Are two partially shaded total 260W panels worth it

[nilespf]

dingysailor, to make sure we are all on the same page, I'm assuming a blocking diode is a series connected diode in which all current passed by the panel must pass through it. A blocking diode is used to block a path of discharge current established when a panel becomes reversed biased. Note there may be any number of special circumstances in which a blocking diodes are necessary but generally they are used if the panel is directly connected to the battery. If the panel has one permanently soldered to the electrical path then maybe the panel has been purposed for just a system.
The following is my summary based upon:


3 identical panels, Voc=24V, Isc=3.15A, 2 bypass diodes (voltage drop neglected)
Shading, only one of the three is shaded and in such a way only one bypass is conducting



Case1--3 panels in parallel, 110W delivered to the controller, 14V @7.9A

Case2--3 panel in series, 100W delivered to the controller, 62V@ 1.6A

Case3-- 3 panels w/ individual controllers, total of 172W available for conversion


hopefully my arithmetic is correct!

For my installation, the case 1 "Y" connections proved useful due to layout constraints.



If only a start battery/house is what your talking about you don't need more than a couple of amps.



pn

[Pizzazz]

If your main engine is petrol, then a portable generator is a no brainier. You can get a 700W inverter generator on Amazon for $215, and it is much smaller than the Yamaha 1000. I would even consider combining the two engines somehow, especially if trying to save weight:

1) Get a bigger generator and switch to electric propulsion. A Honda 2200, will give you the equivalent of 3 hp at the propeller which is significant.

2) Look for an outboard that you can modify to run a generator (an inverter generator would be too difficult). One option that comes to mind is to install a power takeoff on the propeller shaft (or in place of the propeller), then drive the generator with it. I need to think about how to do it, it is unlikely to be cheaper or less trouble free than the $215 mentioned above.

I wish someone came out with an outboard combined with an inverter generator. This way, you get a liquid cooled gas generator. Should not be that hard.

SV Pizzazz

[john61ct]

Reduced output for whatever reason is not IMO a good justification for avoiding solar.

Nor is it an either/or proposition to get a generator, most long-term cruisers need both.

If your batteries are lead, no matter how much genset capacity you have, their lifetime will be drastically shortened without solar if you are away from shore power more than a few days at a time.

If solar conditions are not ideal, your genny runtime is increased, just like when heading away from the equator, or using more power in cold weather.

[dinghysailor]

Pizzaz - I see a 700W continuous rated 4stroke generator branded 'Dirty Hand Tools' on US Amazon, maybe the one you are talking about. Don't see it on UK Amazon but something looking the same is available under a 'Wolf' brand in the UK at about 1/6 price of the Yamaha. Its about the same dimensions as the Yamaha I think, but lighter at 9kg compared with 13kg for Yamaha. Its a bit less output than the Yamaha of course, also noisier according to the DbA rating and unfortunately it is a couple of inches taller which would be a problem for the stowage place I had in mind. I would agree though that on the face of it, it does make the Yamaha, and Honda, look overpriced.


Re electric main propulsion, that might be an option for some boats but probably not for our one. That would need a much bigger generator - at present we have a Mercury 9.9hp 4stroke outboard with the largest 4 blade propeller option and I suspect that we could still do with more thrust for manouvering in a breeze but we need more experience with the boat to know for sure. Even if we had the generator I am not sure there is an appropriate electric outboard and an inboard electric motor with shaft drive would not give the manourverabilty you get with an outboard.



I dont really want to start building this kind of thing from scratch but I did see somewhere that someone adapted a 10hp outboard motor to drive a high output alternator, I think with vee belt drive - it needed a much bigger than standard cowling on the outboard to house it all. Also, someone made his own generator which he said was about the size of a shoe box. He had a garden strimmer engine direct driving a brushless motor as a generator and made his own circuitry to rectify the output and convert to the right voltages for battery charging without needing a separate AC to DC battery charger unit.



I feel that I still need to read more about solar panels to properly understand how they are affected by shading.

[Shaneesprit]

There is a reason a Yamaha costs more than something you get from the other, I don't even need to look to know the other is a Chinese gen, nothing against them but i have worked on them ( probably not the same type ) i also had to rely/use on one out in Russia on a diesel one an offshore concrete oil rig base - its a good job we took 2 with us! the first one wouldn't start on the 2nd day, diesel pump / injector failure, I was out there to replace a Lister Petter Diesel gen that had been started up and left on load for 8000 hours without any kind of service or inspection at all - unless you count a once a month Satellite call to the security cameras outside to ensure it was still there ( just up-rated filters and a oil top up system )

You should just fit some solar and see how it goes - remember the solar works when your not even there - i have one solar panel and never have shore power other than twice year beginning and end of season and that's only to run a dehumidifier, i have a diesel beta but never use it to top up the batteries unless also using to motor.

[Pete7]

Originally Posted by john61ct

Any shading or clouds, or higher latitudes, can easily cut that by at least half.

