Using solar panels of different values

Discussion in 'Solar Power' started by veevee, Aug 13, 2015.

1. veeveeFunster

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We have a 15A rated fuse for the solar input on the Schaudt EBL 101 Elektroblock distribution box in our Hymer and on advice from Schaudt it is not to be exceeded.

We want to fit the max possible solar panels as we have used them on 2 motorhomes so far with good effect. The calculation involves taking the 'short-circuit maximum current' values and adding them together and I believe aim for a maximum of 90% of the fuse value = 13.5A

There is plenty of space on the roof for many panels so any combination will fit

OK. The most efficient way of doing this is to use two panels of unequal value, ie a 130W + a 100W to give 13.66A which is probably near enough.

The question may be silly... does using different value panels have any detrimental effect, ie create an inbalance?

Thanks

2. DBKFunster

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You could couple them in series providing the total voltage was within the regulators tolerance, which for two panels it should be. By putting them in series you don't increase the current. Not sure about your current calculations if you were referring to wiring them in parallel. 230W is near enough 20 Amps at 12 volts but your regulator might keep the panels at say 18 volts for efficiency which would reduce the current. Either way, wiring them in series might be simpler and less risky. But if you did want to wire them in parallel then I don't think a 100W and a 130W panel would cause any problems other than the current issue.

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3. Mike BFunster

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4. veeveeFunster

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Thanks DBK

They're not my calculations but the manufacturers figures in their data sheet giving an open circuit max voltage of 17.5 V and I assume an actually measured max output value? Don't pretend to understand all the whys and wherefores which is why I ask questions.

I thought I read somewhere recently that parallel is possibly more efficient, but maybe I didn't.

Anyway, the answer to the question is there shouldn't be an imbalance problem, thank you again

5. DBKFunster

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That's useful - its advice seems to be "it depends..." in the sense of the actual characteristics of the panels, i.e. are they similar voltages in which case parallel would be better but the maximum current of 15A might still be a limiting factor.

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6. veeveeFunster

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Just taken a look at that site, will take a couple more reads to get my head around it but there is a good point or two in there somewhere. My idea is to use panels from the same manufacturer with the same voltages, but this is starting to look like more trouble than it's worth. It may be best to just lose the extra 30W and fit 2 x 100W panels, but will re-read this a few times more to understand better.

Thank you Mike B

7. JJFunster

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I always connect my various panels in parallel... different ratings... up to four at once... no probs.

More panels = More elctricity.

(Assuming controller is up to the task of course.)

JJ

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8. ReallyretiredFunster

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No problem with wiring different panels in parallel, they just act as one big panel. In practice 230watts is very unlikely to produce more than 15A even at midday in the Med. If you do want to produce more than 15A ( which in practical terms will need at least 300w of panels) then connect the regulator direct to the leisure battery bank and forget the Electrobloc.
I have 400w of panels which produces about 20A in good sun.

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9. veeveeFunster

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I thought of that too as that's the way I wired our S670, bypassing the Elektroblock, but... The ELB 101 in the Starline 680 is one of three Elektroblocks that must use a Schaudt regulator, I think due to the level of control the device has over all things electrical in the motorhome? There are dire warnings that by by-passing the EB it may cause the entire 12v system to shut down. I think that fact they singled out just three of many EB's means there is something about them in particular, so we just got unlucky having that model fitted to ours.
Later this evening I'll study that article about mixing solar panels and make a decision.

We full timed with 160W but that was just before we all had smart phones, tablets, laptops, large TV's and all the other stuff, but apart from northern Europe in the winter we coped quite well without sites for weeks at a time, so with a smart controller and at least 40W more we should be ok I think.

The figures for maximum output are flash readings, but a fuse wont care if it's a fast surge of power or not. The reality of what will go into the EB is usually far less than the optimum stated, but don't want to have to replace an EBL 101 for the sake of an extra 30W

Thanks

10. Lenny HBFunster

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Agree no problem with wiring them in parallel, you can't put them in series with a Schaudt regulator the voltage will be too high. Also in series any shade on one panel and you will loose the output from both.

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11. TechnoFunsterLife Member

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Different wattages are completely fine.
Voltages must be the same and in an ideal world the quoted maximum power voltages of each would be the same but not a disaster if not.

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12. veeveeFunster

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Having re and re read the link above 'mixing solar panels' there is one paragraph that stands out about using an mppt regulator(which I will), assuming that all the facts in the article stand up...

Mixing solar panels with different electrical characteristics is not recommended if you use an MPPT charge controller. Different wattages make impossible for the controller to find the optimal operating voltage and current, since they are different for each panel type.

