Linking solar panels

[longjohnsilver]

I have just ordered an additional flexible panel to use in addition to my existing non flexible panel, both 100watts and both producing a fraction over 20v unloaded. I plan to connect the new panel in parallel (?) ie positive to pos and neg to neg. the supplier says this is not possible to do but I can't see why not. My mptt controller has enough capacity, 15amps and the wiring is well over size.

Can anyone suggest why this could be a problem, as suggested by my supplier?

 

[Champagne Murphy]

Who's the supplier?
I contacted Marlec to ask if it was ok to fit a panel from another supplier in parallel and the response was 'yes, fine'. Only proviso was that the controller must be capable of the additional load. I fitted both outputs to the regulator input and all seems well.

 

[Rigger Mortice]

Your two panels will produce more than 15 amps at full chat so you need a bigger controller.
Your parallel wiring is correct.

 

[longjohnsilver]

Each produces just over 5A max, wish it was 15A + !

 

[Mistroma]

Your two panels will produce more than 15 amps at full chat so you need a bigger controller.
Your parallel wiring is correct.

Are you certain? 200W @ 12.5V gives 16A so a pretty flat battery with blazing sun might reach that. I suspect that output wouldn't actually be that high even with a good MPPT controller and very strong sunlight. I think that charging above 13.8V the panels would only manage 14A.

It's close though and my experience is only with a PWM reg. not MPPT. So I'd be interested to see figures for MPPT and an explanation for the extra Amps. vs. quoted Wattage which always seems optimistic & I think calc'd in ideal conditions (imaginary mountain top at the equator? ).

 

[Rigger Mortice]

That's much what would be expected at our latitudes but the advice you were given was based on the panels working at optimal performance. It's quite likely that it will never be achieved but.........

 

[Rigger Mortice]

Are you certain? 200W @ 12.5V gives 16A so a pretty flat battery with blazing sun might reach that. I suspect that output wouldn't actually be that high even with a good MPPT controller and very strong sunlight. I think that charging above 13.8V the panels would only manage 14A.

It's close though and my experience is only with a PWM reg. not MPPT. So I'd be interested to see figures for MPPT and an explanation for the extra Amps. vs. quoted Wattage which always seems optimistic & I think calc'd in ideal conditions (imaginary mountain top at the equator? ).

It's good practice to build a bit of slack into the system. As you say OP may well get away with it, but he was asking why his supplier gave him the advice he did and, pound to a penny, that's why.

 

[LadyInBed]

To connect them in parallel you need a Male and a Female MC4 Y connector
http://www.ebay.co.uk/itm/251125930829

 

[Rigger Mortice]

To connect them in parallel you need a Male and a Female MC4 Y connector
http://www.ebay.co.uk/itm/251125930829

If they are going to be connected together above deck those connectors may be useful, but they are a bit OTT. If the connections are below deck then ordinary crimped connectors would be fine.

 

[Mistroma]

That's much what would be expected at our latitudes but the advice you were given was based on the panels working at optimal performance. It's quite likely that it will never be achieved but.........

I was trying to get you to state the calculation you are using to determine the panel output. I wanted to find out if you were saying is might be well above 15A or just exceeding it by a tiny margin. You just said "would produce more", so I couldn't tell from the post.

OP said that supplier said connection was impossible, not that it was marginal unless you upgrade the regulator. My point was that I believe panel Wattage is calculated on a basis that doesn't occur outside a laboratory. So regulator was likely to be able to cope with the actual output once losses and other adverse factors are included.

I must admit that I can't see why you can't mix 2 panel types if they have matching electrical characteristics. I have 3 panels (65W + 2x40W) and selected them on basis of similar characteristics. I could only find an output graph for one type but they all matched within 0.1V on max power voltage and open circuit voltage quoted. However, I wasn't mixing rigid & flexible panels.

I wonder how OPs panels compared for max power voltage? I could see that being a problem with MPPT controller, but even then I'd expect the effect to be minimal.

 

[longjohnsilver]

I've had my existing panel for approx 3 years and the max amperage I've seen has been about 5.4 on the sunniest of days in mid summer which tallies pretty closely with what's stated on the panel. New panel states much the same.
I do keep a very careful watch on what goes on with my batteries, I have a meter for each battery bank.

So back to my original question, seems as I suspected there's no reason not to connect new and old panel. And my mppt controller may well be 20 or 30 amp, just can't remember sat here at home, but certainly man enough for 200watts of panels.

