by Planning Engineer
The “green” provisions of the poorly named Inflation Reduction Act are sweeping and it appears they may do more harm than good. The philosophy behind the inflation Reduction Act seems to reflect the belief that if you can get the ball rolling, adding additional wind and solar will get easier. However, as Part 1 discussed, the compounding problems associated with increasing the penetration level of wind and solar generation are extreme.
Replacing conventional synchronous generating resources, which have been the foundation of the power system, with asynchronous intermittent resources will degrade the reliability of the grid and contribute to blackout risk. The power system is the largest, most complicated wonderful machine ever made. At any given time, it must deal with multiple problems and remain stable. No resources are perfect; in a large system you will regularly find numerous problems occurring across the system. Generally, a power system can handle multiple problems and continue to provide reliable service. However, when a system lacks supportive generation sources, it becomes much more likely it will not be able function reliably when problems occur.
Just as a pile of dry wood and flammable material can be sparked from many potential sources, or a very unhealthy person could succumb to many different threats, a weakened power system is more vulnerable to many conditions than a robust one. In this post I discussed responsibility for the Texas winter blackout. Many things went wrong that day in Texas. But often many things do go wrong – the real problem was that the Texas market did not provide incentives for standby resources. In Texas there were not enough committed resources to provide for the system load levels and potential contingencies. Texas relied on an energy market designed to favor wind and solar resources and it failed them. However, many analyses of the Texas blackout focused on the proximate conditions (problems of the sort that are common) ignoring or denying the major underlying problem.
We are seeing blackouts and system problems all over the world now, unlike in the past. There is a common factor for most – high penetration of intermittent asynchronous wind and solar generation. This commonality is generally ignored when evaluating the individual outages as vested interests focus on the triggering conditions. There are always going to be potential triggering conditions. No one anywhere will eliminate triggering conditions so absolving green resources of blame because such things exist in the real world only makes sense as theater. When faced with “green” outages, focusing on the proximate triggers serves to protect “green” interests and helps mask the emerging greater problems to come.
The Inflation Reduction Act is promoting a system with less stability, robustness and reliability. Besides describing how these green programs contribute in general to major outages, I will conclude this article by identifying a specific type of outage likely to become more common due to provisions of the Inflation Reduction Act. Before describing how the Act impacts the system, I will take a detour and describe a specific past incident where a system element which was valuable at one penetration level became a system detriment at a higher penetration level.
Penetration Case Review: Heat Pumps
A heat pump is an efficient way to heat or cool. As a refrigerator transfers the heat out of the refrigerator to the coils in the back to cool or freeze your food while making your house warmer, a heat pump can transfer heat between a home or building and the outdoors. In the winter it transfers heat from the outdoors to the interior. In the summer it transfers heat from the house to the outdoors. With a heat pump you don’t “create” heat you merely use a small amount of electricity to efficiently transfer heat in the preferred direction.
Even when the temperature is cold outside a heat pump can extract heat from the outdoors and use it to warm a home or residence. As the temperature drops below 40 degrees. However. heat pumps become less efficient and as temperatures drop below freezing, the home must be heated with a backup method, usually resistance heating. Resistance heating makes the process more expensive and inefficient. It is possible to exchange heat with a source below the ground or a source of water to get around this problem, or alternatively to provide heat from natural gas backup, but these approaches have not worked out as practical means on any significant scale.
Because of their behavior at colder temperatures, heat pumps are not appropriate for all parts of the country. In the north the many hours they would have to run with resistance heat makes them both environmentally irresponsible and too expensive. Natural gas is a better option. They work where it is hot enough some of the year that air conditioners are installed anyway (thus they don’t increase the summer peak) and where it is cold but not too cold at most times. If they run in resistance mode only a few days a year that does not cancel the net benefits, but with longer time periods the benefits are lost.
Encouraging heat pumps was all the rage, when I first started working in the southeastern US. Most entities in the south did not see winter peak loads, so adding heat pump load in the winter was a great thing. It was a win, win, win situation for all involved. The economics work generally the same for all utilities, but I will describe how they worked for distribution cooperatives.
Distribution co-ops pay a demand charge based on their peak load and an energy charge based on their kwh usage. Residential sales are on a kwh usage, so the peak charge must be recovered through the kwh charge imposed on residential customers. The better a Co-ops’ load factor (total kwhs sold/(peak demand*total hours), the lower their rate can be set. Heat pumps did not raise the demand charge, but increased energy sales and allowed the demand charge to be spread out over more energy sales lowering energy costs for all.
Builders were rewarded with free underground distribution if they committed to building all electric homes which relied on heat pumps. Rebates were given for heat pump installations and often those installing heat pumps were rewarded with free water heaters. My company had a big marketing division supporting the work of the distribution cooperatives to support efforts at increasing heat pumps. It worked well, almost perfectly. The only drawback was that on very cold days the heat pumps would switch to resistance heating and this made the customers’ meters spin at high consumption levels, raising heating costs a lot that day. But with incentives and the saving at most times, those costs were not that significant. The overall winter load increased a lot on those days, but it was still below the summer peak at most times. Plus, when it’s cold you can put a little more load on the power lines and fossil fuel generators can provide more power without overheating. So, the heat pumps did not contribute to increasing fixed costs.
Everything was going well as the penetration level of heat pumps increased. But there was a cloud on the horizon. Looking ahead it seemed like that within the decade our winter peak would move to surpass the summer peak. This meant that the winter peak would soon drive the need for improvements and expansions. Unfortunately, what should be technical disagreements are often political problems as well. In a battle of experts, the consultants working for the marketers disputed the trend. The programs continued and everything was great in the short term.
Sooner than expected the winter peak did hit and it hit hard and it hit regularly. On the coldest days when the resistive heating kicked in, peak demand rose sharply and swiftly. The winter “needle shaped” peak drove investment and costs. The mostly residential cooperatives who had invested big in the heat pump programs had to pay rates based on their demand during the new winter peak, greatly raising their average energy costs.
