Solar Panel Output. Am I right to be disappointed?

Trundlebug

Trundlebug

Well-Known Member
Joined
4 Jan 2007
Messages
2,444
Location
River Trent
Visit site
I fitted a semi flexible 150w solar panel to my sunroof over the winter, after extensive research and planning.

The panel I fitted was this one http://www.titan-energy.co.uk/150w-flexible-mono-solar-panel-122-p.asp

To make the most of its output and wary of the many cheap ebay pretenders I bought what I thought was a reputable charge controller for it, and suitable for its (hopefully) over 10A output. http://www.victronenergy.com/solar-charge-controllers/mppt-75-15

Well on our recent fortnight's holiday to Wells next the Sea I had the time, opportunity and weather to properly evaluate its performance, repeatedly as the weather was superb.

The maximum charge current I've seen is 6.0A.
One day in very early July, 1pm, FULL sun almost overhead (not a cloud in the sky) its output was a meagre 5.5A. I know if I'd started the engines they would have charged at 14.4v and around 15A at the level of discharge of the batteries at that time.

Now I know the output falls off with higher temperature (and it was one of those really hot days a couple of weeks ago).
But I worked out that my 150w panel was producing 82 watts. With a proper MPPT controller.

Does output really fall off that much? i.e. 45%?

I never expected to get 100% efficiency. But I did expect from everything I'd read to get 8-10amps and maybe slightly more.
Originally I thought 150watts, 13 volts equals more than 10 amps (11.5) so that's why I went to the extra expense of a 15 amp charge controller. If I'd known it was going to be so low I could have saved quite a few bob and bought a 10A model.

Has anyone else fitted this combination of panel and controller?
What has your experience been?
Am I right to be disappointed?
 
That does seem low - I have a 60w panel and see 3A or very slightly over that. Given the relative sizes I would be expecting yours to see 7 or even 7.5 A.

Could be worth checking connections and the size of the wiring to ensure you don't have too much resistance or voltage drop.
 
My 5 year old semi flex Solara 2x45W panels (with a PWM reg) chuck out peak 3.8A, bit more to the point over 4 weeks had put out over 125AH into the batteries ( as measured by the gauge for the meter). The 3 domestics + 1 engine start (all AGM's) are always sitting at fully charged when I get back aboard, with the panel chucking out 0.0A... Agree your output seems a bit low, although you are further north than me (so lower noon sun angle) which probably counterbalances the MPPT vs PWM controller
 
Well - if you read the spec on the link you provided you will see that the maximum current it can produce is 8.83A so hoping for >10A might have been a bit optimistic :)
 
The solar panel controller will put current into the batteries according to their charge state up to the max the panels are capable of.
Perhaps your lower than expected current is due to the batteries being well charged. If the batteries are "fully" charged the controller would go to "float" with minimal current going to the batteries.
 
Thanks for the replies so far.

It does seem that maybe the MPPT controller is acting like a PWM so maybe there's an issue.
I may contact Victron to raise the issue with them, but just wanted your opinions and experience first as a check and balance before I get fobbed off.
 
Trundlebug said:
Yeah thanks.
Except that reading the MPPT literature it led me to believe it could increase the current from the nominal output of the panel, unlike a PWM controller.
See section 3, page 3 of this link http://www.victronenergy.com/upload...Which-solar-charge-controller-PWM-or-MPPT.pdf
Click to expand...

I don't see how that is possible. Unless it gets more power from somewhere - it can't output more than it receives in input.

AAUI a MPPT controller is more efficient that a PWM as it always manages to calculate the point where the output is at it's highest in terms of Watts going into the battery.
 
jac said:
I don't see how that is possible. Unless it gets more power from somewhere - it can't output more than it receives in input.

AAUI a MPPT controller is more efficient that a PWM as it always manages to calculate the point where the output is at it's highest in terms of Watts going into the battery.
Click to expand...

It isn't giving out more POWER than it receives, just more current to make up for the reduced voltage, so V1xI1=V2xI2.
 
I have a Blue Sky MPPT controller which has a switchable digital meter which gives voltage/ current from panel/ current out of controller - very useful.

