Solar panel orientation: how to define it correctly

Solar panel orientation, as a simple rule of thumb, is considered optimal when pointing south for northern-hemisphere sites but in most cases, a professional solar calculator software helps optimize PV system exposure for better efficiency

Being able to determine the optimal orientation and inclination of a photovoltaic field can significantly affect the overall efficiency of your system.

But defining these variables isn’t so easy because the incidence angle of the sun’s rays, on a PV field surface, can change throughout the entire day according to the position of the sun in the sky and the PV site’s geo-location.

To makes things a little easier, I recommend using a photovoltaic solar calculator software that will surely help you to find the best orientation for your PV project, considering geographical data and the seasonal periods during which the need for energy is greater.

Azimuth and tilt: definitions and usages

If we observe the sun, we’ll notice that it moves from East to West with a parabolic trajectory; to define the direction of the sun’s rays, with respect to the photovoltaic module surfaces, we need to know two fundamental angles:

• the azimuth angle;
• the tilt angle.

The Azimuth angle, refers to the orientation of the photovoltaic plane with respect to the corresponding meridian. In practice, it measures the deviation of the plane with respect to the orientation towards the South direction (for sites in the northern terrestrial hemisphere) or towards the North (for sites located in the southern hemisphere). Positive values of the azimuth angle indicate a westward orientation and negative values indicate an eastward orientation (as specified by the EN ISO 61194 – Characteristic parameters of stand-alone photovoltaic (PV) systems).

This angle obviously increases with increasing clockwise rotation of the vector. This basically means that:

• with 0° azimuth, the panel will be facing South;
• with 90° azimuth, the panel will be facing West;
• at 180° azimuth, the panel is facing North.

Knowing the sun’s azimuth angle is a fundamental value in order to define the correct orientation of the solar PV panels.

Tilt, or degree of elevation, is defined as the inclination of an object with respect to the ground plane, that is the angle that an object, in side view, forms with the reference ground plane.

In photovoltaic systems, the tilt angle represents the inclination of the photovoltaic plane with respect to the horizontal plane (from IEC/TS 61836 – Solar photovoltaic energy systems – Terms, definitions and symbols).

30-35° Inclination slope – South Direction

How to orient the photovoltaic panels

The higher energy efficiency of a photovoltaic system doesn’t only originate from the quality of the system, but also from the orientation and inclination of the photovoltaic panels.

A photovoltaic system reaches its maximum productivity peak when the solar rays hit the PV Panels perpendicularlaly. That would of course represent an optimal condition but it can’t always be guaranteed throughout the day. In fact, it changes continuously and is also highly dependant on the seasons.

Therefore, to optimize the system, it is necessary to orient the panels in the best possible direction so that the PV system can capture a greater number of sun rays in addition to estimating the following factors too:

• the incident solar radiation;
• the direction of the solar panels;
• the inclination of the photovoltaic panels.

Evaluation of the localtion’s solar radiation

The first factor that we need to calculate to check if a site is suitable for a PV installation, is the amount of solar energy that actually reaches a specific location.

During the course of the year, the sun’s path varies across the earth’s surface and the solar radiation that reaches the earth isn’t constant. As a result, solar energy is not a programmable energy and it can’t always be used when needed, for example during the night hours.

However, to understand the value of the average solar radiation of a given geografical location, the sun’s different paths are shown on solar maps, or solar diagrams,. These are then organized in Polar or Cartesian coordinates.

Polar coordinate solar maps are special charts in which the celestial vault is projected and reduced to a horizontal plane. These diagrams are composed of concentric circles, from the outer perimeter to the center, which represent different values of solar altitude.

Always from the center, other lines also intersect the various circumferences considering the different periods of the year identifying different azimuth values. These maps also show, as curved lines, the sun paths during different months of the year.

For example, the sun’s path during the month of February coincides with October and therefore both represented with a single line. Then we have that each solar diagram is specific to a certain latitude.

Polar solar diagram

Maps in Cartesian coordinates are diagrams on which the celestial vault is projected as if it were the surface of a cylinder projected on a plane.

Thus, at the extremes the cardinal points and the reference center is the South, being the direction towards which the panels should tend to be exposed to. The highest and most outer curve is the sun’s path during the summer period, while the lowest curve is the path followed by the sun during the winter solstice period. Next to the ordinates, you have the values defined as elevations.

To produce these maps, I suggest you use the photovoltaic software with which you can simulate the photovoltaic shading directly on the solar diagram and check the amount of solar energy that reaches your PV panels at a certain time of year.

Solar diagram Solarius PV

Another graphical representation that helps understand the actual amount of energy projected in a given place are the isoradiative curves. It is the representation of the incident solar radiation in a certain location on curved lines. These radiations vary in relation to the latitude: the lower the latitude, the greater the incident solar radiation because the Sun arrives orthogonally to the capturing surface.

