IEEE Power & Energy Magazine - March/April 2022 - 38

Continuing to rely on simplified rules and margins is
convenient but could easily lead to overestimating the
uncertainty of the net load, which, in turn, could lead
to overinvesting in the distribution system. A stochastic
modeling technique can factor in the variability of each
net load element, its probability distribution function, and
its covariance with other net load elements. Because of the
various characteristics of different DERs and their geographical
spread, there is a covariance among elements
that will result in the variability of the net load being significantly
lower than the sum of the uncertainties associated
with each DER. This is an important reason why
probabilistic modeling techniques that take into account
the variability of the net load need to be used to capture the
value of DERs (Figure 3).
Planning With Uncertainty
The growth of DERs will not remove the need for conventional
distribution system upgrades. On the contrary, since
many DERs add net load, we will need to continue increasing
the capacity of our distribution systems as DERs grow.
However, the use of the load and voltage management features
of DERs can help defer investments in upgrades. This
is what the IDRP study showed (see Figure 2). However,
the distribution planning process often requires long lead
times to complete upgrades, such as replacing substations or
reconductoring lines in time to meet the expected increase
in demand. This creates a planner's dilemma: if we invest
too soon in conventional upgrades, the value of DERs cannot
be realized because the deferral value was eliminated by
the upgrade.
On the other hand, DER growth takes time, and, if we miss
the forecast, there is a risk of overloading the feeder and jeopardizing
reliability. This dilemma is illustrated in Figure 4,
where at time t1, conventional distribution planning techniques
would identify the need to complete a capacity
upgrade by time t3 to avoid overloading. At time t1, DERs
have not grown enough to offset the upgrade need. At
time t2, the utility needs to start its work to upgrade the
circuit to finish by time t3. However, at this time, DERs
are growing, but there is still uncertainty as to whether
sufficient capacity will be available to offset the conventional
upgrade. The dilemma is whether to wait for DERs
to grow or take the safer but most costly route of upgrading
the capacity-constrained element even if it may not be
needed for several years.
To solve the distribution planner's dilemma and capture the
value of DERs, utilities must become more nimble and able to
reduce the elapsed time between identifying needs, procuring
equipment, and completing the upgrade. This may mean that
utilities adjust their procurement policy to keep the equipment
for substation and line upgrades readily available for deployment
yet remain flexible on the exact location of the investment
until customers' DER investment patterns become clear.
38
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Conclusion
Three key results from SMUD's recent IDRP study have
been highlighted:
✔ Unless carefully managed, EVs could constitute
up to 10% of the peak load in the next 10 years.
Considering that the timing of EV charging loads
is highly uncertain, this has a profound impact on
planning.
✔ Adding solar PV and battery storage does not introduce
hosting capacity constraints. On the contrary,
they can help offset capacity constraints on the feeder.
✔ Utilizing the flexible load characteristics and control
options for DERs can reduce the costs of distribution
system upgrades up to 10% over 10 years.
The implications for distribution planning with DERs are
profound. In this article, we have identified four practices
that may be needed to capture the value of DERs and plan
for cost-effective distribution system upgrades:
✔ move from system to locational load forecasting
✔ explicitly account for DER impacts by modeling the
managed net load rather than the unmanaged load
✔ adopt expanded chronological modeling and stochastic
modeling techniques
✔ improve flexibility and shorten the construction time
for system upgrades.
For Further Reading
" Incorporating DER into distribution planning, " Electric Power
Research Inst. (EPRI), Palo Alto, CA, USA. https://www.epri
.com/research/products/000000003002010997
" Value of solar primer, " American Public Power Association,
Washington, DC, USA. https://www.publicpower.org/
system/files/documents/ppf_value_of_solar_primer.pdf
" SMUD's 2018 integrated resource plan, " California
Energy Commission, Sacramento, CA, USA. https://efiling
.energy.ca.gov/getdocument.aspx?tn=227887
" SMUD's 2030 zero carbon plan executive summary, "
SMUD, Sacramento, CA, USA. https://www.smud.org/-/
media/Documents/Corporate/Environmental-Leadership/
ZeroCarbon/2030-Zero-Carbon-Plan-Executive-Summary
.ashx
" The promise of hybrid assets: Harnessing distributed energy, "
Energeia, Davis, CA, USA. https://energeia-usa.com/
wp-content/uploads/2016/08/The-Promise-Of-Hybrid-Assets_US.pdf
U.
Siddiqi, M. Dozier, R. Pham, and E. Smith, " 2021 Grid modernization
plan and roadmap, " Seattle City Light, Seattle, WA,
USA. http://www.seattle.gov/documents/Departments/City
Light/GridModRoadmap.pdf
Biography
Olof Bystrom is with Sacramento Municipal Utility District,
Sacramento, California, 95852 USA.
p&e
march/april 2022

https://www.epri.com/research/products/000000003002010997 https://www.epri.com/research/products/000000003002010997 https://www.publicpower.org/system/files/documents/ppf_value_of_solar_primer.pdf https://www.publicpower.org/system/files/documents/ppf_value_of_solar_primer.pdf https://efiling.energy.ca.gov/getdocument.aspx?tn=227887 https://efiling.energy.ca.gov/getdocument.aspx?tn=227887 https://www.smud.org/-/media/Documents/Corporate/Environmental-Leadership/ZeroCarbon/2030-Zero-Carbon-Plan-Executive-Summary.ashx https://www.smud.org/-/media/Documents/Corporate/Environmental-Leadership/ZeroCarbon/2030-Zero-Carbon-Plan-Executive-Summary.ashx https://www.smud.org/-/media/Documents/Corporate/Environmental-Leadership/ZeroCarbon/2030-Zero-Carbon-Plan-Executive-Summary.ashx https://www.smud.org/-/media/Documents/Corporate/Environmental-Leadership/ZeroCarbon/2030-Zero-Carbon-Plan-Executive-Summary.ashx https://www.energeia-usa.com/wp-content/uploads/2016/08/The-Promise-Of-Hybrid-Assets_US.pdf https://www.energeia-usa.com/wp-content/uploads/2016/08/The-Promise-Of-Hybrid-Assets_US.pdf https://www.energeia-usa.com/wp-content/uploads/2016/08/The-Promise-Of-Hybrid-Assets_US.pdf http://www.seattle.gov/documents/Departments/CityLight/GridModRoadmap.pdf http://www.seattle.gov/documents/Departments/CityLight/GridModRoadmap.pdf

IEEE Power & Energy Magazine - March/April 2022

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