"My car runs 100 miles!" instead of "My car runs 100 miles per gallon!", and almost anyone would notice something is amiss. I don't get the difference to mixing "Watts" with "Watts/hour".
Not knowing the difference in miles and miles/gallon will get you stranded in your car pretty quickly. Now knowing the difference between watts and watts/hour will have almost no appreciable effect on your life. You flip a switch, the light turns on, and you get an invoice a month later.
Actually, I thought it was very easy to understand. For instance,
> Fortunately, 2,000 MW of energy storage capacity is coming online by August 1, per the California Public Utility Commission. Much of this capacity will have four hours of battery energy sitting behind it, nearly 8,000 MWh in total.
That's 2 GW of power delivery backed by 8 GWh of storage.
I think this is where the confusion starts: if someone talks about "energy storage capacity", my first association is the amount of energy that can be stored, not the rate at which that energy can be discharged from the storage (i.e. power).
It is a bit confusing, but it isn't wrong, there are just two capacities in question.
We could call them power capacity and energy capacity. This system can deliver 2000MW for four hours, or 1000MW for eight hours, but can't deliver 4000MW for two hours, because that exceeds the power capacity.
It’s not “storage capacity”, it’s “energy storage capacity”. Think of it like “sources of power”. Source 1 is nuclear, Source 2 is Hydro, Source 3 is Energy Storage.
What are our power sources available to the grid today? Nuclear, Hydro, Energy Storage.
The battery energy storage is 8GWh with a power capacity of 2GW. There is no such thing as a power storage capacity, because power is a rate. However, the storage may have a power capacity. pedantic, I know.
Watts are joules / second, so watt * hours cancels time on both sides, it's just energy. Watt-hours are more convenient than "raw" joules only because we tend to be more interested in how many hours a battery will last at a given wattage, not how many seconds it will last.
So energy capacity is correct, it's the amount of energy (not power) one can store in the battery.
Edit: I read this as though you were replying to me, not the comment I was replying to. Swimming upstream, I see that, yes, "energy storage capacity" isn't in watts, but rather watt * hours, but I agree with @renewiltord that it's easy to understand once you factor in that journalists, for the most part, never took physics.
The numbers have the units next to them, after all.
Sure, but you can then read the next sentence and the confusion should disappear.
The right answer is to use power and energy capacity respectively if you’re talking to lay people but this publication is talking to people who disambiguate based off the units pretty easily.
Nuclear capacity/wind capacity/Energy Storage Capacity. Three different delivery methods for power. That’s how they’d read it at the end of the sentence.
But anyway, the trick is to perform either unit disambiguation or perform one sentence lookahead.
And finally, think of it as no different from using the summation convention in tensor notation. You read it and you’re like wtf but that’s because you’re not the audience and you lack the context to get it.
I think this would be very understandable to someone without any of the physics knowledge, by just dumbing it down to:
> Fortunately, 2,000 MW of electricity is coming online by August 1, per the California Public Utility Commission. Much of this will have four hours of battery time sitting behind it, nearly 8,000 MWh in total.
Or alternatively, by using the correct physics terms where applicable:
> Fortunately, 2,000 MW of peak power capacity is coming online by August 1, per the California Public Utility Commission. Much of this capacity will have four hours of battery energy sitting behind it, providing nearly 8,000 MWh of energy in total.
But as is, the author provided the worst of both worlds. To me as a reader, I read "2000 MW of energy storage capacity", stumbled over that, then read on to "8000 MWh in total", understood that that is actually the storage capacity, then had to go back to "2000 MW" to understand that they meant "power", not "energy", to make sense of this whole two-sentence section.
So yes, this all does make sense. After reading it multiple times, some of which are back to front. The information is in there, but it certainly isn't clear or up-front.
Energy storage projects are typically described in terms of maximum power (megawatts) and hours of supply at peak power. Multiplying hours and megawatts gives megawatt hours, a unit of energy. Gigawatts and gigawatt hours are just different magnitude units for the same power and energy values, like meters and millimeters.
Most electrical grids experience peak demand in the early evening when people come home from work, turn on lights, cook dinner, etc. This peak period is usually on the order of 4 hours. This early evening period is also when solar output drops toward zero.
Energy storage projects in CA are currently generally provisioned for 2-4 hours of storage to ensure a good match to this daily evening demand peak and dropping solar output. Storage is still expensive so it doesn't make financial sense to add capacity that isn't going to be used most days.
