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Power Distribution and Delivery
The grid is the infrastructure of electrical transmission and distribution connecting power plants producing electricity to customers using electricity. Transmission infrastructure refers to large corridors of high voltage power lines that can transmit large amounts of electrical power across long distances. The distribution infrastructure refers to the power lines that serve local networks, extending to the customers. The grid connects many different types of power generating stations with many different types of customers.
Most large thermal power plants generate electricity from heat produced by burning biomass, municipal waste, coal, oil or gas, which all produce greenhouse gas emissions. Nuclear power plants use nuclear fission for thermal energy which the plant uses to generate electricity. Large, hydroelectric dams, thermal and geothermal power plants can generate enough electricity to power entire towns and cities depending on their size. Smaller generating assets like neighborhood solar farms and wind installations can also deliver power to the grid, albeit intermittently.
Every generation asset needs to follow a specific set of rules in order to integrate with the electrical grid correctly. The electrical power provided to the grid must be synchronized and matched to the grid’s frequency of Alternating Current (AC), including phase patterns and output matching a specified load. 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.
In an electrical circuit transmitting a set amount of power, the voltage and current share an inverse relationship. The losses in transmission follow the square of the current, meaning a low current high voltage transmission reduces loss and maintains a more efficient transmission of power, especially over long distances. However, high voltage transmission also presents the trade off of being dangerous to nearby people or structures, so high voltage power lines must be positioned high above the ground and away from possible points of unintentional contact like buildings or trees.
Electrical power infrastructure will utilize transformer stations that “step up” or increase the voltage coming out of a generating station which decreases the current. High voltage transmission lines eventually connect to electrical substations which “step down” the high voltage/low current electricity to a voltage/current ratio which is suitable for the next set of connected power lines. Transmission infrastructure can transmit electricity across multiple substations and transformers downstream of other substations depending on the local requirements of municipalities and neighborhoods. Voltage is “stepped” up or down by substations across different grid connections in order to reduce losses as efficiently as possible.
Some grids operating on different frequencies or synchronization patterns are still connected with an interchange allowing load balancing and additional power imports and exports from local grids. Japan for instance has some regional grids operating on 50 hertz, while the rest of the grid operates at 60 hertz. These two grids could not directly connect as their AC frequencies and synchronization would be incompatible, however High Voltage Direct Current (HVDC) transmission lines provide the option to convert the AC from one grid to DC, then back into the preferred AC pattern of the other grid. There are many examples of HVDC transmission lines serving interconnections across European countries and regional networks across Asia.
Substations are important for “stepping down” voltage from large transmission corridors. Transformers can be sized to serve entire towns at a major substation or they can be small enough to fit on a utility pole for stepping down the local voltage to the level appropriate for a household. The grid is structured to deliver the precise amount of electricity that matches the immediate load of every customer and keep the expected voltages and frequencies as precise as possible to expected values.
Much of the cost of the electric bill is dedicated specifically to maintenance and upkeep of the grid itself. The cost of generating electricity is usually around half to a fraction of the price the customer ends up paying. This can vary by locality, but the grid is ultimately an expensive system to maintain. However, it provides tremendous value to modern society.
According to the Energy Information Administration, the average electrical load for a residential US person is 1.213 kilowatts. The messy average of all residents and all residential electrical consumption doesn’t tell the full story of how electricity is used in the US. (Energy Information Administration, 2022) In fact, residential consumption only accounts for ~39% of total electricity consumed in the U.S. (Energy Information Administration, n.d.) There are also commercial and industrial consumption metrics of electricity accounting for substantial portions as well.
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. This pattern can be influenced by a range of factors, like weather conditions, the usage habits of local industries and even a particular commercial break on a popular tv program can cause a rapid spike in demand. Electric kettles, cooking appliances and water pumps responding to toilet flushes during a halftime show in 2021 caused a 1800 Megawatt spike in demand on the grid in the UK. (National Grid ESO, n.d.)
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.
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. This also means fewer gas turbine based generation assets need to be in a state of “spinning reserve,” which burns additional fossil fuels.