Surely at higher latitudes the days are longer during the summer, when most of us go sailing. Sunrise is 5am in June for me. Sunset about 10pm. Added to the cooler air temperatures what do you think this does to the output?

Pete

[Pete7]

Originally Posted by Pizzazz

Some good real world examples here. I have a 100W panel on the dodger, sometimes it makes 4.5A, sometimes as low as 1A. I get about 20AHrs a day from it if I am generous with my calculations. It is not worth it except as an emergency backup, for the radio and the autopilot.

That's a shame, we find 180w of solar fully meets our needs and have spent days at anchor leaving with full batteries.

Originally Posted by Pizzazz

I believe it is much better to invest in a better alternator and a portable generator as backup. Run the engine for two hours, make 120-140 AHrs, which is typical daily consumption, use excess current to make some water, vacuum, you also get hot water. Not so bad.

What sized alternator gives a continuous output of 120-140A for over two hours. Mine starts at 40A and drops quite quickly as the 2 xGp31 batteries charge and increase resistance lowering the current they will absorb. It will be down to 20A after 30 mins.

Originally Posted by Pizzazz

I am thinking of putting one of these small $200 gas generators in the anchor locker (it fits well), routing the exhaust out and into the water. They produce around 50A, leave it on while on the way to the island and five hours later you have 300AHrs. To me this makes more sense.

Please don't, people die from doing stuff like this. If you must run a small portable generator, do it on deck down wind from people and hatches or stick it in the dinghy at anchor. The idea of modifying the exhaust is a no no. How does 5hr x 50A equal 300AH and how are you going to store 300AH? That would likely require a 600AH bank if you are to avoid going less than 50% DOD. On a 31ft yacht do you really have this capacity and accept the weight penalty?

Pete

[Pete7]

Originally Posted by dinghysailor

I would say that this is making me think twice about whether to have solar power on our boat. The boat has a big carbon fibre reinforced mainsail that does not stow well, it becomes a bulky package when flaked down on the racks that extend each side of the boom, so shading could often be worse than just a part of one panel. Maybe the power output that we would actually get even with bright sun would be only a fraction of what one would expect from the rated output of the panels. In that case, as I said before, I am tempted to just get a small portable generator.

We sold the Honda 20i after starting to fit solar, just didn't use it much. We did have a 60w suitcase (folding) panel that I rigged in harbour or at anchor and moved a couple of times a day to point towards the sunshine. Until it slipped and smashed, it was really effective for its size because it was always pointed in the right direction. How about deploying some of the solar panels once you are in harbour or at anchor?

Pete

[john61ct]

Originally Posted by Pete7

Surely at higher latitudes the days are longer during the summer, when most of us go sailing. Sunrise is 5am in June for me. Sunset about 10pm. Added to the cooler air temperatures what do you think this does to the output?



Pete

Sure, but if you're there year round, the much lower **consistency** in insolation requires sizing differently than when staying in the tropics.

Somewhat similar to a shading vs no-shading scenario.

I just brought it up to point out many factors at play, and insolation being sub-optimal is no reason to give up on solar.

[Pete7]

Originally Posted by john61ct

Sure, but if you're there year round, the much lower **consistency** in insolation requires sizing differently than when staying in the tropics.

Somewhat similar to a shading vs no-shading scenario.

I just brought it up to point out many factors at play, and insolation being sub-optimal is no reason to give up on solar.

We hibernate during the winter, its cold and dark

Pete

[Jon Hacking]

Originally Posted by Tenedos

... I am debating whether to put solar panels on the dodger and in front of it. I think I can fit one 160W panel and another 100W panel and connect them in parallel. However the issue is they will always be partially shaded… Thoughts, suggestions?

Tenedos, I haven't read this whole thread, but shaded panels in parallel will never charge the battery. Get panels with similar (ideally, identical) current specs & put 'em in SERIES to mitigate shading issues.

A solar cell generates ~0.5v when it's working, but when shaded it becomes a diode, eating ~0.7v (but not affecting the current significantly). So each shaded cell will decrease your array voltage by ~1.2v.

Putting the panels in series & connecting to an MPPT controller will give you the best results. The MPPT will run the panels at whatever voltage it can to give you the most power. Two 36-cell panels in series will give you a nominal Max Power Point of ~36v (no shading). The MPPT will shut down at ~15v, so you have ~21v in hand. (21v)/(1.2v/cell)=17 cells, so you should be able to tolerate up to 17 shaded cells before the array voltage gets so low that the MPPT gives up.

And pull your boom (& etc) out of the way to minimize shading. Our boom is always off to the side when we're anchored.

[john61ct]

Nope.

but no point arguing.

Get a controller like Victron, gives you the ability to parallel or series, mount the panels and wire them so easy to switch,

and do your own A/B testing with a depleted batt, see for yourself.

Not just Amps output "live", but Ah per day with similar conditions.

