Should PV modules always be oriented towards the North?

We have always learned that photovoltaic system modules must be installed facing North and with an inclination angle equal to the latitude of the location in which they are located.

Is it advantageous, or necessary, to always use this guidance? This is a question that we will answer in this article.

In fact, the modules produce more energy when they are facing North. This rule is valid for locations in the Southern Hemisphere. In the Northern Hemisphere, the modules must be installed with a South orientation.

However, despite the advantage of having the modules facing North (as we are located in the Southern Hemisphere), this installation method is not always justified.

We have already covered this subject in the article Is it worth adjusting the angle of solar modules on roofs?, which brought to light an issue that many designers and installers are unaware of.

The best answer to this question is yes, it is worth it if you have complete freedom to carry out the installation, positioning the modules with the best inclination and azimuth angles. In ground-based plants this is the rule, but in rooftop photovoltaic systems this is more complicated and does not always pay off.

Azimuth is the technical name we give to the orientation angle of the front part of the solar module in relation to the geographic North, as illustrated in Figure 1. We know that it is good to have the modules with their front surface facing North, as in the first illustration , however the tireless search for North or the best inclination angle does not always produce good results in installations.

Gadgets or tricks like the one in Figure 2, the vast majority of which are unsafe, are not uncommon for correcting the orientation of panels installed on roofs. Will the result be worth it?

Despite the possible gain in energy generation, it is necessary to take into account the danger of wind pullout force (Figure 3), the additional cost of the structures and the durability or useful life of the metallic structures that are added to the project.

Quantifying the problem

Next, we will carry out a study to evaluate how much we gain or lose by having the solar modules oriented to the North or to any other azimuth angle.

We will also evaluate the influence of inclination, which, added to the influence of the azimuth angle, can give us clues about the effectiveness of installing photovoltaic modules with azimuths and inclinations different from those found on roofs, through dangerous and unattractive solutions such as the one in Figure two.

For this we will use simulation software PVSyst to quantify the influence of orientation and tilt on photovoltaic module power generation. With PVSyst we were able to carry out sets of simulations with inclination angles between 0º (horizontal module) and 45º in steps of 1.25º and azimuthal orientations from 0º (facing North) to 360º (facing South) in steps of 2.5º. 

In this study, we performed simulations with 5365 tilt and orientation combinations for photovoltaic systems installed in 5 Brazilian cities:

• Porto Alegre (RS), latitude -30º);
• Campinas (SP), latitude -23º);
• Montes Claros (MG), latitude -17º);
• Petrolina (PE), latitude -10º) and;
• Fortaleza (CE), latitude -4º).

The simulated system has two strings of 13 400 Wp modules connected to an inverter Fronius Symo 8.2 kW. Therefore, the system overload is 126%, a typical value for systems of this size. To ensure that the analysis is not influenced by shading between the modules, an assembly was chosen with all the boards on the same line.

Gain or loss analyzes will be carried out based on the reference case, which corresponds to the arrangement oriented to the North and with an inclination of 0º, that is, in the horizontal plane.

Results

The simulations carried out in PVSyst produced the graphs shown below for each of the cities analyzed. The graphs have information about three variables: module inclination angle, module azimuth angle and yield obtained with the combination.

Yield, indicated by the color scale on the graph, is a number that can be greater or less than 100%. The 100% generation corresponds to the reference case that we have already mentioned (horizontal modules and zero azimuth).

The green curve found in the graph shows the azimuth and inclination combinations that provide maximum energy generation in each of the simulated systems. In other words, for a given orientation value, the green curve indicates which slope will provide the most energy. For example, for an orientation of -30º (30º East) the best inclination is approximately 25º.

The red dot at the top of the green graph indicates the best of all possible combinations, that is, the orientation and azimuth values that provide the best result with the studied system. The figures below show the graphs obtained for the cities of Porto Alegre, Campinas, Montes Claros, Petrolina and Fortaleza.

We can notice that the highest generation point is slightly shifted to the East in all tested cases. This indicates that the North orientation is not, strictly speaking, the best choice for installing the modules. Even so, in all cases the best azimuth values found are very close to zero, indicating that in practice this does not make much difference.

Installing a photovoltaic module with zero azimuth (to the North) or with -2.5º azimuth is practically the same thing. This angle of -2.5º (a negligible value) would probably already be found in the measurement error of the installation angle. Analyzing the graphs more rigorously, the simulation results indicate that the best azimuth angles are slightly shifted to the East and do not correspond exactly to azimuth zero (North), as we always thought.

According to the simulation results and the graphs shown above, we have the following list of the best azimuth angles for the cities studied:

• Porto Alegre: -2.5º;
• Campinas: -7.5º;
• Montes Claros: -5º;
• Petrolina: -5º;
• Fortaleza: -7.5º.

According to the results, the best option for the cases studied is not to install the modules facing North, as we have always heard that should be done. How can we explain the better performance (greater energy generation) of photovoltaic systems with non-zero azimuths, moved to the East?

The answer lies in the thermal behavior of photovoltaic modules. Photovoltaic cells are more efficient (produce more energy) when they are at lower temperatures. In the early morning, the modules are cooler than in the late afternoon. Therefore. We can achieve a good result if it is possible to capture more radiation in the morning, to the detriment of the afternoon.

