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

[malborn]

Oh thank you I just got it your answer


I am so curious about that: Let's say I have:
36 volt dc light
2 x 12 volt panel (24 volt)
2 x 12 volt battery (24 volt)
can I connect them to charge controller directly without using converter ? If ı need to use dc to dc converter where should I connect ? between load terminal of mppt and light or to batteries ?

thank you

[Sunking]

Let's say my lighting is 60 watt but 120 volt, should I use converter to convert 24 volt before connect to mppt controller ?

No you use a 24 volt Inverter connected to the batteries.

Panels > Charge Controller > Battery > Inverter.

[malborn]

Thank you very much for very useful information. I combine this informations with the book you offered me It is very helpful

Let's say my lighting is 60 watt led but 120 volt ac, should I use converter to convert 24 volt before connect to mppt controller ?

I just found this product: does it work ? http://www.trcelectronics.com/View/M...APV-8-24.shtml

[Sunking]

It might not possible to be practical but lets say I am using mppt controller and 2 X 12 volt batteries which require 36 volt for charge itself. and my panel Vmp is 38 Volt, 60 cells. Because Vmp of panel is bigger than the required voltages by batteries Can I desing like that ?

OK you are kind of loosing me. Are those two 12 volt batteries in series for 24 volts, or in parallel for 12 volts?

A panel with 60 cells in series should only have a Vmp of around 30 volts which is too low for a 24 volt battery, but fine for a 12 volt battery assuming you use MPPT controller. Are you sure that 60 cell panel Voc is 36 volts and you mistaken it for Vmp. Voc and Vmp are two different ratings.

Perhaps this might help. Regardless if the controller is PWM or MPPT you must have a minimum of 36 cells for every 12 volts of battery. So if you are indeed running 24 volt battery you must have at least 72 cells in series.

With PWM no more and no less than 36 cells per 12 volts of battery. So if you have say 4 36 cell battery panels on a 12 volt battery they must be wired in parallel to maintain 36 cells. If 24 volts they would have to be 2 in series in parallel with 2 in series to maintain 72 cells.

With MPPT you still need a minimum of 36 cells per 12 volt of battery. However depending on your controller could go as high as 100 cells or more. If you look at a MPPT controller it has a spec called Maximum Voc input. Small 15 amp controllers usually have a limit of 70 Voc, while others are 150, 200, 250, and up to 600 volts. But those are going to be you 80 amp controllers. You want to run as high of a voltage as possible to maximize efficiency.

last question why do we need to use only 36 cell solar panel on pwm controller ? lets say I need 300 watt and my panels 36 cell 100 watts. How should I connect them ? If I connect them in series 36 + 36 + 36 = 108 cells which exceeds 36 cells ?

Already answered that, In Parallel, not series. If MPPT then by all means in series if your controller can handle that high of a Voc. Prime numbers are BAD. You only have two options. All in series or all in parallel. Use whole numbers like 1,2 4, 6, 8, 9, 10, 12.....If you have a high voltage Controller of 150 Voc or higher you can get away with Prime number of 3 and 5 in series. But you effed yourself if you have say a 20 amp MPPT with 3 panels, as 3 could likely be more than 70 Voc limit of the controller. 1, 2, 4, and 6 work.

[Logan005]

Several controllers have lighting functions, dusk - dawn. dusk +6 hours.....

I use one of these controllers and it allows you to select how long after sundown to turn off the lights, therefore greatly reducing the size of battery bank and solar panels needed for a particular installation. Unless of course you wish the lights to run dusk to dawn, then you will pay double.

[malborn]

72 total in series. Most all 200 wat GT panels are 72 cells. Battery panels are 36 cells and made for 12 volts. You would have to use two of them in series to make 36 volts and 72 cells. Do not use battery panels with MPPT as you are throwing away money.

Just buy yourself two 200 watt GT panels with 72 cells and install them in parallel.