Which is best will be very clear.

[nilespf]

Jon:


but when shaded it becomes a diode, eating ~0.7v (but not affecting the current significantly).
Not accurate, fully shaded it (the cell) becomes a large resistor that will burn a hole in the panel (because of P= I*V or I^2 / R). If on a late model panel with protection, it will forward bias the bypass diode that will shunt (bypass) an entire string of PV cells. The "loss" will be dependent upon how many cells are in the string that particular bypass diode is protecting. Usually on a 36 cell panel there are 3 strings of 12 cells each. That would be a loss of 1/3 power



Two 36-cell panels in series will give you a nominal Max Power Point of ~36v (no shading).
Careful here, not the entire story, the buck converter (controller) will load the PV to put the PV output voltage where the battery needs it which is by definition not the MPP. The controller will abandon MPP and enter a PWM mode if too far from Vmpp. Power xfer is negatively impacted because the controller has to lower it's output voltage (and thereby load mismatch). MPP is very effective when Vmpp and battery are close which is why most off grid systems are wired in parallel.

[Jon Hacking]

Niles, do you have any references for your claims?

Maybe your cells become resistors, but the way I studied it (as an EE at UCB) & the way my 800W of PV panels work, they become diodes. The process for making diodes is actually very similar to making (monocrystalline) PV cells. Most fixed panels, if they're going to take some shading, get shaded in the same place every day. Having looked at many thousands of panels, I've never seen one with a hole burned in it from shading.

Yes, the OUTPUT voltage of the MPPTC will be where the battery needs it, but I was talking about the INPUT, which will be at the MPP for the panel(s) when the charger is in bulk mode. To say an MPPTC goes into "PWM mode" is a bit misleading, as the DC/DC converter is *always* oscillating, & its design & operation are very different from a PWM controller.

But my main point to the OP was that panels in series (with an MPPTC) handle shading (his main issue) better than panels in parallel. If 1 of a set of panels in parallel gets even 1 cell shaded, it can't reach the voltage of the other panel(s), so it effectively shuts down & it's entire output is lost (OK a very few MPPTCs will search far enough to find a 2nd knee & run the whole array at the lower voltage, but not many). And if both panels have 2-3 cells each shaded, then there's not enough voltage left to charge a battery, so everything is lost. But wiring panels in series gives much more voltage to play with in shading situations, so the MPPTC can continue to charge the battery much longer, albeit at reduced current.

Perhaps we'll have to agree to disagree...

[nilespf]

Jon,
Maybe your cells become resistors, but the way I studied it (as an EE at UCB) & the way my 800W of PV panels work, they become diodes.

I as well but at SMU. Was around to see Clements actually pay off the players. The stigma still persists.

I believe we are talking about the same thing. Just semantics, bottom line the cell loses conduction begins to drop current output (and of course creates and IR drop across it) which generates a local hot spot. IFF the effected cell(s) is/are dark enough (i.e. to fully put the bypass into conduction mode) then we lose the entire string and as you state that string now effectively is a single diode. If the cell is partially shaded it's contribution may be enough to not forward bias the shunt and the (effected string) panel continues to limp along. The manufactures hide behind cost as the reason for having so few bypass diodes. The entire panel is not lost (unless in our example all three strings go dark) which regardless of series/parallel connection, is a catastrophe.
"Yes, the OUTPUT voltage of the MPPTC will be where the battery needs it, but I was talking about the INPUT, which will be at the MPP for the panel(s) when the charger is in bulk mode. To say an MPPTC goes into "PWM mode" is a bit misleading, as the DC/DC converter is *always* oscillating, & its design & operation are very different from a PWM controller."
This one is a bit touchy. Most controllers are PWM implemented using a SMPS (DC/DC converter) as you state . My understanding is most off grid controllers are implemented using a single buck converter. If the panel output has an Vmpp of 36V then the prototypical buck will change the duty cycle (D) of the DC/DC switch to achieve an output voltage desired. Necessarily (because Vpanel=Vbatt/D & Rsolar=Rbatt/D^2) a load miss match ensues and the MppT function has to be abandoned. This fly's in the face of madison Av. and is rarely seen in print but is the reason the controller specs fall off when efficiencies are stated for increasing input voltage. All is a bit touchy in that I would guess there are some non-prototypical controllers that may have a secondary DC/DC converter that will allow high input voltages to be Mpp tracked and also drop the resulting Vout to the batteries Voltage. Most off grid systems are for 12V systems and is the reason most all of our panels available for purchase fall into nice 36 cell panels and the bell curve for controller types peak at single bucks. The Buck/Boost, flybacks and Cuk's are more expensive and are not as prevalent except in on-grid systems.
I scared up enough room to put 300W above the bimini. Had 500W with two controllers previously but that didn't work out so now I have a controller each for the 150's. I dream of enough room for 800W. BTW do you hail from the area your in now or are you lucky enough to be lost.


Phil