While almost no one wanted to see it coming, once the effects hit, most everyone in the power supply chain wished they had. This was a terrible blow to rural electric cooperatives who had invested big to improve their load factor, only to find they had subsidized a worse winter load factor. Residential customers are not charged for contributing to peak demand (the meters don’t measure that) so for them their contribution to the demand charges has no significant penalty. For customers in this region, it still makes sense to put in heat pumps so the problems continue to grow for some to this day.
The Inflation Reduction Act Enabling Blackout Conditions
The Inflation Reduction Act seeks to decarbonize the grid. In looking at the grid, you should not make one goal a priority but should instead seek to balance competing objectives. See Balance and the Grid for a discussion of how efforts to maximize one objective without due attention to other major goals can result in a worsening condition for all goals. It seems apparent that all the “green” measures in the Inflation Reduction Act were included because independently they all seem capable of reducing carbon. I have not seen any evidence that any consideration was given to system reliability or how these measures might interact to create problems.
The green measures encouraged by the inflation Reduction Act will lead to generic blackouts in many situations as described earlier in this essay and in Part 1. Presented below is a chart from a previous posting, titled “Will California “learn” to avoid Peak Rolling Blackouts?” The projected peak that was causing blackout concerns was only around 10% above the average for the previous year’s included in the chart.
The specific prediction of an outage condition I will make here involves winter peak demand conditions. Winter peaks can be extreme, much more so than summer peaks. As temperatures climb in the summer, air conditioners reach a saturation point. The climb in summer peak demand with each additional increase in temperature typically flattens out. In the winter each additional degree drop can increase demand more than the one before. There are a lot of potential sources of resistive heat that increase demand. In severe cold more and more heating elements come into play and the increase in demand rather than flattening can go up exponentially. Peak winter loads tend to hit just before sunrise. The system sees a rapidly rising peak, often described as needle shaped, which drops as the sun comes up and temperatures warm. Such peaks can easily be 5 to 20% above normal winter peaks in many areas. Thus these conditions have the potential to cause more severe concerns than California sees during extreme summer conditions.
The Act encourages solar at the bulk, distribution and residential levels. Solar will be of no benefit during such a peak, but does serve to push out other resources which might support the system during such conditions. Plus, there is a double whammy. Solar power supply supplied to the grid will not be there and at that same time homes usually supplemented with solar will be putting maximal demands on the grid. (Note -The infrastructure needs to supply a home which only puts a demand on the system a few hours a year concurrent with other uses maximum demand is basically the same as the infrastructure need to support a full requirements home. It is challenging to collect that from such customers. When there are rate challenges and it’s difficult to collect system costs, needed infrastructure often is delayed.) In any case widespread adoption and reliance on solar creates concerns around winter morning peaks.
The Act encourages wind development. Like solar, wind will push other better suited resources out of the supply pool. Wind is generally slower just before sunrise and winter is not generally peak wind season. In any case wind is intermittent and some of the times during cold weather wind is not available. Some say that wind tends to rise up as temperatures get colder and there are ways to keep turbines from freezing,. Nonetheless, we do see freezing problems and a tendency for wind to be there is not a guarantee. Green resources perform much better in theory than practice. At least at sometimes wind power will not likely be a great asset during winter morning peaks demand conditions.
The Act encourages efficiency. This could help to reduce load and thereby make severe outages less likely. But the real problem with peak demand is the difference in demand during the extreme peak period and other more normal high load periods. If efficiency reduces load, you will likely see a reduction in generating resources to serve the load at all high load levels. The risk from peak conditions is more attributable to the delta between the winter peak demand and more common high load levels. This is because regular loads drive generation additions more than extreme conditions. I don’t know that efficiency measures work better during the most extreme winter temperatures than it does at normal winter cold temperatures (probably less so), therefore its mitigating impact may be small to none. Also, there are those who might argue that consistent with Jevon’s Paradox efficiency efforts lead to increased energy consumption. The basic mechanism, behind this counterintuitive theorem, is illustrated by mechanisms observed such as individual consumers with more efficient homes choosing to heat more rooms or increase comfort because you get more for your money in an efficient home.
Solar, wind and efficiency are intended to decrease fossil fuel-based resources. Combustion turbines and hydro are generally the most appropriate resource for limited duration demand surges. The expansion potential of hydro is very limited and this resource can not make up for lost combustion turbines in most areas. Combustion turbines perform relatively well in cold conditions and old mostly useless units traditionally have been called on to get the system through short term peak demand conditions.
To be fair, the Act does encourage energy storage and that should help somewhat with peak demand concerns. Care is needed as batteries do not give their best performance in cold temperatures. But in light of all the other changes that is a huge burden to place on technology at this stage of development.
The chart below shows the US typical resource generation by major energy source. Imagine how this chart will look as fossil fuel is phased out. Hydro only makes up about 6% of the mix and expansion there is limited. Nuclear could replace these resources but it is not great for ramping up and down to follow needle peaks. If wind and solar step up to replace fossil fuels this leave us vulnerable to energy shortages during winter peaks just before daybreak. Battery capability would need to be huge, expansive and probably would not be procured in advance of demonstrated needs.
It is frightening to imagine how to serve a vast winter system demand just before daybreak in the green future. But one more feature of the Clean Air Act helps raise concerns to an even higher level. The Inflation Reduction Act subsidizes heat pumps!
Heat pumps are attractive to the Inflation Reeducation Act for only one reason. They help reduce the demand for gas furnaces. Subsidies will be available in areas where today heat pumps are not considered practical. Today it doesn’t make sense to drive resistance heating with electricity generated from fossil fuels. It’s inefficient and environmentally unsound. However, you can theorize that if all electricity is green, inefficient electric heat is green too. Replacing natural gas heat with heat pumps is not a good idea when one considers their impact on the power system during winter peak conditions.
Under the Act’s subsidy provisions people who live in areas where heat pumps don’t make sense may decide to get them anyway with the subsidy. For example, if you live in a cooler area and you’ve gotten by without air conditioning, now your units can be subsidized and the resistance heat will be there for you in the winter too. Green advocates talk of shaping the load to better use resources, but that evidently can be quickly forgotten when other green objectives emerge. Putting in a bunch of heat pumps and building tremendous infrastructure to support their short-term demands is far from environmentally responsible.
