The Duck Curve, NEM 3, and YOU - Addendum 5A
- Jeff Jorgenson
- 3 hours ago
- 14 min read
All power plants are not the same. The type of generation, location, economics, weather, economics and governance dictate the role each will play in ‘The Grid’. You’re going to see another concept called “Grid Operator” that will be covered in Part 6 - our last part.
Part 5A will cover the different physical tools and resources available to the Grid Operators to keep the grid running.
The US Power Grid is often called ‘The largest machine in the world!’ This addendum is not a compendium. What it does do is to attempt to familiarize you with Grid Basics, common terms, Grid components - the nuts and bolts of the Grid. Trying to prepare you for the type of world our Grid Operators are living in. In fact all we do here is take broad industry docs and pull them together in one place.
So take a gander…or have your AI do it.
“The electrical grid works by perfectly matching the amount of power that is produced to the amount of power that is needed. Every minute of every day, the grid has to produce the exact amount of power that is needed and react within seconds if there is an imbalance.
When your air conditioner turns on, a generator somewhere spins just a little slower and has to be rebalanced to maintain voltage. This precise management of generation and usage (loads) happens instantaneously, but preparations for the amount of power that will be needed at any given time are first made across many time frames”
Production from the article The Grid Explained
“Grid Operators have become very effective in predicting roughly how much electricity will be needed every hour of every day. In general, there are usually “day ahead markets” where producers and operators make bids and offers for sales of power capacity or reserve capacity on specific times over the next day. There are also procedures for immediately calling upon more capacity or allowing some available capacity to go unused when the actual load goes outside the expected thresholds of the predictions. Grid operators are on constant watch for real time changes in predictions in addition to real time purchasing and management.”
Baseload power accounts for most of the electricity we use. Always-available power sources are designed to constantly generate large amounts of power, so you and everyone else is assured of a reliable supply of electricity whenever you need it. The most familiar examples of baseload sources are nuclear and fossil-fuel power plants, along with some hydroelectric and geothermal facilities. While baseload plants provide an affordable and dependable source of power, they’re not engineered to keep up with sudden changes in electricity demand. The companies operating them are unable to turn them on or off quickly.
When the demand for electricity shifts — either gradually or suddenly — grid operators turn to either intermediate or peaking power plants. These plants are designed to start up quickly and adapt their power output to meet the varying demand. In most cases, peaking plants supply more frequent and sudden changes, whereas intermediate plants supply more gradual changes.
Load following (aka Mid-merit - from The Grid Explained)
“The load on the grid will change throughout the day, sometimes rapidly. Grid operators have reserved capacity they can call upon and general predictions of what the load and availability will be for the grid every minute of every day. High penetrations of solar and wind capacity have made this task more difficult, as collections of large solar farms producing multiple GW of power can have rapid fluctuations in their output during a partly cloudy day. Inconsistent wind patterns can have a similar effect on wind farm production depending on the weather conditions.”
Mid-merit power (load-following from Energy Education Generation)
“At 5 a.m., for example, energy needs are much less than late afternoon when temperatures rise, air conditioning use ramps up, and electricity demand increases. However, baseload power—which is usually at or near max production—is not prepared to meet these swings or fluctuations in use. This is where mid-merit generation comes into play.
In meeting electricity demand, mid-merit power fills in the gap between baseload power—which is constantly generating—and peaking power—which provides power during unexpected peaks in demand.
What distinguishes these types of generators from their baseload counterparts is their ability to adjust their electricity output relatively quickly.
These types of plants are typically flexible natural gas generators. As renewables continue to increase in efficiency and are paired with battery storage capacity, mid-merit generation is expanding to include solar thermal, hydrogen fuel cells, wind power plants, and other renewable resources as they become efficient and affordable alternatives to traditional resources.”
Peaker Plants (from How the U.S. electrical grid works)
As energy demands change throughout the day, peaking power plants are used to meet demand. These plants can start up quickly and provide power soon after they’re activated. (within minutes) They are sometimes referred to as “dispatch-able generation,” because they respond to orders to increase power supply. Traditional peaking plants burn natural gas or biogas to turn steam turbines, but recently energy storage systems like grid-scale batteries or pumped hydro storage systems have been used to respond to peak demand.
Peaker plants (from Sandia National Labs) “are unique in that they do not have to continuously generate energy. Based on EIA data, peaker plants generally operate only between 2-7 percent of the total hours in a calendar year. Although they are not run on a continuous basis, peakers need to be available in real-time for when baseload capacity has been surpassed and/or demand spikes. This can occur as frequently as every evening when people return home, or as sporadically as when a heatwave occurs.”
