Question about solar array size and compatible charge controller

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

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?

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

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.

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.

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..

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

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

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

Hi Michael, it seems like you re  the person I need to speak to. I followed your responses to the thread in yesterday's daylyish and don't want to hijack that thread which is particularly about 12V. I'm not sure if this is the correct thread for my question either but I'll post it anyway, feel free to move to a more appropriate location.
I am in Spain, living totally off grid and have a small 12v system to run my LED lights and charge my phone.
But it gets really hot here and a fridge or freezer would be really helpful- I could cut down on my travel to town if I could store my food for longer in the heat. Last summer was a struggle using cooler boxes and ice and I'd rather not have to do that again- false economy. Eventually I would like to have my whole house running on solar, including my washing machine and poratble aircon unit - both 230V 2200W beasts, but I cannot afford to do it all  in one go. Due to a lack of secure, cool space and wanting to build longevity into the system, I want to use lithium batteries which adds to the cost. I want to use Pylontech 48V 2.4KWH us2000c batteries . The manufacturer recommends operating at a 0.5C regime of 1200w maximum in charging and discharging the battery. I believe I need at least 3 for them - What the supplier states: The pylontech us 2000C lithium battery recommends a maximum charge and discharge intensity of 25 amps (1200w) per module , so if we want to use them in isolated systems with a 5000w inverter, for example, at least we must acquire a minimum of 4 modules to be able to deliver the inverter power. If the inverter is 3000w with 3 modules, it will be the minimum necessary. Because of this, batteries will have to wait at least a year.
Each battery allows a maximum continuous intensity of 50 amps (2400w) but in order to apply the 10-year warranty we must work at 25 amps as recommended by the manufacturer.
There is an inverter/charge controller combi: Voltronic Axpert IV 5600w 48v mppt 120A 500v that apparently can provide 230V power without connecting to batteries.  Here's the blurb: Axpert IV 5600w 48v mppt 120A 500v wifi
New  axpert IV 5600w 48v mppt 120A wifi hybrid inverter with solar panel input up to 500 volts. The new  hybrid inverter model has increased the power of the mppt regulator to 120 amps and a nominal output of 5600w. The axpert IV 5600w  allows to work with and without batteries. Only by connecting the solar panels to the  hybrid inverter  we will already have a 230v output. Sorry, it's a direct Spanish translation.
I understand the limitations of such a system but am prepared to manage with day time only power for the next year at least. I can manage without the washing machine but a freezer is essential and something I can manage on day time power. I need about 1000/wI know the inverter is huge but I'm trying to buy big enough to meet my eventual load.
My question is, is there a minimum solar array I need to abide by? I am looking at:
Ulica 455w Monocrystalline Perc split cell solar panel . A latest generation panel with 20.4% module efficiency and the advantages of split cell technology in managing partial shading and improving temperature dissipation
- Voltage at maximum power (VMP): 40.9V

- Current at maximum power (IMP): 10.88A

- Open Circuit Voltage (VOC): 49.7V

- Short Circuit Current (ISC): 11.45A

Any advise you can share would be gratefully received.

Hello Sarah, hope I can be of help to you.  Let's throw out some numbers and see what you think.  I'm guessing that your location in Spain is going to get the same number of sunhours as my location in California, maybe 3sh in winter, and 6sh in summer.  A sunhour is NOT the number of hours the sun is up, but a quicky conversion factor to decide how much power you can make in a day.  You multiply the watts of panels by the sh to get the total Wh (or kWh) of power you can make each day.

Based on my own personal experience of powering a frig/freezer 24/7, I can make some suggestions for you.  First, let's add up what you want to see what power level you need.  Feel free to change the numbers I show here to fit your own personal needs.  The numerical values may change, but the math stays the same.  Let's say you want to power a.....

refrigerator: mine is a standard AC kitchen frig consuming ~1200Wh in 24hr, or 1.2kWh
freezer: top opening like mine consumes ~600Wh in 24hr, or 0.6kWh
lighting: 100W X 5hours per day ~500Wh or 0.5kWh
television: 100W X 2 hours per day ~200Wh or 0.2kWh
computer: 150Wh X 2 hours per day ~ 300Wh or 0.3kWh
solar electronics themselves: 30W X 24hr = 720Wh or 0.7kWh

Added all up, that's 3.5kWh of power, each and every day, over the course of a year.  This happens to be very close to what I actually see at my own cabin, with number ranging from ~2.5kWh on days when I am not there, to about 3.5kWh when there full time.

Let's add a bit of a safety margin, and plan on 4.0kWh per day.  We'll plan on making that amount of power on December 21'st, the shortest day of the year, with about 3.0 sunhours at your location.  So, needing 4000Wh of power and having 3 sunhours to make it, you would need 4000Wh/3sh = 1333W of panels.  Very, very doable.  I just bought 1500W of panels in March for 65$each, cash and carry, 390$ with the guy loading them onto my truck.  If you want those 455W panels, get three for 1365W.  That should make you ~ 4kWh per day in December.

Take a look at the rotating solar array frame I made from schedule 40 pipe, The bottom pipe, sunk in concrete is 9cm steel, ~0.9m in the ground, and ~1.5m sticking out.  The pipe that slips over it is 10cm steel pipe, with unistruts making a T.  Then the solar frame, also made of 3m unistruts, is bolted onto the T with regular heavy-duty door hinges.  So the frame can rotate left to right to orient the sun to the time of day, and also tilt up and down to make seasonal sun angle corrections.    In the pic you can see three grid-tie panels mounted in landscape.  By rotating East to West over the day, you could expect the # of sh to go from 3 to 5-6sh.

