Solar Panels - Series or Parallel ?

[ChuckSK]

Originally Posted by s/v Jedi

While I find 56W loss way too much for two diodes (they would flash bang the boat to pieces), it is true that series-parallel would perform a little better. Did you add a bypass diode for each panel in your simulation? If the current is 7 amps and the loss over the diode is 0.6V, then the loss of power is 7 * 0.6 which makes 4.2W. This times two for two shaded panels comes to 8.4W loss, so 260 - 8.4 = 255.8W output, instead of the 234W you found.

Your result is about 6 times as much loss as my math… hmm… I can see 4 times as many diodes, but not 6 times. Maybe the current is higher? Or the diodes have a higher voltage drop? In your simulation, how many bypass diodes were there in the circuit?

However, you should also do the emulation for partially shaded panels. This is where the series connection will outperform the series-parallel connection.

cheers,
Nick.

260-234=26 watts, not 56 watts. Each panel has 2 bypass diodes for a total of 4. The voltage drop on each diode in the model is about .8 volts.

.8 volts * 8 amps * 4 diodes = 26 watts

The emulation of partially shaded panels has been previously posted.

Chuck

[nimblemotors]

Originally Posted by sparrowhawk1

So can we take it even one step further. For shading purposes only wouldn't it be better to connect all the panels in parallel?

Indeed, disregarding costs, when there is shading, the ideal setup is to run a MPPT controller on all panels in parallel. My opinion is just for redundancy to have at least two controllers for two parallel setups.

[CAELESTIS]

Reading too many posts makes me second guess my system.

Two 240w Sanyos mounted butted up to each other with 8ga cables to a Midnite 150 classic controller, to a 550amp house bank at 24v. Panels have a voc of 54v wired in series.

Is series the way to go? Other than mast shadow, I would have -22 rod shadow from the backstay.

Don't really care about the alchemy of how it works, just want maximum charging going into the batteries.

Wide open to suggestions!

[sparrowhawk1]

Originally Posted by CAELESTIS

Reading too many posts makes me second guess my system.

Two 240w Sanyos mounted butted up to each other with 8ga cables to a Midnite 150 classic controller, to a 550amp house bank at 24v. Panels have a voc of 54v wired in series.

Is series the way to go? Other than mast shadow, I would have -22 rod shadow from the backstay.

Don't really care about the alchemy of how it works, just want maximum charging going into the batteries.

Wide open to suggestions!

Just the facts ma'am. One other thing to consider is low light situations like rainy days. It was my understanding that the higher voltage will at least give you some power. That's very important to me because I don't mind conserving electricity on rainy days but I would like enough to run my refrigerator, charge my phone and run some LED's

[s/v Jedi]

Originally Posted by ChuckSK

260-234=26 watts, not 56 watts. Each panel has 2 bypass diodes for a total of 4. The voltage drop on each diode in the model is about .8 volts.

.8 volts * 8 amps * 4 diodes = 26 watts

The emulation of partially shaded panels has been previously posted.

Chuck

okay, so that can be improved to 13W with an extra diode on each panel. The 0.8V is too high, should be 0.6V (because that is the actual voltage drop). At 8A in an optimized circuit we get 1.2V * 8A = 9.6W so 250W vs 260W.

when two panels are partially shaded so that they loose half the output, we get two diodes in the circuit so we get 130 + 130 + 65 + 65 - 10 = 380W. The series-parallel setup becomes 130 + 130 + 0 + 0 = 260W.

Series wins big time here. The question is how often does partial shading allow one section of the panel to keep producing. This is where positioning on the particular type of boat comes into play. No easy simulation for that, so experiment works best. Or put extra money in and a Genasun controller on each panel as technically most optimum, but financially not so good solution.

[s/v Jedi]

Originally Posted by nimblemotors

Indeed, disregarding costs, when there is shading, the ideal setup is to run a MPPT controller on all panels in parallel. My opinion is just for redundancy to have at least two controllers for two parallel setups.

Well, when SHTF, you can always directly connect panels to batteries. I would much prefer one Outback Flex controller over two BlueSky controllers. Sure, two flex controllers is nice but makes sense only for bigger arrays (which cats have)

For smaller arrays, the genasun option is tops.

[careka]

Reading and reading.......... ??
i have 3 x 190w Victron panels, and a Victron MPPT 150/70 ,
and will put them up in series,
i have a Trojan L16 bank of 4 x 6V 390 amp batts =780amp 12V
is it OK to leave the boat in the dock with this system charging the bank al the time ? or do i turn it off after some days.
It is when the boat is not used.

