Section B3: Electricity Load Shapes

B3.1. Electricity Load Shape Coefficients

In representing electricity generation and use, EIA’s models account for the fact that electricity 

generating capacity must be sufficient to meet demand during peak time periods, e.g., summer 

days when electricity use increases because of high demand for space cooling. The models 

therefore estimate electricity load shape coefficients and load shape curves, which are then used 

to project the quantity and types of new electricity generating equipment that electricity suppliers 

will install. Suppliers often use different generating technologies for peak load generation than 

they use for the continuous base load generation.

To compute electricity system load shape coefficients, the models divide the year into seasons, 

e.g., summer, winter, and intermediate (including spring and fall). For each season, the models 

identify a seasonal base period, a seasonal middle period, and a seasonal peak period. The load 

shape coefficient for each time period and end-use demand sector is defined as the proportion of 

the total annual electricity demand accounted for by time period and end-use sector, e.g., 

residential, commercial, industrial. The coefficients determine the load shapes and the load 

shape curves, which vary by geographic area. Tables 1 and 2 show examples of load shape 

coefficients for the United States and China.

Table 1. Example of Load Shape Coefficients for the United States

Summer

base

Summer

middle

Summer 

peak

Winter

base

Winter

middle

Winter

peak

Intermediate

base

Intermediate

middle

Intermediate

peak

Residential 0.206 0.104 0.010 0.270 0.100 0.009 0.207 0.086 0.007

Commercial 0.185 0.137 0.015 0.192 0.139 0.014 0.170 0.134 0.015

Industrial 0.247 0.080 0.007 0.245 0.080 0.007 0.247 0.080 0.007

Transportation 0.226 0.101 0.007 0.227 0.098 0.007 0.229 0.100 0.006

Table 2. Example of Load Shape Coefficients for China

Summer

base

Summer

middle

Summer 

peak

Winter

base

Winter

middle

Winter

peak

Intermediate

base

Intermediate

middle

Intermediate

peak

Residential 0.200 0.086 0.011 0.258 0.107 0.014 0.218 0.094 0.013

Commercial 0.185 0.114 0.009 0.218 0.130 0.010 0.205 0.120 0.010

Industrial 0.247 0.080 0.007 0.245 0.080 0.007 0.247 0.080 0.007

Transportation 0.242 0.082 0.010 0.229 0.091 0.012 0.235 0.088 0.012
The base load electricity generating capacity is used continuously throughout the year. The 

middle period capacity is used during the middle and peak periods in each season, and the peak 

period capacity is used only during the peak period in each season.

The annual load proportions are ultimately multiplied by the actual annual loads in kilowatthours 

(or in Btu) to compute the actual load in each time segment. Similarly, the fraction of a year is 

multiplied by the total hours in a year (8,760) to compute the actual number of hours in each 

time segment. These values can then be used together to create a load duration curve, where the 

height of the curve (capacity) at each point is the number of kilowatthours used per hour, which 

simplifies to kilowatts.

B3.2. Electricity Load Shape Curves

To create electricity load shape curves, we first compute weighted averages, across the end-use 

sectors ss, of the electricity demand ratios. For each season aa and each time period gg (base, 

middle, or peak), let

PPPPPPPPPPPP PP(aa, gg) = ∑ [DDDDDD DD (ss) × PPPPPPPPPPPP PP(ss, aa, gg)] ss

∑ DDDDDD DD (ss) ss

, (B3.2.1)

where

PPPPPPPPPPPP PP(ss, aa, gg) = proportion of the electricity demand accounted for by end-use sector ss

and time period gg in season aa;

PPPPPPPPPPPP PP(aa, gg) = proportion of the electricity demand accounted for by time period gg in 

season aa; and

DDDDDD DD (ss) = total electricity demand accounted for by end-use sector ss.

We weight each end-use sector’s proportional load by the total annual consumption in the sector 

within each region. 

