Navigant Research Blog

What Would a Perma-Eclipse Do to Solar Power?

Adam Forni — August 15, 2017

On August 21, a total solar eclipse will captivate millions of observers across the United States. Early on its 1,800 mph path across the country, the moon’s shadow will block 5.6 GW worth of solar power plants in California, the top solar state. The California Independent System Operator (CAISO), the state’s grid operator, is well prepared to respond with increased flex-ramp usage and regulation service procurement—essentially a combination of demand management and flexible natural gas and hydropower units. CAISO is aided in part by lessons learned from the 2015 eclipse in Europe, which has higher renewables penetration than the United States.

The eclipse reminds us that the sun’s rays can experience volatility beyond known daily and annual cycles and begs the question: what would happen if the sun stopped shining? Though the question may sound alarmist, it is not entirely trivial. A significant impact event would have solar-blocking potential, with impacting objects above 1 km (about half a mile) in diameter potentially ejecting large masses of pulverized rock into the stratosphere. Solar-blocking geoengineering projects, while intentionally limited in scope, are specifically designed to block the sun’s rays. Movie buffs will remember that humanity scorched the sky and purposefully blocked out the sun to battle solar-dependent robots in The Matrix trilogy.

Solar PV accounted for just about 2% of global electricity production in 2016 but was also the world’s leading source of additional power generating capacity. With some grids anticipating 30%, 50%, or higher eventual PV penetrations, the potential degree of vulnerability is significant—though the probability of diminished insolation is low.

Utility-Scale Solar PV Generators and Path of August 21 Solar Eclipse

(Source: US Energy Information Administration)

A Portfolio Approach

The appeal of solar PV, especially when combined with storage, is undeniable. A clean, distributable, and increasingly inexpensive energy source, solar PV will be a crucial source of power globally. But, much like a contrarian stock market investor, it is worthwhile to look beyond the hype to see what risks loom. To use another stock market analogy, asset diversification is important on the electric grid.

Most of our energy ultimately comes from the sun, and this is especially true of today’s zero-carbon resources. Wind energy is partially driven by daily solar cycles and experienced a 10% decline during Europe’s eclipse. Hydropower, a flexible generation resource that will help ramp during California’s eclipse, is also driven by the sun’s ability to evaporate water. Biopower, another important carbon-neutral dispatchable resource, is driven by the sun, though on the longer scale of months to years. Compared to solar power, each of these should be less directly affected by potential solar-blocking phenomena. Meanwhile, nuclear, geothermal, tidal, and carbon-captured fossil fuel power are not dependent on the sun’s rays. A vague threat to the availability of solar energy does not suggest these should be adopted en masse. However, some consideration should be given to adopting a diversified, risk-mitigated portfolio of generation.

What would happen if a heavily solar-dependent Earth suddenly lost that energy source? Our collective gaze would undoubtedly turn from the sky back to the ground—to the likes of nuclear, geothermal, and for the quickest fix, fossil fuels. Being prepared ahead of time with a diversified, efficient, and clean energy mix could help mitigate that risk.

Still, this month’s eclipse will affect the US grid little since fossil fuels still account for most of the national power supply. For now at least, we can use plenty more renewables to diversify our energy portfolio.

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