MPPT Wiring Tricks

[witzgall]

Yep, you are right. I guess I read what I wanted to read. Max 15 amps to te Battery.

Chris

Originally Posted by Paul L

I think you are misreading the ratings on the Morningstar controller. The 200w is for 12v output to the battery. The 400w is for 24v output to the battery. Since yours is a 12v system, it would be 200w max. It is basically a 15amp controller.

[44'cruisingcat]

When a panel is shaded, it will still be producing power. It doesn't suddenly change from a power source to a resistor! It's just that a 100 Watt panel might only produce 5, 10 or 20 Watts.

Talking about SHADE, not total darkness.

So an array wired in series, that might produce 8 amps at 24 volts with both panels in full sun, will even with one panel in the shade, still produce power, and more power than a single panel would, although it might be say, 7 amps at 20 volts, or similar.

I have 6 x 100 Watt panels, wired in series, and having one panel in shade certainly doesn't shut down the whole system.

Even having ALL SIX panels in shade doesn't do that. Right now, the whole boat is in the shade, but the panels are producing 1.2 amps at 66 volts total, pushing 5.5 amps into storage.

[Fuss]

Just for info... I did some research now on the panels I have which are KD135 Kyoceras. They have bypass diodes built into the junction box so these panels have no problems when wired in series.

[witzgall]

Your post seems to run contrary to what Captain Bill wrote. He is stating if multiple panels are wired in series, then they are limited in output. This limitation is equal to the lowest AMPERAGE of the panels.

Does anyone else agree with this?

Chris

Originally Posted by 44'cruisingcat

When a panel is shaded, it will still be producing power. It doesn't suddenly change from a power source to a resistor! It's just that a 100 Watt panel might only produce 5, 10 or 20 Watts.

Talking about SHADE, not total darkness.

So an array wired in series, that might produce 8 amps at 24 volts with both panels in full sun, will even with one panel in the shade, still produce power, and more power than a single panel would, although it might be say, 7 amps at 20 volts, or similar.

I have 6 x 100 Watt panels, wired in series, and having one panel in shade certainly doesn't shut down the whole system.

Even having ALL SIX panels in shade doesn't do that. Right now, the whole boat is in the shade, but the panels are producing 1.2 amps at 66 volts total, pushing 5.5 amps into storage.

[goboatingnow]

Captain Bills post was a very logical runthrough, mind as they say "logic is a way of going wrong with confidence".

So it would seem that wire gauge aside, parallel panels are the best, Actually my electronics brain suggests that the optimum in each panel has its own MPPT controller.!!

Dave

[jaredko]

Bill's post regarding a non-aligning panel is correct. From the individual panel's perspective, it would be similar to being wired in series with a lower wattage panel, which reduces the output of the higher power unit. The best wiring in this case would be parallel (one controller per panel would be ideal!)

From my view, there are these options for non-idea mounting:
Partial shading (ie, from the boom) - go with series. Parallel wiring would cause the entire shaded panel to bypass. Series would cause only the one diode attached the shaded cell to bypass (1/2 - 1/4 of the panel depending on the number of diodes).

Different mounting angles - Parallel due to the current limiting of the series connection

If the panels never get shade and are mounted at the same angle, I'd say go with series because the MPPT controller is more efficient at higher voltages and the loss due to the wire gauge are less (this is how roof mounted arrays are wired for this reason)

[44'cruisingcat]

Originally Posted by witzgall

Your post seems to run contrary to what Captain Bill wrote. He is stating if multiple panels are wired in series, then they are limited in output. This limitation is equal to the lowest AMPERAGE of the panels.

Does anyone else agree with this?

Chris

It's pretty hard to know just what the lowest amperage of the panels would be though. But the fact remains, if one (or even two) of my panels iscompletely in the shade, I still get good power from the others, even though they are in series. I don't have bypass diodes.

The way I see it is that in series each panel adds volts, not amps, to the total. So a shaded panel may add fewer volts than one in full sun, but it still adds. More volts at the same current = more Watts.

[Matt Johnson]

Originally Posted by jaredko

Bill's post regarding a non-aligning panel is correct. From the individual panel's perspective, it would be similar to being wired in series with a lower wattage panel, which reduces the output of the higher power unit. The best wiring in this case would be parallel (one controller per panel would be ideal!)

Ouch... my head hurts!

I have a two Kyocera KD135SX-UPU

135 watts x 2
17.7 VPM

and an Evergreen ES-A-205-fa3

205 watts
18.2 VPM

These three are really connected to a Blue Sky 3024il MPPT solar charger

It will take up to 40 amps and 57 volts.

Are you saying because they are two different size panels that I should wire these in parallel and not series?

[Paul Elliott]

Originally Posted by goboatingnow

sorry wasnt trying to be smart, merely that peole get all het up over diode drops , when in fact designed correctly no power is lost.
Dave

I have to tell you that power is lost in series diodes. Not much, but there is some and it's unavoidable. Say you have a panel putting out 5A, and a series Schottky diode that is dropping 0.5V across it. The diode dissipates 2.5W in heat (5A * 0.5V = 2.5W).

This is 2.5W that a MPPT controller could have converted to charging amps.