Specific Blackout Prediction
With a lot of help from the Inflation Reduction Act, we will likely see these full set of conditions in many areas:
- Very cold pre-dawn extreme temperatures
- Backup quick start fossil fuel combustion turbines have been largely driven out of the resource mix,
- Nuclear, hydro and battery resources are tapped out
- Solar is absent from the distribution side and not available on the generation side
- Wind may or may not be blowing
- Heat pumps are operating maxed out in resistance mode, along with other resistive heating to drive system load to extreme heights
- As with every power system there will be a few problems on the system
- System will be forced to deliberately shed a lot of load or may go unstable and suffer crippling blackouts
To the extent as claimed by some, climate change is driving more extreme winter peaks in the near term, we may see this situation sooner than later. In any case green measures are driving us there with current historical weather patterns. Being without heat and power in extremely cold conditions is highly problematic for most individuals, businesses and industries.
What can be done to prevent such blackouts? Unfortunately, not much attention seems to have been paid to concerns of this sort. It might be argued we need vast surpluses of wind and storage (those not paying attention may argue we need more solar) to support winter load. The cost and environmental impact of these extra mostly underused resources would be large and prohibitive. This would be true weather the resources were wind, solar, batteries or nuclear. Keeping older already manufactured combustion turbines around for emergency conditions would be a much more reasonable means of mitigating risks. The additional environmental impacts of using something already manufactured and placed in service are small compared to building extensive new resources, no matter how green these resources may be claimed to be.
How do we encourage smart ways to provide emergency capacity? Current energy policies are seeking to direct as much money toward “green” resources and costs away from them. As discussed earlier, in Texas they are moving away from recognizing capacity value consistent with a trend towards energy only markets. I’m a big fan of markets, but they don’t do a good job of protecting against extreme conditions especially when no one has ultimate responsibility (except governmental entities) for ensuring load is served. Some measures would need to be employed to compensate for providing and ensuring combustion turbines are available for emergency conditions. But no one seems to be talking about such measures. The Inflation Reduction Act appears to be a single focus approach to a nuanced problem. Cut CO2 emissions and hope for great innovations. Reliability threats apparently are not on their radar, nor are they an articulated or contemplated concerns. It’s a shame because reduced reliability can wreak havoc on the economy and the environment.
Subsidies lead to malinvestment, as wind and solar are weather dependent. Failing to account for wind falling to 3% of rated power during a heat wave, as recently happened in Texas, is inherent with subsidizing wind and solar.
I wish the title was more specific, saying “Increased use of wind and solar power will increase the number of electrical grid blackouts”.
As you add more weather dependent “unreliables” to an electric grid, that grid gets less reliable! The problems may be small until some tipping point is reached — that’s a level of dependence on solar and wind that can no longer be managed. The band-aids of buying electricity from other states and begging customers to reduce their electricity demand don’t work
The chart in the article, as is common, includes hydro in the “renewables” category, which can obscure the small amount of electricity from wind and solar power.
Here’s a detailed breakdown of renewables for the US in 2021.
I would add one word; ““Increased use of wind and solar power will exponentially increase the number of electrical grid blackouts”.
There is an asynchronous wind/solar grid problem beyond intermittency and the need for backup. Unlike spinning generator masses, they provide no grid inertia. That means that as their penetration goes up, voltage/frequency sags occur more frequently (aka brownouts). And the system is designed to ‘trip’ (aka blackout) if this sag exceeds as little as 5% of nominal, in order to protect the system. So the system simply becomes inherently ever more unstable.
The more you add heat pump and EV charging loads, the worse the stability problem gets. There is no ‘fix’ no matter what AOC might believe.
I beg to differ, albeit just slightly.
A direct connected compressor on a heat pump will contribute a little bit of stability as an induction motor does have some inertia. In addition torque vs slip characteristics will provide some damping of local frequency swings. An inverter driven compressor will not provide any help and neither will resistance heating.
EV charging loads can help if the charge rate is adjusted by line frequency, especially with load is shedded when frequency drops more than 0.2 to 0.3Hz.
Having said, I found Planning Engineer’s article to be spot on.
The new air-source heat pumps are all inverter-driven.
Are you telling us that HVDC transmission lines decrease stability? They don’t transmit “inertia.”
You do not understand grid inertia. Has nothing to do with HVDC transmission, which is ‘fed’ inertia at the ac/dc end and disgorges it at the dc/ac end. Has everything to do with massive (~600 ton) rotating generators that also behave as flywheels providing the grid inertia.
You do not understand that the inverters that change the HVDC to AC do not disgorge inertia at the dc-ac end. If they did, then the inverters that change solar panel DC to AC to feed the grid would do the same.
I think he understands that perfectly. You seem to misunderstand him?
Actually this is an interesting technical question on which I could use some informed discussion, namely the impact of large HVDC imports on grid frequency stability.
The earliest HVDC converters were big motor-generators, so they would have spinning mass to contribute inertia to the importing grid. But as I understand it newer links use solid state devices of one type or another. I assume frequency and phase are matched to the destination grid. Does that match automatically adjust should the grid frequency shift, or does that trip a frequency protection breaker and disconnect?
In other words, does a large HVDC import damp, magnify, or simply ride out frequency fluctuations on the importing grid?
Thanks.
Looking through the reportable disruptions for the UK grid (i.e. excursions of more than 0.2 Hz) you will find that HVDC trips are now the most frequent cause. In recent times those excursions have often been upwards when an exporting link fails, but downward was certainly common in import mode. These trips tend not to be at all graceful, so 1GW or more can disappear at once.
The fashion now is looking to grid forming inverters – I.e. with some capability to provide ancillary services including frequency response. It’s still relatively primitive and limited AFAICS, but research is being funded.
That reality has been solved in South Australia by the addition of synchronous condensers. They provide the inertia for the millisecond domain. The system requirement to order gas turbines to run for stability has disappeared since the synchronous condensers were commissioned.
Batteries now take a big slice of the 6s FCAS market in Australia despite their relatively small capacity.
You will never find the line item “synchronous condenser” in any academic paper making estimates for wind and solar projects.
