With TVA already experiencing unprecedented fuel costs and buying more power than ever from outside suppliers, two TVA nuclear plants have been taken offline and two more are operating at 50 percent capacity at the agency's Watts Bar and Browns Ferry sites.
One unit at the Browns Ferry site in northern Alabama was pulled completely offline the morning of August 8 following the discovery of a leak in instrumentation used to monitor temperatures in the plant's main steam lines.
In an unrelated incident the day before, all three Browns Ferry units were reduced to 50 percent power following the failure of a transformer that supplies electricity to cooling tower equipment. Power was reduced in order to keep the temperature of water released from the plant into the river system within regulatory limits, said TVA spokesman John Moulton.
"We never exceeded the thermal limit, which is 90 degrees," Moulton said.
The Watts Bar plant was taken offline August 7 to repair a hydrogen leak inside the main generator that workers have been monitoring since August 1. Power has been decreased incrementally since that time, Moulton said, and with a recent cooling trend it was decided to bring the plant completely offline to make the repair.
Moulton would not say when the plants would be back in operation, calling that information proprietary.
At capacity, Browns Ferry can produce 3,440 megawatts of power, enough to supply 1.3 million homes. Watts Bar, near Spring City, Tenn., has a capacity of about 1,100 megawatts, supplying the equivalent of 650,000 homes. As a result of the outages, TVA has lost approximately 2,255 megawatts of generating capacity.
The shutdowns follow on the heels of an announcement by TVA that customers can expect a sizable increase in their fall electric bills because of spikes in the cost of coal and natural gas, which affect TVA's generating plants and the power it buys from outside suppliers. The agency also said the lingering drought has reduced the amount of hydropower that can be generated by TVA dams and that it has bought 11 percent more power on the open market than during the same period last year.
The financial impact of the most recent incidents won't be known until the outages are over, said Moulton. But a break in the August heat wave should help, he said.
Demand for power was expected to be about 26,200 megawatts, a drop from hotter days earlier in the week when demand ranged from 30,0000 to 31,000 megawatts, Moulton said.
"The fact that we don't have two nuclear units available of course isn't what it would be on a day of high demand," he said. "The price of power right now is about 15 to 20 percent lower than it was earlier in the week."
Moulton called the simultaneous mechanical issues at the plants "unusual" but said that planning for such outages is part of the business.
"You want to keep them to a minimum, but you take it into account," he said. "We know that we're going to have some unplanned shutdowns, and that's taken into account as far as how you're going to meet the demand."
Ontario Clean Grid Plan outlines emissions-free electricity growth, renewable energy procurement, nuclear expansion at Bruce and Darlington, reduced natural gas, grid reliability, and net-zero alignment to meet IESO demand forecasts and EV manufacturing loads.
Key Points
A plan to expand emissions-free power via renewables and nuclear, cut natural gas use, and meet growing demand.
✅ Targets renewables, hydro, and nuclear capacity growth
✅ Aims to reduce reliance on gas for grid reliability
✅ Aligns with IESO demand forecasts and EV manufacturing loads
Ontario is working toward filling all of the province’s quickly growing electricity needs with emissions-free sources, including a plan to secure new renewable generation and clean power options, but isn’t quite ready to commit to a moratorium on natural gas.
Energy Minister Todd Smith announced Monday a plan to address growing energy needs for 2030 to 2050 — the Independent Electricity System Operator projects Ontario’s electricity demand could double by mid-century — and next steps involve looking for new wind, solar and hydroelectric power.
“While we may not need to start building today, government and those in the energy sector need to start planning immediately, so we have new clean, zero-emissions projects ready to go when we need them,” Smith said in Windsor, Ont.
The strategy also includes two nuclear projects announced last week — a new large-scale nuclear plant at Bruce Power on the shore of Lake Huron and three new small modular reactors at the site of the Darlington nuclear plant east of Toronto.