Thank you very much

It might not possible to be practical but lets say I am using mppt controller and 2 X 12 volt batteries which require 36 volt for charge itself. and my panel Vmp is 38 Volt, 60 cells. Because Vmp of panel is bigger than the required voltages by batteries Can I desing like that ?


last question why do we need to use only 36 cell solar panel on pwm controller ? lets say I need 300 watt and my panels 36 cell 100 watts. How should I connect them ? If I connect them in series 36 + 36 + 36 = 108 cells which exceeds 36 cells ?

btw I bought the solar book that you suggested to me on amazon

[Sunking]

Because we are going to use MPPT and 24 volt and you mention MPPT requires 72 cell solar panel, Should we use 72 cell + 72 cell= 144 cell solar panel or 36 cell + 36 cell =72 cell solar panel ?

I couldn't find 200 watt 72 cell 12 Volt solar panel to use?

72 total in series. Most all 200 wat GT panels are 72 cells. Battery panels are 36 cells and made for 12 volts. You would have to use two of them in series to make 36 volts and 72 cells. Do not use battery panels with MPPT as you are throwing away money.

Just buy yourself two 200 watt GT panels with 72 cells and install them in parallel.

[SunEagle]

I ordered the book from amazon Thank you.

Because we are going to use MPPT and 24 volt and you mention MPPT requires 72 cell solar panel, Should we use 72 cell + 72 cell= 144 cell solar panel or 36 cell + 36 cell =72 cell solar panel ?

I couldn't find 200 watt 72 cell 12 Volt solar panel to use?

Most 72 cell panels have a Vmp ~ 36 volts. The battery (12v) panels have about 36 cells which gets a Vmp ~ 18 volts.

Because most MPPT cc's have a higher DC input voltage rating you have the ability to wire multiple panels in series. With a PWM charge controller you are limited on the DC input voltage from the panel and usually have to wire them in parallel.

[malborn]

I ordered the book from amazon Thank you very much. Almost done I have just 4 questions

1) Because we are going to use MPPT and 24 volt and you mentioned MPPT requires 72 cell solar panel, Should we use 72 cell + 72 cell= 144 cell solar panel or 36 cell + 36 cell =72 cell solar panel ?

2) I couldn't find 200 watt 72 cell 12 Volt solar panel to use? is it okay if our one solar panel 200 watt 24 volt 72 cells? 2 x (200 watt, 24 Volt,72 cells) = 400 Watts, 48 Volts,144 cells.

3) Is it a problem to connect 24 Volt 60 watt led; 48 Volt panel and 24 volt battery bank to 15 amp mppt controller?

4) While we size controller ( 380 / 24 volt = 15.8 amp ) are we using battery bank voltage or solar panel voltage or led lighting voltage ?

I am going to send picture of 60 w light when it is working on my garden

[Sunking]

While you were calculating Panel Wattage and using 3,75 sun hours (1000 wh x 1.5 / 3.75 = 400 watts) you multiplied by 1,5 again. Where do it come from this 1.5 ? I think I already multiplied by 1.5 (For mppt) on consumption calculation ? (Consumption = 60 Watt x 11 hours x 1.5 (for MPPT) = 990 Watt.hours )

My bad. Did not read your opening statement. I thought 1 Kwh was your daily. Changes everything.

Panel Wattage = 825 x 1.5 / 3.25 = 380 watts. But no harm or foul using 400 watts
24 volt Battery = 825 x 5 / 24 volts = 172 AH
12 volt = 344 AH
MPPT = 380 / 24 = 15.8

If using the Morningstar Sun saver MPPT is 15 AMPS which works with 400 watts inpuut at 24 volt battery.

Bottom Line if I were you:

Panel - 400 watts
Battery = 24 Volts @ 200 AH
Morningstar Sunsaver MPPT 15 amp.

It is a perfect match made in heaven providing you got the daily watt hours right. December and January are the months you need to watch over. Spring, Summer, and Fall no worries. .

Solar 4 Dummies. There is no design book, its a secret.

[malborn]

Thank you very much I understood clearly. I am very happy now I just have 2 question.

While you were calculating Panel Wattage and using 3,75 sun hours (1000 wh x 1.5 / 3.75 = 400 watts) you multiplied by 1,5 again. Where do it come from this 1.5 ? I think I already multiplied by 1.5 (For mppt) on consumption calculation ? (Consumption = 60 Watt x 11 hours x 1.5 (for MPPT) = 990 Watt.hours )


I couldn't find Morningstar 20 Amp MPPT charge controller on their webpage. could you help me please to find it?

