Solar control

[Brettlimo]

Hello
Can I ask for advise on the amps measured on solar positive wire at controler being a lot lower than battery positive wire at controler and different again on main battery cable pos.
The system is 2 125w panels wired in series with a mppt 2o amp controler moved from its position on the back of panels to close to smart battery box. Sun available not the best. I am using 105 ah deep cycle agm battery
supplying my lights and fridge. This is 3.6 and 1.0 amps.
Also i have generator backup but wanted to ask if a 3 stage Repco charger can run happily on a Chinese gen.
Thanks for any advice hope you are all well
Regards
Brett

 

[PabloP]

Hello
Can I ask for advise on the amps measured on solar positive wire at controler being a lot lower than battery positive wire at controler and different again on main battery cable pos.
The system is 2 125w panels wired in series with a mppt 2o amp controler moved from its position on the back of panels to close to smart battery box. Sun available not the best. I am using 105 ah deep cycle agm battery
supplying my lights and fridge. This is 3.6 and 1.0 amps.
Also i have generator backup but wanted to ask if a 3 stage Repco charger can run happily on a Chinese gen.
Thanks for any advice hope you are all well
Regards
Brett

Your request is a bit like "gobbledegook" I am afraid Brett. ie. not very clear info. But the current in the positive wire between the panel and the controller is likely to be lower than between the controller and the battery, as the voltage at the panel side will be higher and the controller is bringing that voltage down to the battery voltage.
Basically, that is what the controller is meant to be doing. But of course if in low light conditions at some time the voltage from the panel will be lower than the battery voltage so you will get no current flow.

The bit that is most confusing is that the battery +ve wire at the controller and the battery main +ve should be the same. How are you doing the measurements, as if you are disconnecting wires to put a current metre in the line, then things may have changed while doing the wire switching around.

Any charger should run off the Chinese gen, irrespective of the brand "almost". One basic rule is that just measuring current only tells you half the story as you need to understand the voltage and current to know what is really happening.

Rob P.

 

[Brettlimo]

Thanks Rob I stand corrected, i thought I presented it well.
The amp readings are from a mid level clamp meter on single pos wires for both panel pos and bat pos at the
controler. voltage measured accros pos neg at panel controler and battery controler conections.
The voltage and amps where tested at main pos cable on battery box with clamp meter on pos cable and voltage accross the pos and neg main external battery posts.
I will do more testing and give exact readings and locations.
Thanks Rob

 

[Simmo]

Hi Brett,
Why are you running the panels in series (24v?)
Then using the mppt to charge 12v?

I think this is what is going on, you are measuring difference of Voltage in versus Voltage out.
i.e. 24v in @ say 10 amps will equal 12v out @ 20 amps.

 

[Nightjar]

Hi Brett,
Why are you running the panels in series (24v?)
Then using the mppt to charge 12v?

I think this is what is going on, you are measuring difference of Voltage in versus Voltage out.
i.e. 24v in @ say 10 amps will equal 12v out @ 20 amps.

Was directed towards the method of running panels in series into a MPPT to improve overall input.
Two 12V panels in series increases voltage but the amperage remains the same.
The advantage being the input is better on less than sunny days.

 

[Simmo]

Was directed towards the method of running panels in series into a MPPT to improve overall input.
Two 12V panels in series increases voltage but the amperage remains the same.
The advantage being the input is better on less than sunny days.

Not sure about that mate. Happy to be proved wrong, but in series wired systems, like in old school Christmas lights... one goes out and so does the rest after that??
As I said, happy to see your theory.

This from the net:

Why series?

Strictly series connections are mostly utilized in smaller systems with a MPPT Controller. Connecting your panels in series will increase the voltage level and keep the amperage the same. The reason why series connections are utilized with MPPT controllers is that MPPT Controllers actually are able to accept a higher voltage input, and still be able to charge your 12V or more batteries. Renogy MPPT Controllers can accept 100 Volts input. The benefit of series is that it is easy to transfer over long distances. For example you can have 4 Renogy 100 Watt panels in series, run it 100 feet and only use a thin 14 gauge wire.

