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How Many Batteries Does It Take to Kill a Duck (Curve)?

California blows all other states away when it comes to renewable energy. Its solar and wind generation account for 44% and 9% of the nation’s total generation, respectively. All that energy is great for making strides towards California’s goal of 33% retail electric generation from renewables by 2020, but this poses a big problem for power plants. A problem that a man with an electric car and rocket ship might be able to solve.

Obviously, solar power is only generated during the day, coincidentally while most people are at work and load is at its lowest. However, when people get home from work and start flipping their on-switches, power generation must ramp up because, unfortunately, the sun is also going down. This daily phenomenon generates what is called the duck curve.

The graph above from CAISO, the main independent service operator in California, shows the actual load curves from 2012 and 2013, with forecasted curves for 2014 and onward. As the years progress and California nears its renewables goal, the trough in the curves gets deeper and deeper as more and more energy is being generated from solar. If only there was some way to bottle up all that energy generated during the day and use in the evening during peak demand. Well according to Mr. Elon Musk, there is a way, in the form of his Tesla Powerwall.

The Tesla Powerwall is a home battery system that can either store energy generated from solar panels or the grid and discharge that energy later during peak demand. The Powerwall comes in two flavors: a 10 kWh weekly cycle version meant mainly for backup purposes and a 7 kWh daily cycle version meant for everyday use. So what can these batteries do to alleviate our duck problem?

There are of course an infinite number of possibilities on different methods to incorporate battery storage into CAISO’s daily generation profile, but let’s choose a shape similar to the 2013 ramp, since presumably, that was not too much of a strain on the system. The graph below shows both the expected load curve with and without battery storage in 2020. The red shaded area represents the energy required from discharging batteries.

Seems like good news, except once you start crunching the numbers that red shaded area translates to close to 3.5 million, 7 kWh battery units. The graph below shows how many batteries would be required to maintain a similar 2013 net load growth shape from 2015 to 2020.

With a price tag of $3,500 a pop that comes out to a total of about $12.5 billion by 2020, a pretty hefty price tag,  but on a per capita basis for California this represents ~$350 per person.  A fairly manageable investment for the residents of California but at this point the duck is going to keep quacking until production capacity of Powerwalls  catches up to the potential demand.

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Matthew Hoza is a Manager of Energy Analysis for BTU Analytics. Currently he is leading the power team in the development of BTU Analytics’ Power View platform, which provides capacity, generation, and power price outlooks for ISOs and utility areas across the US. Previously, Matthew led the natural gas team that develops and maintains outlooks for natural gas production, demand, pricing, and infrastructure, as well as provided bespoke natural gas market analysis. He holds a M.S. in Finance from the Simon Graduate School of Business at the University of Rochester and B.S. in Physics from Florida State University.

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