IEEE Power & Energy Magazine - November/December 2021 - 73

10,000
15,000
20,000
25,000
30,000
35,000
40,000
45,000
5,000
100
Last 10% of Annual Energy Requires
44% of Total Capacity Running at a
13% Average Capacity Factor
Last 10% of Demand
First 90% of Demand
20
30
40
50
60
70
80
90
10
70
Hours at Demand
(a)
75 80 85
Fraction of Energy Served (%)
(b)
figure 4. (a) Load duration and (b) marginal capacity curves for California in 2013.
occurs during times when the demand is already fully met),
resulting in high incremental costs. Even with declining costs
of wind and solar, at some point, marginal costs will exceed
the benefits of avoided carbon reduction; thus, some other
approach is needed to cost-effectively increase renewable
energy deployment.
Achieving a 100% renewable energy system in a cost-effective
manner requires technologies that can address the longerterm
mismatch of supply and demand with a core set of characteristics.
First, the solution needs to be comparatively economic
with potentially low utilization. Generators meeting the last 10%
of demand will have inherently low capacity factors, whether
in a traditional thermal-based system or a renewable-based one.
These options will tend to favor systems
with relatively low capital costs
and less sensitivity to variable costs.
Second, the solution needs to
be available over a range of time
scales. This includes being available
during net load peaks, which
may occur during different seasons
and even periods of historically
lower demand. Solutions also
need to be available for different
durations of response, including
multiple days. Third, these solutions
will require flexible siting. The last
10% of demand in current systems
is often met by peaking generators
sited in load pockets, including
urban areas. This avoids transmission
congestion and increases operational
reliability.
There are three main options
considered to address the seasonal
mismatch challenge: non-variable
renewable energy, seasonal load
november/december 2021
shifting, and seasonal storage. Non-variable renewable
energy options include geothermal, concentrating solar power
with thermal energy storage, and hydro (including changing
dispatch patterns, hydro upgrades, and adding capacity to nonpowered
dams). The challenges include regional resource availability
and siting limitations.
A somewhat unexplored option is seasonal load shifting
or demand curtailment. Automation of buildings as well as
new information technology and other low-cost communication
technologies may make it possible to incentivize
demand reductions for lower-cost supply-side options
with low utilization. However, any solution on the demand
side must also account for the highly variable and uncertain
Biomass
Renewable Electricity
90 95 100
Hydrogen Via Electrolysis
Refine
Fuel Production
N2
Store
CO2
Reciprocating Engine
Electricity Generation
Combustion Turbine
Fuel Cell
figure 5. Pathways for seasonal electricity storage via fuel production.
ieee power & energy magazine
73
Electricity Demand (MW)
Generator
Marginal Capacity Factor (%)
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
IEEE Power & Energy Magazine - November/December 2021

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2021
