Are batteries just for back up power and not to be used all the time?

[jim naklick]

I want to have a back up battery system (just for critical loads) but am confused as to how they are to be used. If I need to invest 10-15K into a backup battery system are the batteries just to sit there in the event of a grid failure? I was hoping to draw from the batteries on a regular basis, operating whatever load they can to reduce my dependency and bill from the power company. Is this not a recommended use?

 

[Texican]

they are not just for backup. you can use them every night

 

[jim naklick]

they are not just for backup. you can use them every night

could I ask you to elaborate on your response? is it suggested that you would only use them at specific times and not27/7?

 

[Bkord]

I want to have a back up battery system (just for critical loads) but am confused as to how they are to be used. If I need to invest 10-15K into a backup battery system are the batteries just to sit there in the event of a grid failure? I was hoping to draw from the batteries on a regular basis, operating whatever load they can to reduce my dependency and bill from the power company. Is this not a recommended use?

You a use batteries anytime.

 

[SamDeleted]

I want to have a back up battery system (just for critical loads) but am confused as to how they are to be used. If I need to invest 10-15K into a backup battery system are the batteries just to sit there in the event of a grid failure? I was hoping to draw from the batteries on a regular basis, operating whatever load they can to reduce my dependency and bill from the power company. Is this not a recommended use?

Hi Jim . Have you got a solar PV array already?

Generally speaking - your panels charge up the batteries in the day , and then you use stored power in the evening , meaning you can take full advantage of the free electric your solar panels are producing




if you're spending 15k on a battery system, really you're installer should be able to answer all your questions, and install a system that suits your needs.

If they can't do that for you, I'd suggest finding yourself a different company!

 

[42OhmsPA]

Ideally you'd set your batteries up so they are in use all the time. Set a low soc at xx% to switch back to grid and also cover your loads in case the grid goes down.
Calculate your loads and how much reserve you want.

 

[jim naklick]

Hi Jim . Have you got a solar PV array already?

Generally speaking - your panels charge up the batteries in the day , and then you use stored power in the evening , meaning you can take full advantage of the free electric your solar panels are producing




if you're spending 15k on a battery system, really you're installer should be able to answer all your questions, and install a system that suits your needs.

If they can't do that for you, I'd suggest finding yourself a different company!

I currently do not have any solar whatsoever but am in the process of getting quotes and designs. If your batteries are charged during the day and used after sundown, what is powering the home during the day?

 

[SamDeleted]

I currently do not have any solar whatsoever but am in the process of getting quotes and designs. If your batteries are charged during the day and used after sundown, what is powering the home during the day?

The solar panels will power your house directly during the day ( at least when the sun's out ! )

When a cloud comes over , or when it gets dark, your system should seamlessly switch to battery power ... all being well ...

 

[42OhmsPA]

I currently do not have any solar whatsoever but am in the process of getting quotes and designs.

If your batteries are charged during the day and used after sundown, what is powering the home during the day?

Photons my friend, free photons. As many as you can harvest with solar panels.

 

[Texican]

in a normal solar system the panels make enough to power the house loads during the day and also charge the batteries

 

[TomC4306]

Partly cloudy yesterday.
Blue is what we are using, yellow is what we are producing. Between blue and yellow is charging.

 

[Mattb4]

I currently do not have any solar whatsoever but am in the process of getting quotes and designs. If your batteries are charged during the day and used after sundown, what is powering the home during the day?

What is powering your home without the batteries and inverter? The grid. So until you get your PV installed you would have to charge the batteries from the grid during times that they needed charging. Many folks have different grid prices at different times of the day and practice load shifting. This is where they charge the batteries when grid price is low and then run on the batteries when grid price is high. Not sure it makes good economic sense but you would have to do the math.

 

[wiseacre]

could I ask you to elaborate on your response? is it suggested that you would only use them at specific times and not27/7?

The Devil is in the system components.
A transfer switch of some sort will be needed.
In the simplest terms, you set an ATS using battery voltage to provide solar/battery power until a low voltage setting is met, then grid power is used until a high voltage setting is met and power switches back to solar/battery.

I built a simple backup system and then your question arose. How to use some of the power while the grid was up?
Seeing Will's video of the MOES ATS answered that question for me.
Not the most elegant of solutions compared to what is available in high priced tier 1 inverters but more than adequate for modest use.

My backup system components are installed in the garage.
Since I had grid power in the garage it was a simple matter of plugging the ATS in.
Adding a distribution box I ran a line into the house (not in any way connected to the original electrical) to power my aquariums, internet and tv.
In winter solar is dismal and keeping the batteries ready for emergency use severely limits how much battery power I can use, in summer there's plenty of power to run an A/C unit. (2000w of solar panels)

 

[TomC4306]

The Devil is in the system components.
A transfer switch of some sort will be needed.
In the simplest terms, you set an ATS using battery voltage to provide solar/battery power until a low voltage setting is met, then grid power is used until a high voltage setting is met and power switches back to solar/battery.