For each time period gg in each season aa, we divide the proportion of the demand load by the 

proportion of hours within the time period to compute the load height or capacity for the time 

period:

LL LL htt(aa, gg) = (aa, gg)

TT (aa, gg)

, (B10.21)

where

LL LL htt(aa, gg) = system height or capacity needed to meet the electricity demand in 

time period gg of season aa; and

TT (aa, gg) = proportion of hours in time period gg in season aa.

Two examples of the resulting load shapes are shown in the two graphs below, as load duration 

curves for the United States. and China. Although the system load shapes in EIA’s models are 
represented for three seasons and for three time periods within each season, the seasonal data 

have been added together in the graphs to illustrate the use of the load shapes.

The horizontal axis in each graph represents the hours of the year, and the vertical axis represents 

the generation capacity requirements during that period as a proportion of average capacity 

requirements. Note that the average height in each graph is 1.0. Each graph shows the system 

load shapes in 2005, based on the mix of sector consumption in that year, and the projected 

system load shapes for 2035, based on the changed mix of sectoral consumption between 2005 

and 2035.

A key detail to notice is that the load shape for the United States has a higher peak than the load 

shape for China. This is largely a consequence of the mix of end-use sectoral consumption in the 

two countries. In the United States, the residential and commercial sectors account for a large 

part of the electricity consumption. In China, most of the electricity consumption is in the 

industrial sector. The residential and commercial sectors typically have load shapes with peaks 

higher than the industrial sector peak. China therefore needs more baseload electricity 

generation, while the United States needs more peak electricity generation.

Figure 1. Electricity Load Shapes in USA, 2005 and 2035

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 1752 3504 5256 7008 8760

Normalized capacity requirements (originally gigawatss)

Hours in year

Load Shapes in USA, 2005 and 2035

2005

2035
Figure 2. Electricity Load Shapes in China, 2005 and 2035

B10.3. Interpreting Electricity Load Shape Curves

For each season, EIA’s models calculate the overall proportion of electricity demand load and 

time for each time period (base, middle, and peak) within the season. For the demand load, this 

is the sum of the proportions of load for the time periods within the season:

PPPPPPPPPPPP PP(aa) = �PPPPPPPPPPPP PP(aa, gg),

gg

(B3.3.1)

where PPPPPPPPPPPP PP(aa) is the proportion of electricity demand accounted for by season aa. The 

models also add the proportions of time in the three time periods:

TT (aa) = �TT (aa, gg),

gg

(B3.3.2)

where TT (aa) is the proportion of the year accounted for by season aa. 

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1752 3504 5256 7008 8760

Normalized capacity requirements (originally gigawatss)

Hours in year

Load Shapes in China, 2005 and 2035

2005

2035
The models also compute cumulative times and marginal loads for the time periods (base, 

middle, and peak) in each season. The peak electricity generating capacity is used only during 

the peak period. The height of the curves in Figures 1 and 2 indicate the relative amount of 

generating capacity needed during the three time periods, while the area under the curve is the 

total amount of generation (or load) that is needed. The marginal load (or generation) for the 

peak period is the area under the curve for the peak period that lies above the capacity height for 

the middle period. This is the additional generation needed to meet peak demand, relative to the 

amount needed for middle period demand.

The middle period generating capacity is used during both the middle and peak periods of each 

season. The height of the curve in the middle period indicates the amount of generating capacity 

needed, while the area under the curve is the total amount of generation needed. The marginal 

load for the middle period is the area under the curve for the middle period that lies above the 

curve for the base period. 

The base period capacity is used continuously during the entire year. The height of the curve 

indicates the capacity needed, while the area under the curve is the total amount of generation 

needed to meet the baseload demand. For the base period, the marginal load is the area under the 

curve, which is the same as the total load. For each year and each geographic area considered, 

the models compute the height, total load, and marginal load for each season and time period. 

They use these quantities to project the addition of new electricity generating capacity, by 

equipment type, in each time period. For the peak time period, the models add a reserve margin 

(based on historical data and expert judgment) to the peak capacity, to guarantee sufficient 

projected generating capacity for peak periods.