Those projects, enough to power six million homes, will help Ontario end its reliance on natural gas to generate electricity, said Smith, but committing to a natural gas moratorium in 2027 and eliminating natural gas by 2050 is contingent on the federal government helping to speed up the new nuclear facilities.
“Today’s report, the Powering Ontario’s Growth plan, commits us to working towards a 100 per cent clean grid,” Smith said in an interview.
“Hopefully the federal government can get on board with our intentions to build this clean generation as quickly as possible … That will put us in a much better position to use our natural gas facilities less in the future, if we can get those new projects online.”
The IESO has said that natural gas is required to ensure supply and stability in the short to medium term, as Ontario works on balancing demand and emissions across the grid, but that it will also increase greenhouse gas emissions from the electricity sector.
The province is expected to face increased demand for electricity from expanded electric vehicle use and manufacturing in the coming years, even as a $400-billion cost estimate for greening the grid is debated.
Keith Brooks, programs director for Environmental Defence, said the provincial plan could have been much more robust, containing firm timelines and commitments.
“This plan does not commit to getting emissions out of the system,” he said.
“It doesn’t commit to net zero, doesn’t set a timeline for a net zero goal or have any projection around emissions from Ontario’s electricity sector going forward. In fact, it’s not really a plan. It doesn’t set out any real goals and it doesn’t it doesn’t project what Ontario’s supply mix might look like.”
The Canadian Climate Institute applauded the plan’s focus on reducing reliance on gas-fired generation and emphasizing non-emitting generation, but also said there are still some question marks.
“The plan is silent on whether the province intends to construct new gas-fired generation facilities,” even as new gas plant expansions are proposed, senior research director Jason Dion wrote in a statement.
“The province should avoid building new gas plants since cost-effective alternatives are available, and such facilities are likely to end up as stranded assets. The province’s timeline for reaching net zero generation is also unclear. Canada and other G7 countries have set a target for 2035, something Ontario will need to address if it wants to remain competitive.”
Manitoba Hydro capacity constraints challenge clean energy growth as industrial demand, hydrogen projects, EV batteries, and electrification strain the grid; limited surplus, renewables, storage, and transmission bottlenecks hinder new high-load connections.
Key Points
Limited surplus power blocks new energy-intensive loads until added generation and transmission expand Manitoba's grid.
✅ No firm commitments for new energy-intensive industrial customers
✅ Single large load could consume remaining surplus capacity
✅ New renewables need transmission; gas, nuclear face trade-offs
Manitoba Hydro lacks the capacity to provide electricity to any new "energy intensive" industrial customers, the Crown corporation warns in a confidential briefing note that undercuts the idea this province can lure large businesses with an ample supply of clean, green energy, as the need for new power generation looms for the utility.
On July 28, provincial economic development officials unveiled an "energy roadmap" that said Manitoba Hydro must double or triple its generating capacity, as electrical demand could double over the next two decades in order to meet industrial and consumer demand for electricity produced without burning fossil fuels.
Those officials said 18 potential new customers with high energy needs were looking at setting up operations in Manitoba — and warned the province must be careful to choose businesses that provide the greatest economic benefit as well as the lowest environmental impact.
In a briefing note dated Sept. 13, obtained by CBC News, Manitoba Hydro warns it doesn't have enough excess power to hook up any of these new heavy electricity-using customers to the provincial power grid.
There are actually 57 proposals to use large volumes of electricity, Hydro says in the note, including eight projects already in the detailed study phase and nine where the proponents are working on construction agreements.
"Manitoba Hydro is unable to offer firm commitments to prospective customers that may align with Manitoba's energy roadmap and/or provincial economic development objectives," Hydro warns in the note, explaining it is legally obliged to serve all existing customers who need more electricity.
"As such, Manitoba Hydro cannot reserve electric supply for particular projects."
Hydro says in the note its "near-term surplus electricity supply" is so limited amid a Western Canada drought that "a single energy-intensive connection may consume all remaining electrical capacity."
