Category: Balance of Power

Learning the language of electricity

The U.S. electric grid has been called the largest and most complex machine ever made. This vast network is vital to our lives, yet many know very little about it.

Because knowledge is power, this month, Arkansas Living begins a multipart series to educate Arkansas’ electric cooperative members about power generation and the increased challenges facing electric utilities, including the Electric Cooperatives of Arkansas.

But before we can get into operations and obstacles, let us define terminology.

What follows is a glossary of words to energize your understanding of the wholesale power generation industry.

Affordable, Reliable, Responsible: This is the core mission of the Electric Cooperatives of Arkansas, which provides electricity to 1.2 million electric cooperative members in Arkansas and surrounding states.

Balance of Power: A central philosophy of the Electric Cooperatives of Arkansas is to maintain a portfolio of diverse energy generation resources — not put all of our eggs in one basket — to deliver dependable and cost-effective electricity.

Cooperative: A democratically controlled, not-for-profit business that is member-owned. There are more than 900 electric cooperatives in 47 states. The Electric Cooperatives of Arkansas comprise 17 electric distribution cooperatives; Arkansas Electric Cooperatives, Inc. (AECI), a Little Rock-based cooperative that provides services to the distribution cooperatives; and Arkansas Electric Cooperative Corp. (AECC), a generation and transmission cooperative.

The Thomas B. Fitzhugh Generating Station near Ozark uses natural gas to produce 170 megawatts of electricity. Photo by Chance Allmon.

Dispatchable Resources: Dispatchable Resources are the backbone of the wholesale electricity supply. These generation facilities, typically nuclear, coal and natural gas plants, are the workhorses that dependably provide affordable energy to our members. As the name suggests, these resources are available to produce power as needed, regardless of wind, sun or other factors. Affordable and reliable dispatchable resources are at risk due to several factors, including federal policies and proposed regulations. While some may suggest there is no difference between a megawatt of dispatchable resource versus a megawatt of intermittent resource, this is simply not correct. Only Dispatchable Resources can be depended on to provide capacity and energy 24/7/365.

Energy/Capacity: Energy at the wholesale or generation level is measured in megawatt hours (MWh) and measured at the residential or retail level in kilowatt hours (kWh). The ability to produce energy is measured in megawatts (MW) and is referred to as capacity. Capacity is how much can be produced at any one moment in time, and energy (MWh) is how much is actually produced over time. Capacity and energy are related, but they are not the same thing. In simple terms, capacity is like water pressure in a hose, and energy is the flow of water when you open the nozzle.

Intermittent Resources: These are normally weather-dependent resources such as wind and solar; they generate only when the sun shines and the wind blows. While these resources are an important part of a balanced energy portfolio, they do not provide a steady constant supply of electricity (see “Dispatchable Resources”). And there is presently not an affordable, efficient way to store excess intermittent energy. While advancements are being made, battery storage for a large electric system at a reasonable price is not a reality for now or in the near future. Current battery technology only provides energy for four hours or less, much less than is required to cover nighttime periods let alone long periods of clouds or other weather conditions that would disrupt solar or wind production.

Generation/Transmission/Distribution: These are the components of electricity delivery. Explains the U.S. Information Administration: “Power plants generate electricity that is delivered to members through transmission and distribution power lines. High-voltage transmission lines carry electricity over long distances to meet member needs. Higher voltage electricity is more efficient and less expensive for long-distance electricity transmission. Lower voltage electricity is safer for use in homes and businesses. Transformers at substations increase or reduce voltages to adjust to the different stages of the journey from the power plant on long-distance transmission lines to distribution lines that carry electricity to homes and businesses.”

Load Curtailment: When electric demand is extremely high and there is not enough available generation, load curtailments (sometimes called “outages” and “blackouts”) can be mandated (see “Regional Transmission Organizations”) to protect the electric grid from collapsing and to keep power flowing to as many members as possible. A curtailment is a controlled reduction of power. It has a limited duration. It is not widespread. Controlled curtailment is always a last-resort measure to safeguard the electric grid.

Regional Transmission Organizations (RTO)/Independent System Operators (ISO): Nonprofit organizations that coordinate and control transmission systems, often across multiple states. The Electric Cooperatives of Arkansas are members of two different RTOs: Midcontinent Independent System Operator (MISO) in the eastern part of the state and Southwest Power Pool (SPP) in the western part of the state. When load curtailment is mandated, that is a call made by an RTO/ISO; utilities are federally mandated to respond accordingly.

    Next month, we’ll put these terms in action as we explain the challenges that utilities like the Electric Cooperatives of Arkansas face.