Distributed power (from Energy Education Generation)
“Distributed power is a decentralized approach to power where smaller generating units produce electricity near the point of consumption, i.e. office buildings, college campuses, hospitals, or even near your home. Distributed resources include microgrids, backup generators, or even solar panels. As well as VPPs.”
Grid Fundamentals
Load Balancing (from The Grid Explained)
“The load and corresponding production of a grid varies considerably throughout the day. Electricity consumption typically rises in the morning, peaks in the afternoon or evening and falls later at night.
The grid requires precise balancing, synchronization and response to changes, so there is an elaborate system of equipment and procedures in place to maintain this stability. Many of the grid components are designed to be automated in responding to these changes. However, a rapid spike or drop in load can require power producers to “ramp up” or “ramp down” accordingly.
A 1800 MW spike in demand is the equivalent of bringing an average thermal power plant online from zero to full in a few minutes. Fortunately, grid operators are usually prepared for rapid changes in load as some large generation assets can quickly trip offline or shut down if there is a problem. Issues ranging from a transmission fault, plant malfunction or procedural response to a safety indicator can cause a rapid and unexpected drop in power on the grid.”
Dispatchability (from The Grid Explained)
“Dispatchability is the ability for a generating asset to be called upon and respond with specific power outputs. A fully operational gas turbine with a reliable supply of gas can be “ramped up” or “ramped down” in the course of a few seconds to a few minutes depending on the difference.”
Non-dispatchable (from The Grid Explained)
“Solar and wind systems rely on the weather, so they are considered “non-dispatchable,” as they cannot be called upon to produce if the weather is not providing the right conditions. Additionally, if the weather is allowing these assets to produce power, and the grid has too much, the grid operators can order other assets to ramp down or order the weather dependent operators to curtail some of their generated power. “Curtailment” is when an asset is directed to not harvest as much power despite being able to harvest more power. In some cases, grid operators become so desperate to offload excess power, they can pay neighboring grids to consume it, which is called ‘negative pricing’.”
Capacity (from The Grid Explained)
“An asset’s “power capacity” refers to the measurement of the immediate power that can be produced by that asset. If the asset is “dispatchable,” it can sell available capacity on “day ahead markets”. Solar and wind based systems that rely on weather can use weather prediction models to participate, but grid operators also need to have available back up ready from dispatchable sources if the predictions don’t play out as expected.”
Intermittent (from How the U.S. electrical grid works)
“Finally, renewable resources like solar and wind are known as intermittent generation. As some renewable-haters like to point out, the sun doesn’t always shine, and the wind doesn’t always blow. Thankfully, meteorologists can now predict the weather with near-perfect accuracy a day ahead of time, so grid operators can plan for intermittent generation based on predicted conditions and adjust the amount of power generated by other sources in response.”
Before we get to ancillary services and what they are let’s explain what Frequency is and why its important.
Frequency from Electricity Explained.
Frequency literally means the number of times something happens over a period of time.
When you turn on an appliance, it uses alternating current to power it. This means that the current is alternating between a positive and negative voltage.
This backwards-and-forwards motion or “oscillation” is known as electrical frequency. In the US, alternating current oscillates 60 times every second, meaning our frequency is 60 hertz (HZ)
All US appliances and electrical equipment are designed to work at 60Hz. If the frequency is not 60Hz then these appliances won’t work – the tolerance is very small, meaning that we have to keep the frequency within a tight window either side of 60Hz. It’s therefore important to constantly monitor frequency right across the Grid to make sure it stays close to 60hz every second.
Ancillary Services “Services that ensure reliability and support the transmission of electricity from generation sites to customer loads. Such services may include load regulation, spinning reserve, non-spinning reserve, replacement reserve, and voltage support.”
Balancing the grid from The Power Grid Explained
“To balance supply and demand, utilities have traditionally relied on central power stations, and when demand peaks, they have turned to so-called peaker plants that often run on fossil gas. But renewable energy and batteries offer cleaner ways to balance the grid.
Grid services are functions that keep the power grid humming, provided by a wide variety of power sources, equipment and coordinating systems.
On longer timescales of hours to days, a primary concern for grid operators is the grid service of power capacity: They must ensure power generators, such as gas-fired power plants, wind farms and solar arrays, are providing enough electricity to meet ever-changing demand.
On the timescale of seconds to minutes, the grid might need ancillary services to balance the grid. When a power plant goes out or a line goes down, grid operators rely on one such service: reserves. A battery, for example, can fill this role by instantly discharging power to the grid.
