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Question about solar array size and compatible charge controller

 
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I'm confused about sizing an array with a charge controller...  If I go with five 210w panels (specs below) what specs do I need to consider for the compatible charge controller?  Would I need two Epever Tracer4210AN charge controllers for this array?  Is there a problem with two charge controllers?

I don't know what battery bank I am looking at yet, but considering one 200aHr Chins 12v.


Panel specs
Max Power Output(W): 210W
Voltage MPP Vmp(V): 16.77V
Current MPP Imp(A): 12.48A
Voltage Open Circuit Voc(V): 19.83V
Short Circuit Current Isc(A): 13.09A
 
Tim Comer
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And, I don't understand the relationship between the charge controller and the battery bank.  If I wire the panels into the charge controller at 24v to use one charge controller and I have a 12 v battery bank does the charge controller adjust the voltage when charging the batteries or do I need a 24v battery bank?
 
pollinator
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Tim Comer wrote:I'm confused about sizing an array with a charge controller...  If I go with five 210w panels (specs below) what specs do I need to consider for the compatible charge controller?  Would I need two Epever Tracer4210AN charge controllers for this array?  Is there a problem with two charge controllers?

I don't know what battery bank I am looking at yet, but considering one 200aHr Chins 12v.


Panel specs
Max Power Output(W): 210W
Voltage MPP Vmp(V): 16.77V
Current MPP Imp(A): 12.48A
Voltage Open Circuit Voc(V): 19.83V
Short Circuit Current Isc(A): 13.09A


Here is a link to epevers site... under documents
Your max ocv is listed at 92 volt. Max watts 520. https://www.epsolarpv.com/
You might be able to get away with 3 but you will risk burning out the charge circuit. You would use 2 40 amp chargers if using a 12 volt system one with 1 string of 2 and one with one string of 3 but again its risky. The charger voltage is based on your battery bank voltage. An mppt charger reduces the solar voltage down to your battery voltage and gives you more amps...
Cheers,  David
 
pollinator
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Location: Victoria BC
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Any special reason to use 210w panels? ~300w is more the sweet spot for price/watt..

I am not a fan of the tracer kit. Cheap and chinese.. the one I tried had an incorrect charging profile, no resolution despite numerous others with the same problem.. Many better quality options, you get what you pay for, or sometimes less...

Multiple controllers is OK as a general rule. Can be more efficient. Can be a bit more config fiddling.

Your charge controller is responsible for taking the array voltage and charging the battery bank at an appropriate voltage; ie, you can have a 2-panel series array feeding an mppt charge controller ~32v, and it can then charge a 12v battery, or a 24v battery, assuming it supports both voltages.


 
Tim Comer
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Thanks for the replies folks.

I have decided to skip the solar project.  I seem to be getting nowhere in my design.  I'll leave it at that.
 
D Nikolls
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Tim Comer wrote:Thanks for the replies folks.

I have decided to skip the solar project.  I seem to be getting nowhere in my design.  I'll leave it at that.



There is a bit to it, to do it right!

If you decide to move ahead later, some more info would allow for better advice; budget, goals, location..
 
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Why are you giving up only after a single day?  It really only needs some elemental math to get it done.

First and foremost the first advice to give you is to give up 12V completely.  Sticking with 12V appears to be a holdover from the 1980s, when 12V panels were the only thing out there, and panels were 4-5$ per watt.  Now you can get high-voltage grid-tie panels off Craigslist for 4-5W per dollar.  I would design either a 24 or a 48V system.  The size basically dictates the voltage.  

For systems needing less than 1000W, 12V is still OK.  Lights and TV
For systems needing to power things in the 1000-2000W range, power tools for example, then 24V.  Refrigerators, circular saws, ect.
For big systems powering things like 240VAC well pumps, then go with 48V.

At my own homestead over the years, I've designed and built all three.  I currently run 24 and 48V system right now as we speak.

For the charge controller you need to pay attention to two things, the maximal amperage, and the maximal voltage.  New MPPT controllers act as a transformer, taking raw high solar voltage and transforming down to the level the battery wants.  In the process, it converts the extra volts into extra amps, so the battery will charge faster.

