# How many kwh are in a 105 amp hour battery?

Solar Expert Posts: 62 ✭✭✭✭
How do you do the conversion from watts to kwh? How do you tell how many kwh you can get out of each 100 amp hour battery?

• Super Moderators, Administrators Posts: 33,548 admin
Re: How many kwh are in a 105 amp hour battery?

Tough question... If you want to calculate the Peukert based value--Use this spread sheet (points to Smartgauge's tech website).

Batteries are ugly... They are temperature sensitive (cold batteries have less apparent capacity). The faster (higher discharge rate) you discharge the battery, the less apparent capacity. Different battery types (AGM, flooded cell, etc.) have different behaviors (AGM are less negatively affected by high discharge/charging rates). New, batteries with some cycles, and as they age--Capacity changes.

Add that most people only charge the battery bank >90% daily or a few days a week, and battery cells can vary among each other by +/- 10%, etc.

Different loads have different behaviors as the batteries discharge.

The "standard" 20 Hour discharge rate (from 100% full to 0% full with a constant discharge current) is how the 20 hour rate is defined.

However, the most common load (filament lamps) which have a fairly constant discharge current (from 12.7 volts to 10.5 volts) are quite rare today for our off grid systems. We tend to use high efficiency lamps (LED, CFL, etc.) with electronic ballasts/AC inverters that are "constant power" loads on the battery bank.

Say you have a 100 Watt LED or AC load behind an AC Inverter. Power=Voltage*Current. If all is working correctly, the AC inverter (and the AC loads) will be constant power, which to the battery bank looks like:

100 watts * 1/0.85 inverter eff * 1/14.5 volts = 8.1 amps battery at absorb
100 watts * 1/0.85 inverter eff * 1/13.2 volts = 8.9 amps battery "floating"
100 watts * 1/0.85 inverter eff * 1/12.7 volts = 9.3 amps battery full charged
100 watts * 1/0.85 inverter eff * 1/10.5 volts = 11.2 amps battery near dead

So, you can see that for a constant power load, as the battery discharges, for our typical off grid systems, we see the the load current rises as the battery voltage falls.

So--There is the "exact answer" that only works for a battery at a specific temperature, specific age, specific discharge rate, load profile... Or--We use a bunch of engineering deratings that will give us a battery bank that will support the loads for the needed time.

Size the battery bank for the minimum operational temperature, at battery end of life (80% of capacity or less), worst case currents, and such.

Do you have a specific load/battery bank combination you are trying to size or see how long it will operate?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 62 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?

I have two separate systems in my mobile home. I have a small system in the back end of my house that has a brand new 105 amp hour agm battery and 200 watts of solar. It is always full and has plenty of extra power. I use it to run a few lights and my dsl router. These things do not seem to draw to much power. I have 1000 watt continuous inverter 2000 watt max.

I want to attatch a newer efficient washer to this system.

Could I run a load a day off of this system assuming my washer consumes .17 kwh each load???
• Solar Expert Posts: 3,009 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?

And don't forget to let us know the voltage of your battery bank.
A 24 volt 100 amp battery pack will deliver twice the kwh of a 12 volt 100 amp battery, all other things being equal, and a 100 amp 48 volt bank 4 times that of the 12 volt bank.
Also, a 1000 watt inverter usually has a rather large draw just to operate, even with no load, so that could be helping to drain your battery too.
"A few small things". What is small to one person, could be rather big to another. Can you let us know what you are running?
• Solar Expert Posts: 62 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?

I run two 10 watt lights about an hour a day. I run a DSL router that's 9 watts about 4 hours a day. That's pretty much it. I believe I have lots of extra power beacuse my voltage rarely drops below 12.4 even if a run all my lights all night.
I am on a 12 volt system
I only plan on doing a wash load after my battery is fully charged around noon or so. That way im only using the extra energy my battery doesnt need.

I really want to know what size battery you will need to run a .17 kwh load once a day?
• Super Moderators, Administrators Posts: 33,548 admin
Re: How many kwh are in a 105 amp hour battery?

There are two numbers you need... The average Watt*Hours per day (you have given us) and the surge current of the washer (well pump, etc.). Washing machines can be "pretty ugly" regarding surge current. However, we do not have that number.

