Cardinal Sins: The West Versus South Debate

Western facing solar panels align better with peak energy usage, improve load balancing, and could provide additional income from dynamically priced utilities. However, the limited number of these utilities and the existence of other more effective options will likely limit the usefulness of reorienting panels.

The current wisdom is that solar panels must be installed south facing, if at all possible. However a new report by the Pecan Street Institute (via GTM article) suggests that western facing panels may be a superior alternative since it will better align with peak energy usage.

Strictly speaking, a south facing solar panel (for us northern hemisphere folks) is preferred because it is better aligned with the sun during the day. However, most of this sunlight is captured before the energy is used. As we discussed in our previous article, there is a timing issue between solar production and peak electricity usage which could trigger an oversupply of energy during the day with a sharper jump in usage peaks in the early evening.

Installing western facing solar panels shifts that energy capture to the late afternoon and into the early evening as the sun is setting in the west.  For Pecan Street’s study they found that while southern facing panels reduced peak production by 54%, western facing panels reduced peak production by 65%!

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They even found the western facing panels created more energy overall than south facing panels. That result is consistent with the PVWatts data and most likely related to weather conditions. However, on an annual basis, south facing solar panels produce much more energy. 

Don’t Get Back On The Roof Yet

The study was conducted in Austin, Texas during the summer months when the sun is up longer and higher in the sky and spends more time due west during sunset. For southern versus western facing panels, the difference in energy captured by the solar panels is much smaller than during the winter. During the short winter days, the sun spends more time in the south compared to the west so there would be a greater difference in energy captured based on orientation during this time. This difference becomes more extreme as you increase in latitude. Also, electricity rates in Austin are the highest during the summer months due to air conditioning usage.

Smart Solar Options

As more utilites move to smart meters and dynamically priced services, it is clear that there is going to need to be some adjustments made to how consumers and producers of energy behave. While just installing solar panels in the western direction may partially alleviate the escalation towards peak demand in the early evening, it is really only a weak way to adjust. Using this as a solution takes away from much more effective alternatives such as tracking solar panels and battery backup systems.

Compared to fixed systems, one- and two-axis tracking systems are relatively rare. While they are better than fixed panels, they are still limited by sunrise and sunset, so their ability to match peak demand can only go so far.

Given the strong push for battery backup systems with solar, this is going to be the biggest advantage in the future. Choosing panels and orienting them to capture the most sunlight and then feeding the excess energy into an on-site backup battery will quickly become the norm. These batteries will turn on once the sun has set and peak rates set in. For larger consumers, smart batteries will even develop arbitrage schemes where they use energy from the grid to charge up when the rates are lowest and the solar energy produced won’t cover the gap. 

Aaron Hoffer

By Aaron Hoffer

Co-founder and CFO


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