Adding more electrical generating capacity won't be easy, even with new turbine investments underway, and will not happen in time to meet demands from customers looking to set up shop in the province, Hydro warns.
The Crown corporation goes on to say it's grappling with numerous requests from existing and prospective energy-intensive customers, mainly for producing hydrogen, manufacturing electric vehicle batteries and switching from fossil fuels to electricity, such as to use electricity for heat in buildings.
In a statement, Hydro said it wants to ensure Manitobans know the corporation is not running out of power — just the ability to meet the needs of large new customers, and continues to provide clean energy to neighboring provinces today.
"The size of loads looking to come to Manitoba are significantly larger than we typically see, and until additional supply is available, that limits our ability to connect them," Hydro spokesperson Bruce Owen said in a statement.
Adding wind power or battery storage, for example, would require the construction of more transmission lines, and deals such as SaskPower's purchase depend on that interprovincial infrastructure as well.
Natural gas plants are relatively inexpensive to build but do not align with efforts to reduce carbon emissions. Nuclear power plants require at least a decade of lead time to build, and tend to generate local opposition.
Hydro has also ruled out building another hydroelectric dam on the Nelson River, where the Conawapa project was put on hold in 2014.
Commercial Electric Tariffs explain utility rate structures, peak demand charges, kWh vs kW pricing, time-of-use periods, voltage, delivery, capacity ratchets, and riders, guiding facility managers in tariff analysis for accurate energy savings.
Key Points
Commercial electric tariffs define utility pricing for energy, demand, delivery, time-of-use periods, riders, and ratchet charges.
✅ Separate kWh charges from kW peak demand fees.
✅ Verify time-of-use windows and demand interval length.
✅ Review riders, capacity ratchets, and minimum demand clauses.
Especially during these tough economic times, as major changes to electric bills are debated in some states, facility executives who don’t understand how their power is priced have been disappointed when their energy projects failed to produce expected dollar savings. Here’s how not to be one of them.
Your electric rate is spelled out in a document called a “tariff” that can be downloaded from your utility’s web page. A tariff should clearly spell out the costs for each component that is part of your rate, reflecting cost allocation practices in your region. Don’t be surprised to learn that it contains a bunch of them. Unlike residential electric rates, commercial electric bills are not based solely on the quantity of kilowatt-hours (kWh) consumed in a billing period (in the United States, that’s a month). Instead, different rates may apply to how your power is supplied, how it is delivered via electricity delivery charges, when it was consumed, its voltage, how fast it was used (in kW), and other factors.
If a tariff’s lingo and word structure are too opaque, spend some time with a utility account rep to translate it. Many state utility commissions also have customer advocates that may assist as they explore new utility rate designs that affect customers. Alternatively, for a fee, facility managers can privately chat with an energy consultant.
Common mistakes
Many facility managers try to estimate savings based on an averaged electric rate, i.e., annual electric spend divided by annual kWh. However, in markets where electricity demand is flat, such a number may obscure the fastest rising cost component: monthly peak demand charges, measured in dollars per kW (or kilo-volt-amperes, kVA).
This charge is like a monthly speeding ticket, based solely on the highest speed you drove during that time. In some areas, peak demand charges now account for 30 to 60 percent of a facility’s annual electric spend. When projecting energy cost savings, failing to separately account for kW peak demand and kWh consumption may result in erroneous results, and a lot of questions from the C-suite.
How peak demand charges are calculated varies among utilities. Some base it on the highest average speed of use across one hour in a month, while others may use the highest average speed during a 15- or 30-minute period. Others may average several of the highest speeds within a defined time period (for example, 8 a.m. to 6 p.m. on weekdays). It is whatever your tariff says it is.
