What To Consider When Deciding the Direction Your Solar Panels Will Face

The direction that solar panels face has a significant impact on the production and savings that homeowners see. The general guidance is to have panels facing toward the south, but that is only one of several factors that should be considered when creating an optimized solar panel layout. 

Energy from solar panels is generated by sunlight hitting the panels and exciting electrons in the cells. Those excited electrons move from one layer of the cell to the next and produce electricity (DC) that feeds into an inverter which creates power homes can consume (AC). The more intense and direct sunlight that hits those panels, the more energy is produced.  When it comes to producing energy, it’s not just sunlight that we’re looking for, but direct sunlight.

The General Rule Of Thumb

As mentioned above, there is a pretty simple rule of thumb for panel placement. Assuming you live in the northern hemisphere, the best place to put panels would be on the south side of the roof. 

Any roof plane that faces toward the south (direct south, southeast, southwest) will always be your best place to put panels because they will be in direct sunlight for the most amount of time possible through the day. This is flipped for those living in the southern hemisphere, where they would prefer the northern roof. The difference in production gets slimmer the closer you get to the equator because the sun is more directly overhead. 

After South, East and West facing roofs are the next best options. Production-wise, east and west roofs will produce roughly the same amount of energy. There is a slight advantage to the West but the difference is negligible in terms of overall power.

Real Life Numbers

To prove the point of best production, I went to the National Renewable Energy Lab’s (NREL) PV Watts calculator. This free online tool lets anyone input a few variables and output estimated production. 

The following simulations are for an 8kW PV system on a 25-degree pitched roof-mounted array in Illinois. The production numbers will vary if you set the location to a sunnier area like California or Arizona, but the production drop-off still holds. 

As shown below, and unsurprisingly, the southern roof, with the East and West roof planes producing roughly the same amount of energy, is in first place. The northern roof is in last place by a large margin.

The production numbers show that the general rule of thumb is quite correct for maximum production. Compared to a southern roof, east and west-facing panels would experience about a 20% drop in production, and northern-facing roofs have almost a 50% drop in production. 

For practical applications, a home using east, west, or north-facing roof planes would need to use significantly more panels to achieve the same level of consumption offset. 

Generally speaking, the rule of thumb is to never use a northern roof plane because of this production loss. But that is where the more complicated answer begins.

Panel Direction Based on Goals and Product

Production is the main goal with most solar installations because more production equals more savings—in most cases. Basing analysis on production removes a crucial variable from the equation: which is savings. 

Increasingly fewer and fewer electric utilities in the US are offering full-rate 1:1 net metering. As we move further away from net metering, it becomes more important to offset consumption with solar production. Since solar owners get significantly less value from energy sent to the grid, there’s more incentive to use power directly in the home.

If a home uses more energy in the morning, they’d benefit from eastern-facing panels to offset their consumption. If that home uses more energy in the afternoon, they’d benefit from western-facing panels. Another factor to consider is time-of-use pricing, where prices are variable throughout the day based on demand. If your home is on a TOU plan, more power production during peak windows reduces draw from the grid and increases savings. 

Factoring in your consumption is particularly helpful for homes that have no southern roof exposure. If the only option is the east or west face, the best course of action is to assess your consumption and variable utility rate then build the system to mitigate as much draw from the grid as possible.

Installing a battery is becoming a more popular option because the power can be produced whenever and used when the home needs it most. But for those not able to install batteries, planning the solar direction can drastically affect savings. 

Owned vs Leased Systems

The direction panels get placed on a home often also depends on what product a homeowner is being sold. Ownership models like cash and financed purchased solar systems have to make sense as an investment before homeowners will invest in them. 

With ownership models, it benefits homeowners to use only the most productive roof planes because those have a greater effect on ROI. Less productive directions (north or heavily shaded roofs) don’t produce as much energy and have a lower consumption offset. Since homeowners don’t get discounts on northern-facing panels, if they utilize a north roof the cost of the system increases linearly while production and savings do not. 

Third-party-owned (TPO) systems like leases and PPA often utilize every roof plane available because those systems have no ROI. TPO systems only try to produce as much energy as possible and feed it into the home. Since the homeowner isn’t putting up any money to pay for equipment, it doesn’t matter how efficient the system is as long as it produces enough energy.

In Summary

At the end of the day, which direction should panels face? It’s best to stick with the solar rule of thumb and use south, east, or west faces. If you are getting solar quotes for an owned system (cash or finance) and you see northern-facing panels, take a look to see if that makes sense for your home. 

You may find that removing those panels and increasing the efficiency of the system increases the ROI and saves you more over time.