2 x 10 watt lamps * 1 hour per day = 20 Watt*Hours
DSL router 9 Watts * 4 hours per day = 36 Watt*Hours
170 Watt*Hours per day washing machine.
==============================================
256 Watt*Hours per day

By the way, no computer, radio, cell phone charger, etc.? A DSL router without computer/etc.?

Anyway--Assuming the nominal rules of thumb for battery system design:

256 WH * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days of storage * 1/0.50 maximum battery discharge = 100 AH @ 12 volt battery bank

Now--That would be assuming no surge on the washer.... But, say you need a 1,000 Watt AC inverter to run the washer. The needed battery bank capacity uses another rule of thumb--Roughly 400 AH per 1kW of 12 VDC AC inverter... So, if using flooded cell batteries, you would be looking at a ~400 AH @ 12 volt battery bank.

If size/weight were an issue--You might get away with a 100 AH @ 12 volt AGM battery--AGM are much more able to handle high surge current than flooded cell (at about 2x the cost and somewhat shorter battery life time vs a similar flooded cell battery).

Lots of unknowns--But those are my guesses based on what you have said so far.

There are lots of other questions I would have (where is the system to look at hours of sun, what is the voltage/AH rating of the current battery bank, what is the AC inverter rating, what is your solar array wattage, etc.) that I would visit to figure out what size battery bank would be "optimum" for your present configuration (if you were to ask those questions).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 3,009 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?

And keep in mind that it's common for a good 1000 watt pure sine inverter to draw more or less 20 watts X 24 hours = 480 watt hours per day just to keep it idling in case it needs to supply a load. You could well prosper from a second small inverter that would be on 24/7 to run all your little loads, and only turn on the big inverter when you need to run the washer (and/or water pump).
• Solar Expert Posts: 3,741 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?
nobody928 wrote: »
I only plan on doing a wash load after my battery is fully charged around noon or so. That way I'm only using the extra energy my battery doesn't need.

If you have 200 watts of solar panels, they will produce less than 200 watts under almost all conditions. If your washer draws more than that (and most (all?) do), then you will be drawing down your battery while the washer operates. Of course, when the washer finishes its cycle the batteries will start charging again, and you may still end the day with a full charge.

You might want to consider doing the laundry before the battery goes to float... the reason is that once you go to float your controller will stay in float after the laundry (unless you draw down to the rebulk voltage) and not be able to fully charge the battery.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 62 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?
BB. wrote: »
There are two numbers you need... The average Watt*Hours per day (you have given us) and the surge current of the washer (well pump, etc.). Washing machines can be "pretty ugly" regarding surge current. However, we do not have that number.

2 x 10 watt lamps * 1 hour per day = 20 Watt*Hours
DSL router 9 Watts * 4 hours per day = 36 Watt*Hours
170 Watt*Hours per day washing machine.
==============================================
256 Watt*Hours per day

By the way, no computer, radio, cell phone charger, etc.? A DSL router without computer/etc.?

Anyway--Assuming the nominal rules of thumb for battery system design:

256 WH * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days of storage * 1/0.50 maximum battery discharge = 100 AH @ 12 volt battery bank

Now--That would be assuming no surge on the washer.... But, say you need a 1,000 Watt AC inverter to run the washer. The needed battery bank capacity uses another rule of thumb--Roughly 400 AH per 1kW of 12 VDC AC inverter... So, if using flooded cell batteries, you would be looking at a ~400 AH @ 12 volt battery bank.

If size/weight were an issue--You might get away with a 100 AH @ 12 volt AGM battery--AGM are much more able to handle high surge current than flooded cell (at about 2x the cost and somewhat shorter battery life time vs a similar flooded cell battery).

Lots of unknowns--But those are my guesses based on what you have said so far.

There are lots of other questions I would have (where is the system to look at hours of sun, what is the voltage/AH rating of the current battery bank, what is the AC inverter rating, what is your solar array wattage, etc.) that I would visit to figure out what size battery bank would be "optimum" for your present configuration (if you were to ask those questions).