Because some power-consuming (or producing) devices, including those tied to smart home electricity networks, vary in their operation or abilities, they may save money on a few — but not all — of those rate components. If an equipment vendor calculates savings from its product by using an average electric rate, take pause. Tell the vendor to return after the proposal has been redone using tariff-based numbers.
When a vendor is the only person calculating potential savings from using a product, there’s also a built-in conflict of interest: The person profiting from an equipment sale should not also be the one calculating its expected financial return. Before signing any energy project contracts, it’s essential that someone independent of the deal reviews projected savings. That person (typically an energy or engineering consultant) should be quite familiar with your facility’s electric tariff, including any special provisions, riders, discounts, etc., that may pertain. When this doesn’t happen, savings often don’t occur as planned.
For example, some utilities add another form of demand charge, based on the highest kW in a year. It has various names: capacity, contract demand, or the generic term “ratchet charge.” Some utilities also have a minimum ratchet charge which may be based on a percent of a facility’s annual kW peak. It ensures collection of sufficient utility revenue to cover the cost of installed transmission and distribution even when a customer significantly cuts its peak demand.
Ukraine Electricity Exports resume as the EU grid links stabilize; ENTSO-E caps, megawatt capacity, renewables, and infrastructure repairs enable power flows to Moldova, Poland, Slovakia, and Romania despite ongoing Russian strikes.
Key Points
Resumed cross-border power sales showing grid stability under ENTSO-E limits and surplus generation.
✅ Exports restart to Moldova; Poland, Slovakia, Romania next.
✅ ENTSO-E cap limits to 400 MW; more capacity under negotiation.
✅ Revenues fund grid repairs after Russian strikes.
Ukraine began resuming electricity exports to European countries on Tuesday, its energy minister said, a dramatic turnaround from six months ago when fierce Russian bombardment of power stations plunged much of the country into darkness in a bid to demoralize the population.
The announcement by Energy Minister Herman Halushchenko that Ukraine was not only meeting domestic consumption demands but also ready to restart exports to its neighbors was a clear message that Moscow’s attempt to weaken Ukraine by targeting its infrastructure did not work.
Ukraine’s domestic energy demand is “100%” supplied, he told The Associated Press in an interview, and it has reserves to export due to the “titanic work” of its engineers and international partners.
Russia ramped up infrastructure attacks in September, when waves of missiles and exploding drones destroyed about half of Ukraine's energy system, even as it built lines to reactivate the Zaporizhzhia plant in occupied territory. Power cuts were common across the country as temperatures dropped below freezing and tens of millions struggled to keep warm.
Moscow said the strikes were aimed at weakening Ukraine’s ability to defend itself, and both sides have floated a possible agreement on power plant attacks amid mounting civilian harm, while Western officials said the blackouts that caused civilians to suffer amounted to war crimes. Ukrainians said the timing was designed to destroy their morale as the war marked its first anniversary.
Ukraine had to stop exporting electricity in October to meet domestic needs.
Engineers worked around the clock, often risking their lives to come into work at power plants and keep the electricity flowing. Kyiv’s allies also provided help. In December, U.S. Secretary of State Antony Blinken announced $53 million in bilateral aid to help the country acquire electricity grid equipment, on top of $55 million for energy sector support.
Much more work remains to be done, Halushchenko said. Ukraine needs funding to repair damaged generation and transmission lines, and revenue from electricity exports would be one way to do that.
The first country to receive Ukraine’s energy exports will be Moldova, he said.
Besides the heroic work by engineers and Western aid, warmer temperatures are enabling the resumption of exports by making domestic demand lower, and across Europe initiatives like virtual power plants for homes are helping balance grids. Nationwide consumption was already down at least 30% due to the war, Halushchenko said, with many industries having to operate with less power.
Renewables like solar and wind power also come into play as temperatures rise, taking some pressure off nuclear and coal-fired power plants.
But it’s unclear if Ukraine can keep up exports amid the constant threat of Russian bombardment.
