Solar Panels Wiring Series Or Parallel?

[jenevers]

I've got 3 x 100watt solar panels and a 30A MPPT Tracer controller.

My boat wiring is 12 volt.

Looking on Bimbles site it shows wiring for 3 panels in series.

 

http://www.bimblesolar.com/solardiagrams

 

But for a PWM controller in parallel.

 

Why? And what's the reason/advantage of wiring in series for an MPPT?

[nicknorman]

I've got 3 x 100watt solar panels and a 30A MPPT Tracer controller.

My boat wiring is 12 volt.

Looking on Bimbles site it shows wiring for 3 panels in series.

http://www.bimblesolar.com/solardiagrams

But for a PWM controller in parallel.

Why? And what's the reason/advantage of wiring in series for an MPPT?

PWM only controls the voltage by switching it on and off, so the current for panels in series will effectively be limited to their power at say 14v total, wasting a massive amount of power. However an MPPT is more like a transformer, it can step down the voltage whilst stepping up the current so that the output power, at the battery charging voltage, is nearly the same as the max theoretical panel power for the lighting conditions.

 

Wiring the panels in series means the current is only 1/3rd (for 3 panels) of what it would be in parallel, thus thinner wires are needed between panels and controller, and/ or there is less voltage drop = less power wasted.

 

You just have to be careful that the max possible voltage of the 3 panels in series on a cold day, doesn't exceed the rating of the controller.

[Dave Clinton]

I've got 3 x 100watt solar panels and a 30A MPPT Tracer controller.

My boat wiring is 12 volt.

Looking on Bimbles site it shows wiring for 3 panels in series.

 

http://www.bimblesolar.com/solardiagrams

 

But for a PWM controller in parallel.

 

Why? And what's the reason/advantage of wiring in series for an MPPT?

 

Technobabble time:

 

What is the VOC of the panels (written on the back) and probably around 22V. If this figure series. (i.e. plug each panel into the next until you run out of panels and then plug the remaining plugs to the controller).

 

If 30 or more volts then what model Tracer?

[Robbo]

This Excel sheet from Victron may be useful for some for calculating solar stuff..

 

http://www.victronenergy.com/upload/software/VE-MPPT-Calc-2_0.xlsx

[jenevers]

Technobabble time:

 

What is the VOC of the panels (written on the back) and probably around 22V. If this figure series. (i.e. plug each panel into the next until you run out of panels and then plug the remaining plugs to the controller).

 

If 30 or more volts then what model Tracer?

 

Hi the open circuit voltage (VOC?) for each panel is 20.8v

 

The Tracer is a 30Amp.

[nicknorman]

Hi the open circuit voltage (VOC?) for each panel is 20.8v

The Tracer is a 30Amp.

But in the spec for the tracer, what is the max input voltage?

[jenevers]

But in the spec for the tracer, what is the max input voltage?

Don't know!

 

Take your pick !

 

Model Tracer-3215RN

Rated system voltage 12/24V auto work

Rated battery current 30A

Rated load current 20A

Max.battery voltage 32V

Max.PV open circuit voltage 150VDC

Max.PV input power 12V 390W; 24V 780W

Self-consumption <10mA（24V）

Charge Circuit Voltage Drop ≤0.26V

Discharge Circuit Voltage Drop ≤0.15V

Communication TTL232 / 8 pin RJ45

Temp.compensation -30mV/℃/12V（25℃）

Working temperature -35℃～+55℃

Storage temperature range -35℃～+80℃

Humidity 10%-90% NC

Enclosure

Edited June 25, 2015 by jenevers

[nicknorman]

Max PV open circuit voltage 150v.

 

So 3 x 20.8 v = 62.4v which is way below 150v even with low temperature, therefore I would definitely wire in series.

[jenevers]

Max PV open circuit voltage 150v.

So 3 x 20.8 v = 62.4v which is way below 150v even with low temperature, therefore I would definitely wire in series.

Excellent!

Thanks for the advice.

[jenevers]

Max PV open circuit voltage 150v.

So 3 x 20.8 v = 62.4v which is way below 150v even with low temperature, therefore I would definitely wire in series.

One more question though. My 30A MPPT Tracer controller says max Pv input is 390w but Max Open circuit voltage is 150v

So 3 x 100w panels is 300w but only 62.4v in series.

Adding 3 more panels would only raise the voltage to 124.8v which seems OK.

BUT would take the wattage up to 600w which isn't OK.

So is the rule "stop before you break either limit, whichever comes first"?

Or put in simple terms ..... If you add an extra 300w, get a 2nd MPPT controller.

