IEEE Power & Energy Magazine - November/December 2016 - 75

The European Network of Transmission System Operators for Electricity (ENSO-E) conducted studies prior to the
solar eclipse to assess the potential impact on the power
system and to ensure the coordination of operating entities. The main power system concern was the drop off of
solar generation. European solar capacity stood at about
89,000 MW. Germany had the largest concentration of solar
energy, followed by Italy, Spain, and France. A reduction
of 34,000 MW as compared with clear sky was predicted
by the study. The assessment showed power ramps with
decreases as large 400 MW/min and increases as great as
700 MW/min, occurring during periods when photovoltaic
(PV) infeed returns to the system. The ENSO-E study made
recommendations for transmission system operators and for
the continental European synchronous area interconnection.
ENSO-E emphasized the need for
✔ developing day-ahead PV forecasts and recognizing
changes in thermostatic controlled loads and lighting
✔ coordinating operating procedures and improving
situational awareness across jurisdictional boundaries
through increased communication of key operating
parameters and the status of the system
✔ increasing control reserves and verifying the available
power regulation capabilities to help meet frequency
management
✔ training operating personnel
✔ limiting tie line flows.
The actual eclipse decreased generation by 20 GW within
one hour, and it increased generation by 40 GW after the
maximum effect of the eclipse. These ramps, which are
smaller than the study results, were at least partly the result
of overcast skies in Germany. System operators in Italy
prudently reduced the output of many solar installations in
advance to avoid a sudden drop, but German operators apparently did not. Thanks to good preparation, operational issues
were nonexistent. Proper communication and training raised
awareness and informed market players, such as responsible
balancing parties and distribution system operators, all of
whom met their responsibilities. Increased operating reserves
increased costs but improved system security. The variation
from 49.968 to 50.048 Hz showed a good quality frequency
response in continental Europe. The response was also
acceptable in Great Britain, which is a much smaller system.
In addition to implementing these ENSO-E study recommendations, planned equipment outages were minimized and
pumped storage plants were operated strategically to provide
greater system control.
The eclipse resulted in some interesting effects. Even
though lighting load increased, people going outside to watch
the event suppressed demand. Wind generation in some
areas, such as Great Britain, decreased 10% as forecast due
to the reductions in wind speed associated with the eclipse.
The next large-scale eclipses in Europe will occur in 2021
and 2026. Preparations include upgrading market and system
rules, reinforcing regional cooperation across organizations,
november/december 2016

(a)

(b)

figure 3. (a) An annular eclipse and (b) a partial eclipse.
(Photographs by George C. Loehr.)

figure 4. The 15 March 2015 eclipse. The black area
shows the total eclipse and the shaded area shows the
penumbra. (Source: NASA's Scientific Visualization Studio.)

and enabling greater customer responses by leveraging services that PVs can provide to the grid. Several network codes
are being revisited for improvements that will facilitate the
integration and operation of variable resources.

Preparation for the U.S. Eclipse
As for the 21 August 2017 eclipse, there's the usual good
news and bad news. The good news is that North American
power systems have proportionally less solar capacity than
the Europeans. The bad news is that the path of totality goes
right through the heart of the United States. Of course, this
bad news for our power systems is good news for those (like
myself) who have had a strong desire to see a total eclipse of
the sun for a very long time!
The path of totality of the 2017 eclipse will stretch from
Oregon to South Carolina. Actual totality will hit the Oregon Coast about 10:16 a.m. and end on the South Carolina
coast about 2:39 p.m. Time is in local daylight savings times;
it will take the cone of darkness only about 1.5 hours to cross
the continent. Chances of a clear sky should be about 70% in
the west but will decrease to about 50% between Kentucky
and the East Coast.
ieee power & energy magazine

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2016