comparison between astronomical and light sensor feedback sun
comparison between astronomical and light sensor feedback sun
comparison between astronomical and light sensor feedback sun
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COMPARISON BETWEEN ASTRONOMICAL AND LIGHT<br />
SENSOR FEEDBACK SUN-TRACKING ALGORITHMS<br />
October 2010<br />
D. Gomes* | L. Pina** | J. Martins***<br />
* Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.<br />
{davidcoimbragomes@gmail.com}<br />
**WS-Energia, Taguspark Edf Tecnologia II, Pavilhão 46,2740-257 Porto Salvo, Portugal.<br />
{pina@ws-energia.com }<br />
*** CTS, Uninova, Dep.ª de Eng.ª Electrotécnica, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de<br />
Lisboa, 2829-516 Caparica, Portugal. {jf.martins@fct.unl.pt}<br />
www.ws-energia.com<br />
D. Gomes* | L. Pina** | J. Martins***
Structure of the presentation<br />
• Company introduction<br />
• Why track the Sun?<br />
• How to track the Sun?<br />
• High precision <strong>sensor</strong><br />
• Light <strong>sensor</strong><br />
• Astronomical <strong>sensor</strong><br />
• Comparison <strong>between</strong> <strong>sensor</strong>s<br />
www.ws-energia.com
What we do<br />
Core Business<br />
High-Efficiency Photovoltaic Technology<br />
WS Energia develops, designs, manufactures <strong>and</strong><br />
commercializes solar trackers, optics for solar<br />
concentrators <strong>and</strong> robotic controllers for solar<br />
trackers.<br />
Mission<br />
To be the number one in creating leading edge technology <strong>and</strong> know-how in the solar<br />
energy sector.<br />
www.ws-energia.com
Who we are<br />
July 2010<br />
Values<br />
We are<br />
leaders in introducing reliable PV innovation<br />
leaders in customization <strong>and</strong> client benefits<br />
www.ws-energia.com
Our products<br />
Robotic control for solar systems<br />
Monthly capacity of 10.000 units<br />
Photovoltaic Trackers<br />
Monthly capacity of 5.000 units<br />
Photovoltaic Concentrators<br />
Monthly capacity of 1.000 units<br />
www.ws-energia.com
Where we are<br />
Company that installed the largest number of photovoltaic concentration systems in the world (by Photon 2009)<br />
WS ENERGIA WORLDWIDE<br />
2.000 trackers <strong>and</strong> concentrators<br />
WS ENERGIA IN PORTUGAL<br />
> 300 instalations<br />
Until July de 2010<br />
www.ws-energia.com
Why track the Sun?<br />
The performance of a photovoltaic application depends essentially on the amount of solar<br />
energy captured by the cells.<br />
Dual-axis tracking systems can improve the amount of energy collected in about 40% when<br />
compared to static systems.<br />
Fig.1: Comparison <strong>between</strong> a dual-axis tracking system <strong>and</strong> a static one.<br />
www.ws-energia.com
How to track the Sun?<br />
Most Common ways to track the <strong>sun</strong> are:<br />
• The <strong>astronomical</strong> calendar approach<br />
Uses time <strong>and</strong> geographical coordinates<br />
• The <strong>light</strong> <strong>sensor</strong>-based approach<br />
Uses photo-sensitive devices like:<br />
» photoresistors<br />
» photodiodes<br />
• Machine vision<br />
» Phototransistors<br />
Uses arrays of photo-sensitive devices like CCD cameras.<br />
www.ws-energia.com
High precision <strong>sensor</strong><br />
A CCD camera Genius eFace 1300 was used.<br />
Fig.2 a): CCD camera used Fig.2 b): Precision Sensor<br />
Solar filter<br />
The use of a solar filter is crucial to avoid damaging <strong>and</strong> the saturation of the camera.<br />
www.ws-energia.com
High precision <strong>sensor</strong><br />
This <strong>sensor</strong> provides the tracking error in both axis, in degrees.<br />
Fig.3: Illustration of the tracking error in both axes.<br />
Where the system<br />
is pointing to<br />
The center of the<br />
Sun<br />
www.ws-energia.com
Light-<strong>sensor</strong><br />
Works by <strong>comparison</strong>.<br />