Good report. Synchronous condensers are basically unpowered generators, providing the grid inertia. BUT they are as expensive as replacement generators, without the grid power benefits.
When you say “unpowered” I assume you mean there is no mechanical power applied to the synchronous condenser in order to generate power. There is, however, electrical power applied to the synchronous condenser which is what allows it to correct for power factor. If that electrical power supplied to the stator and rotor disappears (e.g. in a blackout) then I don’t understand how the synchronous condenser can supply power to the grid. That means either a backup generator or battery/inverter supply has to be available to excite the synchronous condenser. With nothing to sync to on the grid then you could wind up with multiple synch condensers fighting each other for frequency control with all the problems that implies.
The condenser simply provides VARS to the grid, it is a synchronous motor drawing real power from the grid to spin at 60hz and then operating in Leading power factor mode to provide Vars.
I am aware of a project, a person i know working with siemens to provide 3x200MVA synchronous condensers in the Baltic states to stiffen the grid in anticipation of cutting off from Russia.
The opposite of an induction generator which is simply an induction motor spun by a gas engine to match 60hz, breaker closes and the induction motor draws Vars from the system to provide exciting/magnetizing current to the machine, then the engine increases power but not speed to export KW. Cheap way to get use out of stranded gas, convert to electricity on the grid with small induction generators where needed, but then you need additional VAR support on the Grid.
I think early wind turbines were induction generators but the downside is it has to get up to rated speed in order to be connected to the 60hz grid, they drew VARS from the grid but then the rotating mass of the blades could provide inertia.
Speed issue was fixed by switching to DC generation then using inverter to provide 60hz output, allowing wind turbine to produce usable power over a wider speed range but then sacrificing whatever inertia it could provide.
As always, the lesson is there is no free lunch. For every action there is an equal and opposite reaction.
I would suggest using a bank of supercaps for providing a few second long bursts of power (both sourcing and absorbing power).
SDG&E installed a large synchronous condenser in Oceanside a few years ago, with on the order of one hundred tons of rotating mass.
Perhaps one way of encouraging large renewable generators (i.e. solar and wind farms) to help the cause is to base any subsidy (production tax credit) on the lowest output over the course of an hour. The way things are set up now, there is little penalty for pauses in generation.
How about not subsidizing them at all?
I think you’ll find that supercaps are a DC generating source. They won’t provide for frequency stability. They would still require DC-AC inverters to feed the grid just like batteries would. They might be useful for milli-second voltage sags but not for longer time periods.
Tim, supercaps are best suited for supplying a few seconds worth of power. Trying to discharge one in less then a second will generate a lot of heat.
The next paragraph probably won’t make much sense to anyone who hasn’t had much exposure to electric power system analysis. The transfer of power between two nodes on a transmission line is given by P=sin(delta)xE1xE2/Xline where delta is the phase angle between node 1 and node 2, E1 and E2 are the terminal potentials at node 1 and node 2 respectively and Xline is the series impedance of the transmission line at line frequency (this gets a bit messy when lines get longer than 100 miles). Two key points; First is the line acts like a torsion spring; Second is all hell breaks loose when delta exceeds 90 degrees.
My idea of using suercaps for grid stabilization is to counteract parts of the grid oscillating with respect to each other. By using power to charge the caps when the local line frequency is higher than system average frequency, and discharging the caps when the local frequency drops below line frequency. This is to dampen the torsional oscillation of the local node with respect to the rest of the system. The energy going in and out is MWs not MVARs.
While I haven’t worked for an Electric Utility, I have taken a few electric power systems courses including a couple of fun labs along with an electric machinery course.
Not sure what charging the caps when the frequency is too high or discharging when it is too low will do to help with frequency stability. Phase difference between two distant points or between voltage and current really isn’t dependent on generation frequency.
I suspect what you are really trying to get across is that the caps would be used to correct leading and lagging V/I phase. That’s really what capacitor banks already do when placed near locations with large electric motor loads. That doesn’t help with frequency stability, it only helps reduce the power factor. The supercaps would be helpful for milli-second voltage sags but their exponential discharge curve wouldn’t hold up the voltage very long. Using them with inverters that are automatically adjusting for input voltage would be a better use but would not help power factor correction much nor would it provide much inertia to the grid.
Do a search on “equal area criteria” for power system stability, because you don’t come across as understanding power system stability issues (albeit very few people who haven’t studied electric power systems understand the stability problem). The issue I am talking involves the power system response to transients such as sudden change in load, a generator tripping, or a transmission brought on line or much more serious problem as when a line trips carrying a heavy load. The last example is where the “equal area criteria” becomes important – even though the surviving line(s) can carry the additional load on a steady state basis, they may not have enough margin to keep the system in synchronism immediately after the line trip. THAT is the issue I was suggesting as a use for ultracaps and inverters. These would have to be sized to provide on the order of a few hundred MW for a few seconds to be useful.
Power transmission lines are just that – transmission lines. They can be modeled using lumped capacitance and inductance. As such they cannot impact frequency, they can only impact voltage and current values and/or phase between voltage and current.
As load transients are applied to the grid they can affect the generator connected to the transmission lines and cause it to change frequency. Think grabbing the business end of a hand drill. You can cause its rotational frequency to change by the load you apply using your hand. This is where rotational inertia becomes very important to maintain frequency control on the grid.
The supercapacitors that I know of are all low-voltage devices. They are unusable as power factor correction banks on HVDC or even residential/industrial distribution networks. That means their main use would be as battery replacements sitting behind inverters. As such they would only be useful for support with short-term transient loads, they would provide no frequency support or power factor correction for inductive loads. The inverters themselves might be able to do so but not the supercaps themselves.
Therefore the supercapacitors would have to compete with present battery products for supporting the grid. You will have to provide some actual data to support that supercaps would be a viable replacement for battery banks.
Just an fyi – I had two study concentrations in my EE studies 50 years ago – power and nuclear. I worked for a power company for two years and am familiar with the use of capacitor banks to correct for power factor. I worked for a telephone company for 30 years including designing outside cables and using load coils for correcting the capacitance of long twisted pair cabling. I’ve been an amateur radio operator for 60 years and am very familiar with RF transmission lines and antennas.
