Teaching the Duck to Fly – Timing Electrical Demand to Renewable Supply

Posted by on May 26, 2015

Editor’s note: In this guest article, my friend Marty Grohman, the director of sustainability at GAF Roofing and a legislator in the State of Maine, describes some of the challenges being faced by the utility industry to shave peak loads in electricity demand in an age of growing solar generation. The evening peak in demand, which occurs as solar generation is dropping, argues for orienting solar arrays somewhat to the west to optimize power production late in the day. This is an important discussion as we seek to make the electric grid more resilient.  -Alex Wilson

This duck-shaped graph shows the net power usage vs. time of day for a southern California utility company. If the evening peak is leveled off the graph will appear more like a duck in flight, with the neck stretched out horizontally. Credit: The Regulatory Assistance Project

This duck-shaped graph shows the net power usage vs. time of day for a southern California utility company. If the evening peak is leveled off the graph will appear more like a duck in flight, with the neck stretched out horizontally. Credit: The Regulatory Assistance Project

I recently attended a presentation by David Farnsworth of The Regulatory Assistance Project (RAP). The Vermont based nonprofit seeks to assist to government officials in developing sustainable energy policy. Among the interesting topics covered in David’s presentation was a concept in electrical usage called the Duck. As seen in the illustration, the Duck describes a distinctively shaped plot of typical electrical usage vs time of day at the grid scale that results when a large number of connected users have installed solar power. This particular example is from a southern California utility that is expected to install significant amounts of renewable energy by 2020.

It is clear that solar power generation supplying into this electrical network is softening what was a noontime bump in usage. And as more panels are installed on homes throughout the network, projected here through 2020, it is anticipated that quite a dip in the amount of power the grid needs to supply in the early afternoon will occur. That results from homeowners, such as myself, who install south-facing solar panels which by design generate the most significant amounts power during the sun’s brightest hours in the early afternoon. This offsets what the grid must supply while the sun is bright, and has the effect of creating the ‘belly’ of the duck – a reduction in demand. This ‘belly’ is projected here to continue through 2020 as more solar is installed.

There is nothing new about this demand curve – it has been common since electricity was widely available. What is new is the combination of significant amounts of roof mounted solar power generation, together with the fact that the electrical grid in many areas is reaching maximum capacity. In the evening as we return to our homes and fire up appliances, air conditioners, and electronics, there is a large spike in usage. However, this peak takes place while the sun is getting low in the sky and solar panels (which are typically oriented to capture maximum noonday sun) are producing less power. The concern here is that infrastructure like transformers and lines that go to your home or to a factory must be large enough to supply all the power you might use, whether or not you are using it. If the electrical grid can’t do that, we’ll all as users experience an unsafe low voltage condition that can fry electronics, overheat power lines, and worse. Essentially, to prevent a brownout, electrical utilities must have the capability to provide peak power anytime, whether we’re at home using electricity or not and whether we’re making our own power or not.

To accommodate this need, electrical generation that can quickly respond to rapid changes in demand is of premium value. Typically, natural gas or even older, less efficient oil or coal fired plants are used. In fact, this capacity is often paid to be available even when the electricity is not being used. This is expensive and inefficient. It also can be a poor environmental tradeoff, since these backup plants are often bigger polluters. As such, addressing the evening peak, or ‘teaching the duck to fly’ as RAP’s original developer of the concept Jim Lazar puts it, potentially has great value to the grid.

Cool roofing can reduce air conditioning load and thus soften the evening electrical spike. But that’s only part of the story – solar power, above identified as part of the problem, can actually be the rest. Broadly speaking, renewable energy is sometimes projected as less desirable to the grid because it is unpredictable (wind power is often painted with this brush). Solar power, however, actually is quite predictable. The sun in fact does come up every day! But we also know it is NOT available for that afternoon late peak in demand, at least with typical south facing panels. So that’s the opportunity: when the sun and solar generation are both at their highest through the lunchtime hours, electrical demand is normally fairly steady and not at a level that taxes the grid. At the evening peak, most panels are dropping off in production, meaning those expensive, often more carbon intensive backup sources may need to ramp up and make up the difference.

Therefore, in the absence of battery storage (advances in which continue), solar production in the late afternoon and evening is arguably of greater value than daytime production. Solar trackers, which allow panels to continually face the sun throughout the day, could provide greater value. However, a tracker installation on a residential rooftop would be unusual, at least today, and arguably even unsightly. As such, some propose that orienting panels to the west to catch the setting sun, at the time usage peaks, might make solar power more valuable even if less total electricity would be generated. Widespread incentives for homeowners to orient their panels to the west do not exist today. However, as more and more solar generation comes on to the grid and compensation mechanisms become more sophisticated, this may change.

Essentially, it’s a debate whether a residential solar installation should be arranged for the greater benefit of the grid or the greater benefit of the homeowner. Since grid investments are expensive and are ultimately passed on to ratepayers, both outcomes can result in significant savings on your power bill. However, it can be argued that investments that are for the benefit of the grid should improve resiliency. The work of the Regulatory Assistance Project seeks to add to this discussion as states consider future solar policy.

Martin Grohman

Executive Director, Sustainability at GAF

One Comment

  1. Moving to solar energy has become a necessity of this age. Each house can be self-sufficient in this matter if they have a solar power plant on their roofs. This is the only way that we can get out of the energy crisis that we currently face.


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