-Bill

Bill I have two separate systems. My main one supplies all my tv's electronics chargers and freezer. This smaller 200 watt systems does my bedroom lighting and thats about it. I think I have a ton of battery capacity left every morning. I suspect that the starting surge is going to be around 10 amps max or in the neighborhood of 500 watts
• Super Moderators, Administrators Posts: 33,548 admin
Re: How many kwh are in a 105 amp hour battery?

10 amps at what voltage?

10 amps at 120 VAC is 1,200 VA surge.
10 amps at 12 VDC is 120 Watt surge.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 62 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?

I have not purchased the washer yet. I was just trying to figure out "hypothetically" if I could run the washer on the smaller of my two system. If it is in the relative range of acceptability. I do not need extra days calculated for because I have a generator I can run whenever need be. I also have a 300 watt inverter I can run to save power unless i need to use the washer that will require the 1000 watt inverter.

I was trying to figure out basically if a new energy efficient washer can be ran off of a 100 amp hour battery and 200 watts of solar hypothetically without any extra days of capacity being that I have generator support.
• Solar Expert Posts: 3,009 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?
nobody928 wrote: »
I have not purchased the washer yet. I was trying to figure out basically if a new energy efficient washer can be ran off of a 100 amp hour battery.

That would depend on the washer and it's surges. A 100 ah 12 volt battery is not very big when it comes to loads like a washer, so it wouldn't take much of a surge to drag it's voltage down to the point where the inverter would kick out, even though the battery may still have lots of charge left. Think of how car lights dim while starting the engine.
• Solar Expert Posts: 138
Re: How many kwh are in a 105 amp hour battery?
nobody928 wrote: »
How do you do the conversion from watts to kwh? How do you tell how many kwh you can get out of each 100 amp hour battery?

Assuming you do not discharge the battery below 50%, it is a 12 V lead-acid battery and at the 20 hour rate of discharge (5 A discharge or 12 V * 5 A = 60 W discharge):

100 Ah * 12V * .5 = <b>600 Wh = .6 kWh</b>

If it discharges by less than 5 A, then you get a little more total energy. If it discharges by more than 5 A, then you get a little less total energy. I have doubts that a 12 V, 100 Ah lead-acid battery could start a washing machine. If you are using an inverter, then multiply the energy by 85% to 90% depending on the efficiency of the inverter and wiring. Thus the 600 Wh becomes 510 Wh delivered to the load.
• Solar Expert Posts: 1,032 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?

I don't think I saw an answer to the question, how many kW-hours are in a 105 amp-hour battery (12V)

At 12.0 volts, that would be 105 X 12 = 1.260 kW-hours (100% discharge)
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?
boB wrote: »
I don't think I saw an answer to the question, how many kW-hours are in a 105 amp-hour battery (12V)

At 12.0 volts, that would be 105 X 12 = 1.260 kW-hours (100% discharge)

actually this may be less than that as from the at rest voltages of 12.7v (full charge) to 10.5v (dead) this averages to 11.6v times your 105ah capacity for 1218wh. now for most of us we recommend not exceeding the 50% dod point so the usable wh would be less than or equal to 609wh.
• Solar Expert Posts: 3,009 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?

Then of course, there's the rate of discharge. Unlike a fuel tank, the faster a lead-acid battery is discharged, the less total energy you'll get before it's drained.
• Solar Expert Posts: 722 ✭✭✭
Re: How many kwh are in a 105 amp hour battery?
That would depend on the washer and it's surges. A 100 ah 12 volt battery is not very big when it comes to loads like a washer, so it wouldn't take much of a surge to drag it's voltage down to the point where the inverter would kick out, even though the battery may still have lots of charge left. Think of how car lights dim while starting the engine.

There was a big thread on washers last week. Go have a look at it.

I just bought a new "energy efficient" one and these new models seem to have a direct drive motor rather than a clutch/transmission.

They are VERY quiet when agitating, however they do it by reversing the motor direction every 2 seconds, which causes a surge EVERY two seconds. So although mine uses .14kwh for a load, 75% of the time that is surging from 0 to 800+watts.
Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
• Solar Expert Posts: 62 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?
jcheil wrote: »
There was a big thread on washers last week. Go have a look at it.

I just bought a new "energy efficient" one and these new models seem to have a direct drive motor rather than a clutch/transmission.

