adding more solar panels to MPPT

[LillyPotemkin]

I'm guessing that the following is ok to do.But I thought I'd check with the solar sages on here first

 

I have a 400 watt installation currently going through a eMPPT30 controller.Some one has given me a pair of solar panels I think they are 125watt each and Voc of 19.6v

 

My plan is to connect these two panels together and then run them via a separate cable into the MPPT controller.

 

Does this sound ok ? Thanks for your patience if it's a dumb question

[bottle]

I will not answer the query but add a few more questions.

 

What are the figures for the other panels ?

 

How are the existing wired ?

 

What are the figures for the controller ?

 

ps. not a dumb question.

[bigste]

First thoughts are it won't add up but without all the figures I can't say.

[LillyPotemkin]

further info

 

currently 4 identical 100 watt panels in series, Voc 22V / Imp 5 the controller is rated at 30amps although the manual says its max load at 12 v

is 800 watts.

 

The new panels are different voltages but would the controller cope with two different input voltages ?

 

thanks

[nicknorman]

You can't connect panels of substantially different voltages in parallel to one controller input. At the moment you have 4 x 22V OC panels = 88v

 

Now you want to connect 2 x 19.6V OC panels = 39.2v. So what voltage should the controller pull the panels to? Not going to work!

 

The only possibility might be to put all the panels in series but that will give a V OC of 127v and you would have to carefully check the max voltage of the controller which may well be less than this. Normally you should only put panels in series that are the same size, but adding a couple of 125W panels in series with 100W ones will likely just result in them being limited to about 100W, not too bad.

 

Ed: looks like the emppt30 has a max voltage of 70v (assuming it's not the 48v version) so you are already exceeding the rated voltage.

Edited September 2, 2014 by nicknorman

[Timleech]

Slight thread hijack, but a related question.

Two 100W panels, in series, MPPT controller, 24V system.

Two 50W panels available for 'occasional' connection, similar voltages etc.

Would the 50W panels be better in parallel with the 100W, or in series-parallel? (ie two 50W in parallel with one another, in series with the main panels).

I haven't checked the max controller input volts, but this question assumes it'll handle the extra volts.

Just to complicate things, the smaller panels will be portable, so could be manipulated to get maximum sun, whereas the bigger ones will be fixed.

 

Thanks

Tim

[Grace and Favour]

Slight thread hijack, but a related question.

Two 100W panels, in series, MPPT controller, 24V system.

Two 50W panels available for 'occasional' connection, similar voltages etc.

Would the 50W panels be better in parallel with the 100W, or in series-parallel? (ie two 50W in parallel with one another, in series with the main panels).

I haven't checked the max controller input volts, but this question assumes it'll handle the extra volts.

Just to complicate things, the smaller panels will be portable, so could be manipulated to get maximum sun, whereas the bigger ones will be fixed.

 

Thanks

Tim

I'd reconfigure to have 2 x (100w + 50w) in series parallel I think

[lexicon]

Hijack

 

i have one 235w 30v panel. 20a controller with 100v limit if i got another 200w panel of 30v could i connect it in series ?

[nicknorman]

I'd reconfigure to have 2 x (100w + 50w) in series parallel I think

Not really! For putting solar in series, you want the current rating to be very similar. To put panels in parallel you want the max power voltage to be very similar. So by putting 100w and 50w in series (if I am reading you correctly), you effectively get the 100w panel trying to pump more current through the 50w panel than it wants, so will end up with something closer to 2 50w panels.

 

The caveat to that is that it is really about current and not about power, so you need to compare the operating voltages and not just assume that a 100w panel wants to pass twice as much current as a 50w panel.

 

Without knowing the panel voltages it is hard to comment but ideally I would put the two 100w in series, the two 50w in series and those two things in parallel. But that presumes their voltages are very similar.

[leeco]

Hijack

 

i have one 235w 30v panel. 20a controller with 100v limit if i got another 200w panel of 30v could i connect it in series ?

20amp controller x 12v is 240w so the controller could not take another 200w.

[nicknorman]

Hijack

i have one 235w 30v panel. 20a controller with 100v limit if i got another 200w panel of 30v could i connect it in series ?

Surely your panels in series (which might give you effectively 2 x 200w = 400w = 28A at 14v), is going to be well above the controller's 20A rating? And presumably it is an mppt controller?

further info

 

currently 4 identical 100 watt panels in series, Voc 22V / Imp 5 the controller is rated at 30amps although the manual says its max load at 12 v

is 800 watts.

 

The new panels are different voltages but would the controller cope with two different input voltages ?

 

thanks

So on reflection you could have a string of 2 x 100w panels and a 125w panel all in series (64v OC,) in parallel with a second identical string.

[lexicon]

Surely your panels in series (which might give you effectively 2 x 200w = 400w = 28A at 14v), is going to be well above the controller's 20A rating? And presumably it is an mppt controller?

 

hi nick yes it is a mppt controller so would it not just not utilise the extra amps but give closer to its limit of 20a in times of lower light and winter especially?

