Illustration of figure plugging in to giant outlet (State Dept./Doug Thompson)
(State Dept./Doug Thompson)

Everybody’s seen those tall towers strung with wires that stretch across the landscape. Most people know that those are power-transmission lines, but they may not know they are looking at part of the power grid.

First you need electricity …Illustration of wind turbine, natural gas flame and oil barrel. (State Dept.)

The power grid starts in the places where electricity is made. Electricity once was generated only at central power stations, which usually ran on fossil fuels — coal or natural gas — or nuclear energy. Today more and cleaner options for energy generation are available.

Those options can also cut costs. Distributed energy resources such as rooftop solar panels, can be cheaper because they generate electricity closer to home. That means fewer long power-transmission lines and other expensive grid infrastructure required for centralized distribution.

Transmission and distributionIllustration of power lines. (State Dept.)

After electricity is generated, it must be transmitted and distributed to consumers. The network of transmission and distribution facilities makes up the power grid.

Typically, electricity is transmitted at a very high voltage over the power lines that dot the countryside. The higher the voltage, the less current needed for the same amount of power, and thus less loss of electricity. (Resistance to current in the lines creates heat that causes some loss.)

When the electricity reaches customers’ neighborhoods, transformers convert the high-voltage electricity to a lower voltage for distribution to homes and businesses.

Consumers and “load”Illustration of a plug and outlet. (State Dept.)

When people use electricity for their lights, computers, appliances, heating and cooling, they are drawing on the electrical grid. The total usage by customers is the “demand load,” which must be supplied by power providers. There are peak demand-load periods: at night when more lights are on, or the hottest or coldest times of day. Balancing those voltage loads is where power grid management becomes tricky, because the energy flow must be perfectly balanced at all times to provide exactly the right amount of electricity to customers. Grid operators also are learning to integrate and balance new power streams from distributed energy resources with the demand load.