Grid operators utilize intricate systems of markets and follow many procedures mandated by local policy. There are different rules and procedures depending on how a regional grid is operated however the Federal Energy Regulatory Commision sets some ground rules. Operators usually need to follow rules such as having a designated amount of capacity to call upon, and reserve margins on top of the expected capacity. There are also rules about net metering with consumer solar customers or prioritizing “renewable” or “zero emission” generating assets. There are also requirements of “frequency regulation” and other ancillary services that help with grid stability, which can be provided by storage facilities or producers capable of rapid response.
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.
Generation assets produce the power, transmission and distribution deliver the power to customers and grid operators maintain the intricate system of precisely matching power to load within very specific thresholds across the entire system.
Generating assets can be very different from each other and therefore play different roles in how they can be incorporated into the grid. There are different characteristics of every asset which come with different tradeoffs.
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. Single cycle gas turbines apply energy of gas burning directly to the rotational power offering a better response time with lower fuel efficiency, while combined cycle turbines have an additional steam generator built into the cooling system providing higher fuel efficiency but an additional thermal lag in total response time. Nuclear power plants and coal plants also have known ramping rates and procedures to follow and are more gradual in their response time. Hydroelectric dams have known ramping rates but usually have additional procedures depending on their local regulations as downstream alarms might need to be activated if the flow rate is going to substantially increase.
Storage systems like batteries and pumped hydro can be dispatched but only if they have energy in storage, and are limited to that amount until they can recharge or refill. Most “grid storage” systems only hold enough energy to provide short term relief while other large generators can ramp up and come online. Some conventional hydroelectric generation systems are limited by water availability or flow regulations, reducing the amount of electricity that can be generated on command.
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”.
Grid operators use general terms to distinguish different measurements pertaining to production assets and generation. 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.
Power can be measured in Kilowatts (kW), Megawatts(MW) and Gigawatts (GW). Capacity for thermal assets also have a “thermal rating” which measures the thermal power capacity of the reactor or furnace, often denoted as MWth or GWth. Grid operators are more interested in the “electrical rating,” which measures the electrical output capacity, accounting for the power conversion ratio. The electrical power capacity of the PWR-20 is “20 MWe '' or just “20 MW”.
Every generating asset is rated with an “installed capacity” or “nameplate capacity,” which is typically considered the maximum allowable output. A 100 MW solar farm would produce about 100 MW of electricity on the sunniest day at high noon in ideal conditions. However, that production would drop to zero at night.
“Energy” refers to the power generated over time, which can be measured with Kilowatt hours (kWh), Megawatt hours (MWh), Gigawatt Hours (GWh) or Terawatt hours (TWh).
A 20 MW nuclear reactor has a nameplate capacity for 20 MW but it can run non stop regardless of the weather. 20 MW of electrical output for 8760 hours in a year would generate 175.2 GWh for the year. This would be considered a 100% capacity factor for the year, since it was utilizing 100% of its capacity for the entirety of the measured time frame. The capacity factor of a PWR-20 would change in a refueling and maintenance year or if it needed to load follow in a way which ramped down its output.
A 20 MW solar farm operating with a capacity factor of 17.2% which is the global average as of 2021, would produce a total of 30.1 GWh for the year. (Jaganmohan, 2022) Just because an asset has the same installed capacity as another asset, it doesn’t mean the energy generated over time would be the same.
A grid operator needs to match the power supply (production) to the power demand (load).
As there is always some load on the grid, some large producers like nuclear power plants are referred to as “base load” sources, since they can provide consistent nonstop power to satisfy the “base load” expected from the grid no matter what time of day it is. Due to proportionally low fuel costs, nuclear plants have very little cost differences between running a reactor at half or full power, so it makes the most sense to run at full power whenever they can, maximizing electrical production. Coal plants have higher fuel costs. Every MWh of electricity produced by a coal plant requires an amount of coal that comes at a cost. The furnace design of coal plants have slower rates of ramping, so they are often designated as “base load” but have flexibility to reduce their output at a slower rate than gas turbines or hydroelectric.
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.
California has 17.5 GW of utility scale solar farms, which can go from minimum output to full power in 2 hours on a fully sunny day, and dropping output in the evening just as fast. Bringing 17 GW of electricity offline then back online 6-8 hours later is a monumental balancing task for grid operators with substantial solar capacity to manage. This tendency of solar heavy grids is called “the duck curve,” as the remaining load that needs to be matched throughout the day is curved in the shape of a duck. (CAISO, n.d.)
