Which direction must solar panels face, and what angle should they be tilted at?
The response to this question might seem quite straightforward at first, but in reality, there are a number of answers; when we account for the various factors that we often tend to overlook.
In this article, we explore all the elements that influence the orientation and tilt angle of solar panels.
The direction dilemma.
First off, you need to ask yourself, “Which geographical region do I want to place the panels in?”
The ideal direction that solar panels must face, changes depending on whether you live in the northern hemisphere or the southern hemisphere.
In the northern hemisphere, panels must face south, and north works best for the southern hemisphere.
Now, the next question you might ask is, “Why south or north? Why not east or west?”
To understand the answer, think of a building in the northern hemisphere. The north side of the building is always in the shade. In the morning the west is shaded, and the east is lit-up by the sun, and as the evening unfolds, the west is sunlit, and the east is shaded.
This is because the sun has a southern offset in the northern hemisphere and a northern offset in the southern hemisphere.
If panels were placed facing east or west, they would generate a good amount of energy only during the morning or the evening. However, to get the best of both times, you need a north or south-facing system.
We’re not quite done yet.
There is a new and emerging trend termed as the Time of Use (TOU) pricing. This is a system of pricing where power charges are higher for a pre-defined time of the day, usually when the power usage across the state/country is highest.
Normally, usage is highest between 1 PM and 7 PM. During this time supply of electricity from the already active power plants is stretched to its limits. At a point, the power plants that are farther away turn on as a contingency to avoid failure of supply. This, because of obvious reasons, increases the working cost of the grid. Under TOU, the customer shells out more money to pay their utility bills.
In places like these, it turns out that west-facing panels are more economical when compared to south or north facing panels. This is mainly because west-facing panels generate 49% more electricity during peak demand when compared to south-facing panels, as recorded by a study conducted in Austin, Texas (in the northern hemisphere).
The Tilt Factor.
The fact is that no matter how precisely you calculate the tilt angle for your panels, you will have certain losses. The elusive optimum angle of the panel keeps changing throughout the day and across seasons (unless you have installed a solar tracker, in which case, the panel adjusts itself to face the optimum angle at regular intervals of time using an inbuilt algorithm).
So, the best that you can do is calculate an angle that has the least average annual loss.
The most common way that has been adopted widely is:
(latitude * 0.9) + 29 = optimum tilt angle for winter.
(latitude * 0.9) — 23.5 = optimum tilt angle for summer.
In this method, take the latitude: which is an indication of how much you need to tilt the panel by. Then, account for the shift in the sun’s movement during the summer and the winter by adding some predetermined constants as the sun is lowest in the sky during the winter, and subtracting another predetermined constant during the summer, as the sun is highest in the sky during the summer.
Calculating the losses.
Let’s say that the optimum tilt angle for a certain region is calculated using the approach we just discussed. The losses that this system would incur at any minute can be calculated or measured using instruments such as pyranometer (used to measure solar radiation on a surface), pyrheliometer (used to measure direct beam solar radiation), sunshine recorder (used to measure the time of sunlight available), and more (gadget stuff).
These gadgets are expensive and the returns of investing in them, especially for smaller firms or individuals, isn’t great.
But worry not. There exists a low-budget solution. You can calculate the factors that these losses depend on, such as the declination of the earth, the hour angle, the latitude, the tilt angle of the panel, solar time, and the Surface Azimuth Angle using readily available and easily accessible data such as the latitude, longitude, local time.
Declination is basically the angle subtended by a straight line projected from the equatorial plane, and a line from the centre of the sun projected onto the Earth.
The hour angle is an expression describing the difference between local solar time and solar noon.
The “Surface Azimuth Angle” is measured on the horizontal plane from the true south to the horizontal projection of the normal to the surface.
Solar time is the concept wherein the passage of time is calculated with respect to the apparent position of the sun in the sky.
By using these factors, you will be able to definitively find the angle by which the suns rays are incident on the panel. You can then compare the incidence angle of the sun’s rays when the panel is facing the optimal direction, angle, and the incidence angle to when the panel is not facing an optimal angle, directions; and thereby find the percentage losses with respect to changes in direction and/or angle.
What the future holds in store.
Solar trackers seem to be the most popular option currently being explored. It is an existing technology, but its application is limited to large-scale ground-mounted systems. This is mainly because solar tracker systems are expensive, need more maintenance, and most importantly are not suitable for the wind speeds, and precipitation that they get exposed to on a rooftop.
Self-cleaning, self-maintained tracking systems that incorporate designs that will sustain the conditions on a rooftop are what manufacturers today are working on at their R&D labs.
One such company, Edisun Microgrids, have already designed a new tracking system. Here, in place of the traditional pole mounted trackers that require to be raised by 6 feet, the tracking systems are just a few inches off the roof. Another notable change in design is that these panels pivot from their edge as opposed to traditional trackers that pivot from the centre. The organisation has successfully completed the world’s largest rooftop solar tracking system with 2900 trackers on individual panels in Oxnard, California.
The company believes that its rooftop tracking gear can boost the energy output of a solar project by 30% compared to fixed-tilt trackers.
A simple question can result in the most powerful answers. In this article, we began with one such query. It is clear that more can happen by honest exploration of problems, and there is no limit to what tomorrow’s energy sector could offer to the world.
Written by Pavan Balakrishna, Engineering-Operations at Solarify
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