What you are looking at is what is known as an All in One unit, or an AiO inverter.  I have no experience with them whatsoever.  Inverters can be divided into two main classes, low-frequency transformer based inverters, and high-frequency transformerless inverters. LF units are large, heavy, expensive, but had handle very high starting surges.  HF units are cheaper, lighter, but have little or no starting surge.  AiOs are mostly HF.  So, LF for compressers, pumps, power tools, ect.  HF is OK for computers, lights, TV, ect.  

Starting surge is what happens when an electric motor drive machine gets turned on.  The starting surge, for just 1-2 seconds, is typically 3-5X the running power.  For example, my 240V well pump runs on ~2000W, but it needs ~9100W for 1 second to start.  That is when a HF unit would fault and shut-down.  So, a single 6000W LF inverter can start my pump, but you would need two 6000W HF inverters to start it.  Does that make sense?  I have Schneider inverters, though you should also look at Outback and Magnum.  All high-quality LF units.

Is 2400Wh the specification for the battery you want?  I would say that is far too small for a system powering a home.  Although Li batteries have a better depth of discharge then lead, it's not absolute, so you should just expect to get 75% of capacity out of a Li battery, or for your's, 1800Wh, or 1.8kWh.   Trying to get 3.5kWh out of a 1.8kWh battery is not going to work.  Here is where you need to think about what's called "days of autonomy", or how many days you can run your system if there is no solar.  Imagine a big thunderstorm rolling in, and it's dark for two days.  That's 7kWh of power that needs to be pulled from the batteries before the system goes into shutdown.  So, assuming you need those 7kWh, you'll need 4 parallel strings of those batteries to give you an honest 7kWh.

Hi Michael, thanks for taking the time to give me a very detailed reply. Your advice is much appreciated.
Luckily I don't have any power tools running off 230V -all rechargeable batteries. I know the washing machine and aircon are large loads and probably have high startup surges but I can run them off the genny if need be, even go without aircon if I can use passive cooling tech.
Yeah, 4 batteries is about what I was envisioning and 2.4KW is the smallest size, but the budget won't stretch that far just yet. I could get 2 x 3.55KW as an alternative. Which is why I'm looking to go without batteries for a while - power is only really important for refrigertion during the summer, I can go without fridge/freezer in the winter.
Hence wondering if there is a technical reason to use a certain wattage of panels. 2 panels will give me just under 1000W for 4 hours and possibly another 4 hours of 500W. Unfortunately it's not possible to put the panels on a pivot (too much wind) they will be fixed on a roof. But I could do 4 panels if the inverter will cope with so much power/hour.

OK, let's break this up into more easily digested bites.

I know the washing machine and aircon are large loads and probably have high startup surges but I can run them off the genny if need be, even go without aircon if I can use passive cooling tech.

I built a very-well insulated cabin, and in the middle of summer it is still too hot to sleep upstairs at night.  Passive cooling has not worked well for me.

Yeah, 4 batteries is about what I was envisioning and 2.4KW is the smallest size, but the budget won't stretch that far just yet. I could get 2 x 3.55KW as an alternative. Which is why I'm looking to go without batteries for a while - power is only really important for refrigertion during the summer, I can go without fridge/freezer in the winter.

Lithium is in my opinion very over-priced, and you can get traditional lead-acid batteries far, far cheaper.  Take a look at Costco's 210Ah 6V golf-cart battery.  They are 99$ +tax and core right now.  Assuming you only want to drain lead-acid to 50%, that's still 2500Wh for only 400+$.  Keep a gallon or two of distilled water around so you can top off the batteries every other month.

Hence wondering if there is a technical reason to use a certain wattage of panels. 2 panels will give me just under 1000W for 4 hours and possibly another 4 hours of 500W.

No, they won't.  You almost never get rated power out of panels, because that is determined in an artificial test chamber.  Expect to get no more then 85%.  So, the math is 455W X 2 panels X 85% = 774W.  That is maybe from 11am to 1pm.  Earlier and later is even low.

Yes, the reasons are the controller's limits for voltage and amperage.  Cheaper, budget controllers have a voltage limit of only 100Voc, and your panels in series would be putting at 99.4V at room temperature.  At freezing the voltage would go up to ~111Voc, which could fry a cheaper controller.  I would recommend you get a controller with a 200V limit, like Epever's 6420AN.  You can start out with just two panels, then add another later on.

Unfortunately it's not possible to put the panels on a pivot (too much wind) they will be fixed on a roof.

Look at the trees in the background of my photos.  The oaks I have are in the 18-24" range have gotten toppled in some of my ridgetop thunderstorms, but my arrays have NEVER gotten any damage.  They are extremely sturdy.

But I could do 4 panels if the inverter will cope with so much power/hour.

It's the controller that has the limits for the panels, not the inverter.

HI Sarah,
have you looked into stand alone solar powered fridges, I know Sollatek do an this  fridge for approx $400 in kenya.
Quickest solution
https://yaoota.com/en-ke/product/sollatek-bcd-98-dc-solar-refrigerator-2-price-from-shopit-kenya

For an AC, invest in the inverter type, the difference in start and run current to a traditional one is huge,