“Unfortunately now a lot of things depend on the war,” Halushchenko said. “I would say we feel quite confident now until the next winter.”
Exports to Poland, Slovakia and Romania are also on schedule to resume, he said.
“Today we are starting with Moldova, and we are talking about Poland, we are talking about Slovakia and Romania,” Halushchenko added, noting that how much will depend on their needs.
“For Poland, we have only one line that allows us to export 200 megawatts, but I think this month we will finish another line which will increase this to an additional 400 MW, so these figures could change,” he said.
Export revenue will depend on fluctuating electricity prices in Europe, where stunted hydro and nuclear output may hobble recovery efforts. In 2022, while Ukraine was still able to export energy, Ukrainian companies averaged 40 million to 70 million euros a month depending on prices, Halushchenko said.
“Even if it’s 20 (million euros) it’s still good money. We need financial resources now to restore generation and transmission lines,” he said.
Ukraine has the ability to export more than the 400 megawatt capacity limit imposed by the European Network of Transmission System Operators for Electricity, or ENTSO-E, and rising EU wind and solar output is reshaping cross-border flows. “We are in negotiations to increase this cap because today we can export even more, we have the necessary reserves in the system,” the minister said.
The current capacity limit is in line with what Ukraine was exporting in September 2022 before Ukraine diverted resources to meet domestic needs amid the Russian onslaught.
Nuclear fusion breakthrough signals progress toward clean energy as NIF lasers near ignition and net energy gain, while tokamak designs like ITER advance magnetic confinement, plasma stability, and self-sustaining chain reactions for commercial reactors.
Key Points
A milestone as lab fusion nears ignition and net gain, indicating clean energy via lasers and tokamak confinement.
✅ NIF laser shot approached ignition and triggered self-heating
✅ Tokamak path advances with ITER and stronger magnetic confinement
✅ Net energy gain remains the critical milestone for power plants
Just 100 years ago, when English mathematician and astronomer Arthur Eddington suggested that the stars power themselves through a process of merging atoms to create energy, heat, and light, the idea was an unthinkable novelty. Now, in 2021, we’re getting remarkably close to recreating the process of nuclear fusion here on Earth. Over the last century, scientists have been steadily chasing commercial nuclear fusion, ‘the holy grail of clean energy.’ The first direct demonstration of fusion in a lab took place just 12 years after it was conceptualized, at Cambridge University in 1932, followed by the world’s first attempt to build a fusion reactor in 1938. In 1950, Soviet scientists Andrei Sakharov and Igor Tamm propelled the pursuit forward with their development of the tokamak, a fusion device involving massive magnets which is still at the heart of many major fusion pursuits today, including the world’s biggest nuclear fusion experiment ITER in France.
Since that breakthrough, scientists have been getting closer and closer to achieving nuclear fusion. While fusion has indeed been achieved in labs throughout this timeline, it has always required far more energy than it emits, defeating the purpose of the commercial fusion initiative, and elsewhere in nuclear a new U.S. reactor start-up highlights ongoing progress. If unlocked, commercial nuclear fusion would change life as we know it. It would provide an infinite source of clean energy requiring no fossil fuels and leaving behind no hazardous waste products, and many analysts argue that net-zero emissions may be out of reach without nuclear power, underscoring fusion’s promise.
Nuclear fission, the process which powers all of our nuclear energy production now, including next-gen nuclear designs in development, requires the use of radioactive isotopes to achieve the splitting of atoms, and leaves behind waste products which remain hazardous to human and ecological health for up to tens of thousands of years. Not only does nuclear fusion leave nothing behind, it is many times more powerful. Yet, it has remained elusive despite decades of attempts and considerable investment and collaboration from both public and private entities, such as the Gates-backed mini-reactor concept, around the world.
