3
\$\begingroup\$

My current solar system for home

  1. 12V 100W polycrystalline Solar Panel.
  2. 12V 75Ah Lead Acid solar tubular Battery.
  3. PWM 12V 10A Solar Charge Controller.
  4. 12V Input and 200VA Output Inverter.

Current Problem

Battery not getting charged fully daily because solar panel is getting around 3-4hours sunlight and that too includes sunlight at non-90 degree conditions.

So, I want to add an additional solar panel[preferably 200W or more] which will get 90 degree sunlight from 1pm to 5pm. Also, we get around 50 minutes of on grid supply. During this time inverter charges the battery too.

My questions as per my whole day research

If I add a 24V 200+W solar panel, I have to connect the panels in series because parallel means same voltage but ampere gets added.

Series means same ampere but voltage gets added.

In this cases what changes are needed to charge the 12V battery?

I guess someone will suggest MPPT controller. What is the best controller available in India? budget max6000INR

To avoid huge costs and hastle for the above requirement if I go with 12V 150W panel, then I will just need to connect my 12V 10A with a new 12V 20A controller in parallel to draw 8.6+12.5A=22A approx. current from solar panels.Am I correct here?

During a hot and shiny summer how much watts does a 100W panel produce in 90 degree sun conditions? What is the worst output that I will get in rainy season?

While charging battery from the inverter during grid supply, I see the inverter shows around 6A-9A current supply to the battery. Is it the current only that counts how fast the battery goings to be charged. Does change in voltage plaWattage (Wp) : 100 Voltage at Max Power, Vmp (V): 18 Current at Max Power, Imp (A): 5.56 Open Circuit Voltage, Voc (V): 22.3 Short Circuit Currrent, Isc (A): 6.1y any role?

I want to pull as much current as possible from grid and put it to my battery during that 50min time. What device will let me do so? Logically to charge a 12V 75Ah battery from 0-100 we will need something that putts 900W of power into the battery in an hour.

900/12=70A approx. How much Ampere is safe for longetivity of battery?

P.S: In any circumstances safety and device efficiency is my priority.Please excuse any non-sensical thing if I mentioned above.


Update 20-04-19

As per Russel McMohan's response to this question, I have some doubts when I tried to search more about the topic. Thanks a lot for your efforts sir.

  1. In case there are 2 12V panels:

First Panel Specs[Poly]I own this:

Wattage (Wp) : 100 Voltage at Max Power, Vmp (V): 18 Current at Max Power, Imp (A): 5.56 Open Circuit Voltage, Voc (V): 22.3 Short Circuit Currrent, Isc (A): 6.1

Second Panel Specs[Mono]Looking forward to buy:

Wattage (Wp) : 180 Voltage at Max Power, Vmp (V): 19.95 Current at Max Power, Imp (A): 9.03 Open Circuit Voltage, Voc (V): 23.26 Short Circuit Currrent, Isc (A): 9.31

There is around 2V and 4A difference. However, I can connect them in parallel. Will there be any efficiency issue because of minor Vmp difference?

As per the link mentioned earlier [Reference1][1]https://solarpanelsvenue.com/mixing-solar-panels/

If both panels are connected to individual 10A PWM controllers, then there wont be any such issue like the total ampere is 2* Min Ampere from either panels because I am not connecting both panels directly in parallel here.

Now total Output that I can expect is 12V*(5.56+9.03)A=12V*14.59A=175W approx. Here I considered 12V because PWMs are known for bringing down the voltage to battery level keeping constant curent and wasting rest of the voltage.

If the above estimation is correct, how do I connect the output from two PWMs to single 12V battery?

  1. As per your answer on shading issue, I have fixed the 100W panel position today.However, on searching about the bipass diode, I came to know my panel also has 2 diodes inside a box on the back of the panel.

This is how my front panel looks like: https://drive.google.com/open?id=140r_sGgANmxsevVWQLI8hLYEX1kaQDJx

Rear Panel Junction Box: https://drive.google.com/open?id=1Ekw3ojjdnBEzGS11mx7G5Wf1xuO5bPkz

So, front panel in potrait mode has 9 rows and 4 columns. Basically the columns are strings as you said in your answer and rows are substrings. Two diodes are there in JB, 3 junctions(+,Center and -). One diode connected b/w +ve & Center and another b/w -ve & Center . If 1st or 2nd String are under shade,then 3 and 4 will be active.vice-versa

If 8 substrings from these 4 strings are under shade then I think the diode wont work as by pass, the complete panel will produce current equivalent to 4 strings under shade.