At this point I'm lost or think that I'm looking for perfection where none exists. Ideally fitting panels of the same make, voltages, output and I guess age will be as good as it gets and in my case the Elektroblock limits what I can do there. What does occur is I have never ever seen solar panel(s) at maximum output, not even near to it including being in North Africa for a total of around 5 months, so should I take a chance on 2 x 130A panels?

Thanks Lenny and thanks Andy

13. JeanLucFunster

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As it seems you don't have the regulator yet, can I suggest you get a Schaudt unit. There have been reports of the more recent EBLs (particularly those linked to an LCD control panel) not being too happy when connected to other makes of regulator. You have two to choose from: LR1218 (which is a PWM model) and the recently introduced LRM1218 (which is MPPT). Both come with all the necessary wiring harnesses to link them to the EBL. You will also have the benefit that they charge the starter battery as well as the leisure batteries. I have the LR1218 feeding the output from a 135 watt panel into an EBL99 which works very well. I can therefore only offer specific information on that model but I know both have a maximum input capacity of 18 amps. The LR1218 is supplied with two fuses: 15W and 20W with instructions to use the appropriate one as indicated on the EBL.
This installation instructions for the LR1218 suggest that it can handle up to 275 watts of panels so I presume the LRM1218 will be the same (see attached). It looks as though they have used what in my Kyocera spec sheet is called the max power current at 1000 W/mÂ² irradiance to get their 'nominal current' figure.
In practice, you will never get the maximum output. My 135W panel spec says the maximum power current is 7.63 amps. I cannot remember seeing much more than 5 amps in good sunshine. I would have thought 230 watts of panels would be a very safe bet for you and in the event of a 1 in 1,000 year sunshine event, the EBL fuse will protect it at 15 amps anyway! You could fit 2 x 130 watt panels without any problem.
Hope this helps.

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14. seanooFunster

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i have had a 130 watt and an 80 watt panel and an mppt controller on the roof of my van for the last 5 years no problems whatsoever. the most charge i have ever seen is 13.5 amps when the batteries have been really low and in full sun. just to complicate matters one panel is a mono and the other is a poly! never had flat batteries yet (3 x 125amp/hr alphalines) and they get alot of use.

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15. Don QuixoteFunster

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I have 120 watt and 80 watt panel different makes connected in parallel feed to MPPT controller. On good day full sun get 13.5amps and on bad day (today!) get 1.5amp.
A good MPPT controller makes all the difference.

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16. veeveeFunster

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As it seems you don't have the regulator yet, can I suggest you get a Schaudt unit.
Thanks Philip, LRM1218 already on it's way, didn't have any option with the EBL 101, had to buy a Schaudt unit. Also fitting the LT 320 display but thought it expensive, but having just bought this MH we are either treating our new baby or treating ourselves!

The decision today is what Wattage for the panels, I like what you wrote about the rare occasion that a maximum current is produced and the fact that the EBL is fused anyway. There will also be line fuse(s) before the controller too and of course they would not be greater than 15A. But also read the comments from seanoo and Don Quixote above and they are getting 13.5A from 210W and 200W respectively which is at 90% of the fuse limit so do I need 260W with the latest MPPT controller arriving?

Let you know what I decide, also finding the right supplier who can deliver to France is an interesting combination too.

Thanks for all the inputs

17. Don QuixoteFunster

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I should point out that I'm getting that in Spain and France were the days are cloudless. In the UK best days are around 11amp mark. Don't cut costs on a MPPT controller as you want as much power/amps that you can get from the solar panel/panels and a good MPPT controller will give you 20% / 30% more.

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18. veeveeFunster

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Thanks again John

I think that the Schaudt was the most expensive solar regulator in it's class, but as said I didn't have an option due to the model of Elektroblock that's fitted. The regulator has a capacity for up to 275W of solar input (20A rated), I've just ordered 2 x 130W so within the regulator capacity.
I think as JeanLuc said that the chance of a once in a lifetime maximum power output from the panels is highly unlikely, but we decided it was the best of our four panel options by far. Proof will be in the using of this system, I'll try to remember to post an update when the whole system gets fitted at the end of September.

Our choice was made on the following criteria. A pair of the same make panels, a pair of the same output panels, a pair of the same age panels, a pair of the same voltage panels means we have covered all eventualities hopefully, time will tell.

We are in central France for most of the summer and as we are 100's of km from the sea we have a Continental climate. Not much cloud but intense unpolluted sunlight for about 3 months of the year in summer. During the winter we again get cloudless skies with intense and clear light. Most of our camper travel will be during autumn and winter so apart from when in central France in the summer we will be looking for maximum solar power, another reason we went 260W.

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19. Don QuixoteFunster

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@veevee with 260watts you should have no problems running for weeks. I have gone 37 days of grid on 200watts with 330 amp of batteries. Enjoy

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