But just this month there was an incredible breakthrough that may indicate that we are getting close. “For an almost imperceptible fraction of a second on Aug. 8, massive lasers at a government facility in Northern California re-created the power of the sun in a tiny hot spot no wider than a human hair,” CNET reported in August. This breakthrough occurred at the National Ignition Facility, where scientists used lasers to set off a fusion reaction that emitted a stunning 10 quadrillion watts of power. Although the experiment lasted for just 100 trillionths of a second, the amount of energy it produced was equal to about “6% of the total energy of all the sunshine striking Earth’s surface at any given moment.”
“This phenomenal breakthrough brings us tantalizingly close to a demonstration of ‘net energy gain’ from fusion reactions — just when the planet needs it,” said Arthur Turrell, physicist and nuclear fusion expert. What’s more, scientists and experts are hopeful that the rate of fusion breakthroughs will continue to speed up, as interest in atomic energy is heating up again across markets, and commercial nuclear fusion could be achieved sooner than ever seemed possible before. At a time when it has never been more important or more urgent to find a powerful and affordable means of producing clean energy, and as policies like the U.K.’s green industrial revolution guide the next waves of reactors, commercial nuclear fusion can’t come fast enough.
Boeing 787 More-Electric Architecture replaces pneumatics with bleedless pressurization, VFSG starter-generators, electric brakes, and heated wing anti-ice, leveraging APU, RAT, batteries, and airport ground power for efficient, redundant electrical power distribution.
Key Points
An integrated, bleedless electrical system powering start, pressurization, brakes, and anti-ice via VFSGs, APU and RAT.
✅ VFSGs start engines, then generate 235Vac variable-frequency power
✅ Bleedless pressurization, electric anti-ice improve fuel efficiency
✅ Electric brakes cut hydraulic weight and simplify maintenance
The 787 Dreamliner is different to most commercial aircraft flying the skies today. On the surface it may seem pretty similar to the likes of the 777 and A350, but get under the skin and it’s a whole different aircraft.
When Boeing designed the 787, in order to make it as fuel efficient as possible, it had to completely shake up the way some of the normal aircraft systems operated. Traditionally, systems such as the pressurization, engine start and wing anti-ice were powered by pneumatics. The wheel brakes were powered by the hydraulics. These essential systems required a lot of physical architecture and with that comes weight and maintenance. This got engineers thinking.
What if the brakes didn’t need the hydraulics? What if the engines could be started without the pneumatic system? What if the pressurisation system didn’t need bleed air from the engines? Imagine if all these systems could be powered electrically… so that’s what they did.
Power sources
The 787 uses a lot of electricity. Therefore, to keep up with the demand, it has a number of sources of power, much as grid operators track supply on the GB energy dashboard to balance loads. Depending on whether the aircraft is on the ground with its engines off or in the air with both engines running, different combinations of the power sources are used.
Engine starter/generators
The main source of power comes from four 235Vac variable frequency engine starter/generators (VFSGs). There are two of these in each engine. These function as electrically powered starter motors for the engine start, and once the engine is running, then act as engine driven generators.
The generators in the left engine are designated as L1 and L2, the two in the right engine are R1 and R2. They are connected to their respective engine gearbox to generate electrical power directly proportional to the engine speed. With the engines running, the generators provide electrical power to all the aircraft systems.
APU starter/generators
In the tail of most commercial aircraft sits a small engine, the Auxiliary Power Unit (APU). While this does not provide any power for aircraft propulsion, it does provide electrics for when the engines are not running.
The APU of the 787 has the same generators as each of the engines — two 235Vac VFSGs, designated L and R. They act as starter motors to get the APU going and once running, then act as generators. The power generated is once again directly proportional to the APU speed.
The APU not only provides power to the aircraft on the ground when the engines are switched off, but it can also provide power in flight should there be a problem with one of the engine generators.
Battery power
The aircraft has one main battery and one APU battery. The latter is quite basic, providing power to start the APU and for some of the external aircraft lighting.
