Battery 4 hour storage limit [Utility scale storage]

[RubberToe]

All,
Someone help me understand this. A lot of the stories I read about battery storage have a disclaimer along the lines of "limited to 4-6 hours". And that longer duration storage is needed (see below article).

If someone builds a site with (for example) 100 powerpacks that all charge during the day, what is to prevent that site from discharging 20 of them for 4 hours, the next 20 for the next 4 hours, etc, and then having a total discharge period of 20 hours using lesser output versus discharging them all during the first 4 hours?

If you need 12 hours of battery discharge, just build a battery that is 3x larger and stagger the power output, right?

3 Barriers to Large-Scale Energy Storage Deployment - CleanTechnica

In just one year—from 2020 to 2021—utility-scale battery storage capacity in the United States tripled, progress is impressive, the beginning

cleantechnica.com

 

[jjrandorin]

I dont know anything about "battery storage limited for 4-6 hours"..... Tesla powerwalls allow you to set a 100% backup (which actually is around 92-95%) and leave them there... forever.

So, I dont know what you are reading about 4-6 hour limit, but as far as this subforum (Tesla energy) its not applicable.

 

[Zinc_Saucier]

If someone builds a site with (for example) 100 powerpacks that all charge during the day, what is to prevent that site from discharging 20 of them for 4 hours, the next 20 for the next 4 hours, etc, and then having a total discharge period of 20 hours using lesser output versus discharging them all during the first 4 hours?

It all depends on the discharge rate. Using 100% of one battery at a time before moving on to the next doesn’t make the site last longer. For example, you have 10 10kWh batteries (so 100kWh total capacity), and are discharging at 5kW. It takes 2 hrs for each battery to drain (10kWh / 5kW = 2hr). If you do that in series, it’s 20hrs. If you use them all in parallel, then you’re draining 5kW from a total pool of 100kWh, and it will take you 20hrs to deplete the batteries.

But if there’s demand for 100kW, and all the batteries discharged together, your site would only last 1hr. However, if you tried to supply a demand of 100kW with 40kW of power, you’re going to have a bad day.

 

[RubberToe]

I dont know anything about "battery storage limited for 4-6 hours"..... Tesla powerwalls allow you to set a 100% backup (which actually is around 92-95%) and leave them there... forever.

So, I dont know what you are reading about 4-6 hour limit, but as far as this subforum (Tesla energy) its not applicable.

Poor wording on my part, should have said 4-6 hour discharge period. You can clearly charge it up and keep the energy stored without discharge as long as you want. I'll try and find another story link where this is stated. The upshot is that they state that the battery storage system can only provide 4-6 hours of stored power.

RT

 

[jjrandorin]

Poor wording on my part, should have said 4-6 hour discharge period. You can clearly charge it up and keep the energy stored without discharge as long as you want. I'll try and find another story link where this is stated. The upshot is that they state that the battery storage system can only provide 4-6 hours of stored power.

RT

I still dont understand, though... since I use my powerwalls in self powered mode, and they discharge from when the sun stops hitting them in the evening, till the sun rises in the morning and starts hitting them, and sometimes longer than that if my home load > than PV.

Yesterday (for example) my Powerwalls started discharging at 3:30pm. At that time, they reported they were 98% full. They discharged till they hit my set reserve of 30%, around 3:00am. Most of the time, however, they discharge from about an hour before sundown, till about an hour after sunup, which is significantly longer than 4-6 hours, so I still dont understand what is being mentioned here.

 

[Tam]

...battery storage system can only provide 4-6 hours of stored power....

A natural gas generator can supply electricity as long as the gas is there.

Not with battery. The battery system's capacity is limited until recharged again. Thus, they need to install more battery capacity if they want a longer duration.

California utilities sent out an "Amber Alert" on the cell phone to ask customers to conserve energy from 4 to 9 PM, which is 5 hours. So if a battery system can last 5 hours, that's pretty good!

 

[jjrandorin]

A natural gas generator can supply electricity as long as the gas is there.

Not with battery. The battery system's capacity is limited until recharged again.

I dont understand the point of this statement at all. Providing power to a battery (via solar or otherwise) isnt much different than providing gas to a generator. What point are you making with the above statement?

