How Does a Off grid PV System

[Bendesa1962]

Hi everybody,

I've a question regarding Charge Controllers and Depth Of Discharge. When sizing a Off Grid PV System for a house, for example with a size of 5 kWp, and for the Battery bank you have to make a decision about Depth Of Discharge. I do understand the relation between DOD and Cycle life of batteries. My question is if you designed the system with a DOD of 50%. How does the Charge Controller knows when to stop discharging at 50%? Is it a setting on every charge controller or? Please help me out on this. Most appriciated.

[organic farmer]

Your Charge-Controller has a Low Battery Cut-Off [LBCO] setting.

DO NOT go with 50%

[ButchDeal]

It is the same for off grid as bimodal. You program the system ( usually inverter/charger) to the level you want to discharge to. If the battery gets to that level then you only have two options, start the generator or stop inverting ( lights go out but you stop discharging)
The charge controller can only control the level of charging from solar.
Some CC have a low level output that they control but this is just a smal load

[Bendesa1962]

Hi organic Farmer. Thx for your reply. Can it be set on the charge controller in % Percentages. Or does it needs to be done in voltages? What exactly do you mean by DO NOT go with 50%? Do you mean by that go with 40% or even less?

[organic farmer]

Hi organic Farmer. Thx for your reply. Can it be set on the charge controller in % Percentages. Or does it needs to be done in voltages? What exactly do you mean by DO NOT go with 50%? Do you mean by that go with 40% or even less?

The lower you go you damage your battery.

With my system it is set as a 'open circuit' voltage.

[Mike90250]

........ My question is if you designed the system with a DOD of 50%. How does the Charge Controller knows when to stop discharging at 50%? ......

It's in the design. You determine daily loads. Then you size solar to charge that. Done.
When day 2 comes and it's cloudy, you either cut all loads off to not violate 50%, or you start the generator,
You can make a "crude" guess as to SOC with a volt meter, but if you designed it right, you won't need to, If you added loads after the design, you are up the creek without a light

[Bendesa1962]

Ok Mike. Thanks for your explanation. Let me see if I get it right. You design an off grid system based on daily loads. Then you choose for the DOD for the battery bank. Let's say 50%. Based on the loads and the DOD of 50% you design the battery bank. If you made the design right the load will not exceed the 50% DOD because that's the way it was designed right? So the balance is in the design of the system? If you also included days of autonomy in the system for example 3 days. You designed the battery bank based on daily load, 50% DOD and Days of autonomy. But that would mean that in most cases the DOD will not be 50%, only in case when it's bad weather and you need the extra battery capacity. Right?

[Sunking]

It is real simple. Determine your daily Kwh usage, multiply by 5/ then divide by battery voltage.

So if you live like a fricken Hermit who only uses 10 Kwh per day and use a 48 volt battery is 10,000 wh x 5 / 48 = 1041 Amp Hours, round up to 1100 AH.

ow here is the fun and educational part you are going to love and laugh your arse off about. You get to replace the batteries in about 5 years, first set in 3 years. A 48 volt 1100 AH battery weighs around 3000 pounds. Now that is the Fun part, here is your education, they cost $8,000 to $10,00 and that does not including shipping, spill prevention, yearly inspections by local FD.

Now here is the part where you will laugh your but off about. You could have bought that same power for $1000 from the power company in the same time frame. You just paid 5 to 10 times more than you had to. Buy new batteries and the cost will be higher in 3 to 5 years from now. The fun never ends, you loose money the rest of your life or until you wake up and go back on grid.

[Bendesa1962]

Thanks for your explanation. The point is I live in Indonesia and on many places there is no grid at all. Not even close (-:

[Bendesa1962]

In Indonesia many area's don t have grid at all. So either they use a genset or a Solar Power System. On the long term the Solar System always is more cheap compared to the genset.

[Mike90250]

.... that does not including shipping, spill prevention, yearly inspections by local FD.....

You forgot toxic waste disposal.

Generally, homeowners don't need to follow all the Hazmat rules that Industrial users need to, ( yet ) But, yeah, that replacement cost is killer.

[Sunking]

Generally, homeowners don't need to follow all the Hazmat rules that Industrial users need to, ( yet ) But, yeah, that replacement cost is killer.

The Employment Prevention Agency is blind. They do not care who they put out of biz. Once you cross 500 pounds of Sulfuric Acid requires permits, yearly inspections, spill containment, blah blah under EPCRA 311 and 312 all must comply with.

[Sunking]

My bad, With you being in Indonesia, ignore everything I said and carry on as usual.