California’s Duck-Belly Blues
Behind the meter, we’re ducked.
In colder parts of the country, March comes in like a lion. Here in California, March comes in like a duck. Days are often sunny but not so hot. Solar electricity generation levels are high, but cooling demand is low.
Ten years ago, some prescient energy analysts at CAISO were thinking about how an increase in wind and solar generation might impact grid operations on sunny-but-cool California days. They projected electricity demand net of wind and solar generation (aka “net load”) in a future with increasing solar PV penetration. These projections gave rise to a now-familiar duck:
The CAISO duck curve caught people’s attention because it brought some looming renewable energy integration challenges into clearer focus. One of these challenges lies in the duck’s growing belly. As solar PV penetration increases, net load can bump up against the minimum generation levels of other grid-connected generators. If grid operators can’t find enough demand to soak up the sun, they have to curtail the excess solar generation.
Ten years later, these once-hypothetical over-generation challenges are here for real. Spring after spring, we set new records for renewable energy curtailment. Last April, CAISO reports that a record 596,175 MWh was curtailed. That’s like producing an entire extra day’s worth of electricity in April and then throwing it away.
It’s important to note that solar curtailment need not be a sign of inefficiency. On a highly decarbonized grid, there will be times when our solar supply exceeds our ability to cost-effectively soak it up. But it seems likely that the rates of solar curtailment we’re seeing today are higher than they need to be. So California has been scaling up its efforts to deal with these duck belly blues.
As we head into the 2023 duck season, I’ve been super-curious to see how these efforts have been impacting solar curtailment. This week’s blog post takes a preliminary look at how the duck charts are shaping up this year. And asks how three key curtailment-mitigation strategies are playing out.
A daily duck comparison
Since April 2018, CAISO has been posting – in real-time– hourly demand for grid electricity and the corresponding net load over the course of the day. These data can be used to track our renewable energy integration progress. This year, our March weather has been more lion than duck. But we’ve had a few sunny days. The graph below compares this “daily duck” data from last week (Tuesday, March 7) against a similar (temperature-wise) March day four years ago (Thursday, March 7, 2019).
This comparison is a fast-and-loose way to assess how our renewable energy integration challenges are unfolding. That said, you can clearly see that the mid-day dip in net demand (in purple) has been growing as utility-scale solar PV generation – shown in yellow—has been increasing. Last Tuesday, PV generation was more than 1,500 MW higher in the middle of the day as compared to March 7, 2019.
What these graphs do not show is solar curtailment. CAISO has been releasing daily reports on wind and solar curtailment since 2019. Over 22,000 MWh of solar was curtailed last Tuesday. This is an order of magnitude higher than the solar curtailment we saw in early March of 2019.
It’s discouraging to see solar curtailments rising fast. But perhaps we’d be curtailing even more if not for our efforts on three key fronts: batteries that can store excess supply for later use; regional market integration to help export excess renewable generation to places that can use it; and demand-side efforts to shift/increase load in the duck belly hours.
Battery storage to the rescue?
Solar PV capacity has increased significantly over the past five years. So, too, has battery storage! CAISO posts sub-hourly data on battery storage, so we can see how these batteries are being charged and discharged on ducky spring days. The graph below shows how batteries are assisting with duck belly management.
The blue line tracks battery storage activity in March 2019. Nothing to see here. The orange line summarizes data from last Tuesday. Very cool! You can see batteries storing electricity in the belly of the day and discharging them when the sun goes down.
To put this 2023 battery storage activity into perspective, the dashed yellow line plots the difference in daily utility-scale solar PV across the 2019-2023 March days. In this two-duck comparison, 2023 battery storage goes a long way toward offsetting the increase in utility-scale solar generation. Looking ahead, we should see batteries playing a growing role in mitigating curtailment.
Enhanced grid integration holding steady
As regional grid operations become more integrated, it should be getting easier to export our excess solar if and when there’s excess demand outside of California. The graph below tracks estimates of curtailment avoided in the increasingly integrated Western interconnect, thanks to the Western Energy Imbalance Market (EIM).
