AuthorCharles R. Sensiba, Michael A. Swiger, and Sharon L. White
Page 571
I. Introduction
Hydropower, which generates electricity through falling
water,1 is the nation’s most established and mature renew-
able resource. It accounts for more than 6% of all electric-
ity generation and about one-half of all renewable power in
the United States.2 Hydropower resources serve an essen-
tial role supporting the electric grid by providing low-cost,
exible energy services, a nd a multitude of secondary ben-
ets, such as ood control, irrigation, water supply, and
recreational opportunities. Hydropower also is critical in
maintaining grid reliability and integrating variable gen-
eration resources, such as solar and wind, that continue
to come online in larger numbers. Because solar a nd wind
are intermittent resources, the electric grid ca nnot rely on
them in a ll hours; no other renewa bles but hydropower,
and to a lesser degree geothermal and biomass, are capa-
ble of quickly responding to the variable nature of wind
1. Hydropower also includes hydrokinetic technologies, which generate electric-
ity from waves, currents, and tides within a water body.
2. See U.S. Energy Information Administration, Hydropower Explained, http://
www.eia.gov/energyexplained/?page=hydropower_home (last updated June
13, 2017).
and solar, coming on- and o-line when needed to ensure
proper grid f unctioni ng.3
e Deep Decarbonization Pathways Project (DDPP)
report, Pathways to Deep Decarbonization in the United
States, recognizes the crucial role of hydropower to sustain
our transition to a decarbonized elect ric grid—particularly
with regard to hydropower pumped storage4 and its abil-
ity to balance and integrate non-dispatchable renewables
and water power.5 In fact, the DDPP report assumes that
the installed capacity of pumped storage will need to more
than triple by 2050 to sustain a decarbonized grid.6
3. Combustion gas turbines also have this capability but are not renewable.
4. A pumped storage hydroelectric project can store and generate energy by
pumping water between an upper and lower reservoir at dierent elevations.
During times of low demand, water is pumped to the upper reservoir and
stored, and during periods of high demand, the stored water is released
through the turbines to generate electricity. Pumped storage is currently the
only utility-scale energy storage technology available, although other storage
technologies are emerging.
5. J H. W  ., P  D D  
U S, U.S. 2050 R, V 1: T R 17-20
(Deep Decarbonization Pathways Project & Energy and Environmental
Economics, Inc., 2015), available at http://usddpp.org/downloads/2014-
technical-report.pdf [hereinafter DDPP T R].
6. To achieve this balancing, the authors of the DDPP report assumed the
availability of 72 gigawatts (GW) of available pumped storage—50.4 GW
more than the 21.6 GW installed in the United States as of 2016. E-mails
Chapter 22
by Charles R. Sensiba, Michael A. Swiger, and Sharon L. White
While the Deep Decarbonization Pathways Project reports recognize that pumped storage hydropower is crucial
to sustaining our transition to a decarbonized grid, they do not fully account for the potential for environmen-
tally responsible expansion of new conventional hydropower in the United States by 2050. ey conclude that
conventional hydropower is not expected to keep pace with electricity growth due to sustainability and resource
constraints. Yet, additional hydropower development above current levels—both conventional and pumped
storage—that meets modern environmental requirements must be a component of any proposal to reduce the
United States’ dependence on carbon over the long term. Realizing the full potential of hydropower and even
maintaining the current hydropower eet will likely depend on overcoming a number of impediments to hydro-
power in the United States. Such impediments include lengthy and complex regulatory requirements, failure
of the organized electricity markets to adequately compensate hydropower generators for the grid benets they
provide, environmental opposition to new hydropower, and interest in dam removal. ese challenges can be
overcome with targeted legal and policy reforms that would not roll back environmental standards.
Page 572 Legal Pathways to Deep Decarbonization in the United States
Still, the DDPP report did not fully account for the
potential for environmentally responsible expansion of
new conventional hydropower in the United States by
2050. Since that report was issued, the U.S. Department
of Energy (DOE) released the results of a new investiga-
tion, Hydropower Vision: A New Chapter for America’s 1st
Renewable Electricity Source,7 that sheds new light on the
potential to expand both conventional and pumped stor-
age hydropower. To chart a path for achieving the results
envisioned in both the DDPP and DOE reports, this chap-
ter identies new opportunities for sustainable growth,
explains environmental risks and requirements pertaining
to hydropower, and identies legal and market reforms
needed to capture a greater percentage of environmentally
responsible hydropower—both conventional and pumped
storage. e chapter concludes that, based on its ability
to provide electricity-generation capacity, baseload power,
peaking power, energy storage, load following, a nd other
essential generation features— together with its unique
ability to integrate other renewables such as wind and solar
into the grid—additional hydropower development above
current levels that meets modern environmental require-
ments must be a component of any proposal to reduce the
United States’ dependence on carbon over the long term.
