Page 55 - RSE - Results of the Apollon Project

Results of the APolloN PRoject ANd coNceNtRAtiNg PhotovoltAic PeRsPective

APOLLON Activity and Main Achievements

Sensors

Two different strategies have been evaluated in the project. The frst option was using the magnetic sensor of
HCM505 digital compass of Rion Technologies to provide the pointing error in azimuth. The accuracy specifed in the
datasheet is around 0.1º but that is not in agreement with the feld tests results, probably due to the great variability
of the magnetic felds in this type of environments (metallic structures, high motor currents, etcetera).
The second option was using a CCD based Sun sensor provided by RSE. The data provided by the PSD sensor
of RSE is different from the data provided by the HCM505. The frst only provides the pointing error relative to the
sun while the HCM505 provides the absolute position of the tracker, so the tracking strategies to be adopted were
different. In the frst development phase, the APOLLON system used a hybrid control strategy: frstly, the position
of the sun was calculated with an ephemeris algorithm and when the error was lower than a limit, the PSD sensor
drove the tracker in optimum position.
The sensor was initially installed in the tracker of Solartec company, located in Bilbao, and different tests were
carried out (see Figure 60). As shown in the picture, two sensors were used in the process setting up, because it was
very diffcult to install the sensor on the same plane as the panels ( which justifes the need to use an Intelligent
module with integrated PSD sensor as developed in the APOLLON Project, see previous chapter). This way, the Track
Stat SL1 [7] sensor was used to obtain the best position for the PSD sensor of RSE.

FiguRE 60. Installation of the sun sensor on SolarTec Tracker

Once the sensor was correctly installed and confgured, the control was adjusted in order to avoid residual errors
like the position of the limit switches, the quantifcation error of the encoders, etcetera. This phase was also very
complicated because a glide effect was detected in the movement of both motors, but fnally the results obtained
were satisfactory, providing errors lower than 0.1 deg.
These results were also confrmed later in Italy (Gorizia) in the second development phase of the project. The
solution implemented there used a pointing sensor from Solarmems (ISSD60 [8]) with a large acceptance angle in
order to achieve a frst approximation (similar to open loop control) then working with the PSD sensor.
Electronic Control Systems

Due to the required measurement accuracy and processing capacity, including a great number of non-linear
operations, the development of an exclusive hardware was necessary. A simple Network Time Protocol was also

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