Should I point my solar panels West to optimize for afternoon peak TOU rates? – Solar Power World


By Andrew Gong, research engineer, Aurora Solar

Here at Aurora, we like to tackle hard questions. One question we see often is: “Given that electricity rates are higher from 4 to 9 p.m. in California, should I place my solar panels facing west instead of south to maximize savings?”

In this post we will dive into why west-facing panels might be more advantageous than south-facing ones, and provide recommendations based on your location and how your peak time-of-use (TOU) rate works.

Context: Moving West in California

Aggregate Demand and the Duck Curve

The three main investor-owned utilities in California have been utilizing peak TOU rates from 4 to 9 p.m. since late 2017; customers are charged more for the electricity they use during the late afternoon and evening hours. Prior to this, peak hours in the middle of the day — between 11 a.m. and 6 p.m. — were most common.

The peak hours shift was driven by aggregate demand on California’s grid. Prior to the early 2010s, homeowners and businesses used the most energy in the middle of the day and early evening. Midday peak-pricing provided the financial incentive to reduce energy usage or shift loads to non-peak hours. Since then, the falling cost of solar has drastically shifted the total demand on the grid as seen in the infamous duck curve, pushing the peak demand, and moving peak-pricing to early evenings.


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