Equal Area Criterion only applies to systems that *have* inertia and is a way to measure the response of the system to fault transients. Supercaps won’t prevent faults in any manner since they wouldn’t be able to hold the system up over the time periods a true fault (e.g. a limb on a power line) will entail. Other protective devices and strategies are needed to protect against such faults. In a system with no inertia, i.e. “renewables”, such faults are truly a problem. But they are ones that supercaps won’t help.
As mentioned in an earlier post, I did have a couple of power systems labs. Some of the experiments involved simulating opening and reclosing breakers on one of two parallel transmission lines. Opening the breaker created themost dramatic response, where the generator’s relative phase angle would oscillate around the steady state power angle for single line operation – and those oscillations were very audible and the needles of the wattmeters and ammeters would be doing some significant wiggling. The problem is that the power angle can swing past the point where the operational line can maintain synchronism.
The oscillations are typically dampened by the damper windings on-line synchronous machines, with a bit of damping from on-line induction machines. The damper windings are essentially a squirrel cage induction motor, and the damping action occurs with the dampers causing and increase in power generated when the generator shaft speed was higher than synchronous speed and decrease in generation when shaft speed is lower than synchronous speed. The periods of these oscillations can vary from seconds to minutes.
My suggestion with ultracaps combined with a converter is to increasing damping by absorbing local power when the local line frequency increases to compensate for the excess generation and supplying local power when frequency decreases. Li-PO batteries would be a substitute for ultracaps, especially if the period of system oscillation is more than a fraction of a minute.
Again, this is a subject that is very rarely found outside of books focused on power systems anlysis/engineering — most of the EE’s I know don’t have a clue about power systems stability, and these include a number of very bright people.
In summary, loads on the distribution system are current related, not voltage related. Voltage should be pretty constant except in the case of major faults and backup systems like batteries or supercap couldn’t help control those faults any more than the base generation could. Fault isolation systems are what controls those. Since both supercaps and batteries sit behind inverters neither provide much for frequency stability. Once both are at maximum charge neither are much use in “absorbing” energy, where would that energy go? Into heating the caps or batteries?
If the line voltages begin to sag, say from reduced “green” generating capacity at night, then either could help supplement the power requirements. But on a cost basis, batteries would win every time because of their discharge characteristics compared to capacitors.
FYI Rud, a 1,5 MW wind turbine has 3 blades, each weighing 6 tons. A wind farm with 100 of these turbines has 1800 tons of rotating mass right?
They’re not welded together and rotating in perfect synchronization.
Neither are the shafts of the generators at Hoover dam:
..
https://fineartamerica.com/featured/3-hoover-dam-generator-hall-mark-williamson.html
They are governed and operated so the rotors are in sync with the grid at 60hz, their output does not pass through an inverter which then creates 60hz.
You don’t seem to understand the difference.
The generators at Hoover are synched together. Windmill generator blades are *not* synced together. They operate independently. The inverters at each windmill are synced to the grid. When that disappears then they have no inherent frequency control.
Wind turbines with AC synchronous generators don’t have inverters.
Greg, that does not matter, those turbines feed their power through an inverter to the grid.
It is not a synchronous generator, it operates at a range of wind speeds, which the inverter converting it to 60hz, but that rotating mass provides no inertia to the grid because of the inverter in between, it cannot.
There are now some fancy electronics that attempt to tap the very limited inertia available from the turbine blades just to show it can be done. It really isn’t worth it. Most high renewables grids now rely on batteries to provide an element of synthetic inertia – injections and withdrawals of power as grid frequency changes. It is vastly more expensive than simply relying on conventional generation that provides inertia automatically in accordance with the laws of physics.
Not true. There are wind turbines that have synchronous generators (aka DFIG) https://www.ge.com/renewableenergy/wind-energy/onshore-wind/2mw-platform
If I understand DFIGs correctly, they are designed to reduce stress on the rotors and blades of wind turbines due to wind speed changes if their output was frequency locked to the grid. Given that goal I would expect they would simply allow the turbine to spin at the speed dictated by the wind and adjust the frequency output to match the fluctuations in the grid.
IOW, the inertial energy would not be used to buffer or damp grid frequency dips and spikes.
Someone who knows for sure should chime in.
As you should know inertial energy is given by Iω^2. The rotational speed of a gas or steam turbine generator is 3600 rpm for 60Hz power. The rotational speed of wind turbine blades is roughly proportional to wind speed between cut in speed and the point at which it reaches maximum power output, when it is limited by progressive feathering of the blades. The maximum rotational speed is also inversely related to blade diameter because of aerodynamic limitations on tip speed. The result is that even at maximum rotation speed the wind turbine is providing well over 10,000 times less inertial energy per tonne of mass. At medium and lower wind speeds it becomes completely insignificant.
Greg:
The problem is the turbine shaft speed is not constant, so if turns a conventional AC generator then the output frequency will vary. There are several ways to deal with this. The simplest is to generate DC then invert it. This provides no inertia, and was common on earlier and smaller turbines. Newer and larger ones use a Variable Speed Constant Frequency Generator. I don’t know for sure whether this provides any spinning mass on the output side, but I suspect not.
Exactly. I call it elasticity. It will especially show up when someone tries to start large motors, that “flicker” will only get worse the more renewables penetrate a grid, requiring expensive solutions to mitigate that. Eventually customers will have to call grid authorities for permission to start their system, a real efficient way to operate a business.
It will especially hurt resource industries like we have in Alberta which uses a lot of large motors.
Good post, Rud. I would like to add that nuclear plants have relays that sense the line voltage and frequency from the offsite power system that is the source of power to the motors needed for safe shutdown and accident mitigation when a unit trips offline. if that offsite power has too low a frequency or voltage for a specified time, it will trip the nuclear unit. The units will shut down safely, but if this happens due to blackout or brownout conditions, you can kiss the power from any nuclear unit goodby. And you cannot reconnect them to the grid until it is stable, they will be the last units to be reconnected.
Like this cold evening in Illinois this January, no sun, and wind is <3mph, often zero mph.