The maximal amperage is the amperage that goes into the battery, not the amperage that goes into the controller.  Let's take the example of your panels you mentioned above.  Remember the addage, in series voltage adds while amperage stays the same.  In parallel, amperage adds will voltage stays the same.  For your 5 panels, wired in series (+-+-+-+-+-) you would get 16.77+16.77+16.77+16.77+16.77=83.85V and 12.48A.  In parallel (+++++-----) you would get 12.48A+12.48A+12.48A+12.48A+12.48A=62.4A at 16.77V

Power is V X A =W  In both cases, the power is exactly the same.  83.85V X 12.48A = 1046W.  62.4A X 16.77V = 1046W

In general, it's easier to make high voltage components instead of high amperage ones.  High current = high heat.  High voltage can be transmitted through wire as thick as your hair.  High amperage can be transmitted through wire as thick as your thumb.  So, modern MPPT controllers are designed to work with high voltage instead of high amperage.  BTW, MPPT controller can only transform voltage DOWN,  They CANNOT transform voltage up.

Now, let's design you a system with these ideas in mind.

Take your 5 panels and wire them in series.  You'll be making 12.48amps at 83.85V.  You first connect the charge controller to a 24V battery bank.  That could be four 6V golf-cart batteries (Costco has them for 99$) wired in series for 24V.  Remember, ALWAYS connect the controller to the battery first BEFORE connecting the solar panels.  The controller should give a reading of around 25V or so.  It will NOT be exactly 24V.  After the controller is booted up and talking to the battery, then you connect the solar panels.  Now you program the controller to charge the batteries at the specifications given by the battery manufacturer, usually 28.8V to 29.6V.  The controller will now take the high raw solar voltage and transform it down to the voltage the battery wants.  Charging might start out at ~26V for a discharged battery, going up to the programed limit when fully charged.
In the real world you always include a fudge factor, because nothing is ever 100%.  There is always some loss through heat.  Lets use a 0.85X fudge factor.

So, the math works out to be (1046W/26V) X 0.85FF = 34.2amps at the battery terminals.  So, a 40A controller could safely handle these 5 panels.

Suppose you insist on a 12V system.  The math would be (1046W/13V) X 0.85FF =68.4amps.  Doable, but you'll need a MUCH more expensive controller that can handle 68A.  They make them, but it's 600$ instead of 250$

Now we talk about the voltage.  There are two voltages to talk about here, the working voltage when power is being made, the Vmp (16.77V), and the open circuit voltage, or Voc (19.83V).  The Voc is the voltage you'll measure when the DISCONNECTED bare solar wires are tested with a voltmeter.  For 5 panels in series those numbers would be 83.85Vmp and 99.15Voc.  The cheaper controllers have a max voltage of 100V, and your Voc of 99.15 is dangerously close to that number.  Voltage goes up as the temperature goes down.  At 32F the voltage will go up by 1.12X.  So, on a frosty winter morning, the Voc will shoot up to 99.15Voc X 1.12= 111Voc, enough to fry the controller.  So, you need a controller with a max voltage in the 150V range.

Look at this controller.
https://www.ebay.com/itm/Epever-MPPT-Solar-Charge-Controller-12V-24V-36V-48V-Tracer-AN-Regulator-200V-PV/352541593982?_trkparms=ispr%3D1&hash=item52151dd17e:g:CQsAAOSwuWJbuH2K&amdata=enc%3AAQAFAAACcBaobrjLl8XobRIiIML1V4Imu%252Fn%252BzU5L90Z278x5ickkWpEuxXwAiCNKyBQsQ5%252Fe66X7qH28gIEqHq4MNmUyP4hmaafAjg8CnbeKNCH6eUHrWMo4dMu519lT4YK8AlXDG6UZUeofDO%252BE80upRq4NBeX43gnbuUXvaWCa4U3VkZ9BNSU4dG3t0WMDzU9amC3ShvjzPnpuHVzqQo9ru1YW5bgaUCcMbTqiiiME6aJNQOCPpNGMyBRFI2sau58%252BIdoCp59FTAKnq5KzX%252Fh4MxaoFsQVg%252F4AleP9h4Fr7BPkK%252FKCYZgVnrfspTCYPuIXxiWr9RyFR5TIXrma4xOA8cm8Sr34NFqjyurxRRfsNRLvM2TxdW6W9EV%252F8kVxISH9omc%252FGve37%252FagM8KyAbQRRkmKe5brufCRx7ws1pxl6yOWkFirnBz%252FcJ8qRHhrXTugYm%252Fl736r5QYfL1B1k%252FwT70Aipb%252BWEsJHSfyGU3h3MZ8qG476kqQLxBDnnwTvfFmx96PRNAwHBMfhb%252B4UEwkIWwpDAImB84aof5CokOImnFuDCUzk4tIDjdAylWFeDp%252FpVM5kMiXCovBQ8kYrEg%252FiflVBmyBdOv3VZA96P%252FH0a3HiPhXhuwXQAIray1tmp4KlbdWhzRjgknFRNt5lvA5HX2tpq9snQBPXF6MQ9ilF2gWnyf1kmFEXt8n6mwPrHxJEHCH%252Bnh8tvH4IbBpZV9s%252FURz4S2HeX620uWBeLojbnBVS%252FBAVZi2YgucnnMXXdgVMzIUbIHCNBUx0ZlYeI2v42izDo97oukVQm9lJfX7UpmcEPBuMme%252BgmzOGkx%252FzP%252FkkK%252BwJrg%253D%253D%7Ccksum%3A352541593982dc45811877d847ef8f0ccefab7b8b9d9%7Campid%3APL_CLK%7Cclp%3A2334524
It can handle as many as 50A at 150Voc.  That would be a good choice for your system.

