Basic summary Formula for Battery sizing and PV Sizing.

[Sunking]

Anyone at the MS engineering level who spends all day on a free website telling newbies how wrong they are, is either not an MSEE (anyone can type those letters behind his name on a free, anonymous website), or something else is wrong.

Interesting first post. Did the thought of semi-retirement or retirement ever occur to you?

[russ]

I've seen Sunking's posts, in which he trashes newbies.

First and last warning - you are a newbie that shows up whining - next post like that I hit the ban button.

[Verum_1001]

MSEE PE, really?

I've seen Sunking's posts, in which he trashes newbies.

IF Sunking is really an MSEE PE, why is he spending his time on a free website telling newbies how stupid they are? Engineers at the MS level work with other engineers. They publish in peer reviewed journals, or at least present at engineering conferences. The work of MSEE level engineers is published and passed down to application engineers and technicians.

Anyone at the MS engineering level who spends all day on a free website telling newbies how wrong they are, is either not an MSEE (anyone can type those letters behind his name on a free, anonymous website), or something else is wrong.
Verum_1001

[Sunking]

Plus you need to add an alternative power source such as wind for those days when the sun has disappeared and for night-time charging. The costs are mounting!!

You are correct you need a secondary source of power for a Stand Alone system for cloudy spells and those time when you need more power, so kuddos for that. However that secondary source needs to be prime and fully available and wind is not the answer to that. Any stand Alone system really needs a generator. For example neither wind or solar is capable of a Equalization charge. Without a generator what you have planned for is being in the dark often and ruined batteries.

[Beanyboy57]

Does the list end here?


Cost (in my demographic):
500w Panel $650
1350ah Battery $940
45a MPPT $400
Sub Total $1990
Plus: cables, connectors, switches, fixtures.... etc.

2GRAND to operate 0.430kwh per day? = , aint it?

What about the inverter or perhaps a good quality inverter/charger? You can easily spend $1000 or more on a top quality brand.
Plus you need to add an alternative power source such as wind for those days when the sun has disappeared and for night-time charging. The costs are mounting!!

[brokejame]

looks interesting

Thanks for sharing this knowledge with us...

[Shockah]

1350AH battery bank with 200W of panels?? That would be about a C/80 charge rate, a bit short of C/12.

I do believe his calculation for 270AH batteries would be good for 2 1/2 days to 50% discharge and he could get close to 5 day autonomy with 500AH, use a 45A MPPT with at least 500W of panels.

Does the list end here?

Mr. Offgrid calculates 200W of panel is sufficient for his 0.430kwh daily usage...
and calculates a need of 1350ah battery bank.
But, now, the 200W panel is not enough,
and has to be bumped to 500W panel.

Cost (in my demographic):
500w Panel $650
1350ah Battery $940
45a MPPT $400
Sub Total $1990
Plus: cables, connectors, switches, fixtures.... etc.

2GRAND to operate 0.430kwh per day? = , aint it?

[radzif]

Ok guys

I have decided to forget everything I "think" I know and rewrite Sunkings post in my own words to give myself a better understanding but not forgetting what was taught in this post.I hope this helps other people in some or any way.

Solar Sizing Guide Line

Workout daily loads (Small example of just 1 room)

1. 15W light bulb for 6 hours daily = 90WH
2. 90W Laptop for 2 hours = 180WH
3. 5W Fish tank pump for 8 hours (off when I sleep) = 40WH
5. 5W Bedside Alarm for 24 hours = 120WH
Total WH = 430WH

We now add the inefficiency factor of 2 for system losses like wiring and charge controller and in my case a PWM controller,this would be less and I figure cheaper in the long run if I had a MPPT(Less Panels).

430AH x 2 = 860WH

Next we need to work out our Solar Insolation which will be used for our sunlight hours.I learnt an important lesson here.DONT just use the hours of sunlight in your part of the world,not all sunlight is the same in terms of solar radiation.Remember even though the sun may rise really early or set really late,those begining and end hours suck at charging and cant properly count.Also the figure used here must be the WORST insolation month or you wont produce enough power in that month.The worst isolation WINTER month should be used.Look at a solar map for your area.The data is measured as kWh/m2/day.For me my area has 4.5 kWh/m2/day in June and the worst isolation month of the year (Winter Solstice).This 4.5 kWH wil become my Sun Hour Day or the amount of hours with the best charging.More sun hours would obviously always be better.

So we devide the 860WH by the worst solar insolation month's hours to give us the size PV array we need.

860WH / 4.5 hours = 200 Watts (Rounded off) So I will need 200 Watts of panels.