[Robbo]

One more question though. My 30A MPPT Tracer controller says max Pv input is 390w but Max Open circuit voltage is 150v

So 3 x 100w panels is 300w but only 62.4v in series.

Adding 3 more panels would only raise the voltage to 124.8v which seems OK.

BUT would take the wattage up to 600w which isn't OK.

So is the rule "stop before you break either limit, whichever comes first"?

Or put in simple terms ..... If you add an extra 300w, get a 2nd MPPT controller.

 

It would take the wattage, but you will be limited to 30A max out of the tracer. If with 300Watt panels you rarely get more than 15A, then adding another MPPT for 3 more panels would be pointless.

[nicknorman]

One more question though. My 30A MPPT Tracer controller says max Pv input is 390w but Max Open circuit voltage is 150v

So 3 x 100w panels is 300w but only 62.4v in series.

Adding 3 more panels would only raise the voltage to 124.8v which seems OK.

BUT would take the wattage up to 600w which isn't OK.

So is the rule "stop before you break either limit, whichever comes first"?

Or put in simple terms ..... If you add an extra 300w, get a 2nd MPPT controller.

They are different limits for different reasons. The voltage limit is due to the voltage rating of the transistors, which is a bit like the pressure rating of a water pipe. Too much pressure makes the pipe rupture, too much voltage makes the semiconductor junction rupture.

 

The power limit is to do with heat dissipation. The controller only passes a percentage (albeit a large percentage) of the solar power, the remainder goes to heat up the controller, and there is a limit to how much heat the controller can dissipate. This mostly relates to the current, hence you will notice the max PV power is twice for a 24v system as it is for a 12v system, the current in those two cases being the same.

 

So as you say, you need to respect the first limit you come to, power or voltage.

 

That said, and depending on the specific controller, it may be that the power limit is just the max power the controller will take, rather than the max theoretical panel power allowed. There is a case for having more panel power than controller power - for example, to subsequently add another panel without having to buy a whole new controller. Whilst the full additional power won't be available, it will mean that in cloudy or winter conditions, there is more output.

Edited June 26, 2015 by nicknorman

[jenevers]

It would take the wattage, but you will be limited to 30A max out of the tracer. If with 300Watt panels you rarely get more than 15A, then adding another MPPT for 3 more panels would be pointless.

Hmm...... I'm confused....... Surprise surprise!

They are different limits for different reasons. The voltage limit is due to the voltage rating of the transistors, which is a bit like the pressure rating of a water pipe. Too much pressure makes the pipe rupture, too much voltage makes the semiconductor junction rupture.

The power limit is to do with heat dissipation. The controller only passes a percentage (albeit a large percentage) of the solar power, the remainder goes to heat up the controller, and there is a limit to how much heat the controller can dissipate. This mostly relates to the current, hence you will notice the max PV power is twice for a 24v system as it is for a 12v system, the current in those two cases being the same.

So as you say, you need to respect the first limit you come to, power or voltage.

That said, and depending on the specific controller, it may be that the power limit is just the max power the controller will take, rather than the max theoretical panel power allowed. There is a case for having more panel power than controller power - for example, to subsequently add another panel without having to buy a whole new controller. Whilst the full additional power won't be available, it will mean that in cloudy or winter conditions, there is more output.

Your message came through while I was busy answering Robbo.

So do you think a 2nd MPPT is best practice?

Edited June 26, 2015 by jenevers

[nicknorman]

Hmm...... I'm confused....... Surprise surprise!

 

Your message came through while I was busy answering Robby.

So do you think a 2nd MPPT is best practice?

Yes if you want to add another 300w you should get an additional MPPT, or replace the existing one with a 60A one. I don't have any experience of operating two MPPTs in parallel, I think it should be OK but I suppose there is a possibility of one or both going into float prematurely. I would suggest getting another controller of the same model if you don't want to go the more expensive route of getting a 60A one

[jenevers]

Yes if you want to add another 300w you should get an additional MPPT, or replace the existing one with a 60A one. I don't have any experience of operating two MPPTs in parallel, I think it should be OK but I suppose there is a possibility of one or both going into float prematurely. I would suggest getting another controller of the same model if you don't want to go the more expensive route of getting a 60A one

That's what I was thinking. Just to be on the safe side.

[nicknorman]

Although thinking about it, if you were to buy a 60A one and sell the 30A one, would that be significantly more expensive than buying another 30A one?

[Robbo]

Hmm...... I'm confused....... Surprise surprise!

Your message came through while I was busy answering Robbo.

So do you think a 2nd MPPT is best practice?

 

 

It's okay to add more panels that can potentially produce more amps than the MPPT output, it's the voltage output of the panels that's important to keep within the limits. You just won't benefit from the extra amps the panels could produce if their was enough sun.