Lastly, you will need to install an inverter if you want to run standard 120VAC appliances.  Make sure you get a sine-wave inverter if you want to power a refrigerator or run power tools that run on an electric motor.
https://ressupply.com/inverters/samlex-pst-1500-24-pure-sine-wave-inverter
 
Tim Comer
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Michael Qulek wrote:... Why are you giving up only after a single day?  It really only needs some elemental math to get it done.




Michael, very good explanations.

I think I understand the concept of 24v and its advantages.  That inverter will accept 24v from the battery bank.

I'll look at this again and maybe have some questions about fuses and breakers and their locations.

D Nikolls, I was looking at 210w panels because they are shipped free with no minimum qty.  At the dealers on line I have found shipping close to $200 and minimum orders of five panels.  I don't want to start with a system that big.  I'm just trying to provide a few KW for small appliances and the ability to power necessary appliances in the event of a grid outage.


Thanks,
Tim
 
Michael Qulek
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Don't buy your panels online.  You can get far better deals on Craigslist from local sellers.  Cash and carry.  That's how I'm getting all my panels now.  With 245W panels going for 55$, I can get ~1000W for 220$.

Keep in mind that a few kW is NOT a small amount of power.  At my own cabin, running a refrigerator, lights, TV, and computer, I'm using about 2.6-3.0 kWh per day.  That's when nothing special is happening.  On summer days when I'm pumping irrigation water, I consume 20+kWh per day.

Let's assume you need 3.0kWh of power to run your place, and you get about 3 sunhours in December, and 5 sunhours in June.  A sunhour (sh) is a conversion unit to describe how much power you can get in a day.  It is NOT the number of hours the sun is actually shining.

So, to keep your place running in December you'll need 3000Wh/3sh = 1000W of panels.  So, I'd keep with the plan of buying 1000W of panels.  Just buy them locally, not on the internet with shipping.

Let's say you buy four 8A, 30V 245W grid-tie panels.  They are dirt-cheap now, and everywhere.  Depending on your controller, you could wire either all four panels in one series string (4S1P) or two parallel strings with two panels each (2S2P).  You most likely will not want to wire them in parallel (1S4P) because 30V isn't enough to perform a monthly equalization charge.

Let's say you chose 2S2P to wire your four panels.  You generally gauge fuses for 1.25X what the actively running current is, so that would be 8A X 1.25 = 10A fuse.  You'll need 1 fuse each for each parallel string.  Actually, code does not require fuses/breakers till you have at least three parallel strings, but fusing can't hurt.

You will also want a fuse between the battery and the inverter.  Let's say you pick the 1500W inverter I highlighted above.  The max current would be 1500W/24V = 62.5A.  62.5 X 1.25= 78.1A, so get an 80A fuse.

What will make your life a bit easier is to use a power center instead of trying to fuse everything.  A power center is a box designed to hold all the breakers, and DC cables leading to the batteries and the inverter.  Here's one that is not too pricy.  You can then match breakers to the various connection points instead of fuses to have greater control of your system.
https://ressupply.com/power-panels/midnite-solar-mndc125-mini-dc-disconnect-box
 
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Solar Station Construction Plans - now FREE for a while
https://permies.com/t/138039/Solar-Station-Construction-Plans
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