The main battery is there to power the aircraft up when everything has been switched off and also in cases of extreme electrical failure in flight, and in the grid context, alternatives such as gravity power storage are being explored for long-duration resilience. It provides power to start the APU, acts as a back-up for the brakes and also feeds the captain’s flight instruments until the Ram Air Turbine deploys.
Ram air turbine (RAT) generator
When you need this, you’re really not having a great day. The RAT is a small propeller which automatically drops out of the underside of the aircraft in the event of a double engine failure (or when all three hydraulics system pressures are low). It can also be deployed manually by pressing a switch in the flight deck.
Once deployed into the airflow, the RAT spins up and turns the RAT generator. This provides enough electrical power to operate the captain’s flight instruments and other essentials items for communication, navigation and flight controls.
External power
Using the APU on the ground for electrics is fine, but they do tend to be quite noisy. Not great for airports wishing to keep their noise footprint down. To enable aircraft to be powered without the APU, most big airports will have a ground power system drawing from national grids, including output from facilities such as Barakah Unit 1 as part of the mix. Large cables from the airport power supply connect 115Vac to the aircraft and allow pilots to shut down the APU. This not only keeps the noise down but also saves on the fuel which the APU would use.
The 787 has three external power inputs — two at the front and one at the rear. The forward system is used to power systems required for ground operations such as lighting, cargo door operation and some cabin systems. If only one forward power source is connected, only very limited functions will be available.
The aft external power is only used when the ground power is required for engine start.
Circuit breakers
Most flight decks you visit will have the back wall covered in circuit breakers — CBs. If there is a problem with a system, the circuit breaker may “pop” to preserve the aircraft electrical system. If a particular system is not working, part of the engineers procedure may require them to pull and “collar” a CB — placing a small ring around the CB to stop it from being pushed back in. However, on the 787 there are no physical circuit breakers. You’ve guessed it, they’re electric.
Within the Multi Function Display screen is the Circuit Breaker Indication and Control (CBIC). From here, engineers and pilots are able to access all the “CBs” which would normally be on the back wall of the flight deck. If an operational procedure requires it, engineers are able to electrically pull and collar a CB giving the same result as a conventional CB.
Not only does this mean that the there are no physical CBs which may need replacing, it also creates space behind the flight deck which can be utilised for the galley area and cabin.
A normal flight
While it’s useful to have all these systems, they are never all used at the same time, and, as the power sector’s COVID-19 mitigation strategies showed, resilience planning matters across operations. Depending on the stage of the flight, different power sources will be used, sometimes in conjunction with others, to supply the required power.
On the ground
When we arrive at the aircraft, more often than not the aircraft is plugged into the external power with the APU off. Electricity is the blood of the 787 and it doesn’t like to be without a good supply constantly pumping through its system, and, as seen in NYC electric rhythms during COVID-19, demand patterns can shift quickly. Ground staff will connect two forward external power sources, as this enables us to operate the maximum number of systems as we prepare the aircraft for departure.
Whilst connected to the external source, there is not enough power to run the air conditioning system. As a result, whilst the APU is off, air conditioning is provided by Preconditioned Air (PCA) units on the ground. These connect to the aircraft by a pipe and pump cool air into the cabin to keep the temperature at a comfortable level.
APU start
As we near departure time, we need to start making some changes to the configuration of the electrical system. Before we can push back , the external power needs to be disconnected — the airports don’t take too kindly to us taking their cables with us — and since that supply ultimately comes from the grid, projects like the Bruce Power upgrade increase available capacity during peaks, but we need to generate our own power before we start the engines so to do this, we use the APU.
The APU, like any engine, takes a little time to start up, around 90 seconds or so. If you remember from before, the external power only supplies 115Vac whereas the two VFSGs in the APU each provide 235Vac. As a result, as soon as the APU is running, it automatically takes over the running of the electrical systems. The ground staff are then clear to disconnect the ground power.
