How to calculate the capacity of storage battery?

[maxi_da1]

100MW wind farm

Guys i am working on design of a 100 MW wind farm and i need to know the calculations about energy storage of the system using batteries?

Precisely speaking,

What kind of batteries should be placed ?
What should be the ratings of battery in terms of power output in times of high demand.(Power out to the grid)

Please help me

[russ]

There is no place on the planet that gets 10 sun hours a day. You are confusing daylight hours with sun hours.
When panels are tested they are exposed to a light = 1000W per square meter. that gives them the watts of the panels.
Sun hours are the calculated amount of light in watts per square meter /1000.
Mike gave you a link to find the sun hours for your area. use it to find the sun hours for the lowest month of your year at your location and use that number to calculate how many watts of panels needed.

Except NREL uses the term 'insolation' which is generally kW/m2/day

To dumb it down people all the insolation value sun hours. 5.5 kW/m2/day is sometimes referred to as 5.5 sun hours

[Naptown]

There is no place on the planet that gets 10 sun hours a day. You are confusing daylight hours with sun hours.
When panels are tested they are exposed to a light = 1000W per square meter. that gives them the watts of the panels.
Sun hours are the calculated amount of light in watts per square meter /1000.
Mike gave you a link to find the sun hours for your area. use it to find the sun hours for the lowest month of your year at your location and use that number to calculate how many watts of panels needed.

[tharun]

Anyway, you need to harvest 300 watt hours, divide by ____ sun hours = ______ watts of PV

First of all, thank you mike. Really thank you. You cleared my mind.
lets say in here we have 10 sun hours. so i should buy a 12 volt 30 watts panel?

[Mike90250]

welcome. Lets' un-confuse this a bit.

power consumed by the fan is 50watts.
power required = 50 watts * 3 hours = 150watt hours

Good so far. If you use only 50% of battery, then you need a 300 watt hour battery.
At 12V, that would be a 25amp hour battery.

Now to recharge that battery, to account for all the system losses, you need to have a PV panel with a wattage nameplate that, when multiplied by your SUN hours
use PV watts to find out your hours http://www.nrel.gov/rredc/pvwatts/about.html
Ths solar SUN hours are quite different than when the sun is up , most areas get 6 or fewer hours.

Anyway, you need to harvest 300 watt hours, divide by ____ sun hours = ______ watts of PV

If you use an inverter , add 30% to the needed 300W harvest, you will need to harvest about 400 wh

Hope this helps

[tharun]

need help.. confusing

which is ri8.. case1 or case2?
CASE I:
our fan needs 220 v and 0.2 A for an hour = 50 watts.
a 12volt 7AH battery @20 hour rate -> 7/20 = 0.35 A.
The battery can sustain a 0.35A load for 20 hours.
But we can use only the 50% capacity of battery so tat it doesnt get damaged.
So 0.35A load for 10 hours.
If we consider the losses in invertor, the time will be around 3 hours.
CASE II:
power consumed by the fan is 50watts.
lets consider that we want the fan to run for about 3 hours in battery.
power required = 50 watts * 3 hours = 150watt hours
So, the battery capacity should be 150 watt hours.
what we need : Two 12volt 7AH in parallel. (in parallel v is constant and I= 7+7, so P=12*14=168 watt hours)
Loses in invertor will occur. We can not drain the full power from the battery.

[Mike90250]

It's a giodeline to start. Same batteries, same site, but more batteries, sized to only 20% dishcarge, should last over 5 years. (Deep cycle batteries, not Kmart deep/starter batteries)

[FamilyCamper]

Right, battery cycles, are:
a) Discharge to some value
b) Recharge back to full
= one cycle

Not the same thing as AC powerline frequency (cycles)

So with that said that means that the average battery coming in with a 50% discharge would last less than a year?

[Mike90250]

so it differs with "cycle" in the AC (Alternative Current, Hertz/cycle).
and Depth of Discharge (DOD) is what i just know.

Right, battery cycles, are:
a) Discharge to some value
b) Recharge back to full
= one cycle

Not the same thing as AC powerline frequency (cycles)

[MarineLiner]

Cycles vs Life

Batteries have a shorter life, the deeper you discharge them. example:
1000 cycles 10% discharge
800 cycles 20% discharge
300 cycles 50% discharge
80 cycles 90% discharge
Generally, discharge to no less than 50%, and size 1 day to about 10%
.....
Then you have to recharge it with something.

[Mike90250]

hi, Mick90250,

I want to make an off-grid system, I need to figure out which capacity of battery I should use.

Ok, let me make an example,
Load :2* 11W lamp; 10 hours working time per day.
system voltage:12V
Rainy days: 3 days

Then how will you calculate the capacity of the battery?

Much better question. I knew you were not going to manufacture a battery.

Batteries have a shorter life, the deeper you discharge them. example:
1000 cycles 10% discharge
800 cycles 20% discharge
300 cycles 50% discharge
80 cycles 90% discharge

Generally, discharge to no less than 50%, and size 1 day to about 10%

You are asking for 3 days. I 'll assume 12V CFL, so no inverter losses

Your load is 22W for 10 hrs = 220W hour x 3 days = 660w hour consumed in 3 days

So a battery bank of 1320wh would be the minimum size.

Working all in watts, allows conversion back to any voltage. Volt x Amp = watts

12V = 110A
24V = 55A

So a standard group 24 size battery would be just under the spec, but a group 27 would

http://www.mysears.com/DieHard-Marine-Deep-Cycle-RV-Battery-Group-Size-27M-reviews

just make it. at 105A.

Then you have to recharge it with something.

[solarf.helen]

hi, Mick90250,

Thanks for your answers, but I think you did not catch what I said. You know if I want to make an off-grid system, I need to figure out which capacity of battery I should use.

Ok, let me make an example,
Load :2* 11W lamp; 10 hours working time per day.
system voltage:12V
Rainy days: 3 days

Then how will you calculate the capacity of the battery?

[Mike90250]

The battery manufacturer makes that calculation when they design the battery, and then they put a label on the battery with the specs.

example 12V 110Ah @ 20 hour rate


In reality, you can only use half the power stored, otherwise, you severely shorten the life of the battery. There is a good battery FAQ here:
http://www.windsun.com/Batteries/Battery_FAQ.htm That will answer a lot of questions I hope.

Mike

[solarf.helen]

In stand alone solar system, how do you calculate the capacity of storage battery? Is that any formula?

Please make an example. Thanks so much for any answers.

Helen