Some of these projects publish detailed information about power and energy. Others just publicize power, but given what is known about the California market their energy capacity can still be estimated to a reasonable degree.
> Gigawatts and gigawatt hours are just different magnitude units for the same quantities, like meters and millimeters.
I liken it more to distance vs speed. Power, like speed, is a rate, in particular the instantaneous rate at which energy is transferred.
Expressed using the same scheme we use for speed (distance per time : power per time), power is watt-hours per hour (or 0.0036 megajoules per hour).
I'm guessing we express power differently because James Watt codified the standard unit for power and the standard for electrical energy came from the time-integral of his definition of power.
I referred to megawatts and megawatt hours in my first two sentences. "Gigawatts and gigawatt hours" was indicating counterparts to MW and MWh. Though apparently that grammatical construction was not as clear as I initially believed.
This is what confuses many people, especially with solar and battery storage. "I've got 400 watts of solar feeding into my 400AH of batteries with a 3000w inverter"
Most people will have no idea how much usable power they get and how much energy storage they need to meet their needs. (this example is mostly from an RV perspective)
In general, people are not used to formally separating power and energy as concepts, much less as units of measure.
This makes perfect sense because most of the measurements of things we own or consume are counted in units like area, volume, and energy, which are inherently more tangible than an instantaneous rate like "power". Speed is a bit of an exception to this, but I think that has to do with the ubiquity of speedometers in cars.
To the extent that people broadly understand power as distinct from energy they tend to do so in a mechanical, not an electrical context, and in less precise terms ("That's a powerful truck"). However, some exceptions to this are light bulbs and electric space heaters, where people generally understand power as being proportional to brightness and heat output.
In a way, it's an incredible testament to the engineering of electrical systems that people have been able to largely ignore the difference between power and energy, or just need to flip a circuit breaker if something exceeds a limit.
The reason that battery capacity is measured in amp hours is that you can't know the exact voltage of the battery as it drops with lower levels of charge.
Newer large-capacity battery systems seem more likely to specify battery capacity in (k)Wh. I think this is because they come with sophisticated battery management systems that keep the battery within a narrow charge (20%-80%) range, so therefore they can be assured of the bounds of the voltage.
Also, Li-ion and LiFePO4 batteries have a much different discharge curve than earlier chemistries [1], with much more constant voltage up to 80% discharge.
If voltage drops with lower levels of charge, then so does the current (assuming a load with a constant resistance). Isn't that just another reason to use Watt hours instead?
> "Ive got 400 watts of solar feeding into my 400AH of batteries with a 3000w inverter"
Assuming 12V, that's about 400Ah*12V=4800Wh of storage. 4800Wh/400W = 12 hours to charge those, which seems reasonable for an RV. The thing that seems a bit oversized is the 3000W inverter.
Thanks! I've been noticing these projects mostly from press releases that surface through Google News, and those don't always provide both numbers. It's good to know that there is a detailed source of open data.
No, GW -- as in the pumped storage facilities can deliver 4 GW of power continuously.
The amount of energy that can be stored in California's pumped storage projects is enormous, measured in hundreds, if not thousands, of GWh, but that's mostly irrelevant to this discussion.
> but that's mostly irrelevant to this discussion.
Is it irrelevant? As another thread mentioned, how long you can provide that power for that for and how fast you can replenish capacity seems relevant for its usefulness buffering solar for after hours.
I'm pretty unread on the energy storage situation so your insight or any good resources are very welcome!
California uses something on the order of 1 GWh/day. If they have the ability to store up hundreds of GWh in a reservoir, then the exact amount becomes largely irrelevant. They have enough, and the limiting factor is power rather than energy.
Maybe a few decades ago, but dams have more problems than batteries, especially along near the ring of fire/faults. Hard enough to ensure proper maintenance is done in serene Michigan.
As a Californian who has been watching the CalISO web page since the 90s, what I find most interesting is that the peak usage and total generation now is pretty much the same as it was in the 90s (~50MW).
Based on the energy mix, it looks like lost coal capacity has been replaced with solar and other green energy, and demand has gone down relative to population because of efficiency initiatives and rooftop solar for the largest home consumers (rich people).
I'll bet demand falls even faster as home energy storage gets cheaper and more prevalent.
California still imports a large amount of power from other states (primarily Arizona and Utah, with some hydro from Oregon). So we essentially outsourced a lot of our power production to other states.
