The electrical grid: Key concepts to know

When you flip a light switch, a light turns on. When you plug your phone into an outlet, it charges. That only happens because electricity is generated and transmitted to your home or business across the electrical grid, a web of interconnected transmission and distribution lines that connect the supply to demand, bringing electrical power to where people need it.

The electrical grid is a complex network of electrical generators (i.e., power plants) and transmission lines that dynamically respond to shifts in electrical supply and demand to ensure electricity is always supplied reliably. It's a marvel of modern engineering.

Keeping the grid functioning requires a delicate balance between supply and demand and a highly integrated series of components throughout the country. Grid operators, such as the California Independent System Operator (CAISO) and the Pennsylvania-Jersey-Maryland Regional Transmission Operator (PJM RTO), maintain this balance through a mix of market awareness and insights plus forecasts of weather, demand, and supply, to provide low-cost and reliable electricity service. 

In the US, the grid is split into three sections in the contiguous states: the Eastern Interconnect, the Western Interconnect, and the Electric Reliability Council of Texas (ERCOT). In fact, the Eastern and Western Interconnects even extend into neighboring countries. As a result, if you live in Boston, where EnergySage is located, you are electrically connected to people as far away as Florida. In fact, transmission line or generator outages in one part of an interconnect can cause cascading blackouts to occur hundreds or thousands of miles away, as occurred during the 2003 Northeast blackout.

Before the advent of renewable energy resources, the primary type of electrical production was creating steam to spin a turbine, generating electricity. This is how conventional power plants still operate. For instance, coal-fired power plants burn coal to produce steam to spin a turbine, natural gas-fired power plants burn natural gas, and nuclear power plants use the heat generated by a nuclear reaction.

Many of the original renewable resources functioned similarly: by finding ways to spin a turbine to generate electricity. Wind energy uses the power of the wind to spin a turbine, geothermal power uses the earth's heat to create steam to spin a turbine, and hydropower harnesses flowing water to spin a turbine.

Solar energy functions differently, by collecting sunlight and converting that energy into electrical energy on the face of solar panels. In each instance, the output is the same: either alternating current (AC) or direct current (DC) electricity that can be used in homes and businesses.

The primary difference between conventional and renewable resources is how and when they produce electricity. In the case of conventional resources, these power plants are turned on when needed due to the demand for electricity on the system. On the other hand, renewable resources produce electricity when the energy is available, such as when the sun is shining, or the wind is blowing, which is why solar and wind are often referred to as variable resources. Increasingly, the production from these resources can be stored to be used at a later time using energy storage (battery) technologies, matching production from renewables to demand on the electrical grid.

Unless you have solar panels on your property, the electricity you use at your home or business comes from power plants located far from your home. The transmission and distribution system connects these power plants to the areas where electricity is ultimately used. 

The transmission system consists of much more than just poles and wires. The system relies upon a web of step-up and step-down transformers, substations, breakers, and switches. Each of these components plays an important role in maintaining the reliable operation of the grid.

Our interstate highway system is a convenient metaphor for the electricity transmission and distribution system, especially given the two often run in parallel. In this context, the poles and wires you see above you are like the interwoven roads that connect you from your house to a different city.

For instance, if you’re planning on driving on the highway, you need to quickly reach a much faster speed than you would drive at through your own neighborhood; similarly, when a power plant produces electrons, they need to be “stepped-up” to the voltage of the long-distance transmission lines they are joining (i.e., highways). 

As you drive through a region, you may move from a large, six-lane highway to a smaller, four-lane highway; along the same lines, electricity may move from one major transmission line to another, regional transmission line at a substation.

And, finally, when you near your destination on a highway, you use the off-ramp to slow back down again to the speed of the streets in the new neighborhood; electrons do the exact same thing at “step-down” transformers at substations on the distribution network.

There are two primary types of power lines: high voltage, long-range transmission lines, and lower voltage, shorter-range distribution lines. The high voltage transmission lines are the type you see suspended high above highways in wide clear-cuts of land. The lower voltage distribution lines are the type you see if you look up while walking through your neighborhood. Though the two types of lines do effectively the same thing, moving electrons from their source (a power generator) to an end-user (you), there’s an essential reason for the distinction between the two types of power lines.

During the process of transmitting electricity across the country, some of the original electricity produced is lost. The further you transport the electricity, the greater the losses. However, transmission engineers have found that higher voltage lines lose less electricity per mile traveled. As a result, higher voltage lines are the best solution when electricity needs to be moved across vast distances. 

However, the voltage levels of these high-powered, long-range power lines are much higher than appliances in homes and businesses can handle. Before electricity reaches your home or even your neighborhood, it must be "stepped down" to a lower voltage by a device called a transformer, so-called because it "transforms" electricity from one voltage to another.