  1. On close inspection, I noticed there is a slight crack at the top end of the substring located at 1st column[from left] and 2nd row[from bottom] Is it a severe fault and how badly can it degrade the output of overall panel. I will ask for a replacement if its serious issue.
\$\endgroup\$
  • 1
    \$\begingroup\$ We won't be answering your "what to buy" question, because these are explicitly off-topic here. However, your question is well-asked and researched, so there might be a few good answers about the technical side of all this. \$\endgroup\$ – Marcus Müller Apr 19 at 7:46
  • 1
    \$\begingroup\$ but, honestly, short answer is: no, you don't connect your panels in series or parallel. You get a charger/MPPT controller for every single type of panel, and connect them in parallel to your battery. \$\endgroup\$ – Marcus Müller Apr 19 at 7:47
  • \$\begingroup\$ Do you not find my answer useful? Maybe you need to read it (again)? \$\endgroup\$ – Russell McMahon Apr 20 at 3:26
  • \$\begingroup\$ @RussellMcMahon No sir, your answer was very helpful and learnt a lot of things out of it. I would like to discuss more as I dig deep into this project and I have many doubts to clear so I will be updating my OP from now onwards. \$\endgroup\$ – Rajesh Nayak Apr 20 at 13:22
  • \$\begingroup\$ A crack in the glass is a totally unacceptable fault in a new panel - and a life limiting one in any panel. Panel design is aimed at keeping LIQUID water out - water vapour ALWAYS gets in. Liquid water (even in trace forms and airborne) causes corrosion at hundreds of times the rate of water vapour and early panel deaths. || Two panels of slightly different voltage (say 17 Vmp and 18 Vmp) will PROBABLY produce slightly higher current than the sum of the two - and slightly less power than if used separately. The voltage under full load will be below Vmp of the high V panel so ... \$\endgroup\$ – Russell McMahon Apr 22 at 9:36
0
\$\begingroup\$

PV (Photovoltaic / Solar panels) shoild ideally be identical if used in series or parallel arrangements. However, non identical panels can with varying success be combined if

  • Used in series if of same max current.

  • Used in parallel if of same max voltage.

More details are required to assess specific combinations.

If used in series (12+12 or 12+24) and battery is 12V then you will need a down-converter - MPPT or other.

If used in parallel (12V + 12V) a higher current controller will be needed.


If I add a 24V 200+W solar panel, I have to connect the panels in series because parallel means same voltage but ampere gets added.

Existing 12V 100W = 100 W/12 A ~= 8.3 A max.
New 24V, 200W ~= 200 W/24A ~=,8.3A max. So, yes, you can use them in series with some mismatch with brand, model, age ... .

Series means same ampere but voltage gets added.

SHOULD be same A. V gets added - yes.

In this cases what changes are needed to charge the 12V battery?

Series PV -> downconverter to suit battery.
Parallel battery -> higher current controller.

I guess someone will suggest MPPT controller. What is the best controller available in India? budget max6000INR

India-available brands unknown to me but -

MPPT controller must accommodate Vin max & min, I max, Vout must suit battery charging.

To avoid huge costs and hastle for the above requirement if I go with 12V 150W panel, then I will just need to connect my 12V 10A with a new 12V 20A controller in parallel to draw 8.6 +12.5A = 22A approx. current from solar panels.Am I correct here?

100 W = 12 x 8.333 A
150 W = 12 x 12.5 A
Parallel = 250 W, 12V, 20.833 A.
-> 20A controller adequate in most conditions as long as it can tolerate 100% capacity combination.

Paralleling two controllers MAY work or may cause problems - refer manufacrturers sped sheets.

During a hot and shiny summer how much watts does a 100W panel produce in 90 degree sun conditions? What is the worst output that I will get in rainy season?

Here are the Gaisma insolation and related conditions for Calcutta, India.

The 6th graphic includes average daily insolation per day by month in kWh/day/square-metre.
Calcutta has much steadier year round sun than many locations. Clearness values are presumably typical.

enter image description here

As can be seen - sun input to a panel at midday with panel correctly oriented in about 6+ hours/day in summer and about 4 hours / day in Winter. Multiply this by 1000 W to get Watt-hours / day / metre-squared at the panel surface. Multiply by efficiency (usually 15%-20%) and allowances for unclean surface.

Chart 3 shows the sun angle across the day and gives some idea of the effect of angle.

enter image description here

While charging battery from the inverter during grid supply, I see the inverter shows around 6A-9A current supply to the battery. Is it the current only that counts how fast the battery goings to be charged. Does change in voltage play any role?

Complex, but current a fairly good proxy for charge being accepted.

I want to pull as much current as possible from grid and put it to my battery during that 50min time. What device will let me do so? Logically to charge a 12V 75Ah battery from 0-100 we will need something that putts 900W of power into the battery in an hour.

900/12=70A approx. How much Ampere is safe for longevity of battery?