Avoided curtailment has been pretty steady over time. I found this a little surprising given that the WEIM membership/market size has been increasing over this time period. However, a limitation of the WEIM market is that participating utilities only make a fraction of their transmission capacity available for the generation re-optimization that occurs through the market. This can put a binding constraint on California’s renewable energy exports. With the newly approved Extended Day-Ahead Market (EDAM) participants will make all their transmission capacity available, and I would expect renewable curtailments to decrease further.
Losing ground on the demand side?
Another curtailment mitigation strategy involves “load shifting” into the belly of the day – think smart EV charging and pre-cooling your house. The graph below plots March 7, 2019, and March 7, 2023 grid-electricity demand profiles (i.e. the two green lines from our duck comparison above) in the same graph. What emerges from this comparison is a behind-the-meter (BTM) duck! Electricity consumption net of rooftop solar production is dipping ever-deeper mid-day.
What I take from this picture is that any successes we’ve had with load shifting into middle-of-the-day have been more than met by the increase in rooftop solar. As more BTM solar is installed, reductions in demand for grid electricity in the middle of the day will increase utility-side solar curtailment.
More battery capacity is coming online in California which will help reduce renewable energy curtailment. Enhanced regional grid coordination should also help us export when we’re over-supplied. But progress behind the meter will remain underwhelming so long as consumer-facing electricity prices offer limited incentives to move flexible demand into the belly of the day.
California is thinking about smarter and more dynamic retail rates that could help coordinate renewables integration more efficiently. More dynamic retail rate structures will be somewhat more complicated for consumers…but critical! We need all hands on duck (last duck pun, I promise) to tackle our mounting renewable energy integration challenges.
Suggested citation: Fowlie, Meredith, “California’s Duck-Belly Blues”, Energy Institute Blog, UC Berkeley, March 13, 2023, https://energyathaas.wordpress.com/2023/03/13/californias-duck-belly-blues/
Keep up with Energy Institute blog posts, research, and events on Twitter @energyathaas.
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It’s worth noting that even though most of the commercial/industrial retail rates now offer some sort of spring midday Super Off-Peak, there are effectively no CA residential retail rates where the lowest prices are during the middle of the day. Even the latest “electrification” rates effectively treat the middle of the day and the middle of the night as equally-cheap times to consume electricity during the spring months.
The CalFUSE framework laid out in the linked Demand Flexibility whitepaper holds a lot of potential to align retail rates with grid conditions, but is still quite a few years off. The closest thing to this sort of dynamic hourly retail rate in the nearer term is the upcoming Net Billing Tariff (“NEM 3.0”) export compensation rate, which will be live before the end of the 2023. https://osesmo.shinyapps.io/NBT_ECR_Data_Viewer/
Two points:
1. Approximately half of all solar curtailment is caused by local transmission constraints, not too much solar overall. We have generation pockets with solar trapped inside. If we upgraded the transmission system to eliminate these generation pockets, much of the curtailment could be avoided.
2. Currently, gas-fired generation is almost always the marginal resource. It is curtailed nearly every hour of the year. It will be great day when solar is the marginal resource that is curtailed (or diverted to batteries) to a greater or lesser degree to match load. Curtailing solar will be a feature, not a bug.
Hi,
Thanks for these remarks. Very curious about the second point — do we have a good sense of evidence to show gas being on margin in CA?
It’s no longer the case that gas generation is nearly always the marginal resource. As Marc said, quite a bit of renewables curtailment is due to local transmission constraints, but any time that’s not the case (i.e. it’s being curtailed due to system-level economic conditions), that’s a strong sign that renewables are the marginal resource. CAISO publishes reports every day about the reasons for renewables curtailment in each hour here: http://www.caiso.com/informed/Pages/ManagingOversupply.aspx
If you download the data from https://sgipsignal.com/download-data and look for values of 0 kg CO2/kWh, those are time intervals when renewables are the marginal generator.
