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Using Batteries as a "Buffer" to Stabilize Grid Electricity

Started by Robert Miller November 15, 2017
A friend of mine lives in a remote area. The power grid voltage 
fluctuates causing problems with his equipment. He has tried line 
filters with no success.

I suggested using a bank of SLA batteries as a "buffer".

IOW a grid-connected charger would keep the batteries topped up and 
current could be redrawn via a 110V inverter to power appliances.

In a nutshell, what would be the design criteria and limitations of such 
a system?

To what extent would it be practical to power an entire house?

Robert Miller
On 11/15/2017 10:38 PM, Robert Miller wrote:
> A friend of mine lives in a remote area. The power grid voltage > fluctuates causing problems with his equipment. He has tried line > filters with no success. > > I suggested using a bank of SLA batteries as a "buffer". > > IOW a grid-connected charger would keep the batteries topped up and > current could be redrawn via a 110V inverter to power appliances. > > In a nutshell, what would be the design criteria and limitations of such > a system? > > To what extent would it be practical to power an entire house? > > Robert Miller
<https://en.wikipedia.org/wiki/Uninterruptible_power_supply#Online.2Fdouble-conversion> Pretty sure that you can buy units off the shelf that could supply a couple kVA for at least an hour but they won't be cheap.
On 11/15/2017 10:53 PM, bitrex wrote:
> On 11/15/2017 10:38 PM, Robert Miller wrote: >> A friend of mine lives in a remote area. The power grid voltage >> fluctuates causing problems with his equipment. He has tried line >> filters with no success. >> >> I suggested using a bank of SLA batteries as a "buffer". >> >> IOW a grid-connected charger would keep the batteries topped up and >> current could be redrawn via a 110V inverter to power appliances. >> >> In a nutshell, what would be the design criteria and limitations of >> such a system? >> >> To what extent would it be practical to power an entire house? >> >> Robert Miller > > <https://en.wikipedia.org/wiki/Uninterruptible_power_supply#Online.2Fdouble-conversion> > > > Pretty sure that you can buy units off the shelf that could supply a > couple kVA for at least an hour but they won't be cheap.
The most economical solution to protect against fluctuations and also have protection against longer-term total outages would be to get one of the UPSes that can hold up critical equipment for a couple of minutes until a signal to the backup gas or diesel generator has been sent and it's powered up and ready to take over
On 11/15/2017 7:38 PM, Robert Miller wrote:
> A friend of mine lives in a remote area. The power grid voltage > fluctuates causing problems with his equipment. He has tried line > filters with no success. > > I suggested using a bank of SLA batteries as a "buffer". > > IOW a grid-connected charger would keep the batteries topped up and > current could be redrawn via a 110V inverter to power appliances. > > In a nutshell, what would be the design criteria and limitations of such > a system? > > To what extent would it be practical to power an entire house?
Unless it's life-support, I'd say impractical.
> > Robert Miller
The devil is in the details. Which equipment? What kind of problems? overvoltage? undervoltage? spikes? starting issues? ?????? real numbers on each? Can he be satisfied with 110V only? What happens when you turn on a 220V device like stove or clothes dryer or air conditioner? What are the statistics and timing of the instabilities? What does the utility recommend? What does google have to say about it? https://www.elprocus.com/types-voltage-stabilizers-and-their-working/ https://www.electricaltechnology.org/2016/11/what-is-voltage-stabilizer-how-it-works.html Line filters are good for taking out very short spikes. I have a small variac with a motor on it that takes out longer-term variations. It's only 500W, but the concept scales. There's an old concept that uses a ferroresonant transformer to provide some regulation. The name escapes me at the moment. You might be able to do something similar with an active magnetic amplifier. IMHO, anything requiring a huge battery capacity is a non-starter when you have the grid available. Depending on the details of the problem, it might be simpler to use a transformer to raise the minimum allowable voltage to an acceptable level and use something to buck it down below the maximum allowable. Magnetic amplifiers seem to apply here...depending on the requirements. Requirements definition is the first hard part of the problem.
On 11/15/2017 8:42 PM, mike wrote:
> On 11/15/2017 7:38 PM, Robert Miller wrote: >> A friend of mine lives in a remote area. The power grid voltage >> fluctuates causing problems with his equipment. He has tried line >> filters with no success. >> >> I suggested using a bank of SLA batteries as a "buffer". >> >> IOW a grid-connected charger would keep the batteries topped up and >> current could be redrawn via a 110V inverter to power appliances. >> >> In a nutshell, what would be the design criteria and limitations of such >> a system? >> >> To what extent would it be practical to power an entire house? > Unless it's life-support, I'd say impractical. >> >> Robert Miller > The devil is in the details. > Which equipment? What kind of problems? overvoltage? undervoltage? > spikes? starting issues? ?????? real numbers on each? > Can he be satisfied with 110V only? What happens when you turn > on a 220V device like stove or clothes dryer or air conditioner? > > What are the statistics and timing of the instabilities? > What does the utility recommend? > What does google have to say about it? > > https://www.elprocus.com/types-voltage-stabilizers-and-their-working/ > > https://www.electricaltechnology.org/2016/11/what-is-voltage-stabilizer-how-it-works.html > > > Line filters are good for taking out very short spikes. > > I have a small variac with a motor on it that takes out longer-term > variations. It's only 500W, but the concept scales. > There's an old concept that uses a ferroresonant transformer > to provide some regulation. The name escapes me at the moment. > > You might be able to do something similar with an active magnetic > amplifier. > > IMHO, anything requiring a huge battery capacity is a non-starter > when you have the grid available. > Depending on the details of the problem, it might be simpler to > use a transformer to raise the minimum allowable voltage to an > acceptable level > and use something to buck it down below the maximum allowable. > Magnetic amplifiers seem to apply here...depending on the requirements. > > Requirements definition is the first hard part of the problem.
For some classes of instability, something like this may be all that is needed http://www.brighthubengineering.com/consumer-appliances-electronics/66779-protect-your-home-appliances-with-an-automatic-voltage-stabilizer/
On Thu, 16 Nov 2017 14:38:31 +1100, Robert Miller
<rmiller@teledyne.com> wrote:

>A friend of mine lives in a remote area. The power grid voltage >fluctuates causing problems with his equipment. He has tried line >filters with no success. > >I suggested using a bank of SLA batteries as a "buffer". > >IOW a grid-connected charger would keep the batteries topped up and >current could be redrawn via a 110V inverter to power appliances.
That's roughly what the Tesla Powerwall does. <https://www.tesla.com/powerwall> The problem is that it wasn't quite designed to deal with major outages and regulation issues. It's primary purpose is to charge up when the cost of electricity is cheap, and discharge when it's expensive. In other words, save money by reducing peak power requirements. That's not the same as what you're suggesting, which essentially is a off-grid solution, using grid power as a backup.
>In a nutshell, what would be the design criteria and limitations of such >a system?
Ummm... cost, cost, and cost. Stationary batteries suitable for running a house are not cheap. In off grid power service, lead-acid batteries typical last 5 to 10 years and then need to be replaced. What kills them is mostly the number of charge/discharge cycles and the depth of discharge. In other words, the more you use it, the quicker you lose it. This article on various battery chemistries should help: <https://www.homepower.com/articles/solar-electricity/equipment-products/battery-chemistry?v=print> The problem is that while lead-acid batteries are awful, the other alternatives can be equally awful. It's just that they have a different set of disadvantages. More reading: <https://www.homepower.com/search/content/battery> Switching to alternative or stored energy may also require your friend to make some lifestyle and consumption changes.
>To what extent would it be practical to power an entire house?
I have no idea because you haven't supplied any numbers. It's easy enough to do a back of the envelope estimate on the practicality of running on alternative energy sources and battery power. However, I need numbers in order to produce anything useful. There are numerous calculators online which should give you some idea of what numbers are required. For example: <https://www.altestore.com/store/calculators/off_grid_calculator/> <http://www.batterysizingcalculator.com> <https://www.wholesalesolar.com/solar-information/battery-bank-sizing> <http://www.instructables.com/id/How-to-Size-Your-Off-Grid-Solar-Batteries-1/> etc... A good resource would be Home Power Magazine: <https://www.homepower.com> If your friend has a way to generator power (solar, wind, hydro), and can reduce electicity consumption to a reasonable level, he can probably operate without any grid power. Or he could use grid power as a backup for his alternative energy system. There are lots of examples of such systems in the various articles.
>Robert Miller
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
On Thu, 16 Nov 2017 14:38:31 +1100, Robert Miller
<rmiller@teledyne.com> wrote:

>A friend of mine lives in a remote area. The power grid voltage >fluctuates causing problems with his equipment. He has tried line >filters with no success. > >I suggested using a bank of SLA batteries as a "buffer". > >IOW a grid-connected charger would keep the batteries topped up and >current could be redrawn via a 110V inverter to power appliances. > >In a nutshell, what would be the design criteria and limitations of such >a system? > >To what extent would it be practical to power an entire house? > >Robert Miller
What is his load energy requirements ? Is this an intermittent flicker kind of issue or is it a constant voltage swing and constant brownouts ? A complete house like in the city typically requires somewhere around 30 kW-Hours per day so might be harder to power. Battery based grid-tied inverter might help depending on how fast the voltage variations are. Could pass-through the grid to critical loads and if slow enough swings, generator-support or grid-support modes can smooth out drops in input voltage from the grid. But a WHOLE 200 amp service house would be a bit much unless it was divied up with more inverter/battery systems. Check outbackpower and Schneider Electric (Xantrex) and SMA etc. 48V nominal battery systems.
On 16/11/2017 03:38, Robert Miller wrote:

