In the northern hemisphere, the sun crosses the sky a little to the south, which means putting solar panels on a south-facing roof is the best way for homeowners to capture the most solar energy. But what if you don’t have a suitable south-facing roof?
Well, when it comes to solar panels, west is second-best.
Go west, young one
West-facing roofs get less sun than those that face south, but it’s not as little as you may think. According to the Concord Consortium, makers of Energy3D solar energy modeling software, a home in Boston, MA with panels that face west would get 80% of the electricity that a house with south-facing panels would. That ratio improves to 82% for homes in Los Angeles, California.
On other words, to get the same amount of electricity as a south-facing installation, a west-facing one would need to be 25% bigger. (25% x 80% = 20%). If you have an unshaded, west-facing roof, you can still install solar panels and save money.
But keep in mind, every house is unique. Your roof orientation, material, and shade profile are all part of what makes your home good or bad for solar panels. Your best bet is to connect with a solar expert near you to see whether your home is right for solar.
When west is best
In the afternoon and evening, people arrive home and turn on all their appliances at the same time. Well, maybe not all their appliances, but the change in energy usage is great enough that utility companies call late-afternoon through evening the “peak” period, because of how much more energy is needed during those times.
In our free-market society, when things are more in-demand, they’re more expensive. The same is true for electricity. It’s costlier for the utility companies to buy energy they need to give to their customers at peak times, and those costs are often passed on using a billing arrangement called “Time-of-Use” (ToU) billing.
Under ToU, energy during peak times is more expensive, and in the summer time, those prices go up even further, because the demand for electricity increases as more people turn on their air conditioners.
Enter solar electricity to save the day!
How solar can help avoid peak demand
On a south-facing roof, the panels produce energy when the sun is high in the sky, but as the evening sets in, that production decreases. If the panels face west instead, they get more energy during the afternoon an evening.
For people on a ToU billing plan, west-facing solar panels can help avoid paying the higher peak rates by providing more energy when the cost would be higher. Here’s a diagram showing the average daily sun for a home at 45° N latitude during the summertime:
The diagram shows how the sun passes over a house with solar panels on the south- and west-facing roof surfaces. Let’s walk you through an average day (August 6th, to be exact):
- The Sun rises at 5:52 AM, and begins directly shining on the south-facing panels at 8:15
- At 9:50, the sun is high enough in the sky that the west-facing panels begin to receive some direct light
- At 1 PM, the sun is shining directly out of the southern sky
- After 6 PM, the south-facing roof is no longer receiving direct sunlight
- The sun sets at 8:20 PM, and as long as the west-facing roof isn’t blocked by obstructions, it received light up until the end
Under ToU, summer peak times are typically between 3 and 8 pm. With west-facing panels, you can produce nearly 50% more on-peak electricity.
Here’s a chart with some data from Pecan Street Research Institute that shows how west-facing panels compare to those facing south during peak times:
The bottom line
If you can take advantage of ToU billing and you have a suitable south or west-facing roof, you should investigate your solar potential and find a local solar installer near you. A west-facing roof producing 50% more electricity during peak times can actually save you more money than a system of the same size facing south.