A further point on what’s “marginal”–we need to clearly define the term. Marginal means the increment added to meet added or decremental demand. For electricity, the question is when is the decision made to add load–when we turn on a light switch or when we buy an EV? Turning on a light switch doesn’t really add incremental load–that’s just operating the device that was installed that led to the added incremental load. The minute to minute ups and downs of generation system are not “marginal”–they are simply balancing generation and load. Calling these changes “marginal” is just like saying that pushing a car’s accelerator is the marginal cost of owning an automobile. Of course no one would think of driving a car as the marginal cost. For California, the majority of this type of system balancing (operating the throttle) is supplied by gas plants at the moment, with pondage hydro contributing a substantial amount in wetter years.
Instead we should be looking at the cost of adding a physical resource to meet the added load of a new device (e.g., an EV). That is when a generation owner is exercising their real option to interconnect to the grid. Once that resource is on the grid, the operation of it is simply to pass through the energy is produces and to provide power-load balance to the extent that it can. In the case of California, the additional load is served by the addition of renewables as we move towards 60% and 100% renewable and carbon free electricity.
New transmission will be needed to accept the changes in power flows on the grid. Im seeing that a lot now in ERCOT and Im worrying the transmission is not keeping up with the rapid increases in solar on the grid here. I do solar studies for clients here. https://egpreston.com
Mark:
CAISO noted in its 2021-22 Transmission Plan that California will certainly need greater transmission capacity in future years as utility-scale renewable energy expands pursuant to RPS growth. But I’m not aware of current transmission constraints being responsible for any notable percentage of solar curtailments now. There are transmission limitations in terms of CA solar that could be exported to other states, but to the extent that this problem occurs within CA, I have not seen evidence that it’s significant. Perhaps you’re looking at this issue through a different lens than I.
Thank you for accurate information, Marc.
Curtailing solar is indeed a bug for homeowners and commercial developers, who make no money on a solar investment that isn’t generating power to the grid. As I’ve noted in other posts, sure – we can subsidize solar to the hilt and make it work – for >$1/kWh. That doesn’t work for the people who are already paying among the highest electricity prices in the U.S.
Regarding transmission: both solar and wind are running into fierce opposition, nationwide, from the people who have to live next to it – who have moved to the wide open spaces, and would soon be staring out their window at unnecessary industrial junk.
Not to mention the impact of transmission on wildlife. The U.S. Fish and Wildlife Service estimates U.S. wind turbines kill 320,000 birds each year, but that’s nothing compared to the number of birds killed by transmission infrastructure: up to 11.6 million by electrocution, and 175 million by collision with power lines and towers.
To thwart those pesky nature lovers, there is a bill before State Assembly that would exempt all transmission from CEQA review – as if renewables and their “upgraded” transmission have no environmental impact. As if. I can only imagine the wails of protest if U.S. nuclear plants killed 175 million birds each year, but I have yet to see evidence they’ve killed even one.
What bill are you referring to “that would exempt all transmission from CEQA review”? The only bill I can identify that would even “streamline” CEQA review for transmission is Sen. Josh Becker’s SB 420, but it is nowhere near as sweeping as what you describe. It would require the governor to select a CEQA lead agency to monitor clean energy and transmission projects and to identify and certify environmental leadership development projects THAT MEET SPECIFIED REQUIREMENTS for certain streamlining benefits related to the California Environmental Quality Act.”
A bill to provide a blanket exemption from CEQA to transmission projects would not even make it out of its first committee hearing.
One other thing: How is curtailing solar “a bug for homeowners.” CAISO curtails utility-scale solar. That’s it.
“What bill are you referring to ‘that would exempt all transmission from CEQA review?'”
The bill is AB 914 (Friedman), and to clarify: it would only exempt transmission used to connect renewables to the grid. Because an eagle that flies into a cable connecting a solar farm apparently doesn’t deserve protection. It should know better.