Could you suggest please any good book or source to desing solar ?

[Sunking]

Be I read your very useful post and read some stuffs on web Thank you very much for very useful information and helping me


Consumption = 60 Watt x 11 hours x 1.5 (for MPPT) = 990 Watt.hours

I looked at the average solar radiation data from gaisma, the lowest sun hour for los angeles is about 2.59 hours

Size of Panel =( 990 Watt.hours/ 2,59 hours) = 382 Watts; --> 2 x 191 Watts Solar Panel in series

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

Size of the Battery= 990 Watt.hours / (0,85 x 0,5 x 24 Volt ) x 2.5 days = 242 AH Battery ---> 2 x 121 AH battery 12 Volt in series

pdf: http://www.amerescosolar.com/sites/d...G5SHP_DEKA.pdf

Size of Controller = (2 x 190 Watts / 24 Volt) X 1.2 (Safety factor) = 19 A solar controller

Checkings

Solar Panel : Maximum power (Pmax) 190W 72 cells
Voltage at Pmax (Vmpp) 38.0V
Current at Pmax (Impp) 5.0A
Short circuit current (Isc) 5.5A
Open circuit voltage (Voc) 45.3V
pdf: http://www.amerescosolar.com/sites/d...90J-190W_0.pdf

Checking for Batteries

Because you said "12 volts of battery requires 18 volts of panel Vmp"
2 x 12 Volt batteries in series requires 2 x 18 = 36 Vmp
2 x 190 Watts Panels in series 2 x 38 = 76 Vmpp , so *am I good to use it ?

Checking for Solar Controller

Vpm (system) 2 x 38 Volt = 76 Volt
Voc (system) 2 x 45.3 Volt = 90.6 Volt


*Which MPPT charger controller should we choose at 20 amps ?

Close but no Cigar

Fist you are a little low on Insolation for LA. using latitude tilt 3.75 hours.

Battery First because it is easy peasy since we know 1Kwh/day.
12 volt = 1000wh x 5 /12 volts = 400 AH
24 volt = 200 AH
Close enough

Panel Wattage = 1000 wh x 1.5 / 3.75 = 400 watts

MPPT = 400w / 24 v = 17 amps
MPPT = 400w / 12 v = 35 amps

Should I use fuses or diodes for this simple light?

No fuses between panels and controller. No diodes anywhere. Only fuses on battery term post will show you later what and where.

the last question Why number of solar cell is important? 60 cell 100 watt solar panel is different than the 72 100 watt solar panel?

Cells determine the voltage.. For Voc 1 cell = roughly .61 volts, and Vmp = roughly .5 volt. Minimum Vmp for each 12 volt of battery is 18 volts or 36 cells. So for 24 volt you want a Vmp of at least 36 volts or 72 cells. With PWM controllers you must use 36 cell panels only. MPPT at least 36 or more. More is better to make efficiency higher and keeps cost down but there is a limit as you cannot exceed the MPPT controller max VOC input. That is an issue with small system as 15 to 20 amp controllers usually have a 70 Voc max. That means either 12 or 24 volt battery you are looking at around a max of 80 cells. There are a lot of 200 watt 72 and 80 cell panels for sale. Choose 80 if you get that option but no less than 72 if you intend to run 24 volt battery.

[malborn]

Be I read your very useful post and read some stuffs on web Thank you very much for very useful information and helping me


Consumption = 60 Watt x 11 hours x 1.5 (for MPPT) = 990 Watt.hours

I looked at the average solar radiation data from gaisma, the lowest sun hour for los angeles is about 2.59 hours

Size of Panel =( 990 Watt.hours/ 2,59 hours) = 382 Watts; --> 2 x 191 Watts Solar Panel in series