They are VERY quiet when agitating, however they do it by reversing the motor direction every 2 seconds, which causes a surge EVERY two seconds. So although mine uses .14kwh for a load, 75% of the time that is surging from 0 to 800+watts.

Jcheil, I started that thread, so yes I have read it. I have a regular old power drawing whirlpool washer that will not run off of a 1200 watt generator for some reason so I am trying to upgrade my washing machine and seeking advice on how to do it from solar in order to save gas.
• Solar Expert Posts: 5,183 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?

Is that gen RATED at 1200 W continuous or peak output or is that the measured output? Manufacturers like to play with those numbers.
Like my 1000 W Honda is only 800W continuous...

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada
• Solar Expert Posts: 1,032 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?
niel wrote: »
actually this may be less than that as from the at rest voltages of 12.7v (full charge) to 10.5v (dead) this averages to 11.6v times your 105ah capacity for 1218wh. now for most of us we recommend not exceeding the 50% dod point so the usable wh would be less than or equal to 609wh.

kW-hours only down to 50% DoD wasn't his original question though, Niel. I just figured the question deserved an actual answer
in addition to all the other great discussions.

Strictly speaking though, if the battery actually has a capacity of 105 amp-hours, you can draw that amount out of it.
Yes, 100% DoD can and does happen. Not the best thing to do over long time but that is why they have that rating.

Voltage is always a ball-park, and depends on discharge rate. 12.0 V should be close enough for government work.
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?

boB,
yes, you're right it is close between your figure and mine, but 12v average is being optimistic unless the load is lower than the 20hr rate or in this case 5.25a. even then to the 100% dod point it still must go to 10.5v and will bring the average voltage down farther than 12v. heavier loads will draw down the voltage further yet even with a full battery. the current won't change, but the voltage will draw down significantly causing far less watthours to be realized. there is no black and white answer, but yours is a general answer that is quite optimistic.
• Solar Expert Posts: 722 ✭✭✭
Re: How many kwh are in a 105 amp hour battery?
nobody928 wrote: »
Jcheil, I started that thread, so yes I have read it. I have a regular old power drawing whirlpool washer that will not run off of a 1200 watt generator for some reason so I am trying to upgrade my washing machine and seeking advice on how to do it from solar in order to save gas.

Opps, I didn't realize you started that one

I will try running my new washer on my 1400(rated) generator tomorrow just to see how/if it works.
And my 1400(rated) is BORDERLINE 1400(rated). Even though it says 1400/1800, I am lucky if it doesn't choke around 1200. And it will SURGE to 1800 but the voltage drops so low that appliances (fridge, etc) WILL start, but when I run it thru my VFX3648, the inverter will drop the AC input EVERY TIME the fridge starts (and I have it set to 100v in the inverter min gen ac voltage setting).
Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
• Solar Expert Posts: 1,032 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?
niel wrote: »
boB,
yes, you're right it is close between your figure and mine, but 12v average is being optimistic unless the load is lower than the 20hr rate or in this case 5.25a. even then to the 100% dod point it still must go to 10.5v and will bring the average voltage down farther than 12v. heavier loads will draw down the voltage further yet even with a full battery. the current won't change, but the voltage will draw down significantly causing far less watthours to be realized. there is no black and white answer, but yours is a general answer that is quite optimistic.

10.5 volts is considered as 0% (discharged). I picked 12.0 volts just because it is around 50% full/empty.

But who cares ? Nobody was really interested in how many kW-hours were in a 105 amp-hour 12V battery anyway.
Otherwise, someone would have multiplied two (2) numbers together for a simple (albeit not of the greatest use) answer.

OK, so make it instead, 875 watt-hours of energy if calculating from dead battery voltage. It's still close to 1kW-Hour.

BTW, I looked at this chart... Discharge rate was not taken into account for my calculation so it could have
been based on C/100.

http://www.solar-electric.com/deep-cycle-battery-faq.html
• Solar Expert Posts: 10,300 ✭✭✭✭
Re: How many kwh are in a 105 amp hour battery?

"But who cares ? Nobody was really interested in how many kW-hours were in a 105 amp-hour 12V battery anyway."