The downside to series systems is shading problems. When panels are wired in series, they all in a sense depend on each other. If one panel is shaded it will affect the whole string. This will not happen in a parallel connection.

 

[condor22]

My first Q is; You note the solar controller was fitted to the rear of the panel. Just about every assembly of this type I've seen, the controller is a PWM. I'll stand corrected if it is actually a MPPT, however, there are a number of so called MPPT controllers with it marked on the device, that are not MPPT.

Re volts and amps - There are in a simple system, 2 points between the panel and controller and a further 2 between the controller and battery.

Point 1 - where the cable exits the panel - a V reading here is not subject to voltage drop and is in the range of around 19-21 volts.
Point 2 - where the cable enters the controller (usually several metres of cable) - a voltage reading here may be slightly different to point 1 depending on wire gauge, length of cable and keep in mind as the sun moves or clouds cover the panel, the output will fluctuate. If the panel Wattage output is constant and there is a slight voltage drop, this will also change the amp reading, Ohms Law.

Point 3 and I'll say point 4 - These are either end of the wires coming out of the controller and at the other end on the battery. Given a controller, should be as close to the battery as possible, there will be little if any change. The volts will be at the charge voltage relevant to the charge mode i.e. bulk absorption, float as will amps.

I have 3 panel setups, caravan, 4x4 and portable, where the cable between the panels and controllers are 4M, 4M & up to 10M respectively. However, in all 3 instances, the distance from controller to battery is < 40cm. (Remember that when calculating cable length re voltage drop it is i.e. 4 metres of + plus 4 metres of - = a total cable length of 8M.

More......

 

[condor22]

I've noted this before - On low voltage, low wattage solar systems i.e. 100-200W, connecting parallel or series makes little difference to output. The only real world benefit is when you double voltage you reduce amps and can use thinner wire. Or, use the same wire and reduce voltage drop. In the 1-200W 12V range even here in most setups, not a big issue.

I have a personal dislike of series panel connections when only 2 panels are used. If one panel, or wire in the system fails, you lose the lot. With parallel if one panel or it's wires fail, the other is still giving 100% of its output, or 50% of normal.

 

[condor22]

FYI - Part of Ohms Law;

P(W) = V(V) I(A) (for those that hate acronyms P=Power, W=Watts - V=Volts - I="Intensit de Courant" (French), or current intensity and A=Amps.)

My 110W portable panel has the following stats - Definitions FYI

Max pwr volts =17.8, is the voltage when the power output is the greatest. It is the actual voltage you want to see when it is connected to the MPPT controller.
Max pwr Amps = 6.24, is the current (amps) when the power output is the greatest. It is the actual amperage you want to see when it is connected to an MPPT
Open circuit volts = 21.6, the maximum voltage available from a solar cell, and this occurs at zero current.
Short circuit current = 6.6 amps, is the current through the solar cell when the voltage across the solar cell is zero.

To get a rough idea divide the 110W by the (Vmp) max pwr volts of 17.8, the result is similar to the (Imp) max power amps of 6.24. (efficiency loss or gain)

Going back to Ohms Law -

In parallel 2 x 100W panels with a Vmp of 17.8V = approx 5.6 amps. Therefore W = V x I = 200 = 17.8 x 11.2.

In series the same panels equate thus 200 = 35.6 x 5.6 ( same power, double the volts, half the amps) In both instances the equation balances.

Note - The above is the input to the controller and in both instances, deliver the same Power. At the output of the controller, the voltage and amperage going to the battery will be similar with ether series or parallel connected panels.

 

[Nightjar]

Condor,
Is there less amperage drop in partial shade with panels in series?