Just to be clear, the bill would only apply to subtransmission lines less than 200 kv and would be subject to other limitations.
Another candidate for the original “Duck Curve” was from Ed Kahn of the Berkeley Lab in 1978, superseding the NREL paper by 30 years.
See Figure 2: https://escholarship.org/content/qt3pb9527p/qt3pb9527p_noSplash_bfbc8406dbb763bc4b467b42987816f3.pdf?t=p21n4x
This shows why there should be a program of changing electricity rates depending on demand. It should not be to difficult to get future electric cars on line with the internet and monitoring electricity prices. When the price goes down they charge, when up they discharge. I can imagine one setting the the car to be required to have a minimum charge by a specific time such as 50% by 5pm. Then let the software decided on the most economical charge and discharge during the day. Eventually we will probably have learning algorithms that look at weather forecasts and determine what the best times to charge and discharge will be during the day. Programs that change the rates during the time of day will also help to encourage pre-cooling of homes, use of electric dryers during this time, etc. We may well start to have appliances like water heaters and freezers that increase heat or cooling when power is cheap, allowing them to turn off when power gets more expensive.
Note that if the cost of offshore wind power can be brought down it may be a much better long term renewable energy source than solar if it is more consistent during the day and throughout the year.
First, any year to year comparison of renewable curtailment must account for the much bigger swing of hydro generation. While 2019 was a relatively wet year, we the precipitation came much later than in 2023 and 2023’s is much higher. This is like 1998 when a very wet year disguised the problems in the newly restructured market for a couple of years. The graph should be adjusted for the amount of hydro generated (and even spilled) in each of the years. Much too often energy analysts ignore the importance of this variation in the California market. (But they pay close attention in the PNW.)
It’s good to see storage absorbing much of this higher renewable output already. And important question is what percentage of total renewable generation is being curtailed? A solution suggested by several people is to overbuild renewables because they are now relatively cheap and just simply curtail them as needed. Remember that many of the old steam turbines built in the 1950s and 1960s were intended to be run in baseload but instead ended up being “curtailed” to follow load, thus making them more expensive per kWh than originally calculated. (Ormond Beach built in 1972 had to be remodeled to accommodate load following operations.) Combined cycles had the same evolution, with the CPUC assuming a 90% capacity factor in its original avoided cost calculator in the early 2000s. We could go through the same evolution in thinking about renewables.
As for customer demand, the more striking aspect of that chart is that customer demand has apparently fallen over the past four years. Energy efficiency and self sufficiency should be celebrated, not bemoaned because some large plant owners aren’t able to sell as much power. Why do we care where the power comes from? Yes, there isn’t yet enough EVs on the road to absorb the solar panel output but that will change soon enough. Mismatches of supply and demand are common. Just look at the huge grid scale generation surplus in the 1990s that led to restructuring!
As the article says, we’ve known this was coming for a decade. And nine years ago, when we wrote Teaching the Duck to Fly, we identified some simple strategies to address this challenge. California has addresses only a few of these
Every electric water heater (there are about 2 million of them in California) should be programmed to heat water at mid-day, and save it for evening. While Hawaii, Oregon, Washington, and even North Dakota have run water heater control and timer programs. California is lagging.
Eight years ago, the California Energy Commission was approached about requiring ice or chilled water storage in new large commercial building air conditioning systems. There are tens of thousands of these in operation worldwide, including one of the largest at UC Riverside. Instead the CEC mandated rooftop PV systems in new residential construction, compounding the duck challenge.
Energy efficiency programs should be focused on the early evening hours, when things like kitchen lighting are very active. There has not been a program redesign.
There are a couple of Teaching the Duck to Fly strategies where California doing well.
Most important, inter-regional power exchanges. I’m sorry that Dr. Fowlie did not show how imports vary across the day, using the flexibility of the PNW hydro system to help California. We buy power from California when it is cheap, then sell it back at a higher price a few hours later. It’s good for both regions.
