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Author Topic: 20A charge controller with 200W panel?  (Read 3191 times)
ilovethesun
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« on: February 02, 2015, 02:04:37 PM »

Hi
I remember from school that power = ivy watts  Cheesy
So am I right in thinking that a cheapo 20A charge controller from fleebay can handle a 200w panel? ie 200w/12v = 16.7A
Are all solar panels 12v?
What is the maximum AH battery that I could expect to charge on a daily basis with said panel?
Thanks!
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Scruff
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« Reply #1 on: February 02, 2015, 06:26:26 PM »


So am I right in thinking that a cheapo 20A charge controller from fleebay can handle a 200w panel? ie 200w/12v = 16.7A

Yup. As long as it's on adequate cable. It'd be good to get one that matches your battery manufacturer's recommended charging set points & temperature compensated.
Steer clear of cheap MPPT, most of them are fake.
I'd aim for <3% voltage drop panl to controller & < 0.3% Controller to battery.

Are all solar panels 12v?

Nope 12V panels are ~18V VOC
VOC 36V seem to be the best bang for buck these days (24V batteries).


What is the maximum AH battery that I could expect to charge on a daily basis with said panel?


Sunny day roughly 6 times rating in Ah; so 1.2kWh on a 200W panel.
Cloudy day roughly 3 times.
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rogeriko
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« Reply #2 on: February 02, 2015, 06:48:20 PM »

It all depends on the Amps of the panel. If your 200w panel is 28v MPP (mean peak power) that means it is a 7.14A panel (200w divided by 28v).  That means the maximum Amps from your panel (in the sahara desert) will be 7.14A, In the uk it will be about 6Amps.  Your battery is 12v times 6 amps gives you only 72 watts of power not 200. This is why you have to find a low voltage MPP panel that matches your battery.  Most 12v panels are 100w at 18 volts and 5.5Amps this will give you about 5A of charging power at 12v = only 60 watts not 100w. An ideal battery charging panel would be 13.5/14v but they dont exist.
A solar panel is a constant current device not a constant power device. 
A 28v MPP panel is perfect for charging 24v battery systems. Therefore try and get 2 batteries a 24v system.
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ilovethesun
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« Reply #3 on: February 02, 2015, 08:17:48 PM »

I think I'm following you guys so far   Undecided
So from the attached pic, what voltage is this 190w panel? help


* 190w panel.JPG (296.06 KB, 1200x1600 - viewed 371 times.)
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Scruff
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« Reply #4 on: February 02, 2015, 08:24:38 PM »

Voltage open circuit: 45V
for nominal 36V battery (panel ideally voltage 150% higher than battery)

If you want more that 5.2A outtov that thing you need MPPT.

PWM chargers are just going to cap the output
5.2A * 14.5V = 75W
5.2A * 29V = 150W
5.2A * 36V = 188W
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rogeriko
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« Reply #5 on: February 02, 2015, 08:36:59 PM »

Thats a 5.2 amp panel but as it says at the bottom, that is with 1000W/m2. In other words in the sahara desert, here in the uk you will get what they call the NOCT (Nominal Operating Cell Temperature) output which is about 80% of that. That will give you about 4.5A into your 12v battery, thats only 54w to 60w max. Not so good that panel for charging a 12v battery. That panel would charge 3 12v batteries in series perfectly each battery being charged at 4.5a or 60w each.
« Last Edit: February 02, 2015, 09:12:15 PM by rogeriko » Logged

ilovethesun
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« Reply #6 on: February 02, 2015, 08:47:54 PM »

ok so if I had 3 x 12v batteries then
4.5a x 36v = 162w
does that mean with 6 hours of sunlight I'd be getting 6 x 162w = 972wh?
That's nearly generating 1kw/day? 1kw/day sounds a good start to me!  fingers crossed!
What AH batteries would go with this? Let's say no more than 25% discharge....
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rogeriko
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« Reply #7 on: February 02, 2015, 09:09:54 PM »

In june, july and august yes but in the winter only about 2 hours per day, Sun willing.  The 162w would only be around noon with a gradual rise and fall on either side. If you look at all the posts on here about monthly generation you will see the actual figures like 3.8kw system and how many kwh per month. Just divide the kw system size down to your 200w panel and thats how many kwh you will expect per month.

For instance
My results for January were:

3.87 kWp
Total generation: 158.2kWh
Daily average: 5.1kWh
Generation per kWp: 40.9kWh
Daily average per kWp: 1.32kWh
Best day 30th 9.6kWh

Your output will be 1/19 of that ie only 268wh average per day in january and 560wh per day on the best day. These are the worst figures January. If you check the summer months you can work it out for yourself.  I used to live in Greece and I would get more than 1.5 Kwh per panel per day, but the sun shines there.
« Last Edit: February 02, 2015, 10:52:45 PM by rogeriko » Logged

Scruff
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« Reply #8 on: February 02, 2015, 09:19:16 PM »

ok so if I had 3 x 12v batteries then
4.5a x 36v = 162w
does that mean with 6 hours of sunlight I'd be getting 6 x 162w = 972wh?

Not exactly.

With a 12+ hour day maybe.
Batteries aren't efficient so they'll be losing ~20% of what you feed them and if they're near fully charged then the solar controller is dumping a substantial amount of the panel output.
Ah required depends on how much autonomy you need and what your running loads are. I'd aim for 5%-15% DOD per day.

I've only seen peak output once in two years on a cold day with cloud edging.
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ilovethesun
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« Reply #9 on: February 02, 2015, 09:45:31 PM »

ok then if I had 3 x 110ah batteries in series that is 36v x 110ah = 3960watts
With a DOD of 15% I would be able to take max 600w out of them?
If I added more panels would I wire them in parallel to keep the same voltage?
Then if I wanted to take up to 1.2kw out of the batteries, would I double the number of batteries and wire them in series/parallel? ie 3 of them in series still with the other 3 in parallel
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Scruff
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« Reply #10 on: February 02, 2015, 10:19:57 PM »

I'm only saying 5% to 15% to allow 7 days between full charges. It's all much of a muchness below 50% DOD and above C20.
36V is a very funny bank size, just a bit difficult find any appliances for that voltage.

Series = more volts
Parallel = more amps (amp hours for batteries)


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rogeriko
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« Reply #11 on: February 02, 2015, 10:57:10 PM »

Basically if you had your panel and 3 batteries in a garden shed or stable you could happily run a led light of of each battery every night no problem, longer in summer less in winter. but no real power as you seem to be searching for.
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