Orientation, tilt and shading are three concepts that are important for assessing if your property is a good site for harnessing solar power. Last time, we covered orientation, so this post is dedicated to tilt (also known as pitch or angle).
Building off of concepts from Part 1, we understand that the Earth is in fact round and does move around the Sun. We understand that it rotates about its axis to give us day and night, and this axis itself rotates also, tilting the planet to and away from the Sun, generating the seasons. This then causes the Sun to effectively rise and fall in the sky as these seasons change throughout the year. These relationships are important to understand when assessing your site.
This is where angles come into play, and the tilt of your system becomes an important consideration. The goal of tilting your system is to make it as perpendicular to the Sun’s rays as possible. (Think back to our paint bucket example: You are throwing a bucket of paint at your roof from a given angle. You know as well as many abstract artists know that you will be most effective at coating your roof by throwing the paint straight on, as it will generate the most force and distribute it most evenly.)
There are a couple rules of thumb regarding tilt that help orient your array for optimal solar productivity:
1. The tilt of your system is most optimal at an angle equal to your latitude.
Thanks to the curvature of the Earth, setting your angle equal to latitude gets you to be perpendicular to the Sun.
Due to the effects of Earth’s rotation as shown in Figure 2, the two following rules of thumb are apply to seasonal production.
2. For greater production of solar energy in the summer, a shallowed pitch is preferred.
The Sun is higher in the sky in summer, therefore it is more efficient to have your array tilted under it. This means that if you have a flat/low pitch roof, you will do better in the summer – or near the Equator. (assuming you are an array fixed position on the roof in the Northern Hemisphere).
An advantage to a shallower pitch to your roof is that there is less self-shading from your roof’s ridge. Think back to our paint – if you are throwing morning paint (aka Sun rays), and it splashes hard onto your east-facing roof surface, there will be a certain amount that spills over to the other side. The shallower the pitch of the roof, the more paint is caught on the array.
3. For greater production of solar energy in the winter, a steeper pitch is your best bet.
The Sun is lower in the sky in winter, so it is more efficient for your array to be tipped up to try and meet its gaze. This means that if you have a steep-pitched roof, you will do better in the winter – or farther north on the globe (assuming you are an array fixed position on the roof in the Northern Hemisphere).
A benefit to a steeper pitch is that gravity helps you shed snow in the winter to get more exposure to the Sun (especially for those of us to whom this is a regular problem… in April apparently – yep, we’re salty about it).
This figure here is a great representation of the interconnected and directly related concepts we’ve gone over the past few posts. The summary is that in this solar age, just because your roof may not be the “optimum” South-facing, tilt equals latitude minus ‘k’ solar gold mine, in the current age of solar revolution, opportunity lies all over the place (quite literally).
That’s it for this lesson. See you next time for our last, but perhaps easiest to observe, production factor: shading.
By: Ian Berg
Photo courtesy of Pexels.com