An Overview of the U.S. Electric Power GridGeneration Choices, Reliability, Challenges

Tom Ferguson, P.E.Adjunct InstructorDept. of Electrical EngineeringUniversity of Minnesota, Duluth

Presentation to EE 1001September 19, 2013

Where Electricity Comes From

What Do We Know About This?1. We plug LOADS into it2. It has THREE prongs in standard layout3. The VOLTAGE is ~115 VAC4. The WAVEFORM is sinusoidal5. Only 60 HZ is present6. ELECTRONS come from somewhere7. It’s almost always “ON”

BUT!

1. Limited to 15 AMPS2. Europe uses different plug3. Voltage varies + 5%4. Waveform is usually not “clean”5. Harmonics may be present6. Electrons come from ALL generators7. It’s 99.99% reliable (off for 53 minutes/yr)

The Grid Powers Society

• Human behavior repeats itself daily– Morning routine: lights, hot water, electronics

– Stores open: lights, heating/cooling

– Industry starts: pumps, motors, arc furnaces

• The grid must respond to these loads– generators must be ready and reliable

– generators must be controllable to match load

– transmission/distribution lines must be intact

• It had better work well, as loads increase quickly

A Typical Day on the California Grid

4 a.m.

2 p.m.

1 Megawatt can power about 1000 homes

Ramps up by 4500 MW in 80 minutes

Generating Choices

• What types of generation are used?

• Varies across U.S. according to– availability of fossil fuels– availability of renewable energy sources– water availability– environmental limitations– state policies on renewables and nonrenewable

generation

Generating Choices

• Generators usually fall into one of 3 regions:– Base Load

• Must run essentially 24/7 annually

• Expensive to build, but provides lowest cost over time

– Intermediate Load• Runs less often than base load generation

• Less costly to build, but more costly to run

– Peak Load• Runs only to meet peak demands

• Least expensive to build, most costly to run

• We can visualize these regions on a Load Duration Curve

Base Load Generation

Intermediate Load Generation

PeakLoadGen

Power Generation Technologies

Includes• Hydro• Biomass• Wind• Solid Waste• Geothermal• Solar PV• Solar Thermal

Source: U.S. Energy Information Administration, Electric Power Monthly (June 2013). Percentages based on Table 1.1 for 2012 Calender Year.http://www.eia.gov/electricity/monthly/index.cfm?src=Electricity-f2 Updated 9/2013. Percentages on an ENERGY basis, not capacity.

Coal 37%

Natural Gas 30%

Nuclear 19%

Renewables 12%

2012

Base Load GenerationNuclear, Coal, Geothermal, Wind*, Solar*

Intermediate Load GenerationHydro, Natural Gas, Solid Waste

PeakLoadGenGas,

Hydro

Where Do These Technologies Fit on our Load Duration Curve?

*Wind and solar output must be taken when available, sometimes affecting baseload gen

Challenges with Wind

• Adds no inertia to grid (no energy storage)

• Poor low-voltage behavior

• Limited contribution to peak load capability

• Not dispatchable

• Negative correlation

with loadsWhen loads are greatest during the mid-day, wind generation is lowest.Conversely, wind is highest when least needed (night).

Tying Generators Together with Loads

• High Voltage Transmission Lines – Connects generators with loads– Transmit energy at near speed of light– High voltage reduces current flow (P=V x I)

– Reduced current reduces losses (Ploss=I2R)

Tying Generators Together with Loads

• Three Synchronized Regions in U.S.– Eastern U.S. (east of Rockies)– Western U.S.– Texas

• All generators in

each region are

synchronized

Putting It All Together

“The Grid” = Generators (about 18,000) + HV Transmission Network

Grid Reliability

• Standards exist to ensure reliability– Extensive filings and audits– Severe financial penalties

• Wide-area (multi-state) reliability affected by:– Major outages of generators or transmission lines– Growth of non-dispatchable wind and solar– Inability to run existing or build new baseload gen– Climate change: warmer water and less of it

• Local reliability affected by:– Lightning and high winds– Animals (squirrels, rodents, snakes)– Right-of-way incursions (traffic accidents, train

derailments)

Good Luck!