First foray into Solar. Advice needed

[jiris]

I beg to differ. Solar panels have the bad habit of behaving like resistors when not having enough light. In effect, if you have one like this connected parallel to the one generating power, it will be wasting energy producing heat. There is no need for 2 controllers though. Simply connect each panel to the common lead to controller through a diode. A few quid sufficiently rated (10A?) diodes (I'd suggest Shotky, to minimise losses) will do the job.

 

[RichardS]

I beg to differ. Solar panels have the bad habit of behaving like resistors when not having enough light./QUOTE]

Which is why, if one panel is shaded, they should be connected in parallel. Connection in series is the configuration to be avoided, although under any other circumstances, series is better because of the lower cable losses and other controller-specific reasons. I think you'll find that using a diode of any kind will reduce the output rather than improving it.

Richard

 

[jiris]

I think you'll find that using a diode of any kind will reduce the output rather than improving it.

Richard

Definitely not, especially with Schotsky diode. I didn't crunch the numbers, but just a glance at the situation gives some idea. The margin in voltage on a typical solar panel is huge (they deliver >18 on open) and the drop on the diode is insignificant in comparison. It is generally known, if you connect battery directly (no diode) to a panel, it will discharge overnight more than the panel delivered during the day and the total effect is negative. I've been using this system for years, not bothering about regulator at all. There is no danger of cooking my 1.500 Ah bank with 200W solar. With my power consumption I actually have have to top it up from an external source every now and then. Simple, effective .

 

[TQA]

Two controllers would only be a benefit if the panels were wired in series...in which case they wouldn't be wired in series:ambivalence:
A single controller (whether MPPT or PWM) will be perfectly happy if they're wired in parallel.

Can anyone explain the logic on using 2 controllers on a series setup?

Seems wrong to me.

 

[noelex]

Multiple MPPT controllers (often one per panel) is becoming quite common, and with a few caveats, it is generally best way to harvest the maximum amount from the solar array.

The advantage is the controller can track each panel separately and set the Vmp to suit the individual panel. On a boat it is not unusual for the Vmp to be significantly different for panels especially those in different locations (for example port and starboard). A single MPPT can only choose one Vmp and this will be a compromise for the different panels.

Using multiple MPPT controllers is not necessarily more expensive that a larger single controller, especially on high power installations, but a lot depends on the specifics. Small controllers are often significantly cheaper than larger models compensating for the need to purchase more than one unit.

Multiple controllers are certainly not the only option. There are some pros and cons, but it is an option worth considering.

The output from the controllers is obviosly connected to the batteries in a parallel configuration. The input is normally direct from one panel to one controller, but there are other options. For example with four panels rather than four controllers two controllers could be used. This will be a little less efficient but can be a good compromise in some installations.

 

[RichardS]

Definitely not, especially with Schotsky diode. I didn't crunch the numbers, but just a glance at the situation gives some idea. The margin in voltage on a typical solar panel is huge (they deliver >18 on open) and the drop on the diode is insignificant in comparison. It is generally known, if you connect battery directly (no diode) to a panel, it will discharge overnight more than the panel delivered during the day and the total effect is negative. I've been using this system for years, not bothering about regulator at all. There is no danger of cooking my 1.500 Ah bank with 200W solar. With my power consumption I actually have have to top it up from an external source every now and then. Simple, effective .

I'm afraid that you are confusing many different issues here. We are talking about connecting the panels to the battery through a controller so any references to overnight discharge are totally irrelevant. There is absolutely no prospect that anyone installing 300 - 400W of solar panel like the the OP, never mind 200W, is going to connect that directly to their battery bank. It would be madness unless you were a liveaboard with a continuous power drain and were prepared to disconnect some or all of the panels every time you leave the boat for a few days.

Richard

 

[Dave100456]

Haven't read the entire thread and this may have been mentioned but this website has a good calculator for working out consumption and PV sizes needed.

http://www.bimblesolar.com/solarcalc

 

[Dave100456]

Can anyone explain the logic on using 2 controllers on a series setup?

Seems wrong to me.

+1

I too would like to know why?

 

[RichardS]

Multiple MPPT controllers (often one per panel) is becoming quite common, and with a few caveats, it is generally best way to harvest the maximum amount from the solar array.

If you used one MPPT controller per panel using the small panels as found on most of the sailing vessels that forumites sail, you would have to avoid purchasing those MPPT controllers which work best with a higher voltage. This would rule out Victron, arguably the best, but I can't speak for any other brands.

Richard

 

[RichardS]

+1

I too would like to know why?