[SailFastTri]

Originally Posted by careka

Reading and reading.......... ??
i have 3 x 190w Victron panels, and a Victron MPPT 150/70 ,
and will put them up in series,
i have a Trojan L16 bank of 4 x 6V 390 amp batts =780amp 12V
is it OK to leave the boat in the dock with this system charging the bank al the time ? or do i turn it off after some days.
It is when the boat is not used.

It's better to leave it connected. The MPPT controller will taper back the charge when needed, and maintain the batteries even if there are small loads (such as electronics idle loads, or occasional bilge pump use).

[colemj]

Actually, the answer is a bit more complicated and depends on your controller.

If your controller has a fixed absorption time (many do) and starts every morning thinking the batteries need a full absorption routine, it could spend several hours holding your already charged batteries at 14.8V. While the current will be low, the voltage will be high enough for gassing for several hours each day. This can cause a rapid loss of water from your batteries if you will not be on board to check them.

If your controller is smarter (most are not, but the Victron may be), it will know your batteries are charged from the previous day and spend very little time in absorption.

If your controller is easily adjustable (many are not), you can set your bulk/absorption voltage to (say) 14V while you are away, which should not be high enough to appreciably gas the batteries while it spends those hours in "absorption".

Mark

[s/v Jedi]

I set my absorption and float voltages to 13.2V when I'm not aboard.

[noelex 77]

Originally Posted by colemj

If your controller is easily adjustable (many are not), you can set your bulk/absorption voltage to (say) 14V while you are away, which should not be high enough to appreciably gas the batteries while it spends those hours in "absorption".

Originally Posted by s/v Jedi

I set my absorption and float voltages to 13.2V when I'm not aboard.

+1
If there is little or no draw on the batteries and they are to left for a long time it is worth modifying the charge parameters, if this is possible. (This is another reason why it worth paying a bit more for a regulator with Infinitely adjustable parameters).

Rather than reducing the absorption voltage I tend to usually reducing the absorption time to be very short (say 1min). I usually drop the float by 0.2v
This very short duration of higher voltage once a day stirs up the electrolyte and helps reduce sulphination. I think this optimum, but there are no objective tests that I know of, so its only a guess. ( the other option is to use the equalisation cycle this can be adjusted to lower voltage)

Beware if you are storing the boat in conditions where snow is common that this can completely obscure the panels for long periods. In these conditions you are better to disconnect the solar system. The self consumption of the solar controller combined with the self discharge of the battery can reduce the the SOC to low levels.

The exact voltage values and absorption times are not very critical, but a reduction from the normal parameters are beneficial. On less adjustable controllers consider switching to the "gel" parameters when you are actually using flooded batteries. This will lower the voltages. (Put a big note to change them back when you return)

[Fuss]

Originally Posted by s/v Jedi

I set my absorption and float voltages to 13.2V when I'm not aboard.

That's the problem, if any regulator designers are reading. Two settings are needed that can be selected by an external switch.

Setting 1 for when on board - this setting has maximum bulk voltage and long absorption time.

Setting 2 for when not on board - this setting has reduced bulk voltage etc.

The solution at the moment is to have 2 regulators which makes things too complicated.

[s/v Jedi]

Originally Posted by Fuss

That's the problem, if any regulator designers are reading. Two settings are needed that can be selected by an external switch.

Setting 1 for when on board - this setting has maximum bulk voltage and long absorption time.

Setting 2 for when not on board - this setting has reduced bulk voltage etc.

The solution at the moment is to have 2 regulators which makes things too complicated.

2 regulators? I just change the settings, takes all of 30 seconds.
(this is with an Outback controller).

[colemj]

Originally Posted by s/v Jedi

2 regulators? I just change the settings, takes all of 30 seconds.
(this is with an Outback controller).

Our Morningstar regulator has a built-in webserver for its controls. I can set and monitor ours remotely. Takes 29 seconds.

Mark

[colemj]

Originally Posted by Fuss

That's the problem, if any regulator designers are reading. Two settings are needed that can be selected by an external switch.

Setting 1 for when on board - this setting has maximum bulk voltage and long absorption time.

Setting 2 for when not on board - this setting has reduced bulk voltage etc.

The solution at the moment is to have 2 regulators which makes things too complicated.

These do exist. Like Nick mentions, many can be reconfigured easily in seconds. Others also have quick dip switches for battery type - one of these types is usually "custom", which can be configured in advance just as you wish. Alternately, choose "gel" instead of FLA, and the FLA will not reach gassing voltages.

I think many people have not experienced the higher-end regulators like Outback, Morningstar, Midnite Solar, etc that give one complete and easy control over all aspects of the system.

Mark