Inclinación y azimut
La luz del sol que llega a la tierra es más fuerte cuando incide en una superficie perpendicularmente (con un ángulo de 90 °), sin embargo, la posición del sol en el cielo varía a lo largo del día y del año para cada lugar. Esto significa que para capturar la mayor cantidad de luz solar posible y maximizar la producción, un módulo FV debe colocarse correctamente. Hay dos formas importantes en las que un módulo FV puede colocarse en relación con el sol:
- Dirección relativa a las direcciones cardinales (Norte, Este, Sur, Oeste).
- Ángulo relativo a la superficie de la tierra.
Comprender la orientación y el ángulo ideales requiere una comprensión básica de los movimientos diarios y anuales de la Tierra.
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Movimientos de la tierra
La Tierra está en todo momento girando alrededor de su propio eje (completando una rotación completa aproximadamente cada 24 horas) y orbitando alrededor del Sol (completando una órbita completa aproximadamente cada 365 días).
Rotación diaria
La tierra completa una revolución completa alrededor de su propio eje aproximadamente cada 24 horas. Esto hace que la fuerza del sol varíe a lo largo del día a medida que se arquea en el cielo, ascendiendo por el este y poniéndose por el oeste. La fuerza de los rayos del sol alcanza su punto máximo cuando se encuentra en la parte superior de su arco entre el este y el oeste alrededor de las 12:00.
La tierra gira alrededor de su propio eje una vez al día. Un lado de la tierra siempre está a oscuras.
Órbita anual
La tierra gira alrededor del sol en un círculo casi perfecto una vez cada 365 días. La órbita anual de la tierra alrededor del sol explica la variación en la fuerza de la luz solar en diferentes áreas entre las estaciones. El eje de la tierra está en un ángulo, aproximadamente 23,5 °, lo que crea una variación estacional, ya que el ángulo de los rayos del sol que inciden en cualquier lugar de la tierra varía según la posición de la tierra en su órbita alrededor del sol. Esto también tiene un efecto en la cantidad de horas de luz que recibe una ubicación cada día, que se vuelve más pronunciada al alejarse del ecuador. El 21 de junio en el hemisferio sur es el día más corto del año y el 21 de diciembre es el día más largo del año. Lo contrario es cierto en el hemisferio norte.
La tierra orbita alrededor del sol en un círculo casi perfecto una vez al año. El ángulo del eje de la tierra no varía a medida que se mueve alrededor del sol cada año.
1. 21 de diciembre. 2. 20 de marzo 3. 21 de junio 4. 20 de septiembre
Izquierda: 21 de junio - El hemisferio norte está inclinado hacia el sol y por lo tanto recibe más luz solar directa y tiene más luz del día cada día que el hemisferio sur.
Derecha: 21 de diciembre: el hemisferio sur está inclinado hacia el sol y, por lo tanto, recibe más luz solar directa y tiene más luz del día cada día que el hemisferio norte.
Ángulo de azimut
The most important window for PV system production is between 9:00 and 15:00. At 9:00 the sun is rising in the East and gaining strength. At around 12:00 the sun is reaching the peak if its arc in the sky between East and West. In the Southern hemisphere, the position of the sun in the sky is due North at this point. In the Northern hemisphere it is due South. At 15:00 the sun is beginning to fall towards the West and is losing strength. To maximize the amount of sunlight that a PV module captures, it is ideal to if it is pointed with an azimuth angle of due North (0°) in the Southern hemisphere and due South (180°) in the Northern hemisphere as this enables the PV module to capture the maximum amount of sunlight as the sun arcs from East to West. Additionally, if the PV module is properly facing either of these directions it it will be able to take maximum advantage of the sun's rays when it is at its strongest.