We now need to Determine the Battery Size needed

Batterys last longer when only shallow discharged also the deeper/quicker the disharge the worse something called Peukert's law becomes.In simple terms a battery rated at say 100AH can be reduced to a 80AH battery if it is dischaged deeply/quickly and you basically get robbed of AH.You can see this on the battery manual if you look at the discharge rate section.Ideally we do not want to drain our batterys lower than 80% total capacity (Use only 20%).So we need to make sure we have 5 times our daily load in battery capacity (20% x 5 = 100% our daily load needs)

Since we already know our daily load when we were working out what loads we had in our 1st step,we take this figure and we multiply it by 1.5.The reason for this is there are inefficiencies when it comes to batteries too.Things like only 80% of a battery is available,the fact that rarely do batteries charge at their ideal tempretures.Also the are inefficiencies in the discharge of a battery like Peukerts law as mentioned above.So the daily load we had in our 1st step was 430WH

430WH x 1.5 = 645WH taken daily from the batteries.

We now need to multiply this by 5 as we mentioned to ensure only 20% is taken from the batteries.

645WH x 5 = 3225WH needed.

Batteries are usually given in amp hours so we need to convert Watts hours to Amp hours so we devide by the volts AH = WH/V.My system 12 Volts so...

3225WH / 12 = 270AH (Rounded off) So I will need 270AH of batteries or above for my system for ONE day

There is something we need to look at and that is days of autonomy.Since we dont know when there will be periods of rain,cloud cover etc we need to plan for this so basically days of autonomy is backup power for those days so we dont drain out batteries to nothing.So we multiply our battery for one day above by the amount of "backup" days we need.I amd going to use 5 days as and example but wouldnt suggest anything lower than 3.

270AH x 5 = 1350AH of batteries for my system with 5 days autonomy.

These calculations now provide a ball park as to the sizing of your system.

That concludes my small tutorial.Sunking and the other senior members can validate my calculations and make corrections.I would like to just give a massive thanks to Sunking and Russ for all their assistance provided here.Oscars for both of you lol.If the above information is correct,could you point me in the direction of working out what compromises the system inefficiency in the 1st step above (I used 2 for PWM) ie invertor inefficiency,charge controller inefficiency etc?

offgrid & sunking..how would i say this..u guys really safe my day!! TQ!!.. i'm naval architect student that was given a final year project to build a boat with solar panel..the main thing is that..throughout the years, i was taught on how to build a ship with diesel engine..not to build an fully electro propulsion based boat..which i, myself not too fond and less exposed to solar technology..so i just searching around through out the internet/magazines/articles..all just literally theories ..but none give me a specific detail + info's of pros and cons that might occur during practical as this thread did.. experience is what i'm searching here.. thanks guys

[Rishi]

how to size pv and battery for a system of 6.459kWh/day

please guide me on how to design size the pv array and the battery bank for the system of 6.459kWh/day. The average annual insolation is 4.69 and i require autonomy for 2 days.

[FloridaSun]

and another technical problem .. that you will operate your system as a 12 v system, with a more than 1000 amp hour.
which mean you gonna make them parallel if you use the 12v- 200 ah range batteries .. which is not recommended to parallel.

or you are about to use the 2v- 1000 ah range battaries which is veeeeeeeeery expensive


Regards

happy to heard your respectful comments

It would get even more expensive in ruined batteries with Offgrid's 'ball park' plan of...
"860WH / 4.5 hours = 200 Watts (Rounded off) So I will need 200 Watts of panels.
270AH x 5 = 1350AH of batteries for my system with 5 days autonomy."
1350AH battery bank with 200W of panels?? That would be about a C/80 charge rate, a bit short of C/12.

"430WH x 1.5 = 645WH taken daily from the batteries.
645WH x 5 = 3225WH needed.
3225WH / 12 = 270AH (Rounded off) So I will need 270AH of batteries or above for my system for ONE day
270AH x 5 = 1350AH of batteries for my system with 5 days autonomy."
I do believe his calculation for 270AH batteries would be good for 2 1/2 days to 50% discharge and he could get close to 5 day autonomy with 500AH, use a 45A MPPT with at least 500W of panels

This is an old thread. Wonder how he made out on his project.

[Bishoy Yanni]

young man note

i really appreciate your efforts doing all these calculations, but once you get in designing something you got close to money VS. performance relation

so for a 5 days autonomy you will increase the whole battery bank and put 4 more systems .. you raised the cost so much for something not so much important

actually if i were you i would just duplicate it.

i can see that for anyone who uses a solar energy system you can manage your life even if there is no electricity for 2 or 3 days .. but to save a big amount of money

and another technical problem .. that you will operate your system as a 12 v system, with a more than 1000 amp hour.
which mean you gonna make them parallel if you use the 12v- 200 ah range batteries .. which is not recommended to parallel.

or you are about to use the 2v- 1000 ah range battaries which is veeeeeeeeery expensive


Regards

happy to heard your respectful comments

[Offgrid]

Thanks for the feedback Russ.That's awesome!

[Mike90250]

I must print out before I can comment

[russ]

Let us see what other comments come.

[Offgrid]

Yeah for sure!It's so important to understand the design before implementation.So to you and Sunking,everything looks correct?