 

[Brettlimo]

Hi guys
Thanks for the info. I have been doing a few mods and will report back soon.
Hey the advice is a real learning curve so I thank you very much in no way was it wasted on deaf ears.
Can anyone advise the best value controler for a 250w system. I will respond to all those that helped me and in turn it may well help others.
Again thankyou you help more than you know
Regards
Brett

 

[Simmo]

Hi guys
Thanks for the info. I have been doing a few mods and will report back soon.
Hey the advice is a real learning curve so I thank you very much in no way was it wasted on deaf ears.
Can anyone advise the best value controler for a 250w system. I will respond to all those that helped me and in turn it may well help others.
Again thankyou you help more than you know
Regards
Brett

Mate, this is a very good site that explains things quite well IMO?
It also touches on what Nightjar was saying, right at the end of the article.
However, I find the last section quite contradictory.

https://www.explorist.life/solar-panels-series-vs-parallel/

 

[condor22]

Condor,
Is there less amperage drop in partial shade with panels in series?

In a small system, as above, it's all relative and with solar power generation it's Watts that is the principal factor. The silicone cell doesn't produce as much in lower light conditions.

So, going back to the Ohm's Law formula, if Wattage lowers in less light and the voltage is similar, then amps will also be lower to balance the equation regardless of series or parallel.

I've mentioned this in other threads, there are 2 principal factors re solar output. The first is the quality of the panel. Silicone is "grown" in a Lab, I don't know the specifics, but, it might be a sheet 50cm in dia. The best quality of silicone is in the centre, the further out, the lower the quality.

Companies such as Sun Solar only use the best part of the silicone, the rest is bought up by others. The cell in a good panel may be one piece of silicone, the cheaper ones use the fragments left over and are joined in manufacture, but far less efficient.

The second is; I am also, not ofay on the tech, but most solar cells react to visible light (how sunny or not it is). The cells in my van panels react to IR & UV and as we all know from the skin cancer adds, UV is a danger to us even on cloudy days, but will produce power in my vans panels. My 4x4 panel & blanket are not of the same quality.
The light first thing in the morning and last thing at night is in the IR spectrum due to the low angle of the sun through the atmosphere.

Following the panel is the controller, MPPT is more efficient than PWM, but I have noticed that a 100W panel output won't show much difference. At 200W there is a measurable difference. Which is why I use a Victron MPPT on the van and a cheapy PWM on the others. More....

 

[condor22]

As I want to augment either my van or 4x4 solar by adding the solar blanket in poorer light. The van will then have a total of 320W and the 4x4 230W.

In which case the 75/15 Victron will take that in the van, but the 10A PWM won't in the car. So before connecting it, I'm going to get another 75/15 Victron for the 4x4.

I noted on a really crappy day earlier this year, my 200W panels only put out around 3 amps, so adding another 120W will only add another 2 amps max and still be within it's load.

The connection will be at the controller input by running an Anderson connector in parallel with the existing panels.

I'll do a similar Anderson add to the 4x4 when it gets a Victron. The on roof is 110W and the blanket is 120W for a total of 230W. But that will be next year when I change out the AGM for a Lithium. But only used when needed and not driving.

FYI, my blanket is a Repco purchased, XTM and the controller plugs in via Anderson. Or an extension lead only if I plug in to the Victron.

 

[Simmo]

Condor22..
Did you take look at the link I posted?
I am interested on your thoughts on the authors 'Story' at the end of the article.
i.e. more voltage being available with systems wired in series...

 

[condor22]

Hadn't read it until you noted again, sorry, been busy with other crap.

He makes a good case in some respects. To qualify that; he's giving 3 x 175W of panel = 525W total. For many of us, that is more than most use and about where you might start to consider series as an option.

In a single panel install 80W to 175W, it's just connected to the controller.
In a dual panel setup 2 x 80W to 2 x 175W, it's not worth going series, in my opinion.
In a triple install like he notes, there starts to be a case to do so.

Re shade - in most panels, other than something like an Amorphous Unisolar brand, they are not shade tolerant. Shade 20% of a Unisolar panel, you get 80% approx output etc. However in most Mono Crystalline and Poly Crystalline type panels, put your hand on one corner and you get "bugger all" output and he agrees, move if shaded. So I make sure when I setup, no shade or as little as possible. At my mates place in VIC, I'm in full sun from about 0830, till dusk, as trees block the early morning sun.

