the Fraunhofer ISE since 2005 and has continued to develop the sensor ever since.
The DLR Institute of Solar Research developed a calibration method as well as the data processing software of the new BPI CSR460 sensor which is now licenced to BPI. DLR’s scientists validated the measurements and tested the sensor technology under real environmental conditions at the Plataforma Solar de Almería of the Spanish research partner CIEMAT.
The work was supported by funds of the project SFERA within the EU FP7 program and of the Deutsche Umweltstiftung (German Environmental Foundation).