Arizona, Nevada, and Utah have quite a bit of area for solar PV. It’s fine for California to import from there as long as they use their leverage to force a move away from coal now, and natural gas later. Clean hydro from the PNW is no different than PJM and NYISO grids importing clean nuclear and hydro from Ontario, Canada (which they do).
Drawing solar from states to the east would only make the duck curve worse though, right? Power production would taper off even earlier than the peak demand.
You can charge your residential or utility battery storage from the imported hydro or solar depending on spot prices, no need to consume immediately at that time.
Transmission is crucial for flexibility in balancing generation and consumption, as well as optimizing storage utilization. You can also assume there will be times you’ll throw away (curtail) clean energy as it’s cheaper than it would’ve been to store and then deliver it, but you still need that capacity available at other times (seasonal variability).
It would be made up for in the morning though when that solar starts producing sooner. Unless everything is renewable already, it could offset some non-renewables getting used before sunrise and allow battery charging to start earlier.
In theory that could be the case. I was reading how the Los Angeles Dept. of Water and Power actually owns a coal generating plant in Utah. They are now converting it to a natural gas powered plant, so that's a step in the right direction.
I got my "hybrid" inverter today. My panel size is 330w x 16. So 5.2kWh. Grid tied system. 1 year. Average production 28 kWh on a good day with no grid power cuts.
Well the new hybrid inverter from phocus is supposed to use the generation when grid outside is down internally at home and that opens up a lot of possibilities.
Been thinking about using solar water heating to reduce electricity consumption but that is a big project.
Batteries are still expensive in india. Lithium ion is prohibitively expensive than lead acid. Agreed it pays in time of life but still.
Edit: anyone know if I can incorporate phocus inverter into home assistant ? It has ble so some sort ?
Molten Salt / steam turbine energy storage is 33 times cheaper, safer, and offers a much longer deep cycling lifespan than lithium ion solutions.. i dont understand. we using lithium ion for grid.
If the state reaches the point where we all have electric cars that are recharged overnight by our houses from solar-collected, battery-stored technology, I'd be pretty happy.
60 comments
[ 11.8 ms ] story [ 1342 ms ] thread> Fortunately, 2,000 MW of energy storage capacity is coming online by August 1, per the California Public Utility Commission. Much of this capacity will have four hours of battery energy sitting behind it, nearly 8,000 MWh in total.
That's 2 GW of power delivery backed by 8 GWh of storage.
I think this is where the confusion starts: if someone talks about "energy storage capacity", my first association is the amount of energy that can be stored, not the rate at which that energy can be discharged from the storage (i.e. power).
We could call them power capacity and energy capacity. This system can deliver 2000MW for four hours, or 1000MW for eight hours, but can't deliver 4000MW for two hours, because that exceeds the power capacity.
We don't state that a car with a 100mph top speed has a 100mph capacity.
What are our power sources available to the grid today? Nuclear, Hydro, Energy Storage.
What are the capacities?
Nuclear capacity is 1 GW
Hydro capacity is 1 GW
Energy storage capacity is 2 GW
The battery energy storage is 8GWh with a power capacity of 2GW. There is no such thing as a power storage capacity, because power is a rate. However, the storage may have a power capacity. pedantic, I know.
Watts are joules / second, so watt * hours cancels time on both sides, it's just energy. Watt-hours are more convenient than "raw" joules only because we tend to be more interested in how many hours a battery will last at a given wattage, not how many seconds it will last.
So energy capacity is correct, it's the amount of energy (not power) one can store in the battery.
Edit: I read this as though you were replying to me, not the comment I was replying to. Swimming upstream, I see that, yes, "energy storage capacity" isn't in watts, but rather watt * hours, but I agree with @renewiltord that it's easy to understand once you factor in that journalists, for the most part, never took physics.
The numbers have the units next to them, after all.
The right answer is to use power and energy capacity respectively if you’re talking to lay people but this publication is talking to people who disambiguate based off the units pretty easily.
Nuclear capacity/wind capacity/Energy Storage Capacity. Three different delivery methods for power. That’s how they’d read it at the end of the sentence.
But anyway, the trick is to perform either unit disambiguation or perform one sentence lookahead.
And finally, think of it as no different from using the summation convention in tensor notation. You read it and you’re like wtf but that’s because you’re not the audience and you lack the context to get it.