I read that wind turbines are pretty much useless at <5mph, preferring >14mph for optimum.
An inflation reduction act is not needed. What is needed is an Election Fraud Reduction Act.
For the activists that wrote it & the politicians who voted for it blackouts are a feature not a bug.
Great article. A very important point about heat pump systems is made here about the automatic switch to electric resistance heating mode in cold conditions. The unintended consequence of a “needle” shaped demand spike on the system on the coldest mornings is a big problem. Here in NY there is a big push for heat pumps and irrational hostility to natural gas. So here we are sitting on the Marcellus and Utica shale gas formations with a ban on fracking, and the authorities are pushing “climate action” ideas that will not age well when reality bites.
The IRA Act might cause confusion but some more stock opportunities for government employees.
What is solar geoengineering: sunlight reflection, risks and benefits (cnbc.com)
Once a dystopian fantasy, manipulating sunlight to cool the earth is now on the White House research agenda
Federal Officials Trade Stock in Companies Their Agencies Oversee – WSJ
Government officials invest in companies their agencies oversee | Fox Business
Reduce inflation by more runaway spending?
It’s amazing how many economists continue to believe government spending cannot cause inflation. This is obviously false.
Giving people money with out any productive work (production of goods or services) creates money to spend, but NO goods of services to buy.
So, more money chasing fewer goods, the result is by supply and demand, higher prices.
There is NO other way.
Yes. Next stupid question, please.
@Planning engineer….I presume we are talking about air/air heat pumps… In specific locations (where suitable) a ground source heat pump is a better solution. In the absence of geo-thermal sources average water temperature is in the range of 50°-60°F.. and it is constant thus alleviating some of the wild temperature differentials. Thus a smaller resistance heat unit is necessary.
Beg to differ. We looked into a ground sourced heat pump versus propane furnace when building our north Georgia mountain cabin (3 story 3br/bath). We had an ideal ‘cost less’ spot for the ground piping, the earth backfill over our big buried septic system (even some decomposition extra heat). North Georgia mountains do see frost and occasional snow (which melts in a day or so), but generally not a lot of nights well below freezing. Ground heat pump unequivocally did NOT work out according to the engineering experts we hired. We went 95% efficiency propane furnace.
In N GA you should have plenty of wood to burn. I’ve got around 5 years worth stacked, burn in open hearths. Fun to cut, split and stack. And being a solid fuel I’m not worried about black outs this winter. We will be warm even if they turn off the electric and gas.
A lot depends on the depths of the water table. In most places it’s too far down to be economically viable.
The problem with ground sourced heat pumps is that the installation cost is many times greater than air sourced heat pumps. In many cases, the small efficiency increases will never recover the extra cost.
Yup. That is what we found on our property.
Consistent with Rud’s experience in many areas ground source is not practical. No doubt in some areas ground source is a better solution. Question is in these areas is gas or propane better yet. I would guess overwhelmingly. I would have some respect for the inflation reduction act if it addressed ground source heat pumps as opposed to just pushing generic promoting air/air. Seems that would be more consistent with their goals,
“However. heat pumps become less efficient and as temperatures drop below freezing.”
Modern heat pumps work very well below freezing…..
” heat pumps are not appropriate for all parts of the country”
Not true either
https://www.blocpower.io/posts/cold-climate-heat-pumps
Never one to be shy of an opportunity to go subsidy mining, I got a flyer yesterday to swap out my electric hot water tank for a heat pump hot water system. Total cost $33.
Seems like a good deal, but really depends how quickly they can take a tank of cold water to hot. Are they much slower than resistance heating?
https://www.energy.nsw.gov.au/households/rebates-grants-and-schemes/upgrade-your-hot-water-systemo
Define “works well”…. if you don’t mind having a “heating” system that blows cold air on bitterly cold days! Sorry, I want a heating system that actually produces heat – as in hot air coming from a register or hot radiators.
This ^
Modern heat pumps work well when the resistance heating kicks in. Much higher cost and very low efficiency. That’s why my parents didn’t keep their new heat pump after three years. They changed over to a nat gas furnace!
There is almost nothing that is more efficient that resistance heating. The inefficiency is at the conversion stage, and new NGCC systems are above 60%.
as I understand it this new technology in the testing stage with questionable results. Correct me if I’m wrong but progress wise they are where batteries were a decade or so ago. I will keep my eye on BlocPower but they may be tooting the horn prematurely, Though as a green industry I am sure there are many opportunities for them whether they pan out or not. THe Act is good for theM. https://www.cnbc.com/2021/05/25/blocpower-disruptor-50.html
Who’s theory? The guaranteed output of a wind turbine is ZERO. You can call that the RickWill theory of wind turbines. Not quite as technical as the Betz limit but supported by years of sailing experience.
Any utility using wind generators in reliability calculations will not be very reliable.
The east coast grid in Australia is facing the paralysing dilemma of either paying for reliable fossil fuel generating capacity or incredibly expensive batteries. Paying for fossil fuel capacity goes against ever fibre of green desire and paying the huge cost for batteries has to force up power prices, going against the promise that electricity prices would come down.
Let’s state the obvious here: electric heat pumps do not work when the power goes out.
Homes heated with natural gas also have electricity hooked up and thus they have 2 possibilities for heat. Wood stoves are banned where I live. If fossil fuels are also banned, when the power grid goes down in winter, there is zero heat. (Wood pellet stoves are ok here, but they require electricity to operate.)
Is killing the citizenry the goal with this green nonsense?
You might still be able to get a gas fired room heater that operates with a standing pilot or battery powered electric ignition and millivolt thermocouple control. These will operate just fine with no electricity. Of course the enviro-zealots are getting these banned wherever they can. I have a wood stove (~75% efficiency) and a propane fired room heater with a millivolt control. Also a lot of south facing glass and substantial passive solar heating on sunny days. So we can at least stay warm and keep pipes from freezing even during extended winter power failures. Water is more of a problem, but if necessary can fill a barrel and bring it home.
Or get a nat gas water heater like I have. Doubles as a source of water for drinking as well as for everything else.