[nicknorman]

hi nick yes it is a mppt controller so would it not just not utilise the extra amps but give closer to its limit of 20a in times of lower light and winter especially?

I'm not sure. Certainly by having "overload" capability in terms of panels, as you say you would get 20A more often. But I am not clear whether the 20A rating is a rating it respects, or one that you have to respect. I seem to recall this point being discussed before with no clear answer. Perhaps scrutinising the wording of the spec section of the instruction manual might help.

[Timleech]

Not really! For putting solar in series, you want the current rating to be very similar. To put panels in parallel you want the max power voltage to be very similar. So by putting 100w and 50w in series (if I am reading you correctly), you effectively get the 100w panel trying to pump more current through the 50w panel than it wants, so will end up with something closer to 2 50w panels.

 

The caveat to that is that it is really about current and not about power, so you need to compare the operating voltages and not just assume that a 100w panel wants to pass twice as much current as a 50w panel.

 

Without knowing the panel voltages it is hard to comment but ideally I would put the two 100w in series, the two 50w in series and those two things in parallel. But that presumes their voltages are very similar.

 

In the case I proposed, the voltages are indeed very similar. If the controller will handle the extra voltage, then the series-parallel arrangement I suggested ought to give the best results in less than wonderful sunlight? Simply putting the two sets in parallel would probably be easier, though.

 

Tim

[smileypete]

further info

 

currently 4 identical 100 watt panels in series, Voc 22V / Imp 5 the controller is rated at 30amps although the manual says its max load at 12 v

is 800 watts.

 

The new panels are different voltages but would the controller cope with two different input voltages ?

 

thanks

 

Helps if you can give as much info as poss on both types of panels.

 

It's often on a label on the back, or on the web though googling the panel part number. What's of interest is Voc, Vmp, Isc, Imp, Pmax.

 

Failing for Plan B they can still be measured in practice, but it's more hassle.

 

 

I'm not sure. Certainly by having "overload" capability in terms of panels, as you say you would get 20A more often. But I am not clear whether the 20A rating is a rating it respects, or one that you have to respect. I seem to recall this point being discussed before with no clear answer. Perhaps scrutinising the wording of the spec section of the instruction manual might help.

 

The MPPT controllers should, the classic Tracer MPPT certainly does according to some experiments on another forum.

 

The MPPT has to measure current to do it's MPPT thing, so it would be totally daft not to self limit. That said the controller will be running at full whack while it's giving max current.

 

With the PWMs it's more likely to result in a blown fuse or components.

 

cheers, Pete.

~smpt~

Edited September 2, 2014 by smileypete

[MyLady]

To add another (related) query to this thread...

 

We currently have 2 Isofoton 15W panels connected to a Tracer 30A MPPT controller. The original installer said he'd left sufficient wire to connect a third, so, since Bimble have a finite stock of these panels, we decided to buy another before they've gone.

 

So far, so good, but recently, for the first time, I saw charge current from the present 2 go up to just over 20A,so the extra panel could exceed the 30A limit. More, reading the controller spec. more carefully, it says the maximum power rating is 390W (presumably the 30A x something like a 13V charging voltage), so it seems this controller won't be up to the job. So we went back to Bimble and ordered, and paid for, a 45A eTracer. Wondering why it was taking so long to arrive, we emailed them and discovered that: i) they thought they had had one in stock, but they couldn't find it; and ii) the manufacturer has stopped making them. They are trying to source one from elsewhere, but so far haven't told us they've succeeded. (They've also offered a full refund if we want.)

 

1. The reason we bought the 3rd panel was to cope better in winter - the nights are already drawing in!

2. The panel specs are:

VOC (max) 42.5V - we've frequently seen 80+V from 2 panels, so that seems accurate;

Imax 4.25A - our present controller doesn't show current from the panels, just output current, and

voltage, into the batteries - till recently, although we've frequently seen charging voltages up to

14+V, charging current had only been in single figures or low teens. My guess is that we'd only

seen the later stages of charge, not the bulk stage, which in May, June and July probably

happened before we got up.

3. Winter, and Autumn & Spring will not only have fewer hours daylight, but weaker sun - on the other hand the temperature

coefficient of the panels will mean more leccy from whatever sunlight.

4. The space available where the controller is currently mounted is limited, mostly occupied by our inverter (which gets

minimal use), so we have an issue with any replacement, but I think we could mount the eTracer 45 by using some

ingenuity, however another solution suggested by Bimble - using a second controller for the 3rd panel - would

definitely pose a problem.

5. One advantage of the eTracer is 450 days data-logging, so we'd be able to make better decisions in future.

6. As I understand it, the controller converts excess voltage into extra current, but wiring the panels in parallel means we

won't often, in winter, have any excess voltage - near sunset we often see 15-20V from the 2 in series and proportionately,

in winter and connecting the panels in parallel, I suspect we'll see less than 12V, insufficient to get any charge current.