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

Size of the Battery= 990 Watt.hours / (0,85 x 0,5 x 24 Volt ) x 2.5 days = 242 AH Battery ---> 2 x 121 AH battery 12 Volt in series

pdf: http://www.amerescosolar.com/sites/d...G5SHP_DEKA.pdf

Size of Controller = (2 x 190 Watts / 24 Volt) X 1.2 (Safety factor) = 19 A solar controller

Checkings

Solar Panel : Maximum power (Pmax) 190W 72 cells
Voltage at Pmax (Vmpp) 38.0V
Current at Pmax (Impp) 5.0A
Short circuit current (Isc) 5.5A
Open circuit voltage (Voc) 45.3V
pdf: http://www.amerescosolar.com/sites/d...90J-190W_0.pdf

Checking for Batteries

Because you said "12 volts of battery requires 18 volts of panel Vmp"
2 x 12 Volt batteries in series requires 2 x 18 = 36 Vmp
2 x 190 Watts Panels in series 2 x 38 = 76 Vmpp , so *am I good to use it ?

Checking for Solar Controller

Vpm (system) 2 x 38 Volt = 76 Volt
Voc (system) 2 x 45.3 Volt = 90.6 Volt


*Which MPPT charger controller should we choose at 20 amps ?

*Should I use fuses or diodes for this simple light?

the last question Why number of solar cell is important? 60 cell 100 watt solar panel is different than the 72 100 watt solar panel?


Thank you very much.

[Sunking]

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.

The key here is to use inexpensive Grid Tied Panels and a MPPT controlller, and YES you are on the right path. It takes a 300 watt PWM system to = a 200 watt MPPT system. MPPT controllers are much higher than PWM controllers of a given amperage. The issue is GGT panels are much higher voltage, thus you must use MPPT controllers.

Bu there eis the GOTCHA. A low voltage battery panel cost roughly 2 to 6 times more per watt than GT panels. You can buy GT panels for around $1 to $1.50/watt, and battery panels around $2 to $12/watt. So using the low end you can buy a single 200 watt GT panel for $200 plus a $200 20 amp MPPT controller for a total of $400. If you go the PWM route you need 2-150 watt Battery panels costing some $600 plus a $50 20 amp PWM controller for a total of around $650. That is a significant difference. However the expense does not end there. Two 150 watt paneels requires twice the wire and hardware a single 200 watt panel requires.

OK let's answer your question. A 20 amp MPPT controller like a Morningstar Sun Saver can input 200 watts @ 12 volt battery, and 400 watts @ 24 volt battery to deliver the same 15 amps. But what is not obvious is for each 12 volts of battery requires 18 volts of panel Vmp. All battery panels are rated 17 to 18 volts Vmp. GT panels are higher than that. A typical 200 watt GT panel has 50 cells with a 25 volt Vmp rating, so it could not be used on a 24 volt battery because the voltage is too low. Works just fine on a 12 volt battery.

So what do you do? Simple use a 72 cell panel with a Vmp of 36 volts, or you could use 2 battery panels wired in series. With the Sun Saver MPPT operating you do not have a lot of wiggle room at 24 volt battery with a max Voc voltage of 70 Voc aka Voltage Open Circuit. It can be a bit confusing using two terms Vmp and Voc, but it is really simple. For minimum use the panel Vmp spec and wheen added up is at least 34 to 36 Vmp on a 24 volt battery. On the maximum since you live in LA left coast, maximum is 70 Voc which is roughly about 56 Vmp.

Let's make it even easier for Dummies. Select you panels based on the number of cells in series. No less than 72, and no more than 90. Just remember if you wire the panels in series to add the cells. So if you use say battery panels which have 36 cells, two in series is 36 + 36 = 72 cells. Or two 45 cell GT panels in series is 45 + 45 = 90.

Hint GT panels come in 72 and 80 cells.

[Mike90250]

Cheapest is to use a standard garden light string and run off the standard 12V transformer. Swap bulbs for LED versions, reduce from 60 w to 10 w overall.
or if a 200' extension cord costs more than $500, you can install solar, and run LED's right off the 12V battery. Several controllers have lighting functions, dusk - dawn. dusk +6 hours.....
Some low voltage LED;s are here https://www.wiredco.com/LED_Lighting...age_s/1874.htm