If we placed the modules facing North, we would have the same amount of radiation collected in the morning and afternoon. This would mean we would lose the opportunity to generate a little more energy than if we had prioritized the morning period, orienting the modules slightly to the East.

In summary, maximum energy generation from photovoltaic systems occurs when the modules are slightly oriented to the East, with azimult angles that in our studies ranged from -2.5º to -7.5º. The results obtained with modules facing North are very close to those obtained with azimuth angles considered optimal, according to the simulations. As we stated above, in practice this doesn't make much difference.

For most small and medium-sized photovoltaic systems, the rule is to always orient the modules towards the North. If it is possible to carry out a study like the one we did (which is not always done by designers), we can discover the optimal azimuth angle, but this will not make much difference for practical purposes.

The only caveat to what is stated in the previous paragraph are large plants installed on land. In this case, a small percentage advantage in performance can represent a large amount of energy over the years. In cases like this, it is worth carrying out the study with PVSyst and building the plant with the obtained orientation angle. In Montes Claros, for example, the recommended azimuth would be -5º (that is, 5º towards the East). 

The module used in this study has the thermal coefficients shown in the table below. The power loss indicated in the table is -0.37%/ºC. In other words, for an increase of 10ºC (above the standard temperature of 25ºC) in the module's operating temperature, 3.7% of the nominal peak power is lost. This explains why in the morning, with lower temperatures, the module produces more energy. 

 Table 1 – Thermal coefficients of the photovoltaic module

We talk a lot about the azimuth angle, but the simulation results also provide us with information about the inclination angle of the photovoltaic modules. As we already know, the module tilted at some angle produces more energy than the module positioned horizontally. But this largely depends on where the module is installed.

It is observed that the gains with the panel inclination are greater in percentage the further south the city is located. In Fortaleza (CE), for example, the biggest gain when correcting the slope is 3%, while in Porto Alegre the gain reaches 6.5%.

Case studies

Case 1

To discuss the benefits of correcting or not correcting the inclination angles of the modules, we will study a case like the one shown in Figure 1. Not having a roof with water facing North, the client decided to build a metal frame to correct the orientation (and also the inclination) of the photovoltaic modules.

As seen in Figure 1, the metal structure appears to be very precarious (with the risk of the panels being blown away by the wind), in addition to being aesthetically unpleasant (or in plain English: ugly). What did the customer gain from this? What would he lose if the modules were installed directly on the roof? In our example we consider a system with eight modules inclined at 15º and facing North, located in the city of Porto Alegre.

The alternative solution is to place four modules in the East water and four modules in the West water or the eight modules in just one water. Using Figure 9, about generation in Porto Alegre, we can compare the energy generated in each of the installation solutions.

From the figure we can see that the gain in correcting the modules to the North instead of using the East and West waters is only 7%, a small value and often within the designer's margin of error. For a system of eight modules in Porto Alegre, this generation difference represents only around R$ 200 per year, considering the current electricity tariff.

The cost of the adapted structure would already be enough to eliminate any gains in generation in the first years of the system's operation, in addition to increasing the risk of mechanical failures and the modules being ripped off by the wind.

Case 2

In this case, we are going to analyze a major taboo in solar systems, which is the installation of modules facing South. This occurs when the customer's roof has no other better location. The solution will be to install the modules facing South or build a frame like the one in Figure 10 to correct the position of the modules. Is this compromise worth it, which besides being ugly and dangerous, can be harmless?

The roof studied in this example is oriented towards the Southeast (azimuth of -130º), with a slope of 10º. The client, unhappy with his roof, decided to correct the angle, making it possible to install the modules with zero inclination. We will assume that in this study the system is located in Montes Claros.

To evaluate the effect of the correction, let's look at the graph in Figure 11. In Figure 11 we see that the gain from assembling the structure on the roofs, for the “correct” positioning of the modules, was only 4%, making the same comments applicable here. from the previous case study. In short, it's not worth doing what was done. The best option is to install the modules directly on the roof.

Case 3

Finally, let's consider a roof with an inclination of 5º towards the North, where the designer decided to correct the inclination to 10º in the city of Petrolina. Repeating the analysis, we have a power generation gain of less than 1%, a value that can be easily absorbed by losses in cabling and connectors.

Once again, we concluded that it is not worth changing the installation angles of the modules and it is always recommended to install them directly on the roof.

Conclusion

In the photovoltaic solar energy sector there are still many myths about the best way to install photovoltaic modules. In this article we deconstruct several taboos related to this topic. Many think that the modules should be aligned exactly with the geographic North, but in fact there is a small azimuth angle, facing East, which can provide more energy generation.

In practice, in small and medium-sized systems, this does not make much difference. In large solar plants, on the other hand, a closer look at the project and a simulation in PVSyst can indicate the best azimuth angle, providing significant results.

The incessant and tireless search for optimal orientation and inclination does not always have technical and economic foundations. The gain in energy does not compensate for the effort made, in addition to reducing the system's safety with the risk of the modules being ripped off by the wind.

With the great growth of the photovoltaic sector in Brazil, there is no shortage of examples of roofs with crazy corrections and modules that occasionally fly off. It is the designer's role to thoroughly understand the influence of inclination and orientation and find a safe solution, even if there are energy losses.

A gain of 5% in energy generation can represent an increase of 100% in the chance of the modules flying. You need to seriously think about this when designing and executing a photovoltaic installation.