Fig.4: Illustration of the <strong>sensor</strong>.<br />
• The devices E <strong>and</strong> W are compared to track the <strong>sun</strong> in the horizontal axis.<br />
• The devices N <strong>and</strong> S are compared to track the <strong>sun</strong> in the vertical axis.<br />
www.ws-energia.com
Light-<strong>sensor</strong><br />
Which photosensitive device shall be used?<br />
Several tests were made in order to choose it:<br />
- Light direction.<br />
- Light intensity.<br />
- Electric design.<br />
Fig.5 a): Picture of the test.<br />
Phototransistor Photoresistor Photodiode<br />
Fig.5 b): Assembly of the three devices.<br />
www.ws-energia.com
Light-<strong>sensor</strong><br />
Which photosensitive device shall be used?<br />
Fig.6: Comparison of the three devices with a 1KΩ resistor.<br />
• Photodiode (red)<br />
» Response is too oscilatory<br />
• Photoresistor (blue)<br />
» Good response<br />
• Phototransistor (green)<br />
» Response is too abrupt<br />
www.ws-energia.com
Light-<strong>sensor</strong><br />
Which photosensitive device shall be used?<br />
Fig.6: Comparison of the three devices with a 1KΩ resistor.<br />
• Photodiode (red)<br />
» Response is too oscilatory<br />
• Photoresistor (blue)<br />
» Good response<br />
• Phototransistor (green)<br />
» Response is too abrupt<br />
www.ws-energia.com
Light-<strong>sensor</strong><br />
Photoresistors<br />
Integrated Circuit<br />
Communication with<br />
actuator controller<br />
Fig.7 a): Scheme of the <strong>sensor</strong> Fig.7 b): Picture of the <strong>sensor</strong><br />
1) The <strong>light</strong>-<strong>sensor</strong> uses four photoresistors<br />
2) The PIC compares the readings<br />
3) The information is sent to the tracking controller<br />
www.ws-energia.com
Light-<strong>sensor</strong><br />
Error propagation chain<br />
Fig.11 : Error propagation chain<br />
Fig.10: Assembly error<br />
www.ws-energia.com
Astronomical <strong>sensor</strong><br />
Error propagation chain<br />
Fig.9 a) : Assembly errors<br />
Fig.9 b) : Gravity <strong>sensor</strong> error<br />
Fig.8 : Error propagation chain<br />
www.ws-energia.com
Comparison <strong>between</strong> <strong>astronomical</strong> <strong>and</strong> <strong>light</strong> <strong>sensor</strong><br />
approaches<br />
Sun tracking with <strong>light</strong> <strong>sensor</strong> ( East – West axis )<br />
Fig.12 : Finding the <strong>sun</strong>’s path<br />
True Sun position<br />
Light <strong>sensor</strong><br />
Astronomical<br />
approach<br />
www.ws-energia.com
Comparison <strong>between</strong> <strong>astronomical</strong> <strong>and</strong> <strong>light</strong> <strong>sensor</strong><br />
approaches<br />
Sun tracking with <strong>light</strong> <strong>sensor</strong> ( North – South axis )<br />
Fig.13 : Finding the <strong>sun</strong>’s path<br />
True Sun position<br />
Light <strong>sensor</strong><br />
Astronomical<br />
approach<br />
www.ws-energia.com
Comparison <strong>between</strong> <strong>astronomical</strong> <strong>and</strong> <strong>light</strong> <strong>sensor</strong><br />
approaches<br />
In a cloudy day, the <strong>light</strong> <strong>sensor</strong> approach is not robust<br />
Fig.14 : Sun tracking in a cloudy day with a <strong>light</strong> <strong>sensor</strong><br />
True Sun position<br />
Tracker position<br />
Detected Sun’s<br />
position<br />
www.ws-energia.com
Conclusions<br />
• Light <strong>sensor</strong>:<br />
Very accurate;<br />
Simple <strong>and</strong> economic way to track the <strong>sun</strong>;<br />
Installation misalignments do not influence tracking accuracy;<br />
Not robust in a cloudy day.<br />
• Astronomical approach:<br />
The accuracy does not depend on the weather;<br />
Many sources of error;<br />
Installation misalignments influence tracking accuracy;<br />
No feed-back.<br />
www.ws-energia.com
www.ws-energia.com
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