 

[Zinc_Saucier]

The upshot is that they state that the battery storage system can only provide 4-6 hours of stored power.

Who are “they”, and what is “the battery storage system” that “they” are talking about?

 

[ZenRockGarden]

I would expect a sufficient array of powerwalls can store as many hours as you want. There's more of a design efficiency choice here for the install - do you need 3 days of power at full discharge, or (more likely) does it make more sense to scale the thing to handle either a typical 6 hour peak-outage, or the overnight needs of the house when solar is not available. Decide your preference and install a number of powerwalls to taste.

Nothing in that says that there's some inherent 4 hour limit "on the batteries".

 

[Tam]

I dont understand the point of this statement at all. Providing power to a battery (via solar or otherwise) isnt much different than providing gas to a generator. What point are you making with the above statement?

With a backup gas generator, it can be fired up for hours or days as long as there's still gas available.

With a battery, it's limited to its capacity as it got depleted and it needs to be recharged again.

The article is talking about "Large Scale" so when there's a brownout alert, all the utilities' solar panels are diverted to the customers' consumption and none is allowed to charge the batteries. All of utilites' batteries are to discharge to avert an emergency and not to be charged during the alert.

That's not the same with natural gas Peak-Shaving generator during the alert. It can replenish itself with as much gas as it wants during the alert.

 

[Tam]

...Providing power to a battery (via solar or otherwise) isnt much different than providing gas to a generator...

According to SCE, its Mira Loma Substation "can be charged when demand is low and store up to 80 megawatt-hours, enough energy to power 15,000 homes for four hours."

Innovative Battery Storage Facility at SCE’s Mira Loma Substation Allows for More Renewables

ONTARIO, Calif. — With the steel towers behind the Mira Loma Substation as a backdrop, several rows of large, white rectangular boxes stand in neat formation. Some say this is a...

energized.edison.com

That's the point of this thread: Batteries needs to be charged, and when they are discharged, the above station can only supply energy to a limited number of homes for 4 hours.

 

[jjrandorin]

According to SCE, its Mira Loma Substation "can be charged when demand is low and store up to 80 megawatt-hours, enough energy to power 15,000 homes for four hours."

Innovative Battery Storage Facility at SCE’s Mira Loma Substation Allows for More Renewables

ONTARIO, Calif. — With the steel towers behind the Mira Loma Substation as a backdrop, several rows of large, white rectangular boxes stand in neat formation. Some say this is a...

energized.edison.com

That's the point of this thread: Batteries needs to be charged, and when they are discharged, the above station can only supply energy to a limited number of homes for 4 hours.

Oh,

I thought this was about some question about a technical limitation of only 4 hours of storage of powerwalls, not a capacity question about some substation or other (a discussion I am not interested in).

Thanks for pointing that out.

 

[Zinc_Saucier]

According to SCE, its Mira Loma Substation "can be charged when demand is low and store up to 80 megawatt-hours, enough energy to power 15,000 homes for four hours."

So the batteries allow for storage of energy from when there is low demand to help offset periods of high demand, thereby helping to flatten the demand curve.

That's the point of this thread: Batteries needs to be charged, and when they are discharged, the above station can only supply energy to a limited number of homes for 4 hours.

The point of this thread is unclear at best (I think we need OP to chime back in before stating that conclusively). If the point of the thread is “batteries need to be charged before use”, well…duh. If the point is that this particular station doesn’t have enough capacity, there’s a lot of detail missing before making such a statement.

How much capacity should this station have? Your use of the word “only” indicates that it’s not sufficient, but for helping to ease the peak demand time, 15k homes being powered 100% from batteries for 4 hours seems reasonable to me. Remember, the point is not to replace the baseline power generation, but supplement at times of peak demand.

 

[Tam]

...Remember, the point is not to replace the baseline power generation, but supplement at times of peak demand.

Ideally, solar panels should be able to replace fossil generators.

15,000 homes seem to be a lot, but more than 3 million (3,620,308) Housing Units are in Los Angeles County alone.

There's no technical reason that it can't be done for the whole USA. It's just a matter of scaling up.