I built a simple backup system and then your question arose. How to use some of the power while the grid was up?
Seeing Will's video of the MOES ATS answered that question for me.
Not the most elegant of solutions compared to what is available in high priced tier 1 inverters but more than adequate for modest use.

My backup system components are installed in the garage.
Since I had grid power in the garage it was a simple matter of plugging the ATS in.
Adding a distribution box I ran a line into the house (not in any way connected to the original electrical) to power my aquariums, internet and tv.
In winter solar is dismal and keeping the batteries ready for emergency use severely limits how much battery power I can use, in summer there's plenty of power to run an A/C unit. (2000w of solar panels)

As an alternative, I use a pair of All in one inverters in split phase and feed them grid power.
The output of these feeds a 10 circuit manual transfer switch.
These 10 switches never get switched in daily cycling. That daily cycling switching is managed by the automatic transfer switch in the all-in-ones. They will use solar then battery then grid depending on what is available and what settings I have programmed into all the equipment.

 

[Hedges]

I want to have a back up battery system (just for critical loads) but am confused as to how they are to be used. If I need to invest 10-15K into a backup battery system are the batteries just to sit there in the event of a grid failure? I was hoping to draw from the batteries on a regular basis, operating whatever load they can to reduce my dependency and bill from the power company. Is this not a recommended use?

Cycling batteries or not depends on a few things, including inverter/charger capabilities.
Whether you want to cycle or not depends on cost & cycle life of batteries, and utility tariff (time of use? 100% credit for backfeed under net metering or not?)

Some inverters can blend power from battery, and/or power from PV, with grid. Others are strictly a UPS, either grid or battery supplies loads, and PV can charge battery.

Cycling a battery wears it out. Some could wear out in a fraction of their shelf (or float) life if cycled once per day, others would still have similar life. Cycled multiple times per day would shorten life.

I've seen batteries costing as little as $0.05/kWh of cycle life (server rack or DIY LiFePO4 cells), < $0.05/kWh (salvaged cells), or as high as $0.50/kWh (AGM, name brand lithium like LG-RESU)

I've seen utility rates from $0.05 to $0.50 and higher per kWh.

If cycling a battery costs more than buying from grid, better to just keep battery floated for backup purpose. That's what I do with AGM.

If battery + PV and everything else costs less than grid, then storing and using power can make sense.

If inverter can't blend power with grid, then you need one that can operate off-grid and carry your largest load, including starting motors. This can be very expensive.
If it can blend, then you can size equipment according to how much of your own power you want to make.

There are AC coupled batteries like Tesla PowerWall and others which can offset grid consumption.

If your tariff credits you something like $0.025/kWh and charges $0.50/kWh, then storing to a battery in order to avoid export, and drawing from battery to avoid import (especially at times of day with highest rates) could make sense. California's NEM 3.0 is intended to force you to do this.

DIY grid-tie PV can cost $0.03/kWh (amortized over 20 years), and turn-key installed systems can cost $0.10/kWh. These do blend with grid power. I have a large system like this, plus a small battery backup. When grid is down, PV capacity greater than loads like A/C mostly keep battery floating during the day, so battery only cycles at night.

Batteries are expensive, wear out, represent some degree of safety hazard. I believe in avoiding or minimizing battery unless you need to operate off-grid. A small backup system for telecom could be useful.

 

[jim naklick]

Cycling batteries or not depends on a few things, including inverter/charger capabilities.
Whether you want to cycle or not depends on cost & cycle life of batteries, and utility tariff (time of use? 100% credit for backfeed under net metering or not?)

Some inverters can blend power from battery, and/or power from PV, with grid. Others are strictly a UPS, either grid or battery supplies loads, and PV can charge battery.

Cycling a battery wears it out. Some could wear out in a fraction of their shelf (or float) life if cycled once per day, others would still have similar life. Cycled multiple times per day would shorten life.

I've seen batteries costing as little as $0.05/kWh of cycle life (server rack or DIY LiFePO4 cells), < $0.05/kWh (salvaged cells), or as high as $0.50/kWh (AGM, name brand lithium like LG-RESU)

I've seen utility rates from $0.05 to $0.50 and higher per kWh.

If cycling a battery costs more than buying from grid, better to just keep battery floated for backup purpose. That's what I do with AGM.

If battery + PV and everything else costs less than grid, then storing and using power can make sense.

If inverter can't blend power with grid, then you need one that can operate off-grid and carry your largest load, including starting motors. This can be very expensive.
If it can blend, then you can size equipment according to how much of your own power you want to make.

There are AC coupled batteries like Tesla PowerWall and others which can offset grid consumption.

If your tariff credits you something like $0.025/kWh and charges $0.50/kWh, then storing to a battery in order to avoid export, and drawing from battery to avoid import (especially at times of day with highest rates) could make sense. California's NEM 3.0 is intended to force you to do this.