California has made more progress on rate design than most states, but the Hawaii recent Advanced Rate Design Order, which requires priority-peak rates 3X those in off-peak periods, goes a lot further.
California was late getting started on battery storage, but has moved fairly quickly once it got moving.
EV charging is increasingly important. California has done a good job on time-varying pricing for EV charging, but not such a good job bringing smart chargers to the task, so people can plug in when it’s convenient to do so, and get a charge when it’s ideal for the grid, subject to the minimum range constraints set by the user.
We still have a lot of work to do. Fortunately, we still have a lot of arrows in our quiver.
Teaching the Duck to Fly: Edition, 2014:
Click to access rap-lazar-teachingducktofly-2014-jan.pdf
Second Edition, 2016: https://www.raponline.org/knowledge-center/teaching-the-duck-to-fly-second-edition/
Jim, do you know of any public resources explaining Hawaii’s Advanced Rate Design Order in further detail? All I’ve seen is the info here (https://twitter.com/JulianSpector/status/1590733053563138048/photo/1).
In a memorable article from 2015, Alex Trembath and Jesse Jenkins of the Breakthrough Institute pose the question: “Is There an Upper Limit to Intermittent Renewables?”. In support of their hypothesis, they cite data from a 2013 paper in Energy Economics showing a negative correlation between market penetration and the value of solar and wind generation. As soon as solar and wind achieve market penetration corresponding to their relative capacity factors, they “eat their own lunch”- they are no longer profitable.
https://thebreakthrough.org/issues/energy/a-look-at-wind-and-solar-part-2
Since that time, in every electricity market where that situation has occurred, their hypothesis has proven correct.
So no – it isn’t simply a matter having “smarter and more dynamic retail rates that could help coordinate renewables integration more efficiently.” It’s the fact that for any source of generation intermittency is a deal-breaker. And California is no exception. Already, we’re paying neighboring states exorbitant rates to take our unwanted solar overgeneration (“negative pricing”), and paying solar and wind farms to curtail their output – to *not* generate electricity – to avoid having them destroy our grid. Is there any wonder, over the last decade, why our rates have risen seven times faster than the national average?
Sure, if we force electricity customers to subsidize it, we can make any source of energy profitable (hamster wheels?). But the time to face hard facts is long overdue: solar and wind are losers. Renewable energy is a bust. And if I seem frustrated, it’s because this ideological refusal to face facts is having real implications for climate change. If we don’t cut our losses and build out nuclear energy as quickly as possible, in less than two decades avoiding critical, irreversible tipping points will be impossible.
I run my home off of batteries and they work 24/7 and I switch the charging source around depending on availability and need. The batteries in the morning are at their most depleted state so I installed my solar panels facing them to the southeast for maximum replenishment. Utilities have recommended homeowners install the panels facing southwest to cover the afternoon peak demand for grid-tied systems. From 4:00 PM to 9:00 PM, I run my home off of the batteries not adding to the grid demand then if the batteries become low at any point after 9:00 PM, I can switch on grid tied battery chargers to maintain a backup supply from the overabundant nighttime utility power when demand is low. My off-grid battery system along with My Tesla Solar Glass Roof allowed me to turn off my Natural gas forced air furnace and run electric space heaters and a wood stove for wintertime heat under NEM 2.0. Home Batteries and using them as the main source of power works from March 21 through September 21 each year during the longer days. This allowed for a really big bank of electrical credits from my Grid Tied Tesla Solar Glass Roof under NEM 2.0 for the wintertime buy back of utility power to run battery charging and electric heating. My solar panel and battery system works as a micro grid and anyone saying that solar does not work with storage is not looking at all the data.
I’m looking at all the data, and see someone who can afford a $100,000 Tesla Solar Glass Roof, yet still needs space heaters, a gas-fired forced air furnace, and batteries charged by dirty nighttime utility power (primarily gas-fired power) to maintain their lifestyle.