> A friend of mine lives in a remote area. The power grid voltage > fluctuates causing problems with his equipment. He has tried line > filters with no success. > > I suggested using a bank of SLA batteries as a "buffer".
It would make much more sense to protect only the equipment that is prone to line fluctuations rather than the whole house.
> > IOW a grid-connected charger would keep the batteries topped up and > current could be redrawn via a 110V inverter to power appliances. > > In a nutshell, what would be the design criteria and limitations of such > a system? > > To what extent would it be practical to power an entire house?
For how long and with what criterion and budget? The way we did it for big telescopes was to have a reinforced flywheel going at a fair lick driven by an electric motor driving a dynamo. If the mains fails the clutch decouples the motor and the stored energy in the flywheel is used to stow the scopes and shut down the computers gracefully. You have to be very careful where you point the flywheel - if it ever broke free it would go for miles. The reason for such an eleborate setup was that power would usually go at the onset of a storm and leaving the scopes unstowed could do untold damage. More than one big radio telescope has been trashed by wind loading problems or bad luck. The problem you have is that to get a decent energy density storage is very expensive and comparatively high maintenance whether you do it chemically in batteries or mechanically in a flywheel or pumped storage. -- Regards, Martin Brown
On 11/16/2017 12:20 AM, Martin Brown wrote:
> On 16/11/2017 03:38, Robert Miller wrote: > >> A friend of mine lives in a remote area. The power grid voltage >> fluctuates causing problems with his equipment. He has tried line >> filters with no success. >> >> I suggested using a bank of SLA batteries as a "buffer". > > It would make much more sense to protect only the equipment that is > prone to line fluctuations rather than the whole house. >> >> IOW a grid-connected charger would keep the batteries topped up and >> current could be redrawn via a 110V inverter to power appliances. >> >> In a nutshell, what would be the design criteria and limitations of >> such a system? >> >> To what extent would it be practical to power an entire house? > > For how long and with what criterion and budget? The way we did it for > big telescopes was to have a reinforced flywheel going at a fair lick > driven by an electric motor driving a dynamo. If the mains fails the > clutch decouples the motor and the stored energy in the flywheel is used > to stow the scopes and shut down the computers gracefully. > > You have to be very careful where you point the flywheel - if it ever > broke free it would go for miles. The reason for such an eleborate setup > was that power would usually go at the onset of a storm and leaving the > scopes unstowed could do untold damage. Morethan one big radio > telescope has been trashed by wind loading problems or bad luck. > > The problem you have is that to get a decent energy density storage is > very expensive and comparatively high maintenance whether you do it > chemically in batteries or mechanically in a flywheel or pumped storage. >
About 30 years ago, I attended a trade show where they exhibited flywheel systems. I never understood how it was possible, and they sure didn't want to tell me, but they claimed that they wrote magnetic domains on the "flywheel" in real time so that the output frequency was RPM independent as the energy was extracted as a PM AC generator.
On 16/11/2017 08:45, mike wrote:
> On 11/16/2017 12:20 AM, Martin Brown wrote:
>> For how long and with what criterion and budget? The way we did it for >> big telescopes was to have a reinforced flywheel going at a fair lick >> driven by an electric motor driving a dynamo. If the mains fails the >> clutch decouples the motor and the stored energy in the flywheel is used >> to stow the scopes and shut down the computers gracefully. >> >> You have to be very careful where you point the flywheel - if it ever >> broke free it would go for miles. The reason for such an eleborate setup >> was that power would usually go at the onset of a storm and leaving the >> scopes unstowed could do untold damage. Morethan one big radio >> telescope has been trashed by wind loading problems or bad luck. >> >> The problem you have is that to get a decent energy density storage is >> very expensive and comparatively high maintenance whether you do it >> chemically in batteries or mechanically in a flywheel or pumped storage. >> > About 30 years ago, I attended a trade show where they > exhibited flywheel systems. > I never understood how it was possible, and they sure didn't want to > tell me, > but they claimed that they wrote magnetic domains on the "flywheel" > in real time so that the output frequency was RPM independent as the > energy was extracted as a PM AC generator.
ISTR ours was quite crude in frequency regulation once decoupled. It was designed in the late 1960's. It was good for about 15 minutes and the computer shutdown things in order of their sensitivity/risk of damage. Wright university have some materials on telescope construction and flywheels online that discusses optimal choice of materials. http://cecs.wright.edu/~rsrin/Courses/ME474-674/Winter%202008/Slides-5-no-equations%206%20to%20a%20page.pdf -- Regards, Martin Brown