On the timescale of seconds, frequency regulation is a critical grid service — helping to maintain the grid’s frequency, which in the U.S. is 60 hertz (cycles per second). When too much electricity is being drawn from the grid, the frequency drops. If it falls too low, the lights go out (and the same thing happens if it rises too high).”
Synchronization and frequency control From The Grid Explained
“For large thermal plants using turbines and generators; synchronization and frequency control is built directly into the speed and configuration of the generator. The synchronized power of the grid is referred to as “inertia,” since the spinning generators would carry physical inertia of their rotation like a dynamo against fluctuations in load.
Generating assets with inconsistent and less controllable outputs, like solar panels and some wind turbines, require conversion from Direct Current (DC) to synchronized AC by using an electrical inverter designed to match the pattern required by the local grid.
Some wind turbines generate AC power, but since their rotational speed fluctuates with the speed of the wind, the resulting AC frequency is not synchronized to the grid. There are multiple methods of converting unsynchronized AC to grid synchronized AC. One method involves converting the unsynchronized AC to DC using a bridge rectifier, then converting the DC to synchronized AC by using an electrical inverter. Other techniques are also used however the end goal is to always connect with the grid on the synchronized AC frequency that is expected.”
Generator Synchronization (What You Need to Know) “is the process of matching key electrical parameters such as voltage, system frequency, alternator waveform, phase angle, and phase sequence between a generator and an existing power grid or another generator. It is essential before the generator is reconnected to a source of power. The power system is prepared to run smoothly once these parameters are synchronized with the other generators.”
“Grid frequency is a direct, real-time measurement of the balance between generation and load across an interconnected power system. On a properly synchronized 60 Hz system, frequency deviations indicate immediate power imbalances:
Frequency above 60 Hz: Generation exceeds load—spinning reserve is being absorbed
Frequency below 60 Hz: Load exceeds generation—system reserve is being depleted
Rapid frequency decline (df/dt): Large generation loss or major load trip event”
Frequency response (from Elinta Charge)
“Frequency response is the rapid change in power generation or consumption used to stabilize the electricity grid frequency (60 Hz in North America) after an imbalance between supply and demand. When demand exceeds supply, frequency falls; when supply exceeds demand, frequency rises. Frequency response helps correct this by quickly adjusting power up or down.”
Primary and Secondary Frequency Regulation (from Infinite Power HT) - Regulation refers to the continuous small deviations needed rather than for a Response to a major change in operating frequency though the mechanisms to stabilize are similar.
“Primary Frequency Regulation is a fast-regulation mechanism performed automatically by generators. When the grid frequency deviates from the set value, each operating generator quickly adjusts its output through its governor system to reduce the magnitude of frequency fluctuations. This type of regulation uses droop control, meaning it cannot completely eliminate the frequency deviation but can mitigate its variation. The key features of primary frequency regulation are its immediacy and high level of automation, typically acting within a few seconds. It is suitable for responding to short-term (generally within 10 seconds) and small-amplitude frequency fluctuations.
Secondary Frequency Regulation, also known as Automatic Generation Control (AGC), involves generators providing sufficient adjustable capacity and a specified regulation rate to track frequency in real time within allowable deviation limits, ensuring system frequency stability. Secondary regulation can achieve zero-error frequency control and also monitors and adjusts tie-line power flows. It is implemented on top of primary Regulation through manual or automated measures, aiming to restore the grid frequency to its nominal value. This is usually coordinated by the power dispatch center, which issues instructions to specific power plants to increase or decrease output based on real-time frequency monitoring, or is achieved automatically via the AGC system.
Compared to primary regulation, secondary frequency regulation offers higher control accuracy but a slower response time, as it involves communication, decision-making, and execution processes. It is primarily used to address larger (0.5%–1.5%) and longer-period (10 seconds to 30 minutes) frequency deviations.”
Automatic Generation Control (AGC) (From What is the Power Plants Role): “AGC is an offsite control system that manages the output of multiple power plants within a region. It uses real-time data on frequency, load, and power generation to make adjustments to individual generators. AGC ensures that the power output from different plants is coordinated to match the changing demand and maintain frequency stability.”
Frequency Response: The first line of defense. It happens automatically when the system experiences a sudden event (like a generator unexpectedly shutting down). Assets act via autonomous controls to arrest the drop in frequency.
The second phase works with the first phase to arrest the frequency and find a stabilization point. Once the frequency has stabilized, system operators send computer signals (Automatic Generation Control, or AGC) to actively command power plants and energy storage units to return the system to standard operating frequency.”
