Is my Calculation True for 60 Watt Off-Grid Lighthing ?

[malborn]

In order to make it cheaper by using less solar controller amphere. should I desing it at 24 V ?
and can I do that by connecting two 12 solar panel in series and connecting 12 volt batteries in series ?
Is there anything else that I aware of ?

Thank you.

[malborn]

Thank you very much for helping me. your answers are so useful

[Sunking]

Thank you for useful reply
I have two question:
Could you explain please what is "5" in [60 x 11 x 5] / 12 volts = 275 AH formula ? I want 3 days reserve.

Could I use 2 X 12 Volt battery in paralel 275AH/2 = 137.5 AH ?

Thank you

WWW answered the why to use 5 days (2.5 usable). Never ever parallel batteries unless necessary. Parallel batteries wil just shorten cycle life. It is never necessary to parallel batteries. Get out the 12 volt box. Lead acid batteries are 2 volts, not 12.

EDIT: As Mike noted you DO NOT use average Sun Hours for Off-Grid, or you go dark in the winter. Use worse case.

[Wy_White_Wolf]

Thank you for useful reply
I have two question:
Could you explain please what is "5" in [60 x 11 x 5] / 12 volts = 275 AH formula ? I want 3 days reserve.

Could I use 2 X 12 Volt battery in paralel 275AH/2 = 137.5 AH ?

Thank you

You should never use more than 20% of the battery in a day. So multiplying by 5 is the same as dividing by 20%. That also gives you 2.5 days autonomy before hitting the 50% SOC that you should never go below. If you still desire to have 3 days than substitute 6 instead of 5.

You could use 2 12v batteries in parallel but would be better off to use 2 6v in series.

WWW

[malborn]

Incorrect but you are on the right track.

Where you went wrong is with your correction factor [CF] of 1.25. The CF depends on what type of Charge Controller you use. If you intend to go the very expensive route and use a PWM controller CF = 2. If you go the least expensive route and use MPPT CF = 1.5. It will take you a while to figure out why MPPT is less expensive. MPPT controllers are roughly 5 times more expensive.

So assuming you use MPPT Panel Wattage = [60 watts x 11 hours x 1.5] 4.2 hours = 235 watts. So you buy a single 250 watt GT panel and a 20 amp MPPT controller Should cost you around $500. Don't go cheap on Charge Controllers. A good 20 amp unit is $200

For PWM you would need [60 x 11 x 2] /4.2 = 315 watts. That required 3 110 watt Battery panels and a 20 amp PWM controler. That will cost you $700.

Last part is the battery. Assuming 12 volt system will require [60 x 11 x 5] / 12 volts = 275 AH. That will be 2 6-volt 275 AH battery. A decent 3 to 4 year battery will cost you roughly $400 every 3 or 4 years. An excellent choice would be a pair of Trojan T-145's

Thank you for useful reply
I have two question:
Could you explain please what is "5" in [60 x 11 x 5] / 12 volts = 275 AH formula ? I want 3 days reserve.

Could I use 2 X 12 Volt battery in paralel 275AH/2 = 137.5 AH ?

Thank you

[Mike90250]

I looked at the average solar radiation data from gaisma, average sun hour for los angeles is about 4,2 hours

Is that the yearly average, or the winter time average? You need to use the Winter (shortest sun month) as your design start point. (or whatever month is the shortest month you will be using loads, maybe you don't use garden lights in Dec)

[Sunking]

I want to desing 60 W off grid lighting for my garden in los angeles. and It is going to light all the night (11 hours) is my calculation true ?

Consumption = 60 Watt x 11 hours x 1.25 (safety factor) = 825 Watt.hours

Incorrect but you are on the right track.

Where you went wrong is with your correction factor [CF] of 1.25. The CF depends on what type of Charge Controller you use. If you intend to go the very expensive route and use a PWM controller CF = 2. If you go the least expensive route and use MPPT CF = 1.5. It will take you a while to figure out why MPPT is less expensive. MPPT controllers are roughly 5 times more expensive.

So assuming you use MPPT Panel Wattage = [60 watts x 11 hours x 1.5] 4.2 hours = 235 watts. So you buy a single 250 watt GT panel and a 20 amp MPPT controller Should cost you around $500. Don't go cheap on Charge Controllers. A good 20 amp unit is $200

For PWM you would need [60 x 11 x 2] /4.2 = 315 watts. That required 3 110 watt Battery panels and a 20 amp PWM controler. That will cost you $700.

Last part is the battery. Assuming 12 volt system will require [60 x 11 x 5] / 12 volts = 275 AH. That will be 2 6-volt 275 AH battery. A decent 3 to 4 year battery will cost you roughly $400 every 3 or 4 years. An excellent choice would be a pair of Trojan T-145's

[malborn]

I want to desing 60 W off grid lighting for my garden in los angeles. and It is going to light all the night (11 hours) is my calculation true ?

Consumption = 60 Watt x 11 hours x 1.25 (safety factor) = 825 Watt.hours

I looked at the average solar radiation data from gaisma, average sun hour for los angeles is about 4,2 hours

Size of Panel =( 825 Watt.hours/ 4.2 hours) = 196,42 --> 200 Watt panel

all losses =0,85
Dept of Discharge = 0,5
3 days reserve

Size of the Battery= 825 Watt.hours / (0,85 x 0,5 x 12 Volt ) x 3 days = 485 AH Battery ---> 2 x 242 AH battery 12 Volt

Size of Controller = (200 Watts / 12V) X 1.2 (Safety factor) = 20 A solar controller


If I use 2 x 100 Watts solar panel for desinging 24 Volt system is it better ?


Thank you.