IEEE Power & Energy Magazine - July/August 2018 - 80

research in the united states indicates that reducing overall
greenhouse gas emissions to 80% below 1990 levels by 2050,
a level adopted by the united states and other governments as
compatible with international agreements to protect the climate,
will require a 90%+ reduction in the average emissions intensity
of electricity generation in the united states over the same time
period. three observations help explain the need for a disproportionally large reduction in emissions from electricity.
✔ Electricity generation in a very low-carbon energy system will need to grow significantly, from 4 pWh/year
today to around 7 pWh/year in 2050, an increase
of 1 pWh/decade. this growth is a necessary consequence of widespread electrification, even assuming
rapid progress in energy efficiency.
✔ Because the carbon benefits of electrification are
contingent on emissions reductions in electricity, the
greater those reductions are, the more attractive and
effective electrification will become as a carbon strategy. put another way, because their combined effect on
emissions is multiplicative, not linear, these strategies
are mutually reinforcing.
✔ reducing emissions intensity in electricity is of moderate cost compared to alternatives in other sectors, and
thus it makes economic sense from society's standpoint
to reserve any remaining emissions budget for high
marginal abatement cost applications in transportation
and industry. reducing emissions by less than 80% in
these areas implies larger reductions in other areas,
particularly electricity generation, if the overall emissions goal for the united states is to be met.
accepting the premise that deep decarbonization requires
profound changes in the electricity mix, three generation
types are likely candidates: renewables, nuclear, and carbon capture and storage (ccs). We define renewables here

Jan.

Apr.

Month

Growth in Average GW

600
500
400
300

July

broadly, but the primary focus is on wind and solar given that
these two resources have the largest technical and economic
potential. Between the three generation types, renewables have
emerged as the front-runner and have made up most of the
capacity added in the united states over the last ten years. this
trend is expected to continue, in part due to strong policy support
on a regional basis. Even in prior deep decarbonization scenarios
emphasizing nuclear and ccs, results suggest that renewables
will still comprise a plurality of generation by midcentury.

Physical Characteristics
of Highly Electrified and
Highly Renewable Electricity Systems
Given two premises, that deep decarbonization requires both
high levels of electrification and a near complete decarbonization of electricity and the most likely method of electricity
decarbonization is large deployments of renewable energy,
some significant changes in the physical supply-demand dynamics of the future u.s. electricity system can be anticipated. in studies, these characteristics start to emerge when
the penetrations of wind and solar production exceed about
50% of energy consumption, driven by the nature of both newly
variable generation and electrified loads.

Newly Electrified Loads Will Be Large
but Potentially Flexible
the largest loads with the potential to be electrified are heating, electric vehicles, and, in some cases, electric fuel production (for example, electrolysis of water to produce hydrogen).
figure 1 shows demand-side load growth between 2020 and
2050 in a high-electrification scenario, broken down by end
use. a key feature of these loads is that heating, vehicles, and
electric fuels all have inherent storage potential (thermal or
chemical) that can be used to shift energy in time.
Electric fuel production is a
nonfirm load (meaning it can be
curtailed) with a high operatingOct.
to-capital-cost ratio that can shift
Light-Duty Vehicles
vast amounts of energy seasonally.
Water Heating
Space Heating
heating and vehicle loads are funOther
gible over much shorter timescales
but can still solve shorter timescale energy imbalance and, critically, mitigate their own impact
on the need for new system infrastructure build.

200

New Loads Can Have Very
High and Unpredictable
Instantaneous Demand

100
0
1

24 1

figure 1. The month-hour average load growth from 2018 to 2050 in the DDPP
high-renewables scenario by end use. The vehicle-charging profile shown before
flexible charging is applied.
80

ieee power & energy magazine

Electric vehicle rapid-charging has
become a selling point for new electric vehicles, and as battery charge
management continues to improve,
public dc charging of light-duty
july/august 2018

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2018