 

[Rigger Mortice]

I was trying to get you to state the calculation you are using to determine the panel output. I wanted to find out if you were saying is might be well above 15A or just exceeding it by a tiny margin. You just said "would produce more", so I couldn't tell from the post.
.

200 watts at 12 volts is 16.6 amps, but your figures are fine too. Whichever you take it's not good practice to work so close to the design limit of electrical gizmo's. Particularly with solar panels which you will want to be charging batteries 24/7, and that includes when you are not on board. As you say, odds are OP will get away with it, but he did ask why he was given the advice he was.........

 

[LadyInBed]

If they are going to be connected together above deck those connectors may be useful, but they are a bit OTT. If the connections are below deck then ordinary crimped connectors would be fine.

You pays your money and takes your choice!
With Y connectors on the tails from the panels, you only run one pair of wires from panels down to reg, paralleling up below deck means you run 4 wires down from panels.

 

[JumbleDuck]

OP said that supplier said connection was impossible, not that it was marginal unless you upgrade the regulator. My point was that I believe panel Wattage is calculated on a basis that doesn't occur outside a laboratory. So regulator was likely to be able to cope with the actual output once losses and other adverse factors are included.

The highest power and lowest voltage that the controller could put out would be 200W and 13.8V, which is 14.5A. In reality the input power will be (a lot) less, the output voltage will probably be higher and the input voltage will certainly be a lot higher. I can't see any reasonable way of getting more than 15A at any point.

I must admit that I can't see why you can't mix 2 panel types if they have matching electrical characteristics.

It would be interesting to know what would would happen if a panel with blocking diode and an un-blocked panel were wired in parallel, but it's unlikely that a 100W panel would have a blocking diode, as they all, as far as I can see, expect a controller to be used. Later this week I will be wiring the controller into two different 50W panels on my boat, from Remytek and Photonic Universe. If it blows up I'll let you know.

 

[William_H]

Panel quoted power is usually a product of max voltage times max current. So usually 100w panel max current is 5 amps. (max voltage 20volts) With a panel directly connected to a 12v battery regardless of battery voltage be it 11 or 14v max current will be 5 amps. The dat plate usually quoptes max current and max voltage.
Now regarding MPPT controller that will be a max 10 amps input. The MPPT controller by it's nature is like an automatically adjusting transformer. It will take 10 amps in at probably around 18volts amybe 20v depending on sun intensity. (the panel voltage falls as current is drawn) and transform the power going in to the required voltage to charge the battery ie 11v for a really flat battery to nearer 14.5volts for a near charged battery. In transforming the voltage down it can increse the current to reflect the wattage going in to the controller. So 20 volts in at 5 amps gives 100watts which can come out at 14volts at about 7 amps. 100watts. In fact somehat less due to inefficiencies in the transforming process. say 95 watts.or 6 and a bit amps.
The MPPT contoller has the ability to figure out how best to extract the powwer of the panel considering the conditions then transform this to what the battery needs.
A PWM controller is essentially the panel attached to the battery for most charging just turning off and on when battery is charged.
A panel connected to a battery will produce 20volts but lose 6 volts in the internal resistance of the panel. So you only see 14v at the battery. (or less) The panels are made ith enough cells to produce 20volts so that in less than max light they still produce enough voltage to charge a battery ie more than 14v. Both kinds of charge controllers can have a "snart charge multi stage charge voltage regime)

So the OP needs to check if the 10amp rating of the MPPT controller is input or output. Often an MPPT controller will have higher voltae input rating as for the same power it is switching less current so can handle a higher power. So often it is desirable to wire panels in series. Home PV systems usually wire panels in series so mine runs at max 360 volts input 8 panels at 40 volts each. It is an MPPT type controller even though the output is switched to 240vAC rather than a DC for battery charging.

 

[longjohnsilver]

So the OP needs to check if the 10amp rating of the MPPT controller is input or output. Often an MPPT controller will have higher voltae input rating as for the same power it is switching less current so can handle a higher power.

It is 15amps, so I can't see any problem with linking these panels. I'll find out soon enough.

 

[Cardo]

We have two rigid 100w panels connected in parallel with a semi-flexible 100w panel. No issues that I've noticed. Max we ever get out of all three panels is 15 amps, as expected.

 

[JumbleDuck]

Particularly with solar panels which you will want to be charging batteries 24/7, and that includes when you are not on board.

Is the OP planning to spent much time above the Arctic Circle?

 

[longjohnsilver]

Is the OP planning to spent much time above the Arctic Circle?

The newer panels will charge even in moonlight, or so I've been told