Though it might help California’s wealthiest feel like they’re being environmentally responsible, for the other 99% that luxurious deception is beyond their means.
Carl, who is going to lead the way to show us how it is possible to live without fossil fuels? It may not be currently economically feasible for most people, but a demonstration that it can be done by an individual is vitally important. Did you get a color TV when they arrived on the scene? Did your first inkjet printer cost nearly a thousand dollars?
Old Surfer Dude, I’m not unempathetic to your point of view. In 2008 Musk & friends were designing Tesla’s first commercial car, the Roadster, and Big Fossil was fighting hard to kill Tesla by any means it could. But before Elon Musk was a household name he brought the fight right back to it, and succeeded in delivering the longest range, fastest electric car in history.
Its MSRP was a whopping $100,000, and now you can buy an electric car with 3x the range, at 1/3 the price. But there would be no electric cars today if it wasn’t for Elon Musk’s grit and determination.
I imagine solar advocates feel the same way today – that everyone is piling on against them, that it’s just a matter of time and determination to bring the cost down. But that’s not what is holding solar back (and to a lesser extent, wind).
It’s physics – specifically energy density, and intermittency.The general public has no idea how little energy there is in sunlight – like trying to grow a vegetable garden in the desert, powering a car or an electric oven with sunlight is an uphill battle all the way. Sure, if you arrange enough reservoirs around your garden, you might be able to save enough water to grow a tomato or two at the right time of year. But at other times, your garden will be dried-out twigs in a week or two.
Don’t get me wrong – those who live in the desert would be far more successful with solar panels than a garden, and here in coastal California I have friends who save money with their rooftop solar. But right now, all the solar and wind in the world generate 4% of its primary energy. There isn’t enough time nor money to power all electricity grids and all transportation, with renewables, in time to make a difference with climate change. It’s just not going to work.
I would have to agree with you, Carl, it’s not enough. Fossil sources are going to kill us, so that’s not going to work, and nuclear will require the sacrifice of land, plus we need to build 15 a year just to replace what we have, so that’s not going to work. And humans are too fat and lazy to change their ways, so that’s not going to work.
Yup, I feel just like Jack Nicholson in “The One Who Flew Over the Cuckoo’s Nest”. I may not be able to lift the granite fountain, but at least I tried.
Shift more load to the middle of the day such as EV charging. Storage can help clip the head of the duck.
My take-away here is that we need much more garage storage, more rooftop generation and a whole lot less solar and battery farms. And, “yes”, these very small installations will need to have their battery load and generation controlled by an entity that is honest and fair.
Ah, but that will never happen because the construction-companies-that-sell-electric-energy-as-a-side-gig have too much control of the electric energy market. And I don’t think Diogenes every found what he sought.
On a side note, just about every duck curve I’ve seen has not include the line of total load. Why is that?
Between the hours of 9AM and 2PM, every day of the year. California solar is being curtailed. The problem is not that we don’t have enough solar, it’s that we already have too much.
“….every duck curve I’ve seen has not include the line of total load. Why is that?”
A picture is worth (at least) a thousand words:
The Failure of California Electricity Policy in One Image
https://californiaglobe.com/articles/the-failure-of-california-electricity-policy-in-one-image/
Do you have data showing that solar is being curtailed every day of the year? The image that you link to shows one of the lowest load days of the year in April when the peak is half of the highest peak and 50% lower than the summer average. As with the deception of the CAISO duck curve that chose the lowest load day in March, these charts distort the true story about curtailment.
“Do you have data showing that solar is being curtailed every day of the year?”
Data? It’s easy to see by looking at the graph of solar generation for any day of the year.
Solar irradiance is the cosine of the sun’s angle in the sky at that moment:
I = S cos(θ)
where I is irradiance in W/m^2, S is a constant, and θ is the sun’s zenith angle. Though it varies from location to location, statewide it averages out to a smooth curve with little tails on each end, showing reflected sunlight before dawn and after sunset.