Proper load following is supported by a range of technologies and procedures. Large grid connected storage batteries can help with frequency regulation to keep the grid’s AC frequency synchronized. Storage facilities with proper planning can also use their capacities for simple “load shifting,” which involves buying up and charging their banks when power is abundant and cheap and selling it back to the grid at higher rates when power is in high demand. There isn’t nearly enough storage to firm up the total intermittency of all solar and wind generators, but the price differences across hourly markets can help recuperate costs for grid scale storage facilities.
“Gas Peaker plants” are plants that can rapidly respond to periods of high demand yet often charge a premium for their services. Operators often manage loads with sharp spikes and deep dips due to the chaotic production patterns of weather dependent assets. The common response involves ramping a fleet of gas turbines up and down to match the remaining load pattern, yet operating gas plants like this will burn more fuel than the same amount of electricity generated for a gradual load pattern.
The grid is a critical foundation of modern infrastructure and is tremendously important for human well being. Reliable electricity from the grid is more than just “keeping the lights on,” it also powers medical equipment, heating and other essential devices people’s lives depend on. Hospitals will often have backup generators that can keep all of their essential systems powered when the grid goes down. However, most customers relying on electricity from the grid do not have home generators, as they can be rather expensive. Reliable and consistent electricity from the grid is crucial to all of those who need it to survive.
Power demand is often highest during extreme weather events. Extreme cold snaps can lead to much higher rates of electrical consumption due to customers using more electricity to power electrical heating systems. A common grid policy also involves directing gas line infrastructure to prioritize availability to residential customers for heat, while gas power plants are left with whatever is left over in the supply system. A lack of residential heating can be deadly. However, many customers rely on electrical heating systems. Households solely reliant on electrical heating systems will not have heat when the grid goes down as a result of gas plants not having fuel to power their own turbines to produce electricity. Many gas plants do not have substantial onsite gas storage since their fuel supply comes directly from a pipe that is usually sufficient under normal circumstances. Policies could be enacted to require gas power plants to have an onsite reserve, yet this is not the case in most regions.
Heat waves present another challenge for grids, as electrical cooling systems from air conditioning to food storage can add substantially to the load on the grid. The grid going down during a heat wave is also dangerous, as extreme heat can cause medical emergencies and lead to fatalities in some circumstances.
Extreme weather events can also impact the structural integrity of the grid. Non-winterized components can freeze and become inoperable, forcing fuel lines to seize up or power plants to shut down. High winds can knock down trees or power lines, creating obstacles and cutting power. Heavy snowfall can block transportation routes, which can effectively block fuel deliveries or accessibility for workers who are essential for keeping the grid operational. Some grid components also become less efficient during extreme heat events. Wildfires often threaten grid infrastructure, like power lines and transformers. Poorly maintained grid infrastructure can also cause wildfires if faulty components overheat and ignite combustible materials. (Solis, 2022)
A household refrigerator’s worth of soiled food can be the consequence of a single customer losing power for an extended period of time during a blackout. If a grocery store loses power, all of the refrigerated and frozen inventory could possibly spoil during extended black outs. Losing power can lead to these inventory losses, but it can also shut down the ability for business and industrial operations to function. Storefronts need electronic payment systems to process sales, and factories need electricity to power their machinery, meaning a loss of power can shut down businesses big and small. Economic losses due to blackouts in the US were estimated to be about $80 Billion every year. (Chen, 2005) When the grid goes down, the economic activities that support human livelihood get interrupted in ways that can cause tremendous economic losses.
Conventional nuclear has almost always been positioned as a reliable baseload by grid operators due to its constant output and dependability. Most large scale reactors were designed with this positioning in mind, knowing the most efficient and cost effective way to run the reactor was to gradually bring it up to full power and run it non stop until it is time for refueling and maintenance once every 2 years or so. No matter what the paying rate per electricity, the change in fuel consumption was so minimal for nuclear power, it simply makes sense to run the reactor at full power. Other thermal plants, and in some cases hydroelectric, could be incentivized to reduce their output if the cost basis and other factors instruct that outcome.
