More solar panels queries!!!!sry

[Scooby]

I have 3 x 165 watt panels with 43v voc each, i also have 1 x 100 watt panels 21v voc and also 1 x 100 watt panel 19v voc.

 

I have 1 x mppt 60 amp outback 150v max(800 watt max/12v), and also a 20 amp etracer 100v max(240watt max/12v).

 

3 of the 165w panels wired in series would be like 130volts which is a bit high i think so my plan was 1 x 165watt and adding 1 x 100watt to make one string and doing the same again, so 2 strings (1 @ 64v and 1 @ 62v and both into the controller(outback), and then that leaves 1 panel of 165 watt going into my other other 20 amp controller.

 

Does this sound like the best option given what i have, its a bit mismatched because i have bought the panels at different times and no more room for more.

Edited September 6, 2014 by Scooby

[nicknorman]

I don't see what is wrong with putting the 3 x 165W in series. It may seem high to you but it is well within the controller's spec and the best way to wire them. Then put the 2x 100w panels in series with the other controller.

 

If you put different panels in series, you are looking for the currents at max power to match, which of course is not necessarily the same as them having the same wattage. You don't quote the max power voltage so we can't work out the max power current, but probably the 165 w panels at 43v OC will have a similar current to the 100w at 21v so perhaps they wouldn't be too mismatched in series, but I would still stick to my first suggestion. The 100w panels are obviously not perfectly matched for series (slightly different voltages, same power) but again we need to know the max power current to make that judgement and I think they will be close.

Edited September 6, 2014 by nicknorman

[Scooby]

ocv=43.8

max power voltage is 35v.

 

Thats for the 3 x 165 watt panels.

 

So would they be ok wired in series, and then the other 2 x 100 watts would be fine on the other controller.

1 of the 100 watt panels says 26 open circuit and 21 max power v

[nicknorman]

ocv=43.8

max power voltage is 35v.

 

Thats for the 3 x 165 watt panels.

 

So would they be ok wired in series, and then the other 2 x 100 watts would be fine on the other controller.1 of the 100 watt panels says 26 open circuit and 21 max power v

Yes that's how I would do it (says me having no solar!). For the 100w panels as I said, you need to check the max power current (which you can derive from the max power voltage and overall power if necessary) and bear in mind that the string will pretty much then be limited to the lower figure of the 2 panels. The alternative is to put the 100ws in parallel, but for that it is the max power voltages that have to be pretty closely matched, and parallel has the disadvantage of doubling the current hence doubling the voltage drop in the panel wiring or requiring cable twice as thick. So with the limited info you provide, I think series is best for the 100ws.

[Justme]

I would not put the 3 x 165 in series. At 27deg c below the rated temp they will go over 150v.

 

Going over V kills the controller.

 

Most are rated at 20 to 25c so going over voltage is easily done in a mild winter that drops a few deg c below freezing.

 

 

I would look at the 3 x 165 in parallel in to the FM60 & the two 100 watts either in parallel or series into the etracer.

 

Its also possible that the 2 x 100 watts could make up a 4th string into the FM 60 but that would depend on the max power voltage points of all panels.

[Scooby]

How about (2 strings of 165+100) for the fm60.

 

Then one parallel 165 for the etracer?

[nicknorman]

I would not put the 3 x 165 in series. At 27deg c below the rated temp they will go over 150v.

 

Going over V kills the controller.

 

Most are rated at 20 to 25c so going over voltage is easily done in a mild winter that drops a few deg c below freezing.

Its a valid point but my thinking was that in winter it is unlikely that the solar will fully recharge the batteries. You only get the high voltages when the controller stops taking current from them. But yes I suppose it could happen, eg when you are away from the boat with all services off. And depends on total solar as well of course.

Edited September 6, 2014 by nicknorman

[smileypete]

I think the 43.8V 165W in series to 150V MPPT is a little close but fine in practice, for a boat I'd be happy with it.

 

You'd need less than -15°C panel temp, perfect panel angle, and fully charged batts or end of absorption. Never say never but at that tiny risk level there's other more important things to worry about.

 

Say 15% Voc margin for a boat install, 20% for a UK domestic roof install. Temp coefficient seems to be up to 0.35% for mono or poly.

 

cheers, Pete.

~smpt~

Edited September 6, 2014 by smileypete

[Justme]

Its a valid point but my thinking was that in winter it is unlikely that the solar will fully recharge the batteries. You only get the high voltages when the controller stops taking current from them. But yes I suppose it could happen, eg when you are away from the boat with all services off. And depends on total solar as well of course.

 

 

Full bats is not the only time you get high voltages. You get them on start up as the controller does a sweep to see what power point to use. You will also get it again on shut down as it stop charging the bats.

