The ultimate integrated instrument for sun tracking accuracy assessment and DNI measurement

Some solar systems, photovoltaic or thermal, are set into motion by appropriate mechanical structures in such a way that they are always orientated perpendicularly to the direction of the solar radiation, allowing a more effective collection of the power emitted by the Sun. In some cases, these solar systems are mounted on mechanical or electro-mechanical structures which are able to follow the Sun in its apparent movement and, therefore, they allow such systems always to be orientated perpendicularly to the direct solar radiation, or rather, to the radiation which arrives directly from the solar disc. This system, as well, allows the maximising of the efficiency of the collection of solar radiation over the range of the whole day.

The producers of solar tracking systems usually specify the precision with which the system is able to align itself in the direction of solar radiation. However, the instrumental proof of this indication is very rarely furnished. Furthermore, the alignment error can depend on environmental conditions (force of the wind, thermal deformation, clouds) or by contingent conditions (dust accumulated on the positioning optical sensors, errors in the timetable used for the calculation of the solar ephemerides). The use of an instrument preset for the measurement of angular precision with which the movement system tracks the Sun is, therefore, of extreme importance for supplying a quantitative indication of the error committed and of the temporal trend of such error, in such a way as to be able to correlate particular environmental conditions or contingencies.

The instruments currently on the market for the detection of the solar tracking precision, typically make use of positioning sensors (CCD, CMOS or PSD) which, for their intrinsic characteristics, cannot supply precise radiometric measurements of the incident luminous intensity on the sensor.

Solar tracking is the most effective way to maximize the energy production of photovoltaic modules, and it is a mandatory issue in concentrating solar power (CSP) systems.

Sun tracking errors may occur for many reasons: wind load, uneven thermal expansion of the tracking structure, sun sensor thermal drift, or errors of the tracking algorithm.

The assessment of the tracking accuracy is mandatory to qualify performance and reliability of trackers in operative conditions and provides a pathway to identify and correct tracking errors thanks to a high precision digital feedback.

AKKUtrack™ is an advanced tool that allows to measure quantitatively the degree of accuracy of solar tracking systems and simultaneously provide an indication of sunlight intensity at different wavelengths, offering the advantage of having two different functions in one instrument. It’s a real monitoring station for measuring the direct solar radiation that uses a multispectral camera.

The great amount of data provided by AKKUtrack™, not only gives measurements of solar irradiance at various wavelengths, but it also allows to validate the data recorded by a measure of the error in the pointing of the solar source.

Image processing provides a variety of informations unavailable through conventional measurements.

The integration of DNI measurement feature into AKKUtrack™, makes it a simple and powerful instrument. The software analysis of the field of view provides a validation of DNI measurement and identifies the source of irradiance drops. 

A patented technique implemented in EVA allows to retrieve the wide spectrum DNI from monochromatic images of the solar disc.

The log file can be easily analyzed in real time to retrieve the energy production loss due to tracking errors.

AKKUtrack instrument is a real innovation in the field of diagnostic systems for photovoltaics and allows the user to obtain a measure of all the parameters necessary to evaluate the productivity and reliability of photovoltaic systems based on solar tracking.

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PRODUCT SPECIFICATIONS:

FIELD OF VIEW: 4.5° x 2.9° (HxV) DNI RANGE: 100 ÷ 15000 W/m2
RESOLUTION: 0.01° RESPONSE TIME: < 0.1 s
RELATIVE ACCURACY: ± 0.01 ° ACCURACY: ± 20 W/m2
SAMPLING RATE: 60 frames / s OPERATING TEMPERATURE RANGE: –30 ÷ +70 °C
DATALOGGING RATE: from 4/hour to 20/minute TEMPERATURE DEPENDANCE ON SENSITIVITY (-20°C to 50°C): < 10 %
ENVIRONMENTAL PROTECTION CLASS: IP 66 RoHS COMPLIANCE: YES
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