Most solar homeowners put their solar panels on the roof, and which direction your roof faces is one of the more important variables that determines how your system will perform.
What do we mean by the direction of your roof? Simply, your solar panels will be mounted flat against your roof, so you therefore want your roof facing the sun for most of the day. Traditionally, this means that in the United States, you want your roof facing south. In the illustration below, the house has a simple roof with sections that face southwest and northeast:
(While you still can generate electricity with solar panels facing north, their power output for homes with a typical pitch (ie. roof slope) will be significantly less than with panels facing south, so this practice is usually discouraged.)
However, many homes have roofs that are more complicated, with multiple intersecting segments or features like dormers:
In cases like this, your solar panels may need to be mounted on more than one section of your roof, and the different groups of solar panels will receive different amounts of sunlight throughout the day.
But for the purposes of this article, we’ll talk about the more straightforward case where you have a simple roof, and all of your panels are facing the same direciton.
When you live anywhere in the United States, assuming that you have a sky unobstructed by trees or buildings, your solar panels will receive the most sunlight if they face south, because the sun is in the southern sky. But does that mean your solar panels have to face south if you want to maximize your return on investment?
It turns out that the answer is no. Your solar panels don’t always have to face south if you want the maximum return on investment. The best choice depends on the billing and net metering plan that you have with your utility company. If you have net billing or a time-of-use (TOU) plan, you will often receive a higher credit for electricity that you send into the grid in the evening. This means that it may be better if your solar panels face west or southwest.
If you’re not sure, check with your utility to see if you have a TOU plan, have net billing, or live in California and have Net Metering 2.0 (NEM 2.0). If the answer is yes to any of these, there’s a good chance you’re better off facing your panels west or southwest.
If these terms are unfamiliar and seem complicated, don’t worry! This guide will explain them. You can check out our guide to solar power for homeowners for in-depth information, but in this article we’ll do a high level review of the important concepts of net metering and how time-of-use billing works.
Net metering is a policy that gives you full credit for solar electricity that you send into the grid. Those credits are banked and later spent when you use power from the grid.
For example, if you’re at work on a sunny day, your house may use little or no electricity, but your solar panels will be generating lots of electricity. That unused electricity will get sent into the grid, which is recorded by your utility meter. If you have net metering, you’ll get full credit for that electricity. This means that if you pay $0.18 for one kWh of electricity taken from the grid, you’ll get $0.18 back when you send one kWh of electricity into the gird.
If you have net billing, you don’t get full credit for excess electricity you send into the grid. Instead, you are paid at a lower rate, often called the avoided cost rate. That rate is typically the wholesale cost of electricity that your utility would pay to a power generator.
For example, let’s say you pay $0.18 per kWh of electricity, which is about the average in the US.
Under net billing, you would get paid less than that. Let’s pretend that your avoided cost rate is $0.10 per kWh. That means if your house sends 20 kWh of power into the grid while you’re at work, under net billing you would get only a $2.00 credit for your electricity instead of the $3.60 you would get if you had full net metering. Over a course of a year, that can make a big difference in the economics of your photovoltaic system.
The avoided cost rate that you earn for the solar electricity you send into the grid varies from utility to utility. Check with yours to find your current rate.
When you have time-of-use (TOU) billing with your utility, the price you pay for electricity changes with the time of day. You will pay more - sometimes much more - for electricity during periods of peak demand compared to off-peak periods (such as the middle of the night) when demand is very low.
New solar customers in California are required to have a TOU plan, so this topic is an important one to understand.
The key thing that California solar homeowners need to know is that your net metering credits are affected by the TOU plan. While California does have true net metering, you will earn higher credits for solar electricity you send into the grid during peak hours - roughly, late afternoon and evening when demand on the electric grid is highest.
There’s more to know about time-of-use plans, so I wrote a whole article that covers it indepth.
TOU plans and net billing both have a similiar effect on solar homeowners: they reward homeowners for generating electricity when demand is highest. This usually means facing solar panels toward the west so they capture more energy late in the day.
With net billing, you want to use as much of your own solar electricity and send as little into the grid as possible. For most people, their electricity usage is highest in the early evening, so pointing your panels west will make sense.
Not everybody works a 9-5 shift however, and it’s also possible to use smart home devices and timers to shift much of your electricity usage to the middle of the day when south-facing solar panels will generate the most electricity. Because of this, it’s possible with net billing to optimize your electricity usage to make south-facing solar (or different orientations) work well for you.
TOU plans tend to make the decision more straightforward: on-peak billing for utility companies are nearly always scheduled for weekday late afternoons and early evenings. Because of this, southwest or west-facing solar panels will often be the best choice to maximize the value of your solar electricity.
Unless there’s shade in the way, you’ll generate more electricity if you face your solar panels south. However, your electricity could be more valuable if you instead face your panels west or southwest. Here are the situations when west-facing panels may make the most sense:
While about 95% of homeowners choose rooftop solar, ground-mounted solar is a more costly option but often a better one if you have room in your backyard.
One reason is easier maintenance, but another is that ground-mounting offers the possibility of solar mounts that are manually tiltable or automatically track the sun. While these mounts do get expensive and generally only make economic sense for larger solar farms, they offer an option for the homeowner who is trying to squeeze every electron possible out of their systems. You can read more about ground-mounted solar and the different types of tracking systems.
A qualified solar installer will help you navigate these choices. Their project proposal will forecast the energy production of your rooftop, help you to understand your utility’s rate structure, and examine your electricity usage so that your system is sized appropriately.
If you use The Solar Nerd to get a solar quote, you’ll work with a network of prescreened qualified solar contractors who will get you a fair quote.