IEEE Power & Energy Magazine - November/December 2017 - 30

Power (MW)

Available MW
Minimum Allowed MW
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Commanded MW
Measured (MW)

30-MW
Headroom

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Relative Time (s)

figure 4. The results of a midday AGC test using a First
Solar 300-MW PV plant in the CAISO service area.

of system inertia because these resources do not generate
electricity in the same manner as synchronous machines.
However, recent analysis also indicates that appropriately
equipped wind and solar resources can contribute to the
stability of interconnected power systems. Simulations conducted with General Electric's Positive Sequence Load Flow
dynamic simulation software have shown that wind and solar
resources with commercially available active power controls
could be used to contribute to frequency response. A pioneering applied demonstration project performed jointly by
CAISO, First Solar, and the National Renewable Energy Laboratory evaluated a 300-MW utility-scale solar PV plant's
ability to contribute to grid reliability. That work shows that
properly equipped utility-scale solar generation can provide
active and reactive power controls (including participation
in AGC), primary frequency control, ramp-rate control, and
voltage regulation.
Figure 4 shows the response of a First Solar facility to
AGC signals provided by CAISO in August 2016. Comparisons between the 300-MW utility-scale solar PV plant and
conventional technologies showed that the accuracy with
which solar PV follows AGC was significantly faster than
that of gas turbine technologies. The regulation response rate
by the PV plant observed in the 2016 tests outperformed conventional technologies such as combined-cycle, gas turbine,
and hydropower generation by 24-30 points.

Conclusions
As a mainstream source of electricity production, wind
and solar generation is growing considerably around the
world and can be used to help reliably and economically
meet the electricity needs of modern economies. Modest
penetration levels of wind and solar (20-30% of annual
demand) appear to be well within the capabilities of current technologies and have already been demonstrated in
various diverse power systems (e.g., California, Ireland, and
Denmark). How far these resources can go toward meeting
the world's seemingly insatiable need for energy remains
to be seen. One thing, however, is clear: policy makers and

ieee power & energy magazine

engineers are setting ever higher goals for wind, solar, and
modern power systems. Futures with 50-80% penetration
levels of renewables are being studied in detail by system
operators and researchers, and, in many areas, legislated
requirements already exist for these levels. Even futures
with nearly 100% of all electricity generated by renewable
resources dominated by wind and solar PV are garnering
attention worldwide and will likely be subject to detailed
operational study soon.

For Further Reading
D. Palchak, J. Cochran, A. Ehlen, B. McBennett, M. Milligan, I. Chernyakhovskiy, R. Deshmukh, N. Abhyankar,
S. K. Soonee, S.R. Narasimhan, and M. Joshi. (2017).
Greening the grid: Pathways to integrate 160 gigawatts of
wind and solar energy into India's electric grid. NREL/
TP-6A20-68530. Golden, CO: National Renewable Energy
Laboratory. [Online]. Available: http://www.nrel.gov/docs/
fy17osti/68530.pdf
J. Antonanzas, N. Osorio, R. Escobar, R. Urraca, F. J. Martinez-de-Pison, and F. Antonanzas-Torres. Review of photovoltaic power forecasting. Solar Energy, vol. 136, pp. 78-111,
2016. [Online]. Available: http://dx.doi.org/10.1016/j.solener
.2016.06.069
C. Loutan, P. Klauer, S. Chowdhury, S. Hall, M. Morjaria, V. Chadliev, N. Milam, C. Milan, and V. Gevorgian, 2017.
"Demonstration of essential reliability services by a 300-MW
solar photovoltaic power plant," NREL/TP-5D00-67799.
Golden, CO: National Renewable Energy Laboratory.
[Online]. Available: http://www.nrel.gov/docs/fy17osti/
67799.pdf
EPRI. (2016). Wholesale electricity market design initiatives in the United States: Survey and research needs. EPRI,
Palo Alto, CA. [Online]. Available: https://www.epri.com
/#/pages/product/000000003002009273/
[Online]. Available: http://www.aemo.com.au/-/media/
Files/Electricity/NEM/Planning_and_Forecasting/SA_Ad
visory/2016/2016_SAER.pdf

Biographies
Aaron Bloom is with the National Renewable Energy Laboratory, Golden, Colorado.
Udi Helman is with Helman Analytics, San Francisco,
California.
Hannele Holttinen is with the VTT Technical Research
Centre of Finland, Espoo.
Kate Summers is with Pacific Hydro, Melbourne, Australia.
Jordan Bakke is with the Midcontinent Independent System
Operator, Eagan, Minnesota.
Gregory Brinkman is with the National Renewable Energy
Laboratory, Golden, Colorado.
Anthony Lopez is with the National Renewable Energy Laboratory, Golden, Colorado.
p&e

november/december 2017

http://www.nrel.gov/docs/ http://dx.doi.org/10.1016/j.solener http://www.nrel.gov/docs/fy17osti/ https://www.epri.com http://www.aemo.com.au/-/media/

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