On an ideal day, my 85W Kyocera solid panel will give up to 6.5 amps after the controller, about an amp less without it.
 
Gladys said:
8.83 A for 150 W means a tiddle under 17 V, seems reasonable.
Click to expand...

Yes I agree.
But I'm only getting 5.5A at 13.5v, 75 watts, not quite so reasonable.
The 8.83A is the quoted figure for the panel and is how they calculated the power output - so it would seem reasonable when you think about it :)
 
Last edited:
Trundlebug said:
Yes I agree.
But I'm only getting 5.5A at 13.5v, 75 watts, not quite so reasonable.
The 8.83A is the quoted figure for the panel and is how they calculated the power output - so it would seem reasonable when you think about it :)
Click to expand...

But the fifure they are giving is the maximum possible output (possibly? on zero load) that you can ever get downhill with a following wind etc... What about any shadow crossing the panel?
 
Gladys said:
But the fifure they are giving is the maximum possible output (possibly? on zero load) that you can ever get downhill with a following wind etc... What about any shadow crossing the panel?
Click to expand...

No, the figure they are quoting is 18v x 8.33A = 149.94 watts or 150watts to you and me.
That's in conditions of light at 1000w/m2 , the standard conditions used for solar panel output.
 
Trundlebug said:
Thanks for the replies so far.

It does seem that maybe the MPPT controller is acting like a PWM so maybe there's an issue.
I may contact Victron to raise the issue with them, but just wanted your opinions and experience first as a check and balance before I get fobbed off.
Click to expand...

Have you tried loading the system to see if you get the expected output when the demand is there.

An MPPT controller will control the solar panel at its maximum power point while there is demand but as the battery charges ITYWF the output from the controller to the battery will be controlled by pulse width modulation.
If you have reached the point at which a simple PWM controller would start to reduce the charging current you will observe a similar behaviour. with you MPPT controller.
 
I have the same controller fed from an 80 watt Victron solar panel (solid) and get about 6 amps out. Had it two years now and quite pleased with it. I have the fridge on 24hrs and lights in the cabins on for possibly 3-4 hrs at night and the Batts are usually recharged by mid day here in the Solent if the suns out!
 
My domestic installation is 2.2kW nominal; the highest output I've seen is 2.0kW; that is, a bit less than 10% less than the nominal output. That's south facing, and tilted towards the sun at the angle of the pitch of the roof. When the installers were consulted, they reckoned that was pretty good for a UK installation - apparently the nominal output is at a higher insolation than is possible in the UK. Based on that, I'd say your output was too low, but perhaps not a lot too low.
 
Don't know if this will help you but...

I have 450w. Occasionally in the morning, I have seen over 20A when the batteries have been working all night. As the batteries charge up (normally by about midday) the input drops to 4/5A. If I increase the load on the batteries (using the inverter), the input goes up accordingly and can reach 20A again. All through a 30A MPPT. Sad but true, I have kept some records correlating this all to the voltage of the batteries, so I think that you need to consider the SOC of your batteries before condemning the controller.
 
Best way to check the solar installation for performance is to have it charging a battery at midday. Turn on all the power sucking devices you can, to load the battery and hence the charge controller. Thus one can presume that if you have a decent load on, that the solar panel and controller are flat out.
If you feel the output is still down then check the panel output itself. You can put an amp meter directly across the output which should then show max current. Disconnect the panel from the battery of course and don't leave connected for too long. This short circuit will not hurt the panel due to internal resistance. If the panel seems OK to spec then the shortfall may well be in the MPPT controller. Not always as efficeint as claimed. good luck olewill
 
You must log in or register to reply here.

Other threads that may be of interest

D
Solar Panel wiring question
Replies
3
Views
214
William_H
W
Refueler
80W Solar panel arrived with a 'crease'
2
Replies
34
Views
649
Refueler
Refueler
Refueler
Change Solar panel - Old is NAPS 27962 55W flexi
Replies
19
Views
390
Refueler
Refueler
webcraft
Resetting SmartShunt to 100%
Replies
7
Views
340
webcraft
webcraft

Share this page

Top