7. Due to the centre line anchorage, ventilation mushrooms and the side hatch top flap, roof space for panels is a significant

constraint.

8. The present setup has provided enough power to run our fridge - our major consumer of power.

 

Given all of this is there any better solution than chucking away the 3rd panel, spending a helluvalot of brass on an Outback controller, or chucking the lot and starting afresh - or are we safe to stick with the 30A Tracer?

 

If more info is needed, I'll try to look up the specs on Bimble's website...

 

Thanks in advance,

 

Roger

 

ed. to correct layout.

Edited September 3, 2014 by MyLady

[smileypete]

Given all of this is there any better solution than chucking away the 3rd panel, spending a helluvalot of brass on an Outback controller, or chucking the lot and starting afresh - or are we safe to stick with the 30A Tracer?

 

If more info is needed, I'll try to look up the specs on Bimble's website...

 

I'd use the three 165W panels with the existing 30A Tracer MPPT. As mentioned in post #15 it will limit itself to 30A output.

 

If the max input voltage of the Tracer is 100V I'd connect them in parallel with MC4 splitters, but if the max input voltage is 150V then series is fine.

 

Nice thing about the 30A Tracer is that it has the same case and heatsink as the 40A model, so that'll help it to run a bit cooler. Someone the other day had a suspected failed eTracer so I'd rather stick to the classic Tracer MPPTs.

 

If the fridge is power hungry this can be due to lack of ventilation, sometimes fans can help, google 'site:canalworld.net fridge fans' for some ideas.

 

cheers, Pete.

~smpt~

Edited September 3, 2014 by smileypete

[MyLady]

I'd use the three 165W panels with the existing 30A Tracer MPPT. As mentioned in post #15 it will limit itself to 30A output.

 

If the max input voltage of the Tracer is 100V I'd connect them in parallel with MC4 splitters, but if the max input voltage is 150V then series is fine.

 

Nice thing about the 30A Tracer is that it has the same case and heatsink as the 40A model, so that'll help it to run a bit cooler. Someone the other day had a suspected failed eTracer so I'd rather stick to the classic Tracer MPPTs.

 

If the fridge is power hungry this can be due to lack of ventilation, sometimes fans can help, google 'site:canalworld.net fridge fans' for some ideas.

 

cheers, Pete.

~smpt~

 

Hi Pete,

 

Thanks a lot for that. most of the time it won't be an issue: lack of sun, good SOC, etc. will mean it won't get near the 30A limit. Especially in Winter, but now and again the system will push the envelope.

 

Odd that Bimble didn't know that - or maybe they did, but wanted to sell some more kit!

 

The fridge is only 'power hungry' by comparison with the rest of the boat. Compared to a few LEDs, pumps and phone- & computer-charging, the 24/7 thirst for a couple of amps is big. In absolute terms, it isn't. We're not true live-aboards, just 30-35 weeks a year. The washing machine, TV and Dyson etc. drink mains, at home!

 

More important, I have to tell people that the Tracer is no longer for sale and I don't need the eTracer. That 450day data logging would have been nice though.

 

Thanks again,

 

Roger

[smileypete]

Odd that Bimble didn't know that - or maybe they did, but wanted to sell some more kit.

I don't blame them really if they do know, if in their shoes I'd do the same.

When dealing with possible novices, best keep things super super simple, even if not the cheapest solution.

MPPT current limiting has come up before a few times, plus it's easy to check with a clamp meter.

 

Slight thread hijack, but a related question.

Two 100W panels, in series, MPPT controller, 24V system.

Two 50W panels available for 'occasional' connection, similar voltages etc.

Would the 50W panels be better in parallel with the 100W, or in series-parallel? (ie two 50W in parallel with one another, in series with the main panels).

I haven't checked the max controller input volts, but this question assumes it'll handle the extra volts.

Just to complicate things, the smaller panels will be portable, so could be manipulated to get maximum sun, whereas the bigger ones will be fixed.

 

As mentioned, helps if you can give as much info as poss on both types of panels.

 

It's often on a label on the back, or on the web though googling the panel part number. What's of interest is Voc, Vmp, Isc, Imp, Pmax.

Hijack

 

i have one 235w 30v panel. 20a controller with 100v limit if i got another 200w panel of 30v could i connect it in series ?

 

If a Tracer MPPT I'd put in parallel as the voltages match, other genuine MPPTs it may be best to test in practice with clamp meter.

 

cheers, Pete.

~smpt~

Edited September 4, 2014 by smileypete

[MyLady]

I don't blame them really if they do know, if in their shoes I'd do the same.

When dealing with possible novices, best keep things super super simple, even if not the cheapest solution.

MPPT current limiting has come up before a few times, plus it's easy to check with a clamp meter.

 

I asked them if it was safe to use the 30A controller, and again, what I could do to protect it - their replies didn't directly address those parts of my messages. The closest to doing so was to say "you'd be pushing it" to use the Tracer...

 

Roger