Creating two arrays. in two different locations, with different panel types.

[field]

The story...
I have an off grid cottage with two 265W panels on the A frame style roof.
They provide power to a midnight solar Kid controller, and 4 GC2 golf cart batteries wired for 12V.
This feeds the inverter which puts out 120V AC and everything has worked fine for 5 years now.
Runs the lights and a mini fridge freezer, radio
My plan is to add more panels on a different section of the property about 100 feet away from the cabin.
i purchased 3 x 400W panels and plan to wire in series (100V) to help cover the long distance.
These new panels would be oriented at 90 degrees to the original roof mounted panels.
Roof panels get sun from 9am to 1PM, then almost nothing due to trees.
The new panels would be facing lake and get light from 1PM to sunset.
Can this work with one Kid controller with 30 amp, 140V max rating?
does battery voltage factor in to these limits?
Diodes on both arrays required?
I know Im oversizing the array. but expect to add future appliances which will draw off extra current.
Anyways, thoughts, opinions, expert advice?????/
Thanks.

 

[MisterSandals]

i purchased 3 x 400W panels and plan to wire in series (100V)

This does not sound possible to have 3 large panels in series have a Voc 15% below 100V.
What is the Voc of these panels, the coldest temps you expect and the SCC you have in mind?

 

[rmaddy]

FYI - 3 400W panels in series is likely to be more like 130V, not 100V. What is the actual Voc and Vmp of the 400W panels? A Voc of 130V could easily exceed the 150V max if the temperature gets below -15ºF/-26ºC. Though the 162V max of HyperVoc would work down to about -70ºF/-57ºC.

 

[MichaelK]

I have an off grid cottage with two 265W panels on the A frame style roof
This most likely is around 60Vmp if wired in series, is that correct?

i purchased 3 x 400W panels and plan to wire in series (100V) to help cover the long distance
A 100V string parallel to a 60V string is NOT going to work.

I know Im oversizing the array. but expect to add future appliances which will draw off extra current
This is not how it works. You need to respect the limits of the electronics BEFORE the power gets to the load.

Let's look at the battery you have right now, four golf-carts wired 2S2P. That would give you what, 500Ah at 12V? You really want to charge the GC at 1/8C, so you should have been feeding them 500Ah X 0.125C X 13Vcharging X 1.175fudgefactor = 955W. 62A is more than double what your Kid can handle, so you really need to replace it, or add a second controller. Since the two strings are so divergent, the second controller (at least 80A) makes sense.

 

[field]

This does not sound possible to have 3 large panels in series have a Voc 15% below 100V.
What is the Voc of these panels, the coldest temps you expect and the SCC you have in mind?

I have an off grid cottage with two 265W panels on the A frame style roof
This most likely is around 60Vmp if wired in series, is that correct?

i purchased 3 x 400W panels and plan to wire in series (100V) to help cover the long distance
A 100V string parallel to a 60V string is NOT going to work.

I know Im oversizing the array. but expect to add future appliances which will draw off extra current
This is not how it works. You need to respect the limits of the electronics BEFORE the power gets to the load.

Let's look at the battery you have right now, four golf-carts wired 2S2P. That would give you what, 500Ah at 12V? You really want to charge the GC at 1/8C, so you should have been feeding them 500Ah X 0.125C X 13Vcharging X 1.175fudgefactor = 955W. 62A is more than double what your Kid can handle, so you really need to replace it, or add a second controller. Since the two strings are so divergent, the second controller (at least 80A) makes sense.

Hello Sorcerer. Thanks for replying to my inquiry.
I will try to explain why I think this will work. Keep in mind I am not looking to maximize efficiency and necessarily have perfectly matched inputs and outputs. This is an off grid cabin used only in summer with no electrical draws other than lights and one, sometimes two mini fridges.
So, as you mentioned, I have way too much power going to the controller. This may be wasteful, but I do not see it damaging anything as the Kid is limited to around 500W with 12V batteries. It regulates battery charging quite well, and goes into float mode when bats are at capacity.
So what happens to all that surplus energy from the array? There wont be any. Electricity does not flow unless the Kid controller allows it to. And once the battery is charged, thats it, other than the float. All the extra power is never created. Its wasted potential, but thats it.
So why do this? Its been my experience that not every day is sunny. and the sun moves around quite a bit. So why not have two arrays at different locations to track the sun for the full day. And why not have too many panels so when its cloudy you can still get enough power (maybe) to keep everything working and charging. From what Ive read, solar panels are diode protected to prevent dangerous back feeding from multiple array set ups. So my two arrays would be isolated from each other. One set providing morning power, then almost nothing, the second afternoon to sunset power.
Anyways, I would appreciate comments, warnings or better ideas. According to the Kid if I change bat voltage to 24 it will double its charging output so maybe thats a good idea.

 

[MichaelK]

From what Ive read, solar panels are diode protected to prevent dangerous back feeding from multiple array set ups. So my two arrays would be isolated from each other. One set providing morning power, then almost nothing, the second afternoon to sunset power.
Anyways, I would appreciate comments, warnings or better ideas. According to the Kid if I change bat voltage to 24 it will double its charging output so maybe thats a good idea.

Again, this is not how it works. Even shaded panels will be putting out about the same voltage, it's just that the amperage will be drastically lower than when exposed to full sun. So, your 3-panel string is still going to be putting out maybe 0.5A at 100V all morning long, until they get full sunlight exposure. Two different voltage inputs is going to confuse the controller, and it might not be able to figure out what voltage to act on.

So, the PROPER way to do this is to have either 1) two strings that differ by amperage, but closely match in voltage (δV <5%), or 2) two separate controllers that can handle widely differing voltages.

 

[sunshine]

i purchased 3 x 400W panels and plan to wire in series (100V) to help cover the long distance.

There is no voltage drop if no load!
I would just leave out one of the 400w panels to match the V of the strings and avoid any back feeding issues if another CC isn't the way you go.
You can add the spare in // to one of the other 400w panels or get another panel for 2 strings of 3.
The orientation should keep the total available power through the cc down.

Even if the mppt of the CC maybe off having one series in shade and the other in sun this wont be anywhere as inefficient as having one string with at 100v and the other at 60v.. the details would only be known if one knew that particular CCs mppt algorithm methods.