e DDPP report analyzes four distinct scenarios
to achieve signicant reductions in U.S. greenhouse gas
(GHG) emissions by 2050, organized by the primary
energy choices for electricity: (1)renewable energy (High
Renewables Scenario); (2) nuclear (High Nuclear Sce-
nario); (3)fossil fuels with carbon capture and storage
(CCS) (High CCS Scenario); and (4)the Mixed Scenario
with roughly equivalent generation from all three primary
energy resources. In all but the High CCS Scenario, the
percentage share of hydropower in overall electricity gen-
eration decreases from current levels. In the Mixed Sce-
nario, which is the main ca se for the report, the percentage
share of hydro in overall electricity generation decreases
from 6.2% in 2014 to 5.6% in 2050 due to overall growth
in electricity consumption but without substantial new
growth in hydropower re sources.8 e report a sserts that
hydropower is not expected to keep pace with electric-
ity growth because “ development of new hydropower
resources is .. . limited for sustainability reasons” as well
as resource constraints.9
It is correct that hydropower is more site-limited than
other resources; it requires a site where the natural ow
From Jim Williams and Ryan Jones, Authors of the DDPP Report (Nov.
14-16, 2017) (on le with authors).
7. DOE, H V: A N C  A’ 1 R
E S (2016) (DOE/GO-102016-4689) [hereinafter H-
 V], available at http://energy.gov/sites/prod/les/2016/10/f33/
8. DDPP T R, supra note 5, tbl. 7.
9. Id. at 12.
and falling of water ca n be captured. However, the DDPP
report does not explain its conclusion that hydropower is
limited due to “sustainability.” e report itself assumes
that the amount of pumped storage must triple to eec-
tively balance non-d ispatcha ble renewables and nuclea r
power. 10 Moreover, the report makes no mention of devel-
opment opportunities for conventional hydropower by
adding hydropower infrastruct ure at existing da ms, mak-
ing capacity and eciency upgrades at e xisting hydropower
projects, implementing new technologie s at low-head
dams that were once infeasible, and deploying emerging
marine a nd hydroki netic (MHK) technologies to achieve
emissions reduction goals—a ll of which, if developed in
accordance with modern environmental requirements, ca n
enhance balancing of the grid, add dispatchable resources,
and meet “sust ainabil ity” considerations.
In its Hydropower Vision report, which was relea sed
after the DDPP report, DOE estimates that hydropower
in the United States could feasibly grow from 101 giga-
watts (GW) of emissions-free11 generating a nd storage
capacity to nearly 150 GW by 2050, avoiding 5.6 billion
metric tons of carbon dioxide (CO2) emissions, saving
$209 billion in avoided global damages from CO2 emis-
sions, and creating more than 195,000 new jobs.12 While
much of this potential—consistent with the assumptions
in the DDPP report—comes from a signicant increase in
pumped storage,13 the DOE report nds opportunity for
13 GW of new conventional hydropower generation capac-
ity at new and existing facilities.14 e Hydropower Vision
report did not include MHK technologies, which represent
potential additional sources of hydropower development
in future years. Beyond the modeled increases of hydro-
power in the DDPP report, the DOE report demonstrates
the considerable role that hydropower—both conventional
and pumped storage—c ould play in nationwide decarbon-
ization, and indicates that there are more available oppor-
tunities and pathways for the expansion of hydropower
to meet the nation’s climate goals than the DDPP report
assumes. e legal pathways described in this chapter for
hydropower provide additional approaches to achieving
the 80% reduction in GHG emissions by 2050 envisioned
in the DDPP report, provide additional options to pub-
lic and private decisionmakers (including options that are
10. See supra note 6.
11. While some research asserts that reservoirs created by dams are important
sources of GHG emissions, DOE’s Hydropower Vision report notes that “[g]
iven the state of scientic understanding and discourse, including persistent
uncertainties, the [report] does not attempt to address hydropower-related
biogenic GHG emissions.” H V, supra note 7, at 43.
Moreover, the research analyzed reservoirs impounded by both hydroelectric
and non-hydroelectric dams, and only 3% of U.S. dams currently have a
hydroelectric component. us, adding hydropower at these existing dams
would not result in an increase in GHG emissions.
12. Id. at 3, 23.
13. See supra note 6.
14. H V, supra note 7, at xvii, 1, 7, 31.

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