If you read my article on how the 787 is pressurised, you’ll know that it’s powered by the electrical system. As soon as the APU is supplying the electricity, there is enough power to run the aircraft air conditioning. The PCA can then be removed.
Engine start
Once all doors and hatches are closed, external cables and pipes have been removed and the APU is running, we’re ready to push back from the gate and start our engines. Both engines are normally started at the same time, unless the outside air temperature is below 5°C.
On other aircraft types, the engines require high pressure air from the APU to turn the starter in the engine. This requires a lot of power from the APU and is also quite noisy. On the 787, the engine start is entirely electrical.
Power is drawn from the APU and feeds the VFSGs in the engines. If you remember from earlier, these fist act as starter motors. The starter motor starts the turn the turbines in the middle of the engine. These in turn start to turn the forward stages of the engine. Once there is enough airflow through the engine, and the fuel is igniting, there is enough energy to continue running itself.
After start
Once the engine is running, the VFSGs stop acting as starter motors and revert to acting as generators. As these generators are the preferred power source, they automatically take over the running of the electrical systems from the APU, which can then be switched off. The aircraft is now in the desired configuration for flight, with the 4 VFSGs in both engines providing all the power the aircraft needs.
As the aircraft moves away towards the runway, another electrically powered system is used — the brakes. On other aircraft types, the brakes are powered by the hydraulics system. This requires extra pipe work and the associated weight that goes with that. Hydraulically powered brake units can also be time consuming to replace.
By having electric brakes, the 787 is able to reduce the weight of the hydraulics system and it also makes it easier to change brake units. “Plug in and play” brakes are far quicker to change, keeping maintenance costs down and reducing flight delays.
In-flight
Another system which is powered electrically on the 787 is the anti-ice system. As aircraft fly though clouds in cold temperatures, ice can build up along the leading edge of the wing. As this reduces the efficiency of the the wing, we need to get rid of this.
Other aircraft types use hot air from the engines to melt it. On the 787, we have electrically powered pads along the leading edge which heat up to melt the ice.
Not only does this keep more power in the engines, but it also reduces the drag created as the hot air leaves the structure of the wing. A double win for fuel savings.
Once on the ground at the destination, it’s time to start thinking about the electrical configuration again. As we make our way to the gate, we start the APU in preparation for the engine shut down. However, because the engine generators have a high priority than the APU generators, the APU does not automatically take over. Instead, an indication on the EICAS shows APU RUNNING, to inform us that the APU is ready to take the electrical load.
Shutdown
With the park brake set, it’s time to shut the engines down. A final check that the APU is indeed running is made before moving the engine control switches to shut off. Plunging the cabin into darkness isn’t a smooth move. As the engines are shut down, the APU automatically takes over the power supply for the aircraft. Once the ground staff have connected the external power, we then have the option to also shut down the APU.
However, before doing this, we consider the cabin environment. If there is no PCA available and it’s hot outside, without the APU the cabin temperature will rise pretty quickly. In situations like this we’ll wait until all the passengers are off the aircraft until we shut down the APU.
Once on external power, the full flight cycle is complete. The aircraft can now be cleaned and catered, ready for the next crew to take over.
Bottom line
Electricity is a fundamental part of operating the 787. Even when there are no passengers on board, some power is required to keep the systems running, ready for the arrival of the next crew. As we prepare the aircraft for departure and start the engines, various methods of powering the aircraft are used.
The aircraft has six electrical generators, of which only four are used in normal flights. Should one fail, there are back-ups available. Should these back-ups fail, there are back-ups for the back-ups in the form of the battery. Should this back-up fail, there is yet another layer of contingency in the form of the RAT. A highly unlikely event.
The 787 was built around improving efficiency and lowering carbon emissions whilst ensuring unrivalled levels safety, and, in the wider energy landscape, perspectives like nuclear beyond electricity highlight complementary paths to decarbonization — a mission it’s able to achieve on hundreds of flights every single day.
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