It's obviously not possible to achieve such a configuration so it's either a misunderstanding or a mis-speak.

Richard

 

[GrahamM376]

The design of the panel attachment is a work in progress. I intend to use the guardrails, not rigid tube.....Flex panels on a plastic backing could be good......Also considered flex panels in an ally frame.....Any other ideas welcomed.
Tony

Before we had the gantry, the panels were mounted on the guard wires. Clamped a stainless tube along the long centre line of the panel, inserted soft plastic pipe and fed the wire through that. Angle was adjusted with lines to toe rail. A bit of a lash up but was OK for a season.

 

[noelex]

If you used one MPPT controller per panel using the small panels as found on most of the sailing vessels that forumites sail, you would have to avoid purchasing those MPPT controllers which work best with a higher voltage. This would rule out Victron, arguably the best, but I can't speak for any other brands.

Yes, one controller per panel does not tend to be viable with very small panels, especially with the Victron controllers. Grouping a couple of panels together and, for example, having one controller for the port panels, and one for the starboard panels, can sometimes be a good option with Victron controllers if you wish to use small panels.

With the OPs wish for 2x 150-200w one controller per panel including the Victron range is fine.

The Victron controllers are a popular choice but they have quite a high start up voltage. This makes them not ideal for a 12v panel, or multiple 12v panels connected in parallel. They can still be used very successfully for a one panel to one controller option but the panels need to be higher voltage models. Most of the good medium to large panels are high voltage panels.

With the Victron controllers if you are using an older single controller layout you also have limitations. Higher voltage panels are still needed, or you can connect some panels in series, but this tends to reduce the output in shaded conditions that are common on a boat. These limitations are annoying as the Victron controllers are otherwise very good. Other MPPT controllers do not have these limitations.

 

[Chris_Robb]

If you used one MPPT controller per panel using the small panels as found on most of the sailing vessels that forumites sail, you would have to avoid purchasing those MPPT controllers which work best with a higher voltage. This would rule out Victron, arguably the best, but I can't speak for any other brands.

Richard

Richard - perhaps I have fallen for the sales pitch from Victron, - they specifically on my 2 x 85 watt panels said to connect the panels in parallel. He said the the Blue Solar 75/15 was the one to go for - which I did, to replace the 9 years old Steca controller. The reason was that shading of one would effect output on both if connected in series.

What should one expect from 2 panels in perfect settings?

I have 2 x 85watt - =170 watt. Divide by voltage 12V - 14 amps, or divide by 14V = 12 amps.(probably the better equation.)

However the max i ever see (the Steca shows both amps from the panels and what is going into the battery separately) is 9 amps.

A combination of BM1, Steca output to battery and output from panels all seem to agree - one can see the Steca go to float. Incidentally it goes to float before the input to the battery drops..... which surely means the batteries are still accepting good charge and must be way off full!

EDIT: I think my 10 year olds panels have an open voltage of 20 Volts. if that is relevant info.

 

[noelex]

Richard - perhaps I have fallen for the sales pitch from Victron, - they specifically on my 2 x 85 watt panels said to connect the panels in parallel. He said the the Blue Solar 75/15 was the one to go for - which I did, to replace the 9 years old Steca controller. The reason was that shading of one would effect output on both if connected in series.

What are the specifications for the panels. Particularly the Vmp and Voc.

 

[jiris]

I'm afraid that you are confusing many different issues here. We are talking about connecting the panels to the battery through a controller so any references to overnight discharge are totally irrelevant. There is absolutely no prospect that anyone installing 300 - 400W of solar panel like the the OP, never mind 200W, is going to connect that directly to their battery bank. It would be madness unless you were a liveaboard with a continuous power drain and were prepared to disconnect some or all of the panels every time you leave the boat for a few days.

Richard

Thanks, Richard! I can assure you I am not confused or confusing issues at all . I used the example of the overnight discharge only for illustrating the possible magnitude of the consumption a shadowed panel can have and if the separating diode could be justified. Sorry, if I didn't stress it enough.
As for the "madness" of connecting 200 W panel directly to the bank: it goes down to the size of the bank, that I stated clearly is in my case 1.500 Ah. 200 W panels can deliver AT THE PEAK of a nice sunny day about 12 A, what can be considered as trickle charging for a bank of this size. Now, even in Australia we don't have sunshine for 24 hours a day, do we...
I also mentioned my consumption - sorry, I didn't elaborate, but it includes a decent refrigeration, ultrasonic antifouling, GPS monitoring etc - that is when I am not aboard. When aboard (very often), the solar is in fact grossly inadequate and 300 W wind plus occasional use of petrol generator is saving my days. I also stated, I've been using this system for years, so, frankly, there is little new I can learn about it. Anyway, I am always ready to accept somebody knows more than I do...

