Production & Distribution of Electricity (Ch. 8)

THM: more complicated than you might think.
 take-home messages for each sectiion

  1. Energy is diversely produced/used; imports dominate petroleum.
  2. Electricity sources are diverse and growing with only hydroelectric and nuclear saturating, while uses are evenly distributed; losses are 2/3 of produced electricity.
  3. Building new electric plants is balancing act of predicting future usages and profits-to-costs ratio for different sources.
  4. The ratio of base to cyclic load (including peak) influences the distribution of the size of electric plants.
  5. Estimating costs of different size plants is tricky: weighting (i) costs versus hours of operation and (ii) capital versus operating costs.
  6. Transforming power plant voltage to much higher transmission line voltage can dramatically decrease transmission losses.

Diversity of sources and uses of energy

Units (exa- = 1018; quadrillion = 1015 (for us))

exajoule (EJ) ~ quadrillion British Thermal Units
EJ ~ 1015 BTU = Quad

2006 Energy Flow (percentages of ~100 Quads)
Domestic Production Imports
CoalGasOilNucRenSubtotals PetrolOther
2322168776 2424omit

Historical & Current Electricity Data

Can you trust this?
Electric Consumption 1950-2000
2004 Electricity Flow: 40.8 Quad BTU
Sources CoalGasNucRenMisc.
274 442

Produced electricity is 1/3 of fuels used to produce it.

What drives building of electric plants


Profits. Most states regulate profits as fixed percentage of costs -- due to monopoly position granted utilities.
Attempts at deregulation has produced only limited saving and redistribution of suppliers.

Different use create different loads

Industrial use is predictable & sets base load.

Cyclic use, for example, due to residential and commercial uses can typically double the load at some hours.

Peak load ( >20%) arise from peaks in daily and seasonal demand. Utilities may buy power from other utilities with spare capacity.

Different sources provide different loads.

Conclusion: Peak users pay more than cyclic users who pay more than base users.

Economy of scale is the reasonable belief that costs are not linear in plant size: truer for plants with larger fraction of capital costs.
Minus is that idled large plant impacts supply more than small.

Mix of generating facilities

Screening curves plots total cost of generating facility versus hours of operation.    

Total costs include:
Capital costs: planning, construction, fees, and interest amortized over estimated lifetime of facility.
Operating expenses: fuel, salaries, maintenance.
Screening curves. The black curves are based on 2005 EIA data corrected for fuel costs changes; the two in red reflect 2007 guesses for nuclear captical costs and 2007 estimate for IGCC.
TEB revised screening curve
Intercept is capital cost per installed kWh.
Slope is steeper for greater running costs.
Note: Some curves stop due to limits on sun light, average wind availability or water behind a dam.
IGCC is Integrated Gasification Combined Cycle
[(1) gasification of heavy-sulfur coal into clean gas;
(2) gas-driven generator plus waste heat used to make steam in a separate steam turbine]

Transporting Electricity

Two essential elements.

  1. Transformer. Two coils -- with vastly different number of turns can transform voltage from high to low or vice-versa. Neglecting any losses in the transformer: The conserved power P
          P = Vhigh-volt Ihigh-volt= Vlow-volt Ilow-volt
  2. High-voltage Transmission line. Again assume power is conserved. Convert power plant voltage to higher voltage: 150-750 kV.   Vplant Iplant= Vline Iline
    Lower line current substantially cuts heating loses in transmission. Ploss = (Iline) 2 R.

    Generator voltage has increased with time, typically 20-30 kV. Transmission line voltage has increased also, 300-1500 kV. So ratio of reduction in losses due to higher line voltages are 102 to 105.