Let’s pick a state for an experiment on the viability of green renewables. California just raised its hand. What we do is isolate California from any fossil fuel power production and see how long it can last. Evaluate the evidence and see if we really want to go “renewable”. The question would be, how many people in California do we let die before the rest of the country steps in and stops the madness.
I would strongly disagree with the statement that heat pumps and fossil fuel systems do not work well. They work extremely will allowing the best of both from a comfort level and an economy point as well. My system is a heat pump with hot water backup. The boiler is cold start so only runs when extra heat is needed. Also I have a de-superheater on the system which provides most of my domestic hot water. That makes the hot water free in the summer and cheap in the winter. Even when oil was around $2.50 a gal the heat pump was less expensive to operate through most of the winter. I have an older 13 SEER pump. Really need to upgrade. In the eastern PA section where I now live a properly sized single stage heat pump should reach the break even point around 20 degrees but depending on the efficiency of the heat pump, cost of fossil fuel, the price of electricity and the insulation of the house the economy crossover point may be higher. One of the problems with heat pumps is that they also cool as well. It is typically sized for proper A/C and in cooler climates that will make it to small for the heating season. An inverter heat pump can be better sized for the heat load since they will operate at reduced load to match the cooling needs in the summer. Add to that the efficiency has greatly increased even at colder temperatures. Ground loop heat pumps in this area are usually somewhat more expensive because they need the loop to be vertical. Drilling holes in the ground is not cheap but over the life of the heat pump there will be money in the pocket. The efficiency is rather impressive with SEER ratings in the early 30s. In most cases the electric backup in a ground loop system is really emergency heating should the heat pump fail. To summarize: Duel fuel systems (electric and fossil fuel) work extremely well allowing the use of both worlds. The efficiency of the newer systems allow them to be sized more for the heat load greatly decreasing the use of electric resistance heat when that is the backup heat. Ground loop where wells must be drilled are expensive but pay for themselves over the life of the system. Also the ground loop itself is a one time investment. A personal note. My system is simple. A hot water coil added to the duct work and an oil fired boiler for backup. Last oil fill was almost $5 and gal. My heat pump is much cheaper to run. The de-superheater did add to the complexity of the control system but putting that together was the fun part. Think I will have a nice cheap hot shower and hit the sack. Ken L
My nat gas water heater does all this and is *very* much lower in initial cost. It doesn’t do AC but it is reliable during power outages.
I have a heat pump. Had heat pumps in my last 4 homes. Don’t hate heat pumps. For an individual, often a great choice. In some instances can be good for utilities to promote. But not a one size fits all good product for anyone everywhere.
Very nice but I need an explanation of resistance heat.
In a heat pump it would be wire coils in the air handler that get hot when powered with electricity. Think of the typical electric space heater with the red hot wire coils. Same idea.
Thank you.
Think a bread toaster. Or an old fashioned light bulb. Just more expensive.
Thank you.
Frosty the heat pump. Sorry, I couldn’t resist. The image is actually a heat pump with a defective defrost board and it was unable to go into a periodic defrost cycle by running as an air conditioner for a few minutes. It borrows the heat in the house to melt the ice buildup then returns to heat mode.
That said, my power bill during the peak of winter is over $100 less than my AC bill in the summer. This unit lacks a backup source of heat so it would be best in a climate that only dips a little below freezing during the winter. Phoenix meets that requirement and other than the fact the output air is only lukewarm on cold day, I am pretty happy with the unit. I have to be as propane isn’t practical and the neighborhood lacks natural gas.
Are you suggesting that it is cheaper to heat a house in the Phoenix winter than cool it in Phoenix summer? Who would have though
🙂
With my experience, summer heat pump maxes out around $300/month. Winter maxes out about $200/month and in-between about $120/month. The house is all electric so the numbers might appear a bit high however there is no gas bill. In my moms case, her house is shaded by trees and has a lower summer bill maxing our around $200 and a similar bill in the winter when you add in the natural gas bill. It’s a problem of comparing apples and oranges however you aren’t going to get a winter bill like back east.
One Christmas Eve way back ours froze like that. Could not get the ice off. Had everyone put on big coats and set the Thermostat to cool the house to 40 degrees. Pump took what little heat we had out of the house and ejected it outdoors to the frozen exchanger. Melted the ice in about 15 minutes as the house got colder. Put the unit back to 72 and we were soon warm again.
Novice question..Is a heat pump (I’m not familiar with that term in Australia) the same as reverse cycle air conditioning such as this Fujitsu ducted system..
Yes, A heat pump is an AC in reverse. Engineered to work that was of course.
If you plan to modify your home or office electricals, be sure to include as item one “Take back my smart meter and re-install the old type.”
Rebel me refused to have a smart meter. Gains exceed losses, as I cannot be a target for remote disconnection of supply.
Keep your smart meter if you subscribe to and enjoy the old commercial that “Unseen forces direct our lives.” In that case, welcome, sheep person. Geoff S
IMO there are other reasons to want to avoid heat pumps, especially if being comfortable in your own dwelling in cold weather is important. Personally I would refuse to ever live in a house with a heat pump unless (2 things): one – I was to move pretty far down south (like south Carolina or further south), or two – the system had a fossil fuel back up.
Every home I’ve ever had the displeasure to be in for any length of time that had a heat pump was either cold, drafty or unbearably stuffy. I’ll never forget when I was a teen and I was babysitting for my cousin and his wife. It was during a cold spell and nights were in the low teens (cold for central Maryland but not totally uncommon) and I could not get warm in their house, I kept checking the thermostat, which was set to 70F, but the registers on the floor behind the couch kept pumping out chilly air. I couldn’t believe it – temp set at 70 and I was freezing…and my parents forced air oil heated house was set at 68 and it felt much warmer!
When I was dating my husband before we married, he was renting a home that had a heat pump. We came back to his house after being out one night and it was well below freezing, and it might as well have also been so inside as nothing but bitter air was coming out of the vents! could have sworn the AC was on….indoor temp was set at 68 of 70, but still felt so cold.
We live in a house now that has baseboard (hot water) oil heat and winter temp is set to 68. I am quite comfortable…no chilly drafts and no cold air coming out of anything (well, save for maybe the one bathroom window with a busted seal….).