For example, in Italy from the South to the North, the level of solar radiation will tend to decrease. In fact, we’ll get about 5.2 kWh/m²/day in the islands and 3.8 kWh/m²/day across the Alps.

Isoradiative curves

Direction of solar panels

A photovoltaic system is more productive when the solar rays are perpendicular to the solar panels and the orientation of the photovoltaic panels is better in a southerly direction with an azimuth angle of 0°.

If it’s not possible to set up and size a PV system in a southerly direction or if there are obstacles that cause shading, you can then resort to changing the panel orientation:

• orienting the panels at a maximum of 45° S-E and S-W, annual production would suffer a rather small annual reduction (1-3%);
• if the orientation angle is greater than 45° with respect to the South, the production will start to decrease considerably.

Less significant is the radiation that can have a panel exposed to the East or, even less, a panel exposed to the West, as it would only capture morning or evening radiation.

Solar panel orientation: south direction

Solar panel inclination

The optimal inclination of a photovoltaic panel is influenced by the geographical location’s latitude where the panels are to be mounted.

As a simplifying rule, we can say that the optimal panel inclination for maximum annual energy production is equal to the latitude L of the installation site. For example, if you have a latitude of 40°, you can install the panel with an inclination between 30 and 40°.

Photovoltaic panels Tilt angle

To determine the correct inclination of a panel, we also need to consider the surface on which the photovoltaic panels will be installed:

• if a photovoltaic system is installed on a roof top, the panels will be installed in a coplanarly to the roff slabs;
• if the system is installed on the ground or on a flat roof, you then need to calculate the inclination accurately in order to avoid that the panels placed in front do not cause, during certiain periods of the year, shading on panels placed on a nearby rear row.

To accurately calculate the minimum installation distance of the rows of photovoltaic panels and the correct inclination, I suggest you rely on a photovoltaic calculation software that can automatically calculate this dimension on any surface (horizontal, vertical or inclined).

How to optimize the orientation of the panels: solar trackers

The orientation of the photovoltaic panels is therefore crucial to maximize the yield of the photovoltaic system. To optimize the solar arrangement throughout the year, it is possible to install specific electronic devices that allow you to follow the trajectory of the sun: we talk about solar tracking system or solar trackers.

What are solar trackers?

Solar photovoltaic trackers are special devices and mechanisms that allow you to move and rotate the photovoltaic panel so that they are always oriented in the solar direction. With this system, therefore, the panel is not fixed, but mobile.

Solar tracker system

How do solar trackers work?

Solar trackers allow you to always maintain the 90° inclination between the panel and the sun’s rays in order to optimize the orientation of the photovoltaic panels and, therefore, the energy efficiency rating.

There are different types and depending on the type the operating mechanism varies.

The main types of solar trackers are:

• monoaxial solar trackers;
• biaxial solar trackers.

Monoaxial solar trackers “chase” solar radiation by rotating around their axis and, based on its orientation, can be classified into:

• tilt trackers: revolve around the tilt angle, or East-West and chase the sun’s altitude in the sky;
• roll chasers: chase the sun during its path across the sky; in this case the rotation axis is North-South;
• azimuth trackers: they rotate around a vertical axis perpendicular to the ground and need large spaces for installation;
• polaraxis trackers: track solar radiation, rotating around an axis parallel to the Earth’s axis of rotation.

The biaxial solar trackers, on the other hand, have two rotation axes perpendicular to each other, which allow to perfectly point the panels in the direction of the sun using an electrical powered movement system. Depending on its orientation, they are divided into:

• azimuth-elevation trackers: these are capable of intercepting the solar radiation, allowing the panels to automatcally orient themselves perfectly perpendicular to the sun’s rays, throughout the day;
• tilt-roll trackers: avoid shaded areas.

In conclusion, according to the type of system that allows its movement to orient itself towards the sun, they can be classified into:

• active solar trackers;
• passive solar trackers.

The active solar trackers are composed of electric motors that move the photovoltaic panels accurately and slowly. These are divided into:

• analogue: movement is generated by sensors that identify the best position for the absorption of solar radiation;
• digital: operated by a microprocessor that, through the storage of data on the positioning of the sun, manages to orient the panels in the direction with greater light.

Passive trackers, on the other hand, use autonomous physical phenomena independent of the positioning of the sun with respect to the panel, such as the thermal expansion of a compressed fluid gas that is heated by the sun generating a hydraulic pressure that allows the movement of the structure of the solar panels.

Performance of Solarius PV photovoltaic panels

To optimally define the orientation of the panels of a system without a solar tracking system, I recommend you to immediately try the photovoltaic software for free, where by entering the installation location and the azimuth and tilt values, you can detect the monthly average daily irradiation data and obtain a general analysis of the PV system’s performance in terms of energy productivity levels.