Solar resource

Calculating the Optimal solar panel Angle

As a rule of thumb, solar panels should be more vertical during winter to gain most of the low winter sun, and more tilted during summer to maximize the output. Here two simple methods for calculating approximate solar panel angle according to your latitude.

Calculation method one

The optimum tilt angle is calculated by adding 15 degrees to your latitude during winter, and subtracting 15 degrees from your latitude during summer. For instance, if your latitude is 34°, the optimum tilt angle for your solar panels during winter will be 34 + 15 = 49°. The summer optimum tilt angle on the other hand will be 34 – 15 = 19°.

Calculation method two

This is an improvement of the general method that gives better results. In this method, the optimum tilt angle for solar panels during winter is calculated by multiplying the latitude by 0.9 and then adding 29°. In the above case example of a latitude of 34°, the tilt angle will be (34 * 0.9) + 29 = 59.6°. This angle is 10° steeper than in the general method but very effective at tapping the midday sun which is the hottest in the short winter days. For summer, the tilt angle is calculated by multiplying the latitude by 0.9 and subtracting 23.5°. In the above case example, this angle would be (34 * 0.9) – 23.5 = 7.1°. For optimum tilt angles during spring and fall, 2.5° is subtracted from the latitude. 

But what inclination should the solar panel have?

As a rule, installers use the latitude where they are located to tilt the solar panels. Thus, the solar panels are installed at an angle equal to the latitude of the area in which they are located, thus achieving stable performance throughout the year! Although summer is always superior when compared to winter!

And for this reason, this rule is not always the most adequate. During the winter, solar panels should be installed as vertically as possible to make the most of solar energy! Is that even horizontally they can take advantage of solar energy!

So, as a rule, for a good energy efficiency of the solar panels during the inversion, they should have a higher inclination, of 10-15 degrees, in relation to the latitude angle where they will be installed! Thus, you can get the most out of it during the winter, as the sun's rays have a greater horizontality.

Now, in summer, we must do the opposite of winter! Thus, we must have a lower inclination, 10-15 degrees, relative to the latitude angle where they will be installed. As I mentioned, in the summer solar panels can be more horizontal! That's how you make the best use of the hours of sunshine, as it's when the sun is highest in the sky!

This rules and calcs, however, does not replace the generation analysis performed by software such as PVSyst based on historical solarimetric data. There are climatic factors, not just geometric ones, that affect the correct choice of inclination angle in photovoltaic systems.

Solar resource Portugal maps

The maps and data for Portugal have been released in parallel with Global Solar Atlas, which is published by the World Bank Group, funded by ESMAP, and prepared by and to Solargis. All maps on this page are licensed by The World Bank under the Creative Commons Attribution license (CC BY 4.0) with the mandatory and binding addition presented in Global Solar Atlas terms. You are free to download, share, adapt, use the maps but you must give appropriate attribution:

© 2022 The World Bank, Source: Global Solar Atlas 2.7, Solar resource data: Solargis. 

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