> Fortunately, 2,000 MW of electricity is coming online by August 1, per the California Public Utility Commission. Much of this will have four hours of battery time sitting behind it, nearly 8,000 MWh in total.
Or alternatively, by using the correct physics terms where applicable:
> Fortunately, 2,000 MW of peak power capacity is coming online by August 1, per the California Public Utility Commission. Much of this capacity will have four hours of battery energy sitting behind it, providing nearly 8,000 MWh of energy in total.
But as is, the author provided the worst of both worlds. To me as a reader, I read "2000 MW of energy storage capacity", stumbled over that, then read on to "8000 MWh in total", understood that that is actually the storage capacity, then had to go back to "2000 MW" to understand that they meant "power", not "energy", to make sense of this whole two-sentence section.
So yes, this all does make sense. After reading it multiple times, some of which are back to front. The information is in there, but it certainly isn't clear or up-front.
Most electrical grids experience peak demand in the early evening when people come home from work, turn on lights, cook dinner, etc. This peak period is usually on the order of 4 hours. This early evening period is also when solar output drops toward zero.
Energy storage projects in CA are currently generally provisioned for 2-4 hours of storage to ensure a good match to this daily evening demand peak and dropping solar output. Storage is still expensive so it doesn't make financial sense to add capacity that isn't going to be used most days.
Some of these projects publish detailed information about power and energy. Others just publicize power, but given what is known about the California market their energy capacity can still be estimated to a reasonable degree.
I liken it more to distance vs speed. Power, like speed, is a rate, in particular the instantaneous rate at which energy is transferred.
Expressed using the same scheme we use for speed (distance per time : power per time), power is watt-hours per hour (or 0.0036 megajoules per hour).
I'm guessing we express power differently because James Watt codified the standard unit for power and the standard for electrical energy came from the time-integral of his definition of power.
This makes perfect sense because most of the measurements of things we own or consume are counted in units like area, volume, and energy, which are inherently more tangible than an instantaneous rate like "power". Speed is a bit of an exception to this, but I think that has to do with the ubiquity of speedometers in cars.
To the extent that people broadly understand power as distinct from energy they tend to do so in a mechanical, not an electrical context, and in less precise terms ("That's a powerful truck"). However, some exceptions to this are light bulbs and electric space heaters, where people generally understand power as being proportional to brightness and heat output.
In a way, it's an incredible testament to the engineering of electrical systems that people have been able to largely ignore the difference between power and energy, or just need to flip a circuit breaker if something exceeds a limit.
Also, Li-ion and LiFePO4 batteries have a much different discharge curve than earlier chemistries [1], with much more constant voltage up to 80% discharge.
1. https://www.powertechsystems.eu/wp-content/uploads/sites/6/2...
Assuming 12V, that's about 400Ah*12V=4800Wh of storage. 4800Wh/400W = 12 hours to charge those, which seems reasonable for an RV. The thing that seems a bit oversized is the 3000W inverter.
Gonna be a gnarly market.
The amount of energy that can be stored in California's pumped storage projects is enormous, measured in hundreds, if not thousands, of GWh, but that's mostly irrelevant to this discussion.
Is it irrelevant? As another thread mentioned, how long you can provide that power for that for and how fast you can replenish capacity seems relevant for its usefulness buffering solar for after hours.
I'm pretty unread on the energy storage situation so your insight or any good resources are very welcome!
What kind of home PV solar panels should a person ask a contractor for? How do you know they're giving you quality rated panels?
Based on the energy mix, it looks like lost coal capacity has been replaced with solar and other green energy, and demand has gone down relative to population because of efficiency initiatives and rooftop solar for the largest home consumers (rich people).
I'll bet demand falls even faster as home energy storage gets cheaper and more prevalent.
Transmission is crucial for flexibility in balancing generation and consumption, as well as optimizing storage utilization. You can also assume there will be times you’ll throw away (curtail) clean energy as it’s cheaper than it would’ve been to store and then deliver it, but you still need that capacity available at other times (seasonal variability).
https://www.latimes.com/business/la-fi-utah-coal-los-angeles...
Well the new hybrid inverter from phocus is supposed to use the generation when grid outside is down internally at home and that opens up a lot of possibilities.
Been thinking about using solar water heating to reduce electricity consumption but that is a big project.
Batteries are still expensive in india. Lithium ion is prohibitively expensive than lead acid. Agreed it pays in time of life but still.
Edit: anyone know if I can incorporate phocus inverter into home assistant ? It has ble so some sort ?