 

[noelex]

EDIT: I think my 10 year olds panels have an open voltage of 20 Volts. if that is relevant info.

I see your edit.

If the Voc is 20v parallel configuration is not ideal for the Victron controllers, especialły in a warmer climate like the Med.

This is a pity as parallel connection is the best option (appart from one controller for each panel) if shade is present. Shade is always a problem on a boat.

The controller will work, but you may notice you miss out on some early morning solar especially if the batteries are reasonably charged and it is hot.

I prefer parallel connection on a boat,but in your case I would at least trial series connection. I think the total output will be higher.

The other option, if you notice the controller has not woken up, is to briefly turn on a high load to "fool" the controller into starting in the morning You need to get the battery voltage at least 5v below the solar panel voltage for the controller to start. The bluetooth diplay will show the relevant voltages. Once started the controller only needs a 1v differential.

 

[Jabs]

Interesting post. Noelex, why do you prefer two controllers??

That was my thought but if you read the above, the general opinion is no!

As to 'tricking' the controller, it's hard if you are at home!!

Thanks

Tony

 

[GHA]

Back to the first post - did that - what a difference!

2 x 100w panels, one each side on the guard rails, victron bluesolar controller with panels wired in parallel . Not sure about victron being 'not ideal'? Works fine for me. A few thoughts -

• Mine are mounted with plastic plumbing pipe close to the top edge - at some point I'll fabricate something in stainless - bit flimsy.
• More than 100w panels might be a bit big.
• Angle is take care of by some cord from the bottom of the panel up to above head height on the mast into a cleat. Really quick to angle but looks a bit messy & more bits of sting to get caught - some point I'll fit some sort of quick adjustable brace down to deck level.

 

[noelex]

Interesting post. Noelex, why do you prefer two controllers??

It allows the controllers to adjust the input voltage to suit each solar panel. Therefore one controller per panel is the most shade tolerant option and will deliver the most Ahrs from the solar array (subject to a few caveats).

It also has the advantage of redundancy. If one controller fails you will still produce power. MPPT controllers are not the most reliable of electronics, so this can be valuable. The main drawback is the wiring is more complex. Total cost can be anything from similar to reasonably more expensive depending on the specifics.

As to 'tricking' the controller, it's hard if you are at home!!

Very true . However, the Victron controller will still start (with a 20v Voc panel). The loss of power would be annoying in some circumstances, but will only be small (and in many situations there will be no loss). If you were away from the boat this slight loss is probably not going to be of great concern.

 

[RichardS]

Richard - perhaps I have fallen for the sales pitch from Victron, - they specifically on my 2 x 85 watt panels said to connect the panels in parallel. He said the the Blue Solar 75/15 was the one to go for - which I did, to replace the 9 years old Steca controller. The reason was that shading of one would effect output on both if connected in series.

What should one expect from 2 panels in perfect settings?

I have 2 x 85watt - =170 watt. Divide by voltage 12V - 14 amps, or divide by 14V = 12 amps.(probably the better equation.)

However the max i ever see (the Steca shows both amps from the panels and what is going into the battery separately) is 9 amps.

A combination of BM1, Steca output to battery and output from panels all seem to agree - one can see the Steca go to float. Incidentally it goes to float before the input to the battery drops..... which surely means the batteries are still accepting good charge and must be way off full!

EDIT: I think my 10 year olds panels have an open voltage of 20 Volts. if that is relevant info.

Noelex is right with his answer. Ideally the Victron work work better with your two panels connected in series and neither of them in the shade for most of the time. However, if you don't have this luxury, then parallel connection will be better. Your figures seem to be about what you might expect but you will be suffering some degradation in output because the Victron needs to reach its trigger voltage which, from memory, I think is 5V above battery voltage.

There could be an argument that a MPPT controller which has a lower trigger voltage might have been better but contradicting that is the fact the once the Victron does start it apparently has a very effective tracking algorithm so you are probably making up for much of the "lost time".

The only way to be sure you have the best configuration is to switch the wiring from parallel to series and then check the total output over a few 24 hour periods. The Victron dongle will do this but I'm not sure whether you can do it with your equipment. However, you'll probably find that if you happen to be lying with the sun directly on the stern and the boat drifting around to keep this orientation then your series output beats all your records .... but, unfortunately, on the vast majority of normal days, the series output is worse than the parallel.

Richard