Consult the battery spec sheet - BUT - that rate is liable to be excessive for most batteries of that capacity.
At nominal 75Ah in 50 minutes charge rate = 75 * 60/50 mins x 1/efficiency.
Say 75 x 60/50 * say 1/.9 = 100A at > 12V (up to 14.x) so say 1400-1500 Watts


Shading

Shading of ANY cells will drastically reduce panel output

  • Shading of any cell or cells reduced output of the string concerned to that of the most shade affected cell.

  • In panels where individual cells or sub-strings of strings are equipped with antishading diodes, the shaded cell or cells bridged by a single diode will contribute NO voltage output and will reduce the current from the other cells very slightly.

DO NOT SHADE ANY CELLS for best performance. For panels with a single string of PV cells in series and with shaded cells the max current for the panel will be the current of the shaded cell. A SINGLE SHADED CELL CAN REDUCE THE OUTPUT OF THE WHOLE PANEL TO 5% OF WHAT IT WOULD OTHERWISE GIVE.

Panels with diode across shaded cells will reduce voltage by the lost cell voltage but lose only a small amount of panel current capacity.

Panels with diodes across series connected strings with 1 one more shaded cells will reduce panel current to the current of the MOST shade affected cell in that string. eg panel with 72 cells, and Vmp = 18V Imp = 10A. Divide into 4 series substrings of 18 cells each and connect a protection diode across each group of 18 cells. If you shade ONE cell in ONE substring to say 10% of ambient solar level then in full sun:

  • Imp for shaded string is about 10A x 10% light = 1A BUT this is unusable as string is bypassed by its protection diode. This protects the whole panel against major current loss but reduces whole-panel voltage

  • Vmp for string with shaded cell is about -1V. (minus!)

  • Vmp for whole panel = 18V x 3/4 - 1V = 12.5V

  • Imp for whole panel ~= 10A

Same panel but with no diodes

  • Panel Vmp = 18V - 0.5V - 1 V ~~= 16.5V

  • Panel Imp = 1A (reduced to Imp of shaded cell)


Ask questions.

\$\endgroup\$
  • \$\begingroup\$ 1.As per my research on some 12V panels, there is slight difference in both Vmp and Imp? For ex, with respect to my current panel [18Vmp/5.56Imp ], I saw some panels with 18-20Vmp/8.22-11.12Imp. How much difference is decent for the setup? 2. However, for a 12+24V setup, you said down-converter[DOC] required to suit battery. What if I buy another 12V 75Ah battery and connect it in series with my other battery. Same Ampere voltage ADDED. 3. Is a DOC and MPPT same device? I was thinking to buy a MPPT, in that case DOC won't be required I guess? \$\endgroup\$ – Rajesh Nayak Apr 19 at 17:49
  • \$\begingroup\$ Today I came to know about one more interesting fact here link In my case, I was going to keep 100W panel in a shady region because it gets partial sunlight from 9AM to 3PM.Only 25 cells out of 36 get sunlight. So, I was thinking to keep it there and bring another panel of higher watts around 180-200W and keep it in an area where it will get full sunlight from 1PM-6PM. But,after going through the link I guess, the output of the bigger panel will be wasted because smaller panel will be under less Volts. Correct me if I am wrong? \$\endgroup\$ – Rajesh Nayak Apr 19 at 19:02
  • \$\begingroup\$ If you went through the above link, at the end of the page, they have the solution to my problem if I want to merge my 12V 100W panel with a new mono 12V 180W panel I will need to do that with 2 charge controllers connected parallely. But, he also talked about some DC cominer boxes and fuses. What are these? It would be helpful if I get a more detailed circuit for the connection. \$\endgroup\$ – Rajesh Nayak Apr 19 at 19:21
  • \$\begingroup\$ 1. For panels in series the max current will be ~= the max current of the lowest current panel. 2. For panels in parallel the max voltage will be ~= the voltage of the lowest voltage panel (These two facts can be established from the reference that you cited.) \$\endgroup\$ – Russell McMahon Apr 20 at 1:36
  • \$\begingroup\$ 3. DO NOT SHADE ANY CELLS for best performance. For panels with a single string of PV cells in series and with shaded cells the max current for the panel will be the current of the shaded cell. A SINGLE SHADED CELL CAN REDUCE THE OUTPUT OF THE WHOLE PANEL TO 5% OF WHAT IT WOULD OTHERWISE GIVE. || Panels with diode across shaded cells will reduce voltage by the lost cell voltage but lose only a small amount of panel current capacity. || Panels with diodes across strings with 1 one more shaded cells will reduce panel current to the current of the MOST shade affected cell in that string. \$\endgroup\$ – Russell McMahon Apr 20 at 1:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.