• Adam H. Cooke

Solar Panel Angle Difference I

It is a major investment to put in solar. You want to make the most of your investment, whether you are a homeowner or a business looking to invest a few thousand dollars.

The tilting of solar panels can make a huge difference in energy output and financial return.

What is the Deal with Tilt Angle?

It is well-known that solar panels have a tilt effect on their output. How big is the effect? Is it a major economic change or a minor benefit?

We used Aurora Solar software to model a flat roof in Phoenix. To see how much additional energy can be gained each year, we started with flat panels. We then increased the tilt angle to the south. The rule of thumb seems to be that the optimal tilt angle should roughly equal the latitude of the site. We include a result with a tilt of 33.4°, which is the latitude at Phoenix. The graph below shows the results.

Annual energy output vs panel tilt angle, for a South-facing 5 kW array in Phoenix, Arizona

The tilting of the panels can significantly increase energy output. At 30 degrees tilt, the maximum energy output is 14% more than that of flat panels. This is a lot of energy over the 25-year life span of the panels. Titling should be considered for roofs with flat roofs.

If your roof has a pitch of 20 degrees to the south, it will only get you an additional 1.5% by adding 10 degrees to increase its tilt to reach a total of thirty degrees. It is unlikely that the small increase in energy production is worth the additional cost. There is more hardware and more labor required to tilt panels.

The graph shows that while the optimal angle was close to Phoenix's latitude (33.4 degrees), it is not at the exact same angle. The angle of tilt can only be approximated by using the latitude.

How would this change if we moved further from the Equator, to Boston? Boston lies at 42.4 degrees North.

Annual energy output vs panel tilt angle, for a South-facing 5 kW array in Boston

First, notice that Phoenix's energy output is significantly lower than Phoenix's. At 35 degrees tilt, Boston can produce 7,150 kWh/year while Phoenix produced 9,600 kWh/year. Boston is further away from the Equator, and therefore has more cloudy days.

Panels tilted at 35° had 19% higher energy output than flat panels. This means that tilting had a greater positive effect on Phoenix's panels. Boston's maximum point is also farther away from the latitude value.

However, tilting 15 degrees more than the 20-degree pitch roof might prove to be too much energy.

What about East and West Facing Roofs

These results are for south-facing roofs, which have the highest solar performance. What happens if your roof faces East or West instead of south?

The previous results were repeated for Phoenix with panels facing east and west. Below is a graph showing the results.

Tilt can make things worse for east-facing panels as well as west-facing ones, surprisingly. Flat panels produce the highest energy output. Flat panels are more difficult to maintain because water doesn't run well so they don't self-clean'. A tilt of 10 degrees is recommended for good self-cleaning. The graph shows that the energy doesn’t drop at 10 degrees tilt, so 10 degrees tilt is a good choice for panels facing east or west.

Tilting panels can make an enormous difference in the energy output of a panel. However, each situation must be considered carefully to determine if tilting is the right option.

Tilting can increase energy output per panel if you have a flat roof with lots of space. It is also a great investment that can provide excellent value. Tilting can help increase your roof's energy output.

If you have a flat roof, or if space is tight, flat panels are a better option.


Is tilting important?

A tilted solar panel can dramatically increase its power output and should be considered during the design phase. Tilting may not be necessary if your roof has an excellent angle.

Can tilting increase output from a north-facing roofing?

Most definitely. You can tilt the roof up to 40 degrees relative the roof, which can significantly increase the output energy. This is similar to what you get from a south-facing roofing.

I have a flat roofing.What is the best angle for tilting?

It depends. It all depends on where you live. If space isn't an issue, 30 degrees tilt to the south will produce the highest energy output. If space is tight, you can fit more panels if they are flat. This will produce more power.

Do flat panels work?

Flat panels are best if you have limited space. Water does not drain well so 'self-cleaning is not possible. The panels will need to be checked and cleaned more often. A good amount of self cleaning can be achieved by tilting the panel at 10 degrees.