Wherever you see that ragged horizontal line kicking in at 9AM and cutting out at 3PM, it indicates engineers at CAISO are frantically trying to keep solar from taking their grid down.
So in fact, your assertion about when curtailment occurs is pure speculation unsupported by any factual data. Stating the obvious about solar irradiance does not lead to the conclusion that curtailment occurs often, and the recorded data on curtailments contradicts your assertion–its simply too little to match your claim. You’re also speculating about what any of the patterns in the load curve mean.
The green line is “demand” and that is the “load” on the system in the graph #3. Residential loads are only 30% of the total load the grid has to supply yet is the most focused on in most online blogs. When a large plant, Like Tesla in Fremont, California adds a second shift, nighttime demand goes up 100% for the plant Monday through Friday then drops off to 10% over the weekend if not working overtime. Solar and wind are producing power 365 days a year. Tesla builds mega battery power packs and could install those at the Fremont factory and store up the unused “weekend power” to release at peak hours the rest of the week metering it in to lower the demand from 4:00 PM to 9:00 PM every day of the week. This is what PG&E does at the Moss Landing mega battery storage facility next to their two-exiting power “Peaker” plants there. One size does not fit all, and weekday demand verses weekend demand are totally different. CAISO claimed it was on a Saturday, from 12:15 PM to 12:30 PM that 100% of its acquired California power was from solar and wind. I expect to see battery storage added into the mix and see more days with Solar, Wind and storage covering more hours of demand in the near future.
“Residential loads are only 30% of the total load the grid has to supply yet is the most focused on in most online blogs.”
Yet you’ll notice at 9AM solar inexplicably flattens out until 2-3 PM. Does a cloud front roll over California at 9AM, then disappear at 3PM every day? Of course not – that bumpy line is solar being curtailed to a maximum level of 10GW, every day of the year, to prevent the serious instability problems it introduces. Adding more solar won’t reduce carbon emissions – it will only increase curtailment.
“This is what PG&E does at the Moss Landing mega battery storage facility next to their two-exiting power ‘Peaker’ plants there.”
Though the public has been conditioned to believe batteries discharge only clean energy, that depends entirely on what source is used to charge them. In nearly all cases, storing it makes electricity dirtier.
Case in point: Moss Landing Energy Storage Project, the largest in the world, was built adjacent to Moss Landing Power Plant, the fifth-largest in California, to be able to charge from the gas plant’s direct output (the power plant is not “exiting”, as much as gas promoters want us to believe it is). And because battery storage increases CO2 emissions by up to 407 kg/MWh, power from the storage project is up to 45% dirtier than electricity coming straight out of the gas plant.
https://pubs.acs.org/doi/abs/10.1021/es505027p
Where did you get the idea that solar is curtailed at 10 GW? Between grid scale and DER solar, about 40,000 MW is installed, with about 60% grid scale. https://www.seia.org/state-solar-policy/california-solar. CAISO isn’t curtailed 15,000 MW of solar.
Whether Moss Landing was directly tethered to the battery or exporting the power and the battery is taking it from the grid makes no difference whatsoever in the accounting of emissions from the system. It’s just what resources are running. And the battery is obviously grid connected because it’s exporting at times when the generator isn’t running.
“Whether Moss Landing was directly tethered to the battery or exporting the power and the battery is taking it from the grid makes no difference whatsoever in the accounting of emissions from the system.”
It makes all the difference in the world. Here’s why:
When Moss Landing is generating straight to the grid, at average U.S. emission rates for gas, it would be emitting 957 lbs/MWh.
When the battery is exporting 100 MWh that was charged directly from the gas plant, however, it will be emitting up to 1,364 lbs CO2/MWh, due to resistance and bi-directional inversion losses from the battery.
Those lovely “clean” batteries at the Moss Landing Energy Storage Project are responsible for 43% more CO2 emissions, to produce the same amount of energy, than electricity straight from Moss Landing Power Plant.