 

If your current 3 panels produce around 15amps and under and occasionally more in the real world (ie not paper world), then adding 3 more panels so doubling the wattage would produce around 30amps, but only occasionally more, so adding an additional or larger MPPT would only get you little gain. So knowing what you get now should decide if a larger or another MPPT is needed.

Edited June 26, 2015 by Robbo

[nicknorman]

It's okay to add more panels that can potentially produce more amps than the MPPT output, it's the voltage output of the panels that's important to keep within the limits. You just won't benefit from the extra amps the panels could produce if their was enough sun.

 

If your current 3 panels produce around 15amps and under and occasionally more in the real world (ie not paper world), then adding 3 more panels so doubling the wattage would produce around 30amps, but only occasionally more, so adding an additional or larger MPPT would only get you little gain. So knowing what you get now should decide if a larger or another MPPT is needed.

This is all quite true, but I would have thought the OP is likely to get more than 15A in summer from his current setup, so if he wants to add 3 panels then I think another controller would be advisable, whereas if he only wanted to add one then probably not, but as you say, it depends on how much current he normally gets, and we don't know that!

[jenevers]

Although thinking about it, if you were to buy a 60A one and sell the 30A one, would that be significantly more expensive than buying another 30A one?

Yes a 60A MPPT is significantly more expensive than 2 x 30A .

 

eg £490 vs £252 (£126 x 2)

Edited June 26, 2015 by jenevers

[by'eck]

This is all quite true, but I would have thought the OP is likely to get more than 15A in summer from his current setup, so if he wants to add 3 panels then I think another controller would be advisable, whereas if he only wanted to add one then probably not, but as you say, it depends on how much current he normally gets, and we don't know that!

 

Surely its a matter of choosing a controller that can cope with the max (Voc) voltage as well as max current (manufacturers spec or calculated), dependant on whether pv panels are connected in series (add voltages) or parallel (add currents). There will always be a time even in the UK when panels do produce their max rated output and when the batteries/loads are able to draw that. Choosing a controller only able to cope with what the OP normally gets seems bad policy.

[jenevers]

Choosing a controller only able to cope with what the OP normally gets seems bad policy.

That's my thinking too.

[nicknorman]

Surely its a matter of choosing a controller that can cope with the max (Voc) voltage as well as max current (manufacturers spec or calculated), dependant on whether pv panels are connected in series (add voltages) or parallel (add currents). There will always be a time even in the UK when panels do produce their max rated output and when the batteries/loads are able to draw that. Choosing a controller only able to cope with what the OP normally gets seems bad policy.

With decent MPPT controllers there seems to be no hazard to operating them with more panel power than their rating. They claim to be able to operate at max current and max controller temperature without coming to any harm. They have extensive protection systems that simply keep the current within the max rating, or even reduce it further if the controller is getting too hot.

 

It therefore becomes a matter of economics. Do you want to spend more on a larger controller that only gives the benefit of its extra rating rarely, if ever? Or do you want instead to spend the money on more panels so that the controller is putting out max current for more of the time, and more current in winter / cloudy days. I suggest the latter represents more useful power.

 

Edit: Voc is of course a different matter, that should not be exceeded.

Edited June 26, 2015 by nicknorman

[Robbo]

This is all quite true, but I would have thought the OP is likely to get more than 15A in summer from his current setup, so if he wants to add 3 panels then I think another controller would be advisable, whereas if he only wanted to add one then probably not, but as you say, it depends on how much current he normally gets, and we don't know that!

 

Even if he gets 20A or touching 25A, it will only be for a few hours a day so the amount of AH's per day you gain from a larger MPPT may be small and not actually needed. The only way to truly know is monitoring at regular points through the day and how many AH's you use during the day and over a long period of days.

Edited June 26, 2015 by Robbo

[Robbo]

With decent MPPT controllers there seems to be no hazard to operating them with more panel power than their rating. They claim to be able to operate at max current and max controller temperature without coming to any harm. They have extensive protection systems that simply keep the current within the max rating, or even reduce it further if the controller is getting too hot.

 

It's more that the solar panels doesn't produce the current if it's not asked for. Wind generators are different, you'll need to be within the current capabilities with a load dump with these.

Edited June 26, 2015 by Robbo

[Dave Clinton]

Edit: Voc is of course a different matter, that should not be exceeded.

Have you read the Tracer MPPT manual?

 

additionally most of what you and Robbo have written is wrong but there's no point in adding more tech-speak.

 

to the OP. your original question is answered; wire them in series. When you want add more seek proper advice.