How to determine the best angle for solar panels

How to determine the best angle for solar panels

August 16, 2021 Uncategorized 0
Solar panel angle | Wolf Track Energy

It’s important to think about the best angle for solar panels when designing a new system. After all, the way the panels are arranged will play a big part in determining how much energy they produce. 

The optimal angle will differ based on where you live, and the design of the system itself. 

But panel tilt isn’t the only factor solar installers have to think about. There’s also azimuth, or the compass direction the panels will face. 

In some cases, such as roof-mounted systems, installers don’t have much wiggle room for adjusting tilt and azimuth. But that information will help system designers determine how much solar energy a system will produce.  

In this blog, we’ll tackle some basic concepts of solar design, including panel tilt and azimuth. We’ll also discuss adjustable solar arrays that can help harness more solar energy when the sun’s angle changes. 

Addressing azimuth

Solar panels work by converting solar energy into electricity. They do that best when the panels are facing directly at the sun. 

So if the sun rises in the east and sets in the west, shouldn’t we install solar panels facing directly up? 

In reality, the sun doesn’t follow a straight path from east to west. Its path is tilted, which means the sun spends most of its time in the southern half of the sky. At the summer solstice, when the sun is highest in the sky, “the noon sun is still toward the south,” according to this explainer from Weber State University. 

During the winter, the sun’s path drifts further to the south. That’s due to the planet’s tilt and our position on the northern hemisphere. That means the sun rises in the southeast and sets in the southwest, which helps explain why the days are so short in the winter. 

Sunny to the south

The sun doesn’t follow the same path throughout the year, so its angle relative to the horizon is constantly changing. But given our position on the planet, panels will ideally face south. Azimuth is measured in degrees away from true north, so south would be 180 degrees.

A customer’s roof may not allow for south-facing panels, but we have installed successful projects using panels that face east and west. 

Using the National Renewable Energy Laboratory’s PVWatts tool, I found that a solar system with a 20-degree tilt in Duluth will produce about 17% less solar energy over the course of the year if it’s facing east rather than south. That decrease is larger if the panels have a steeper tilt. (But I’m getting ahead of myself.) 

So while it’s not ideal to have panels that aren’t facing at least somewhat south, it’s far from a deal-breaker. 

Now that we’ve tackled azimuth, let’s discuss panel tilt. 

The thing about tilt

Like I mentioned above, the sun’s path in the sky is constantly changing. That means it’s lower in the sky in the winter and higher in the summer. 

Because solar panels are most efficient when they’re perpendicular to the sun, installers have to consider their tilt. 

Solar panel installation | Wolf Track Energy

In roof-mounted systems, the roof’s pitch will determine the panel’s tilt. The installer can’t do much to change that, but they’ll have to factor in the panel tilt to calculate the system’s expected solar production. 

And as with azimuth, a ground-mounted system offers more flexibility to install panels with an optimal tilt. 

But what is the best angle for solar panels? That’s where it gets complicated.

A latitude attitude

Solar systems in northern states like Minnesota and Wisconsin tend to have panels with a higher tilt than those installed in the south. That’s because the sun is lower in the sky up here. Using your location’s latitude is a good way to start determining your solar panels’ tilt. 

EnergySage, a renewable energy marketplace backed by the federal government, says the panels’ tilt should match your location’s latitude. For Duluth, that would be about 47 degrees. 

Still, more than half of utility-scale solar power generators in Minnesota have panel tilts between 20 and 30 degrees, according to federal data. That suggests that latitude isn’t a silver bullet to determine optimal tilt. 

But how much does a change in angle matter?

Checking math

I did some quick calculations using PVWatts (again) to demonstrate how panel tilt can affect solar production. I started with a 4 kW system in Duluth that faces directly south. Reducing the tilt from 47 degrees to 20 degrees resulted in less than a 5% decrease in annual energy production.

That’s not a drastic reduction. And I more than made up for it by adding one 300-watt panel to the array. 

While the annual production didn’t change much, adjusting the panel tilt can make big differences on a month-to-month basis. 

For instance, increasing the above system’s panel tilt from 20 degrees to 47 degrees increased energy production by 40% during the month of December. Remember, that’s the time of year when the sun is lowest in the sky, so a steeper tilt will capture more energy.

Making adjustments

Using an adjustable array, solar users can flatten the angle of their panels during the summer and give them a steeper pitch in the winter. In fact, we installed an ground mount array in Duluth’s Lincoln Park that has adjustable racks. 

Rensselaer Polytechnic Institute says 15 degrees should be added to the tilt in the winter, and 15 degrees should be subtracted in the summer. 

On top of optimizing solar production, adjustable systems can also make it easier to remove snow during the winter by allowing the owner to set them at a steeper angle. 

Adjustable arrays are better suited for ground mount projects rather than being installed on a roof. The latter setup can cause issues with wind and shade when they’re tilted up. 

But generally, ground-mounted arrays are more expensive than ones installed on a roof. So if you’re able to install more panels on your roof at a less-than-ideal angle, that may be a better option than an adjustable ground-mount system.  

So while adjustable systems have some advantages, it might make more sense financially to add more panels to your system instead. That way, you’re making up for an imperfect tilt by creating a larger area for the solar energy to hit. 

Making a determination

As you’ve probably determined, there’s no easy way to find the best angle for solar panels. There are a lot of variables that will go into that answer, including site constraints.

But don’t be discouraged if your roof isn’t facing directly south or has an “imperfect” pitch. These are factors that can be overcome with the right design.

Thankfully, the experienced solar professionals at Wolf Track Energy can help you sort through these variables and come up with a system that will work for you and your budget. Give us a call today to see how we can help meet your renewable energy goals.

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