 

The team that made the initial outback range now sell under the midnight solar range. They redeveloped the controller so that the max voltage was nearer 200v as it was such a problem.

 

I'll have to dig out my stats to see if the winter voltages are consistently higher than the summer ones.

(just checked, I stoped keeping the peak V readings after a couple of months so I dont have any data that helps. The stuff I do have shows that whilst my normal running V is around 80-100v it has hit peaks of 127v in July & August)

 

 

Yes you could do a 165 + 100 string as there peak amps are very similar (4.7).

I think the 43.8V 165W in series to 150V MPPT is a little close but fine in practice, for a boat I'd be happy with it.

 

You'd need less than -15°C panel temp, perfect panel angle, and fully charged batts or end of absorption. Never say never but at that tiny risk level there's other more important things to worry about.

 

Say 15% Voc margin for a boat install, 20% for a UK domestic roof install. Temp coefficient seems to be up to 0.35% for mono or poly.

 

cheers, Pete.

~smpt~

 

 

You might be happy to cut it fine & chance the numbers but on a £500 controller I would prefer to hedge my bets especially if I am advising someone else to risk their £500.

 

The winter I think 3 years back we had temps lower than -15c all over the country. As I said above you dont just get high V with a full bat.

 

What if the alternator is on churning out 100 amps?

 

What about the power max sweeps?

What about the start up process?

Edited September 6, 2014 by Justme

[smileypete]

The winter I think 3 years back we had temps lower than -15c all over the country. As I said above you dont just get high V with a full bat.

 

As I said it's panel temp, they soon warm up in the sun. For a canal boat what would you expect for the very lowest panel temp in full sun?

 

To get full sun on a panel below -15°C you'd need the perfect combination of local overnight temp, panel angle, sun position, total cloud from dawn then sudden full sun.

 

Not saying it's absolutely impossible, but I feel it's pretty infinitesimal... Maybe the outback isn't that reliable near it's max solar voltage anyway, in which case sure, go parallel.

 

ETA: Looking at the manual, the Outback MX60 has an operational max of 140V:

 

150 VDC Maximum (ETL Rating for UL1741Standard)

operational max = 141 VDC temperature corrrected VOC

 

In which case it would be best not to put the three 165W panels in series!

 

But reading their forums it looks like it has an input relay with voltage sensing for protection, so going a bit above 140V would be unlikely to cause damage as it should then disconnect the panels.

 

cheers, Pete.

~smpt~

Edited September 6, 2014 by smileypete

[Justme]

The speed at which the voltage rises is the problem. It does not need full sun. You dont need to be making any power for the voltage to rise.

Do you think that the electronics will blow quicker that a panel can warm up?

Would you bet £500 on it?

 

Over voltage is not covered by the warranty.

 

You dont need full sun to get high voltages.

The panels wont have time to warm up before the voltage rises enough to fry the controller.

 

Dont know about the FM60 but my FM80 has a working limit of 145v & dies at 150v.

If the controller hits the working voltage limit & stops charging the bank what do you then think happens to the arrays voltage?

 

As mentioned the Midnight solar range has been designed (called HyperVOC) with the same operating voltage (or 200v on the 200 range) but so that over voltage does not have the same effect.

 

 

Read this PDF

 

http://www.midnitesolar.com/pdfs/whyHyperVOC.pdf

 

Using the temp chart on it I would use the -16 to -20c as we have had those temps in the last 5 years.

 

So thats 3 x 43.8 x 1.18 = 155.05 V

 

Even the -6 to -10c takes it to 149.79V

[smileypete]

You dont need full sun to get high voltages.

 

Sure, but to get max Voc it needs overhead sun.

 

I'm sure panels on a roof in the highlands could see less than -15°C with full sun. But on a boat, at -15°C daytime temps you'll be hugging the stove or down the pub, not on the roof twiddling with solar panels.

 

So you could allow 20% over Voc for cold temps which should see you down to -27°C , 15% for down to about -15°C would be cutting it fine, but would do for me.

 

cheers, Pete.

~smpt~

Edited September 7, 2014 by smileypete

[Justme]

 

Sure, but to get max Voc it needs overhead sun.

 

I'm sure panels on a roof in the highlands could see less than -15°C with full sun.

 

But on a boat, at -15°C daytime temps you'll be hugging the stove or down the pub, not on the roof twiddling with solar panels.

 

So you could allow 20% over Voc for cold temps which should see you down to -27°C , 15% for down to about -15°C would be cutting it fine, but would do for me.

 

cheers, Pete.

~smpt~

 

 

You dont need over head sun to get the max VOC.

 

I think it was two or three winters back that we had -18c here & much lower in some places. I am not in the highlands.

