Solar Eclipse Effect of Solar PV Systems

Are you wondering how the August 21, 2017 solar eclipse will affect your rooftop solar system? The short answer – it’s going to cost you money. How much? Let’s look at the numbers.
In San Antonio, the moon will partially block the sun for approximately 3 hours, which will cause a dip in system production. Per the NASA website, the eclipse starts at 11:40am and ends at 2:38pm with an obscuration peak of 61% around 1:00pm. Using solar production modeling software, the normal production on a typical August 21 was adjusted for the solar eclipse event. With the production loss (see the graph), we are able to estimate the loss in dollars. For a 8kW system, the eclipse is going to cost you $0.84!

Typical Solar PV Production on August 21, 2017

Not everyone has an 8kW system. For every kW of installed capacity, the financial loss is $0.11. Match your System Size (kW) to the Loss ($) column – this is the amount that you’ll lose over the 3-hour eclipse. Let us know if you want to buy solar eclipse insurance!

How does San Antonio compare to other parts of the US? Let’s compare an 8 kW solar PV systems in Los Angeles and St Louis to the system in San Antonio.

Solar Production loss in Los Angeles

The same size system in Los Angeles (LA) performs similar to the San Antonio (SA) system because the solar irradiance levels of 5-6 kWh/m2/day are similar. Plus, the 2017 solar eclipse obscuration rates of 62.2% in SA is very close to the LA rate of 62%.

Let’s look at the differences. Due to the different times zones, the solar eclipse will occur during the morning hours in LA (9am – 11am) compared to SA which will experience the eclipse during midday (11:30am – 2:30pm). Peak solar production occurs midday so SA loses more production. Not so fast, energy costs are higher in LA. While the lost solar production is less in LA, it has higher value. The higher value energy in LA offsets the lower production loss so systems in SA and LA experience the same financial impact. The PV systems in SA and LA lose $0.84 and $0.85 respectively.

Solar Production loss in St Louis

St Louis falls in the direct path of the solar eclipse this year so the solar obscuration rate is 100%. Hello total eclipse! The solar PV system production will drop to zero! How does the total eclipse effect the financial performance? Is it better or worse than Los Angeles and San Antonio? Surprisingly, the financial impact is better, which means the system loses less money during the eclipse. But it’s a total eclipse, why does it lose less money? Because the solar irradiance levels are lower (4 kWh/m2/day) so the system generates less energy to begin with. Plus, energy costs in St Louis are lower than the rates in LA and SA. Relative to the systems in LA and SA, the system generates less energy so during the eclipse it loses less energy. Plus, the lost energy is less valuable. The overall financial impact of the solar eclipse is $0.64 for a 8kW system in St Louis.

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