He also states if in series one panel breaks, replace it. That's fine if happens in your driveway, a bit more of an issue 500kms north of Kalgoorlie.

BTW Amorphous panels are generally larger for less output than Mono or Poly panels.

However, I still maintain for 2 panels - Parallel connection with a cushioned DC circuit breaker on each is the best install.
a. If one panel fails, you can isolate it and continue on albeit with half output.
b. If charging an AGM from another smart charger source, you can turn the panels off without disconnecting terminals. I'm going to get in touch with my mate as the Pylontech Lithium I have with it's own BMS may well be able to have 2 charge sources on at the same time, I vaguely remember him saying something about that a while back. My 240VAC is a 30A and max panel out is 13+A which it will happily accept.

 

[condor22]

At the end of the day, "you" do what "you" want to do that works for "you". Much of what I say on the Forum is geared to a couple of 100W panels on top of a van and similar.

Most caravan roof installs have somewhere between 3-5M of cable between panels and controller and less than 1M to the battery. Given the voltage and current of 200-300W of panels, voltage drop is not a huge issue.

FYI - I have the Victron 15A controller, its terminals for solar in/out comfortably take 4mm sq wire, 5mm sq will fit with care and 6mm just won't go in. In larger controllers the wire capacity is larger, you need to check.

One way of overcoming wire gauge voltage drop, if necessary - Run 6mm from the panel/s to a terminal block near the controller, then drop the gauge to fit the controller with a short run to the controller input.

 

[Nightjar]

With my ute set up I have two panels connected in series to a mppt and one panel to a pwm. The ute alternator and panels connected to same battery. The panels remain connected while driving.

 

[condor22]

I did a quick "jerry rig" hook up in the caravan today re solar connections. Removed the +/- panel inputs from the controller, added extra wires to jump to the controller and another set to the Anderson plug normally used for the fridge. (quickest way to get into the van with an existing cable and plug)

I plugged in the 120W solar blanket to the hitch Anderson connector. Had to wait till the sun conditions stabilised as there was passing cloud.

It is winter sun and was around midday - I have a circuit breaker on each of the 100W roof panels and able to plug in the blanket inside the van. My battery was full, so I loaded up the battery with TV and lights etc to show a 9.2 amp stable load. As I switched each panel on the net load reduced as the panel added its input. I'll show calculated net panel input.

With one of the 100W on, my monitor showed panel input at 2.8 amps.
With both of the 100W on, my monitor showed panel input at 5.5 amps.
When I added the 120W blanket, input rose to 8.7 amps, an increase of 3.2 amps, which is what I expected at more than aa 50% increase.

I then disconnected each in the same order connected and noted similar figures at each point. The test proved the expected improvement, so will shortly make the mod more permanent. (of note, before I turned everything off, overcast cloud covered the sun and input from the 2 roof panels, no blanket, dropped to a combined 2.2 amps)

In better summer conditions, I regularly see double digit amps from the 2 panels up to 13+A so no need for the extra input.

 

[bicter]

Condor22..
Did you take look at the link I posted?
I am interested on your thoughts on the authors 'Story' at the end of the article.
i.e. more voltage being available with systems wired in series...

Simmo, it's been a long time since I investigated series/parallel benefits.
From memory, the authors 'Story' at the end of the article is referring to the voltage at which the regulator turns on. Ie at dawn, voltage at the regulator input gradually rises from 0V (dark) through to max voltage/current during the middle of the day.
The voltage into the regulator, with a parallel system may not get to the regulator turn on voltage as soon as when using the series panels whose voltage will reach the reg turn on voltage earlier.
What this suggests is that you will achieve more "Sun hours" using series panels. This should then equate to more amps fed into the batteries.
The benefit of the above will depend on the type and design of the regulator.
P.S. I'm typing this on a touchscreen so I've truncated it a bit