DIY grid-tie PV can cost $0.03/kWh (amortized over 20 years), and turn-key installed systems can cost $0.10/kWh. These do blend with grid power. I have a large system like this, plus a small battery backup. When grid is down, PV capacity greater than loads like A/C mostly keep battery floating during the day, so battery only cycles at night.

Batteries are expensive, wear out, represent some degree of safety hazard. I believe in avoiding or minimizing battery unless you need to operate off-grid. A small backup system for telecom could be useful.

thank you for that informative explanation. I was under the impression that batteries of this sort could be charged and discharged thousands of times with only slight degradation? My hope is to have a system that in the event of grid down operate just a critical loads panel. Hard to say if that could be several hours or months?

 

[Hedges]

Automotive batteries maybe 10 to 50 cycles.
AGM 200 to 700 cycles
FLA, hundreds to couple thousand.
Shallow cycles e.g. 15% proportionally more than deep 50% to 80%, so forklift batteries can last 20 years.
Deeper discharge > 80% to 100%, you get significantly fewer Ah of lifetime cycling. Time spent at low SoC also causes shorter life.

Lithium and LiFePO4, we see claims of 2000, 4000, 7000 cycles.
One study cycling many (at rates around 1C discharge, 0.5C charge), perhaps 5% of models actually made it to spec's life. I recall Sony had one. The others failed, either got repaired, replaced, or test stopped.

Degradation often quoted at 80% of original capacity. At least for lead-acid, we also see proportional (or worse) decrease in "cranking" current or high load capability. For lithium, thought is that likelihood of catastrophic failure increases, so don't think of them as being 80% usable. For lead-acid, different behavior between cells accelerates failure of others (BMS/balancers not common, so others get over/under charged.)

Big lithium batteries are relatively new, and some have been rapidly cycle tested but we don't have field experience for 10 to 30 year life. Accelerated life tests, but degradation mechanisms and acceleration factor (accuracy) won't be well understood.

If you want to make/save money cycling lithium batteries, I suggest looking for break-even at no more than 25% of claimed life.
Given the death of Net Metering, and prices like $0.03/kWh PV, $0.05/kWh batteries, and $0.50/kWh utility rates, the gamble appears worth taking. Around 12% of claimed life is all you need to break even (battery neglecting inverter costs.)

But consider fire safety above all else.

Hours or months is quite doable with PV to recharge, and critical loads panel can be small enough to be affordable (as opposed to powering an electric in-ground swimming pool heater.)

I have a large (10kW) GT PV system, excessively large (23kW) AC coupled battery inverter system, and undersized (20kWh gross, 14kWh useable) AGM battery. Charging is programmed for 4kW, and surplus PV is curtailed when grid is down. Central A/C and all other loads are powered PV direct while the sun shines. Whole house including electric furnace are battery backed up, so I need to manually disable excessive loads, and some moderate loads just to make it through the night. I expect 10 year float life, and to use only 100 or so of 700 cycles to 70% DoD. Power I actually cycle through the battery will have cost me $3.50/kWh, but during power outages, 10x as much power goes direct to loads.

You can select an AIO or component system with modest battery size, have critical loads automatically backed up, and manually backfeed main breaker panel to supply any load you want while manually shutting off others. (e.g. operate garage door opener but not electric oven.)

 

[SamDeleted]

Degradation often quoted at 80% of original capacity. At least for lead-acid, we also see proportional (or worse) decrease in "cranking" current or high load capability. For lithium, thought is that likelihood of catastrophic failure increases, so don't think of them as being 80% usable. For lead-acid, different behavior between cells accelerates failure of others (BMS/balancers not common, so others get over/under charged.)

Big lithium batteries are relatively new, and some have been rapidly cycle tested but we don't have field experience for 10 to 30 year life. Accelerated life tests, but degradation mechanisms and acceleration factor (accuracy) won't be well understood.

And that is why I'm hesitant to put any money into lititum!

 

[Supervstech]

And that is why I'm hesitant to put any money into lititum!

Why? The more invested in the tech, the better tested and reliable and affordable it will become.

 

[SamDeleted]

Why? The more invested in the tech, the better tested and reliable and affordable it will become.

that's a good point , but I think it'll be a few more years before I'm willing to part with my hard earned cash

 

[Mattb4]

that's a good point , but I think it'll be a few more years before I'm willing to part with my hard earned cash

If you already are invested in LA batteries it would be hard to justify switching to lithium. It is at the point of replacement, or if building new, that weighing the merits and costs of the two that it might push you towards the LiFePO4. I am running dirt cheap lithium and if I get a few years of operation out of them I will consider it a successful thing.

 

[kundip]

I produce 12KW every night from 5PM until 7AM or 900Watts for 14 hours
Going two years now no effect on batteries yet.
I have 18KW of storage.
The battery protectors set at 23.5V - so that's the lowest voltage they go.
I charge LiFePo4 to 28V every night.
I watch Gumtree & Facebook sites & buy, my good quality only LiFePo4, batteries 1/2 Price only 1-2 years old.
Sometimes I have to wait 3 months for a good set of batteries.