Southern hemisphere: A PV module on a fixed mounting structure will maximize yearly production by facing directly towards the North:
June 21, 9:00 in Quelimane, Mozambique (17°S). The sun rises in the East.[1]
June 21, 15:00 in Quelimane, Mozambique (17°S). The sun descends in the West.[1]
Northern hemisphere: A PV module on a fixed mounting structure will maximize yearly production by facing directly towards the South:
Dec 21, 9:00 in Oaxaca, Mexico (17°N). The sun rises in the East.[1]
Dec 21, 15:00 in Oaxaca, Mexico (17° N). The sun descends in the West.[1]
Magnetic declination
A compass is necessary to determine the cardinal directions in order to point PV in the right direction. PV modules maximize production when pointed true North/South, but an unadjusted compass provides magnetic North/South which can vary significantly depending on the magnetic field in the location where the PV system is being installed. The adjustment factor between magnetic North and true north is called magnetic declination. This value can be found on some paper maps, but the most accurate and easiest source is the internet. There are many different free tools such as the NOAA Magnetic Declination Tool.
The needle of a compass points towards magnetic North. This compass has been adjusted for a 23° East magnetic declination (true North is 23° to the West of magnetic north) to determine true North.
Non-standard azimuth angles
In some cases, it is not possible or not convenient to face a PV module true North/South. If an array is slightly off from true North/South it is unlikely to affect production greatly in any case, but the effect does become more pronounced moving further from the equator. How much production is affected varies significantly, for example:
- A system with a tilt of 5° facing true East (90°) or true West (270°) at 0° latitude will produce an estimated 5% less than a system facing true North (0°).[2]
- A system with a tilt of 17° facing true East (90°) or true West (270°) at 17°S latitude will produce an estimated 7.7% less than a system facing true North (0°)[2]
- A system with a tilt of 41° facing true East (90°) or true West (270°) at 41°S latitude will produce an estimated 19.8% less than a system facing true North (0°)[2]
Tilt angle
The path that the sun takes through the sky changes each day as the earth moves through its orbit. The change becomes more pronounced as one moves away from the equator. A PV module is able to collect the most energy as the sun changes position in the sky throughout the year if a PV module is placed at an angle that is equivalent to the latitude of the location. At the equator it is important to still tilt the panel with at least a 5° tilt to ensure that water will run off the panel to shed dust.
Pole mount system with a tilt of 41° with true North azimuth (0°). The path of the sun in Bariloche, Argentina 41°S at 12:00 on December 21 (summer solstice) and June 21 (winter solstice).[1]
Pole mount system with a tilt of 5° with true South azimuth (180°). The path of the sun in Kampala, Uganda .3°N at 12:00 on December 21 and June 21.[1]
Pole mount system with a tilt of 41° with true South azimuth (180°). The path of the sun in the Gobi Desert, Mongolia 41°N at 12:00 on December 21 (winter solstice) and June 21 (summer solstice).[1]
Non-standard tilt angles
Under some conditions it makes sense to use a tilt for a PV module that is different than latitude.
- It is often the simplest, cheapest and most theft-proof option to install PV modules on the roof of a home. In this case, typically the angle of the existing roof is used as the tilt angle for the PV module. An 17° latitude, an array with a tilt angle of 7° will only produce an estimated 2.1% less than an array with a tilt angle of 17°.[2]
- Mounting systems are frequently build that enable users to change the angle of the PV modules through the course of the year to maximize production at higher latitudes. The standard array angle adjustment is +15° at the fall solstice and -15° at the spring solstice. At 41° latitude, a system that is adjusted at the two solstices will produce an estimated 6% more than a system that is at a fixed 41° tilt. This additional energy can be crucial in the winter.[2]
- If PV system is only going to be used seasonally then mounting the PV modules at an angle that maximizes production during that time of the year is advisable.
- As in the example systems above, it is not advisable to mount PV modules at an angle of 0° near the equator as they are unable to shed water and will lose significant production as they become increasingly soiled. At least a 5° angle is recommended.
Notes
NOAA Magnetic Declination Tool https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml#declination