Spinning reserve (from The Grid Explained)
“Conventionally, power producers offer something called “spinning reserve”, which would be the equivalent of a generation asset that is kept spinning at the synchronized frequency of the grid, yet without the “load” applied in a manner that would slow it down or require additional fuel. This is similar to how running a car engine at 3000 RPM in neutral will require very little fuel compared to running the same engine in top gear accelerating onto a highway.
In more recent years, rapid response grid storage systems are utilizing large lithium batteries and other load management methods called “operating reserve”. It might take a few seconds to a few minutes for a large generating asset on stand by to be brought online to full power, so the ability for large lithium batteries to immediately respond with high output capacity to fill that gap is tremendously valuable for grid stability.”
What are Reserves (from FERC Ancillary Services)
“Operating Reserves: backup power which can quickly replace lost power generation due to unexpected events.
There are three types of these reserves:
Spinning reserves are provided by an already-online generator with spare capacity and capable of increasing output within a specified time frame (for example, 10 minutes);
Non-spinning reserves include backup power sources that are not currently online but can be started and connected to the grid relatively quickly (typically 10 minutes. This includes power plants and demand-side resources (like programs that reduce customer electricity use during peak times); and
Supplemental reserves include backup power that takes longer to become available than spinning or non-spinning reserves and is not necessarily connected to the grid.”
However as NERC states in their Balancing and Frequency Control Reference:
Understanding Reserves
There is often confusion when operators and planners talk about reserves. One major reason for misunderstanding is a lack of common definitions; NERC’s definitions have changed over time. In addition, most NERC Regions developed their own definitions.
Contingency Reserve: The provision of capacity deployed by the BA to respond to a Balancing Contingency Event and other contingency requirements (such as Energy Emergency Alerts as specified in the associated NERC Standards). This is the left column of Operating Reserves in Figure 4.1 (below).
Frequency-responsive reserve: On-line generation with headroom that has been tested and verified to be capable of providing droop as described in the Primary Frequency Response guideline. Variable load that mirrors governor droop and dead-band may also be considered frequency responsive reserve.
Interruptible Load: Demand that the end-use customer makes available to its Load-Serving Entity via contract or agreement for curtailment that can be interrupted within 10 minutes.
Operating Reserve: That capability above firm system demand required to provide for regulation, load forecasting error, equipment forced and scheduled outages, and local area protection.
Operating Reserve–Spinning: Generation synchronized to the system and fully available to serve load within the Disturbance Recovery Period following the contingency event or Load fully removable from the system within the Disturbance Recovery Period following the contingency event deployable in 10 minutes.
Operating Reserve Supplemental: Generation (synchronized or capable of being synchronized to the system) that is fully available to serve load within the Disturbance Recovery Period following the contingency event or Load fully removable from the system within the Disturbance Recovery Period following the contingency event that can be removed from the system, within 10 minutes.
Planning reserve: The difference between a BA’s expected annual peak capability and its expected annual peak demand expressed as a percentage of the annual peak demand. See BAL-502-RF-03 for additional discussion.
Regulating Reserve: An amount of Operating Reserve – Spinning responsive to Automatic Generation Control, which is sufficient to provide normal regulating margin.
Replacement reserve: NOTE: Each NERC Region sets times for reserve restoration, typically in the 60–90-minute range. The NERC default contingency reserve restoration period is 90 minutes after the disturbance recovery period.
Supplemental Reserve Service: Provides additional capacity from electricity generators that can be used to respond to a contingency within a short period, usually ten minutes. An ancillary service identified in FERC Order 888 as necessary to affect a transfer of electricity between purchasing and selling entities. This is effectively FERC’s equivalent to NERC’s Operating Reserve.
Much like parts kept in a storeroom, reserves are meant to be used when the need arises. Reserves can be low for short periods of time due to plant equipment problems and unit trips and can also be misstated.
Black Start Capability: “a power plant or other power supply resource that has the capability to start and restore power to an energy grid without relying on external electricity, which can be essential after a major grid event such as a blackout.”
Similarly to Frequency Regulation, Voltage control is the routine process of maintaining specific voltage targets across the system, while Voltage support is similar to Frequency Response and refers to the dynamic, emergency injection (or absorption) of reactive power to stabilize the grid during disturbances.
Voltage control “is achieved through the use of controllers that remotely operate actuators such as tap-changer transformers and switched capacitor banks, which are strategically placed in the distribution grid.”
Voltage support uses Voltage Source Converters, STATCOMs, and Static Frequency Converts to react to inject or absorb reactive power dynamically, responding almost instantaneously to system needs.
Lenz’s law - Lenz’s law upholds the general principle of the conservation of energy stating an induced electric current flows in a direction that opposes the change in magnetic flux that produced it.