The problem you are describing is still sadly common. The duct work is to small for the system. This saves on the cost of the installation but the result is a system that does not heat well or efficiently. The end result is to few registers and each one blasting out more air then they were designed for. As with so many things in our world it is not the equipment but the way it was installed.
Another problem is that the air coming out of a conventional system has a higher temperature. If you have 80 degree air blowing on a 98 degree surface that air will have a cooling effect, even if it is raising the temperature of the room.
Hydronic heating is the go. Very comfortable radiant heat.
That chart is very misleading as it is installed generation capacity, nameplate. and shows up as 20% of the total. The actual electricity produced the renewables and used is a fraction of that.
Disappointing.
False. That chart is annual generation. It isn’t capacity, it’s generation. The reason that “renewables” are 20% is because it combines Wind, Hydro, Solar, and other renewable (i.e. solid municipal, bio-fuels, bio-waste, geothermal, and a couple others that I forget). Check the source before complaining that a chart is misleading.
The basic lie of the Biden administration, or if you prefer that its their fraud, is that the green investments in the IRA will reduce consumer energy costs, something that has never occurred anywhere in the world in history that it has been tried.
It always leads to higher costs, without exception.
So the whole thing is a clear and obvious lie to anyone who can read and think for themselves.
Griff and progressive need not apply, we will not be mean and demand you exceed your capabilities and think.
Could a solution be not to increase electricity storage, but heat storage in individual homes. Solar heat collectors, especially the vacuum tubes in winter have a good efficiency, and 85-90% of incoming solar energy is converted to heat. If houses had a water tank to store heat, the heat pumps could use that energy first at dawn without needing to go into resistive heating. The heat pumps could also draw on the heat, if the temperature of the heat storage goes above a certain threshold, which would increase efficiency compared to drawing the heat from outside. In Europe at least some heating systems are coupled with water tanks (domestic water + heat storage) and solar heat collectors.
Solar heat collectors really only provide hot water in summer. In winter, insolation is inadequate even on sunny days, and they are far from guaranteed. Sunlight hours are short, and sun angles low, which means that installations may often be in the shade of trees or other buildings. Water tanks do allow for heating using cheaper overnight power where available, so they can still be useful. But gas heating offers no such benefit.
Blackouts in very cold weather affect everyone, whether they have heat pumps or gas furnaces. Without power most gas furnaces won’t operate, ditto blowers and circulation pumps. Keeping the heat on requires a backup generator as well.
The other thing that happens in areas not used to prolonged freezing temperatures is without some heat penetrating exterior walls from inside, inadequately insulated water pipes freeze and burst.
On the bright side, reactor 3 at Plant Vogtle starts fuel load tonight on its way to a 1st quarter 2023 in-service date. That’s another 1117 MW of reliable carbon-free power coming online soon at a grid near you. And identical new reactor 4 should follow six months later.
The persistent fantasy of green energy is perfectly understandable in a world where people who claim to “believe in science” will flock to stores selling magical crystals for easing mental illness or attracting wealth and warding off evil spirits.
Excellent article. Couple counter points though:
1) Electric heating isn’t that inefficient compared to direct natural gas. We can compare “best of” and consider a 95% efficient condensing natural gas heater with a boiler rather than forced air (which tends to lose energy in attics), and a 64% efficient NGCC system. Alternatively you could compare an 80% efficient non-condensing system with 10% attic losses to a 50% NGCT. Either way a 30% improvement for direct burn. However, that needs to be balanced with the reality that most of the time (even in extreme environments) the system will operate in heat-pump mode. I suspect over the course of the year less natural gas is used in the heat-pump system (with electric resistance backup) than the direct burn system.
2) The extra capacity is indeed needed for a winter peaking system. However, the traditional Natural Gas system has that same burden. The difference is the burden is placed on NG piping (i.e. “first therm” cost). For a genuine comparison you need to consider whether the cost of new electricity capacity is greater than the cost of maintaining a NG distribution system. My suspicion is that it is close to a wash. However, I haven’t ever run the numbers. There may be one of these two that has a much higher maintenance cost than the other. I suspect being able to drop the NG infrastructure entirely (i.e. electric only) would end up being a cost saver, even if the electric capital requirements are raised.
3) The cost of having a natural gas system available is pretty low. When I run these models what happens is that the existing NG infrastrucutre stays online and runs at a low capacity (20-30% annual). That would be a death blow for a nuclear, but is fine for Natural Gas. You are correct that if the peaks are peakier then we would need new capacity. Storage is one possibility, but that is really only viable if it’s used more than 5 times per year. My personal preference is the F-150 hybrid. You know, the one with a built in back-up generator. Now to be fair, you don’t want that automatically turning on in your garage. But imagine all the F-150’s currently on the road being able to push power into the grid during emergency situations (i.e. the cost of electricity is higher than the cost of diesel fuel). That alone would more than cover emergency peaks.
4) I love ERCOT. They have been running into problems though. The main basis of their problem is not wind/solar or capacity vs. energy only markets. Their biggest problem is that their grid keeps growing while the rest of the US is stagnant to down. They have problems because even though they are building new Natural Gas, new wind, and new solar they aren’t building fast enough. Then each year there is a “crap, we can’t meet this new highest high peak” while California struggles to meet a peak equal to 20 years ago.
Not numbered because it isn’t a counter point) I love your generation chart. Most people are unaware that generation in the US has been flat almost 20 years (I guess a pause?). The reality is that the infrastructure is due for a turn-over anyway.
All that said, great article. I appreciate the clear thinking, the clear treatment of the issue, and a recognition of cost/benefit of multiple different options.
One more point: energy storage
Personally I think batteries are a poor solution. However, most homes already have a hot water heater with storage. A good solution to the needle problem would be to over-heat the hot water heater (140-150) with a regulator on the exit that mixes the stored water with incoming water for personal use, but the system is able to tap into that stored heat at the beginning of the day. The problem is that you would want a “smart” tank that would know which days to do that. I would lean toward a smart tank that doesn’t get its information from the grid operators because I don’t want to give them access to my tank. However, as a whole this would fix the needle problem by leveling demand over the cold night.