Since the load on the grid is fluctuating and subject to rapid changes due to other chaotically intermittent generating assets, some have argued conventional nuclear is not equipped to “load follow.” Many large nuclear power plants were never designed to ramp their output in accordance with the chaotic intermittency of massive solar and wind capacities. However, some conventional nuclear power plants have been designed to load follow on the grid that existed when they were constructed. The French fleet of reactors routinely load follow, which is why they have lower annual capacity factors compared to nuclear stations operating on grids with lower nuclear penetration. Nuclear powered naval vessels are designed to rapidly increase or decrease their power output and routinely operate in this manner. Nuclear power is not fundamentally incapable of load following or rapid flexibility. There are just many conventional plants that were never designed with such requirements in mind. Moving forward, there are many design changes that can reshape how nuclear plants can adapt to these demands from the grid, ranging from how a reactor or plant is designed to rapid response storage configurations.
Another advantage of nuclear grid integration is the use of existing infrastructure. New wind and solar farms often need to be positioned in places which require the construction of entirely new power conduits and transmission corridors. Large solar fields or wind farms require power lines to connect every row of panels and every wind turbine. Large, remote wind farms will also require access roads to be built for every turbine, which becomes particularly tedious if the locations are on mountain ridges or extreme terrain. A nuclear plant constructing a new onsite reactor or a former power station upgrading their site to host nuclear generation can plug directly into the transmission infrastructure in place.
Some are opposed to large power generating stations based on the “centralized” nature of the power plant where they would prefer to see a grid of “decentralized” power generating assets. Some opposition can stem from political or economic leanings. However, there is often a technical argument presented which insists decentralized systems are more resilient than centralized systems. Part of this concern stems from the “bottleneck” of power that can become a single point of failure.
Distributed power generation across existing local infrastructure is entirely possible. No new major transmission corridors or continental super grids are needed with Last Energy’s PWR-20. Massive transmission infrastructure is often presented as a partial solution to the intermittency of wind and solar, yet permitting, approvals and completions of these proposals are often difficult to achieve. Last energy delivers reliable energy wherever it is installed on the grid with no reliance on weather or large scale infrastructure projects.
The PWR-20 provides dispatchable power on demand regardless of the weather or short term supply chain issues. Full capacity 24/7 power output lasting years between refueling cycles presents a level of energy security that can provide reliability for customers and grid operators alike.
A grid supported by multiple PWR-20 systems distributed locally to areas of high demand would also have the benefit of structural resilience. If there is a grid disruption or point of failure in the network, the distributed nature of the power generating assets provides additional security in keeping the rest of the grid operational.
The ease of delivery and installation allows for precise scalability according to customer needs. PWR-20s can be ordered and installed as needed, scaling with economic growth and local demand. The requirements of the grid change year after year and the PWR-20 is positioned as a favorable generation asset for any grid operator.
CAISO. (n.d.). What the duck curve tells us about managing a green grid. https://www.caiso.com/documents/flexibleresourceshelprenewables_fastfacts.pdf
Chen, A. (2005, February 2). Berkeley Lab Study Estimates $80 Billion Annual Cost of Power Interruptions - Berkeley Lab. News. Retrieved January 30, 2023, from https://newscenter.lbl.gov/2005/02/02/berkeley-lab-study-estimates-80-billion-annual-cost-of-power-interruptions/
Energy Information Administration. (n.d.). Use of electricity - U.S. Energy Information Administration. EIA. Retrieved January 26, 2023, from https://www.eia.gov/energyexplained/electricity/use-of-electricity.php
Energy Information Administration. (2022, October 12). How much electricity does an American home use? Frequently Asked Questions (FAQs) - U.S. Energy Information Administration (EIA). Retrieved January 26, 2023, from https://www.eia.gov/tools/faqs/faq.php?id=97&t=3
Jaganmohan, M. (2022, August 4). Global solar PV capacity factor 2021. Statista. Retrieved January 31, 2023, from https://www.statista.com/statistics/799330/global-solar-pv-installation-cost-per-kilowatt/
National Grid ESO. (n.d.). Last night’s #Euro2020 between #ENGITA final saw our control room register a TV pick-up of 1800MW. https://twitter.com/NationalGridESO/status/1414508508318507008
Solis, N. (2022, October 2). Former PG&E executives agree to $117-million settlement over California wildfires. Los Angeles Times. Retrieved January 30, 2023, from https://www.latimes.com/california/story/2022-09-29/former-pg-e-executives-announce-117-million-settlement-over-california-wildfires
