West is best when it comes to benefits of solar

April 01, 2015

By Marc Romito, APS Manager for Renewable Energy

At APS, our job is to provide all customers with reliable power at all times, in all weather.

With the many great things about solar power, one tricky problem remains: The sun doesn’t shine 24 hours a day. Even in Arizona.

Even when the sun is shining, all daylight hours are not created equal.

Our customers use the most energy – what we call “peak load” or “peak demand” – in the late afternoons and early evenings on weekdays. That’s when people are coming home from work, turning on their air conditioners and getting dinner ready.

This is why solar energy produced later in the afternoon provides far more benefit for customers than energy produced at noon or 1 p.m.

But most rooftop solar systems are installed facing south or east. They produce most of their power between noon and 1 p.m., when demand is low, and produce very little later in the afternoon, when our customers need it most.

Panels that face west or southwest offer an advantage because they provide more energy during higher use times. While solar, even when facing west, still does not match the maximum APS system peak, it makes sense to get the most “bang for the buck” possible.

Several APS solar initiatives are following this notion of providing solar energy later in the day.

One is the Solana Solar Generating Station near Gila Bend, which uses molten salt storage to continue producing power even after the sun goes down. In other words, even if the sun is shining brightest at noon, we can save the power until 6 p.m. when it benefits our customers the most.

Another example is six of our AZ Sun solar plants located around the state that use trackers to follow the sun. Unlike the typical panels on a roof that don’t move, these panels rotate so they face east in the morning and west in the afternoon, to maximize production.

Lastly, with our AZ Solar Partner program, APS will install solar systems on about 1,500 customer roofs. Almost all of these systems will face west or southwest, and all power produced by the systems will flow back to the grid to serve all customers.

Basic rules of supply and demand tell you that something is more valuable when demand is high and supply is low. That’s the importance of west-facing solar.