 

[RKCRLR]

Ideally, solar panels should be able to replace fossil generators.

I don't see solar plus battery storage alone ever being able to replace fossil generators. The solar would need to be sized for winter production and the batteries would need to be sized to last for days or weeks during storms or other periods of low production. While theoretically possible it wouldn't be practical. Perhaps if combined with wind, hydro storage, and other renewables it could be done but there are many areas of the US that don't get the sun California does, especially in the winter. Each area needs to come up with the bet solution for it's particular circumstances.

 

[Tam]

...While theoretically possible it wouldn't be practical...

Correct. It's a matter of will, but the technology is already here.

 

[RKCRLR]

Correct. It's a matter of will, but the technology is already here.

Will, and a lot of dollars. You'd be talking about paying for kilowatt hours in dollars and not cents.

 

[ZenRockGarden]

I don't see solar plus battery storage alone ever being able to replace fossil generators. The solar would need to be sized for winter production and the batteries would need to be sized to last for days or weeks during storms or other periods of low production. While theoretically possible it wouldn't be practical. Perhaps if combined with wind, hydro storage, and other renewables it could be done but there are many areas of the US that don't get the sun California does, especially in the winter. Each area needs to come up with the bet solution for it's particular circumstances.

I don't think anyone expects solar+battery alone. Wind, hydro, geothermal, wave power - we're expecting all kinds of sources, of which only one is daytime-centric (solar) which is fine since consumption is highest during the day.

 

[RubberToe]

So the batteries allow for storage of energy from when there is low demand to help offset periods of high demand, thereby helping to flatten the demand curve.

The point of this thread is unclear at best (I think we need OP to chime back in before stating that conclusively). If the point of the thread is “batteries need to be charged before use”, well…duh. If the point is that this particular station doesn’t have enough capacity, there’s a lot of detail missing before making such a statement.

How much capacity should this station have? Your use of the word “only” indicates that it’s not sufficient, but for helping to ease the peak demand time, 15k homes being powered 100% from batteries for 4 hours seems reasonable to me. Remember, the point is not to replace the baseline power generation, but supplement at times of peak demand.

The link and comment that @Tam made is what I am talking about. How much power can a utility scale battery station supply and for how long. This link covers this exact topic. So "We calculate a battery’s duration by using the ratio of energy capacity (measured in megawatt-hours [MWh]) to power capacity (in MW). Energy capacity refers to the total amount of energy these batteries can store."

A station with a 100MW power capacity is able to generate 100MW of power. If the energy capacity is 400MWh, it can generate that 100MW of power for 4 hours. And the linked article also shows the capacity and duration for energy shifting applications:

So this is likely where the "4 hours" number that is typically referenced comes from, though note that there are many sites that provide more than 4 hours of power generation.

The point that I was originally trying to make, is that many articles I read like this one often mention 4 hours of power capacity. While there are another whole universe of articles that complain about needing longer term storage, because 4 hours isn't sufficient, like this one also mention 4 hours as a kind of "upper limit":

My point being that utility scale battery storage sites can provide power for any duration required. A 10MW power capacity system with 1000MWh of energy capacity can provide 100 hours of 10MW of power. Now, whether that is practical or not, I have no idea.

Question: If a plant is designed with a 100MW power capacity, and 400MWh of storage capacity, does it have to ALWAYS provide 100MW of power when discharging, or could it be operated to provide 50MW of power, and therefore be able to run for 8 hours?

I totally get that batteries aren't likely to be able to get us from say 90% renewable to 100% renewable due to having to be sized very large for the winter scenario where there are 10 cloudy days in a row. For that you likely need seasonal storage (electrolyzed hydrogen stored and burned in gas turbines).

Apologies for the confusion and not being clearer in my original post. Hope this clears things up.

RT

 

[MJ_CA_2019]

These observations are similar to ones I made during the recent VPP events that coincided with the CA heat wave.
The PW2 has a sustained output of 5 kW (per PW2) but a usable capacity of 13.5 kWh (per PW2). That's 2.7 hours.
This ratio works pretty well to support an individual home; it's not good for grid support IMO.