 

Even if it took full sun to hit the max VOC it does not take very long for the voltage to rise. It would take time to heat the panel. You would hit a high voltage well before the panel temp rose.

 

 

 

On cold mornings the PV panels will put out full voltage even before you can see the

sun. Ambient light may not have much current behind it but it does have voltage

exceeding the possible voltage limits that destroy the controller. The fact that there is

no power behind the output voltage means that the controller will not be able to turn

on and drag the panels down from VOC to max power voltage.

 

 

Why does it matter if you are snuggled up by the stove, down the pub or on the roof? It wont alter the air temp or the VOC.

Edited September 7, 2014 by Justme

[smileypete]

 

You dont need over head sun to get the max VOC.

 

Doesn't look that way to me, this is typical:

 

https://www.google.co.uk/search?q=voc+irradiance&source=lnms&tbm=isch

 

cheers, Pete.

~smpt~

Edited September 7, 2014 by smileypete

[Justme]

Your looking at current & MPP's.

 

The graph is showing how the current is pulled down if you let the V go up above the MPP (which looks to be about 27v on that graph).

 

You can have high V with little or no current.

 

If you have a power source, when does it show the highest V?

 

a, under no load

or

b, under load

 

So when a panel has no current flowing IE no load it will show the highest V it can.

Even a small flow will collapse that V until there is enough power to maintain current flow & V.

 

Until the panel is making enough power to run the controller it will stay open circuit & have a high V.

 

 

My own system has 3 strings of 5 panels.

 

Each panel is

 

17.64V MPP

21.88V OCV

 

But both have a +2 rating so could be as high as 19.64 & 23.88. I bet the OP's panels have a similar tolerance as well as most electrical stuff does.

 

That gives me a max voltage of

98.2V MPP

119.4V OCV

 

My panels are rated at 0.33% per deg c below rated temp (25c). So I have a very safe margin before I would get to the kill zone.

 

That matches quite well my readings. Looking at the last 180 days & the highest reading is 113V. The highest I have on record is 127V. That was not during the coldest year as I was not taking readings then. I have a very large safety margin mainly as funds at the time (when it was £2.70 per watt) did not allow 3 strings of 6 panels.

 

Even looking at the readings now in the almost dark at 21:30 the array is producing a few volts but no current.

Edited September 7, 2014 by Justme

[nicknorman]

However the graph has a zero current axis. The OC voltage is shown to vary between around 34 and 38 according to solar radiation levels 200 to 1000 w msq. What is the max theoretical solar radiation in mid winter vs mid summer in uk?

[smileypete]

I think me and Justme will have to agree to disagree!

 

Or we could be in for another 5 pages..

 

cheers, Pete.

~smpt~

[Scooby]

Its all wired in now, i went for 1 x 165+ 1 x100w (2 strings into the outback) and then one panel 165w into the other controller.

 

The outback was showing about 53volts at about 6-7pm with 1 amp(at this point though i only had 1 string connected,so 265 watts) going into the batteries but the sun had basically gone behind the trees, the other showing about 30v and 0.6amps going in, will have better readings this morning, the outback is clicking trying to come off snooze.

Its working now, outback showing 1.7amp charging at 7-30am, so its working nicely, the sun just coming up through the clouds,

[smileypete]

Could look at each string with a clamp meter measuring DC current, in full sun and with heavy charge/load (batts below 12.8V).

 

If they're quite different, might be better off with 3x165w in parallel to the outback, the two 100W in series (or parallel) into the eTracer.

 

cheers, Pete.

~smpt~

[Scooby]

Yeah think 3 x 165 parallel must be better it doesnt seam to be putting much in, at the moment i am getting 1.9 amps form the 100w and the 165watt together but on the other controller with just a 165watt on its getting 2.7 amps.

[smileypete]

At what batt voltage? Maybe they're near full charged and the controllers are at slightly different charge voltages.

 

With a heavy charge/load (batt voltages <12.8) the solar current into the outback should be twice the solar current into the eTracer.

 

To work it out without measuring, 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 Pmax, Vmp, Voc, Isc, Imp, sometimes the first two or three numbers will do.

 

cheers, Pete.

~smpt~

Edited September 9, 2014 by smileypete

[Justme]

The 165 & the 100 have very similar peak amps so the panels within the string are suitably matched.

[smileypete]

The 165 & the 100 have very similar peak amps so the panels within the string are suitably matched.

 

Where does the OP give the Vmp or Imp, or how did you work it out?

 

Would be a 3 minute job with clamp meter though.

 

cheers, Pete.

~smpt~

[Justme]

I used the MPP & the wattage to calc the peak amps.

 

Not 100% but close enough.

[smileypete]

Didn't see Vmp given by the OP.

 

cheers, Pete.

~smpt~