From Scott Carlberg

Electricity travels at a certain speed, but not all power generation sources can be ready to make electricity at the same speed. “Dispatch” is the term in the electric utility business that refers to the time it takes to make power to deliver. How fast a power source can get off the starting block, you might say.

Why should a consumer care about this idea at all? Because it keeps our grid operating well, helping homes, small businesses, manufacturers … our economy … all of us. In electricity, balance counts.

Dispatchable generation is electricity that can be sent out according to what the market needs. Market need is not constant, though. Demand changes all the time. Society will need more electricity, for instance, when it is very hot or cold (AC, heat) or during the weekdays (offices and factories are running). Demand changes by the second and season.

Not all ways to generate electricity are available at the snap of the fingers — when the market wants juice. Let’s take this explanation in steps. A good description that puts the concept of dispatchability in perspective is this: “To run a power system and supply households and businesses with the electricity they need, system operators around the world need two things. First, the power system has to be predictable. That way, we know what to expect and we are ready to do whatever is needed to keep the system balanced between supply and demand, and operating securely and reliably for consumers. And, equal first, the power system must be dispatchable. That means we are able to pull any reins we need to, to maintain that balance and secure, reliable operation.”

Society needs a certain amount of power just to operate. A base of energy; the energy hurdle the nation needs to function. That hurdle can change as people conserve or use more power, though there is always a minimum to “keep the lights on,” as the old saying goes. “Base load plants are usually large-scale and are key components of an efficient electric grid. Base load plants produce power at a constant rate and are not designed to respond to peak demands or emergencies. The base load power generation can rely on both renewable or non-renewable resources.” That definition from Penn State’s energy research.

Base load power has been provided by nuclear and coal plants that continually dispatch. Predictable and constant. Storage may replace some of this base load eventually, though it is a big gap to fill as these traditional sources of base load power retire.

Dispatchable generation can be on, adjustable, or off, as needed. Some renewable sources of electricity, like biomass, geothermal or hydro, are dispatchable. They can be controlled. Non-dispatchable energy sources like solar PV [photovoltaic] or wind cannot be always be controlled by a plant operator. The sun or wind may not be there.

Dispatchable sources must ramp up or shut down quickly in time intervals within a few seconds or hours. Keep in mind that fast or slow dispatchability does not mean good or bad, it just is the way it is, and each has a place in the system. Different types of power plants have different dispatch times:

  • Fast (seconds): Capacitors (can dispatch within milliseconds if they need to, due to the energy stored in them already being electrical), hydroelectric facilities,
  • Medium (minutes): Natural gas turbines, solar thermal power plants.
  • Slow (hours): Biomass, nuclear, coal

The ability to control is critical to maintain the grid and get power to your home or business. That’s where the idea of energy storage comes in and may transform the idea of what is dispatchable.

An article in Forbes, Power Shift: Anything Coal And Gas Can Do, Renewables And Energy Storage Can Do Cheaper, notes the way storage can change some of the rules, “Dispatchable power is the ability to respond to requests from the power network to increase or decrease generation and here, it is the pairing of battery storage with wind and solar to enable these intermittent sources of generation to tackle fluctuations in demand by smoothing output or diverting power into batteries to be used at a later date.”

Why is the idea of energy storage important? The source of dispatchable electricity may change – it may not just be from a power generation plant. “Cost competitive batteries mean that variable renewables will increasingly be able to run when the wind isn’t blowing and the sun isn’t shining,” says Bloomberg New Energy Finance. In simplest terms, store the energy from the sun for later, when it is needed.

In the Carolinas we have varied energy generations sources. That is positive. The system will evolve as technology evolves. There will be new sources, and importantly, a proper infrastructure to make and dispatch the electricity for our homes and businesses. As we collectively discuss those resources, customers may want to keep in mind that our system is changing but the important concept of dispatchable electric resources is always there and relevant to consumers.