A solar power system will generate the most energy if you optimize the orientation of the solar panels. But, does that mean it worth it to tilt the solar panels on the roof?
First, let’s talk about the best orientation for solar panels. In the northern hemisphere, you will get the best annual energy output if your solar panels are facing due south at a tilt angle just under your latitude. This means if you are in the southern part of the US at a latitude of 35, your system will give you the most kilowatt hours (kwh) if you face the panels south and tilt them at about 33 or 34 degrees from horizontal.
Most roofs do not provide this ideal orientation. Your roof might south but the pitch is only 17 degrees. Your roof might not face south at all. It could also just be flat. Should you add hardware to tilt your solar panels to achieve that optimal production?
Adding tilt legs to the solar racking will require more racking equipment and more labor to install it. Wind uplift loads are also a factor. When the solar panels are tilted, they are like a sail on your roof and more roof attachments would be required to ensure the solar panels stay put in gusty winds. All of this means higher upfront costs.
Another consideration is that if the solar panels are tilted, the rows must be spread apart to avoid the solar panels in the front row shading the solar panels in the row behind it.
Last but not least, there is the aesthetic factor. The purpose of solar is to save money not look pretty, but your system still shouldn’t be an eyesore.
For the roof that is pitched at 17 degrees to the south, tilting the panels will generally not pay off. It would probably only gain about 5% annual output which will generally not be worth the added cost of the tilt hardware, extra roof attachments and labor.
This is especially true if you are on a “time of use” or TOU electric rate pay more per kwh in the summer. If your solar panels are tilted at the lower 17 degree angle, they will actually produce more in the summer when the sun is higher in the sky to hit the lower tilted panels at a better angle. So, while you lose a little kwh over the period of the year, you will be generating more in the summer when kwh are worth more.
Also, imagine for a moment how those tilted solar panels would look on your roof. Your neighbors would probably appreciate it if you kept them parallel with the roof surface.
As for the case of a roof that is sloped to the east or west, tilting to the south does not gain much because they will still be somewhat angled east or west unless you build a very elaborate wing-like structure to flatten out that east or west tilt. This will likely result in a great amount of expense, a roof attachment at every rafter and complaining neighbors. On a west-facing roof, this is especially unnecessary because tilting solar panels to the west produces more in the afternoons which would benefit you on a TOU electric rate because afternoon kwh rates are the highest.
A flat roof is a little bit different situation. The overall annual energy loss for flat solar panels versus solar panels tilted at the perfect angle is about 10% in the southern states and 15% in the northern states. That much loss might be worth the extra hardware and effort.
Flat roofs also have ballasted racking options that require fewer (if any) holes in the roof, so the added wind load of tilting the solar panels does not necessarily mean more attachments to install. Aesthetics are usually less of a concern as flat roofs are often taller and hidden from view by parapet walls.
With the flat roof, your biggest consideration is the inter-row spacing required to avoid shade on the solar panels. You will get higher kwh production per square foot if you mount the solar panels flat versus tilting them and spacing them apart. But, if you do tilt them, you will get more kwh per solar panel with a better return on the investment of your upfront cost.
This means the decision to tilt solar panels on a flat roof depends on your priorities. If you want the best return on investment and you have plenty of roof space, tilt the solar panels. If you want the most energy possible from a limited amount of roof space, install the panels flat.
So if you have been pondering the question, to tilt or not to tilt, the answer depends on all these factors. When in doubt, you can always get the quote for equipment, installation and estimated energy output for both options and make the decision based on the system cost, the potential energy output and aesthetics.