Upload
tplpt
View
49
Download
0
Embed Size (px)
Citation preview
www.ws-energia.com
COMPARISON BETWEEN ASTRONOMICAL AND LIGHT
SENSOR FEEDBACK SUN-TRACKING ALGORITHMS
October 2010
D. Gomes* | L. Pina** | J. Martins***
* Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
**WS-Energia, Taguspark Edf Tecnologia II, Pavilhão 46,2740-257 Porto Salvo, Portugal.
*** CTS, Uninova, Dep.ª de Eng.ª Electrotécnica, Faculdade de Ciências e Tecnologia, FCT, Universidade Nova de
Lisboa, 2829-516 Caparica, Portugal. {[email protected]}
D. Gomes* | L. Pina** | J. Martins***
www.ws-energia.com
Structure of the presentation
• Company introduction
• Why track the Sun?
• How to track the Sun?
• High precision sensor
• Light sensor
• Astronomical sensor
• Comparison between sensors
www.ws-energia.com
What we do
Core Business
High-Efficiency Photovoltaic Technology
WS Energia develops, designs, manufactures and
commercializes solar trackers, optics for solar
concentrators and robotic controllers for solar
trackers.
Mission
To be the number one in creating leading edge technology and know-how in the solar
energy sector.
www.ws-energia.com
Values
We are
leaders in introducing reliable PV innovation
leaders in customization and client benefits
Who we are
July 2010
www.ws-energia.com
Our products
Photovoltaic Concentrators
Monthly capacity of 1.000 units
Photovoltaic Trackers
Monthly capacity of 5.000 units
Robotic control for solar systems
Monthly capacity of 10.000 units
www.ws-energia.com
Where we are
WS ENERGIA WORLDWIDE
2.000 trackers and concentrators
WS ENERGIA IN PORTUGAL
> 300 instalations
Company that installed the largest number of photovoltaic concentration systems in the world (by Photon 2009)
Until July de 2010
www.ws-energia.com
Why track the Sun?
Fig.1: Comparison between a dual-axis tracking system and a static one.
The performance of a photovoltaic application depends essentially on the amount of solar
energy captured by the cells.
Dual-axis tracking systems can improve the amount of energy collected in about 40% when
compared to static systems.
www.ws-energia.com
How to track the Sun?
Most Common ways to track the sun are:
• The astronomical calendar approach
Uses time and geographical coordinates
• The light sensor-based approach
Uses photo-sensitive devices like:
» photoresistors
» photodiodes
» Phototransistors
• Machine vision
Uses arrays of photo-sensitive devices like CCD cameras.
www.ws-energia.com
A CCD camera Genius eFace 1300 was used.
Solar filter
Fig.2 a): CCD camera used Fig.2 b): Precision Sensor
The use of a solar filter is crucial to avoid damaging and the saturation of the camera.
High precision sensor
www.ws-energia.com
This sensor provides the tracking error in both axis, in degrees.
Where the system
is pointing to
The center of the
SunFig.3: Illustration of the tracking error in both axes.
High precision sensor
www.ws-energia.com
Light-sensor
Works by comparison.
Fig.4: Illustration of the sensor.
• The devices E and W are compared to track the sun in the horizontal axis.
• The devices N and S are compared to track the sun in the vertical axis.
www.ws-energia.com
Which photosensitive device shall be used?
Several tests were made in order to choose it:
- Light direction.
- Light intensity.
- Electric design.
Fig.5 a): Picture of the test. Fig.5 b): Assembly of the three devices.
Light-sensor
Phototransistor Photoresistor Photodiode
www.ws-energia.com
Fig.6: Comparison of the three devices with a 1KΩ resistor.
Which photosensitive device shall be used?
Light-sensor
• Photodiode (red)
» Response is too oscilatory
• Photoresistor (blue)
» Good response
• Phototransistor (green)
» Response is too abrupt
www.ws-energia.com
Which photosensitive device shall be used?
Light-sensor
• Photodiode (red)
» Response is too oscilatory
• Photoresistor (blue)
» Good response
• Phototransistor (green)
» Response is too abrupt
Fig.6: Comparison of the three devices with a 1KΩ resistor.
www.ws-energia.com
Light-sensor
1) The light-sensor uses four photoresistors
2) The PIC compares the readings
3) The information is sent to the tracking controller
Fig.7 a): Scheme of the sensor Fig.7 b): Picture of the sensor
Photoresistors
Integrated Circuit
Communication with
actuator controller
www.ws-energia.com
Fig.11 : Error propagation chain
Fig.10: Assembly error
Light-sensor
Error propagation chain
www.ws-energia.com
Astronomical sensor
Fig.8 : Error propagation chain
Error propagation chain
Fig.9 b) : Gravity sensor error
Fig.9 a) : Assembly errors
www.ws-energia.com
True Sun position
Light sensor
Astronomical
approach
Fig.12 : Finding the sun’s path
Sun tracking with light sensor ( East – West axis )
Comparison between astronomical and light sensor
approaches
www.ws-energia.com
Fig.13 : Finding the sun’s path
Comparison between astronomical and light sensor
approaches
Sun tracking with light sensor ( North – South axis )
True Sun position
Light sensor
Astronomical
approach
www.ws-energia.com
Fig.14 : Sun tracking in a cloudy day with a light sensor
Comparison between astronomical and light sensor
approaches
In a cloudy day, the light sensor approach is not robust
True Sun position
Tracker position
Detected Sun’s
position
www.ws-energia.com
Conclusions
• Light sensor:
Very accurate;
Simple and economic way to track the sun;
Installation misalignments do not influence tracking accuracy;
Not robust in a cloudy day.
• Astronomical approach:
The accuracy does not depend on the weather;
Many sources of error;
Installation misalignments influence tracking accuracy;
No feed-back.
www.ws-energia.com