Embedding a Visual Range Camera in a Solar Receiver

Abstract One of the main problems in CSP (Concentrating Solar Power) technology is correctly evaluating the flux on the solar receiver. What we would like to know in a perfect world is how much energy each heliostat contributes at all times, and at what part of the receiver it aims. It has always been difficult to know this since there has not been a way to photograph all the heliostats in the solar field from the extremely hot receiver. Current methods use cameras located at a distance from the receiver panels to capture images of the heliostats, and then extrapolate the expected behavior of the heliostats during normal operation. Because the cameras are sensitive to heat, the number of heliostats that they can capture at one time is limited, and the data they capture is of heliostats aiming at locations other than the receiver itself. The information thecameras gather is processed offline, and does not give the current status in realtime. To perform these measurements, the heliostats must stop fluxing on the receiver and flux on the cameras instead, which reduces the total available energy. BrightSource has createda new type of camera – the pinhole camera – that can be embedded inside the solar receiver's high-temperature environment where standard cameras cannot be installed. The proposed pinhole camera method embeds cameras inside the solar receiver in various locations. The pinhole camera captures images of the heliostats at all times, including during flux operations. Post-processing of the visual image allows us to precisely calculate the flux on the camera's position, and the exact contribution of each individual heliostat at that position. By extrapolation, it is possible to estimate the flux map of the entire receiver. The data from each individual heliostat is also used to evaluate the heliostat's behavior: the quality of its aiming, its cleanliness, reflectivity, and other parameters. This paper describes the pinhole camera hardware solution, and the method's algorithm in a conceptual and qualitative manner.