If you are not using a MPPT, but a traditional controller (or directly connecting the panel to the battery), the diode power-loss is probably ignorable, since the panel will put out approximately 5A with or without the diode. Since the panel isn't a true constant-current source, there will still be some loss of charging current, but it will be barely measurable.

[capnorv]

I've installed quite a few MPPT systems, and monitored their effectiveness for years. I have successfully mixed and matched panels in arrays, even running some panels in parallel to come up to a semicomparable series string output. I have ran 2 50w panels in series with satisfactory results. I've ran 1200w-125v systems with satisfactory results. My latest brainstorm is reviving 78 22w, 1.9v panels into a series system that works. As long as you have at least your minimum input charging voltage and whatever amperage is being milked into your controllers, you'll charge. Heck I've seen my house system charging after sunset many times just on the refractive light input! Think of your Mppt controller as a sponge soaking up all the energy it can, wringing itself out with a controlled drip the charge to your batteries. Reverse discharge is also stopped by most controllers so just let those panels do their job (collect energy) and your controller will do the rest. Clear as mud?

[goboatingnow]

I have to tell you that power is lost in series diodes. Not much, but there is some and it's unavoidable. Say you have a panel putting out 5A, and a series Schottky diode that is dropping 0.5V across it. The diode dissipates 2.5W in heat (5A * 0.5V = 2.5W).

This is 2.5W that a MPPT controller could have converted to charging amps.

Well yes, heat loss, but its neglible in practice, compared to other inefficiencies, I was referring that having the voltage drop persay isnt an issue.

often the power/temperature coefficents are more problematic for panel looses, often approaching -0.5%/K

dave

[capnorv]

Speaking of heat loss, where I used to live it wasn't uncommon for 70df temp changes during the day, and it seemed panel output decreased about 20% with the increase. The tropics probably aren't the most efficient area for solar energy production. Anybody down there notice panels don't put out (as much)?

[jaredko]

Originally Posted by funjohnson

Ouch... my head hurts!

I have a two Kyocera KD135SX-UPU

135 watts x 2
17.7 VPM

and an Evergreen ES-A-205-fa3

205 watts
18.2 VPM

These three are really connected to a Blue Sky 3024il MPPT solar charger

It will take up to 40 amps and 57 volts.

Are you saying because they are two different size panels that I should wire these in parallel and not series?

Right. Solar cells don't work well if they are having more current pushed through them than they are trying to create. Each panel will have a similar number of cells (say 36 x 0.5 volts). The difference between the 135 and 205 watt panels is each cell on the 205 will put out more amps (11.3 amp x 0.5v) while on the 135 each cell will put out 7.5. When you try to force 11.3 amp through the lower capacity cells in the kyocera, the cell's resistance increases and the power you get out of the string drops.

Because the voltage of the panels is similar, you can probably get away with connecting all 3 in parallel.

[goboatingnow]

Well 20% is a lot , typically it should be at those figures around 10% in my estimation, but the curve isnt linear.

dave

[jaredko]

Originally Posted by Captain Bill

Keeping in mind the fact that in series circuit amperage is constant, if the panels are mounted in series and both are in full sunlight the array can produce 10 amps (max output of each panel) at 24 volts. Now let’s assume that a shadow fall across one of the series groups in the first panel. That panel now is still producing 12 volts from the other three series group but is now capable of producing only 7.5 amps. Since Voltage is additive in the series circuit, the total output of the array is still 24 volts, but since amperage is constant, the amperage becomes limited by the partially shaded panel and is now limited to 7.5 amps. If the shadow falls across another series group the output falls to 5 amps, and if the shadow falls across all of the series groups in the panel the output is now zero amps. Since the amperage is constant in a series circuit the output from the whole array is now zero. Since daylight is somewhat diffuse and shadows seldom produce absolute darkness the output never actually drops to zero, but can come pretty close. Bypass diodes work between parallel groups within a panel or between parallel wired panels. Bypass diodes are important because a panel that still has a voltage applied by the other series groups tend to get very hot. These bypass diodes protect the panel.

Bill, hope you can clarify for me. As you say, the amperage in a series string is constant. Assuming a set of solar panels connected in series, each of which is a set of solar cells also in series. When one unit of the group of cells (that share a single bypass diode) is shaded, that group is bypassed. The result would be a drop in the voltage for the panel. The amps output remain the same.

So, assuming we have 2 18v 200w panels. Each panel could consist of 4 sets of 9 cells each producing 0.5v and 11.1a. Optimally, this setup will output 400w, 11.1a at 36v. If one cell on one panel is shaded, that set of cells is bypassed, so the panel's output is reduced by the 4.5 volts that those 9 cells added to the circuit (ignoring the drop in voltage due to the now active diode which would convert approx 6w to heat). The partially shaded panel now produces 150w (13.5v, 11.1a). The voltage is added to the unshaded panel to give 31.5v, 11.1a so 350w output.

If the 2 panels were connected in parallel, since the shaded panel is now delivering a lower voltage, the bypass diodes engage to prevent it from drawing current from the higher voltage panel and causing hot spots. So our total output from the array in this case is 200w.

I'm not a professional, so I am definitely curious to see if I'm understanding this right.