What is your real live solar system performance?

Z

Zirdu

Senior Member
Joined
Aug 17, 2016
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110
Location
St. George, UT
I am curious as to what others are getting for real live solar system performance. I have a Victron 100/30 MPPT Controller with a "dongle" that communicates with an app on my smart phone that acts as a solar system performance monitor. I understand that the Victron charge controllers now can come with this bluetooth monitor built in. At any rate, this is a very useful monitor which you can use to monitor your solar system performance.

I have four 120 watt Solar Cynergy flexible solar panels on my roof, for a "nominal" or theoretical maximum of 480 watts of production. We all know that it is almost impossible to get the maximum production from solar panels mounted flat on your roof. But how close do you all come? I know it varies according to the time of year, time of day, weather (cloud or clear), temperature, etc. But I would be interested in having whoever is interested post their real life solar system performance here.

Heres my reading for today: 480 watt Solar Cynergy flexible panels. Jan 26th in extreme southern Utah (near Arizona border). Clear sunny day, 50 degrees. My system monitor says I got a PV maximum today of 210 Watts. 210 / 480 = 44%.

So today I got 44% of my theoretical maximum performance. I guess this is OK, given the time of year. One thing I am testing by the way is to make sure all my panels are performing properly, since a few months ago I damaged them driving into the garage. Also, I noted today that my panels were somewhat dirty. I plan to clean them and measure again tomorrow.
 
One question would be how much power did your battery need today? Are you sure your batteries were in bulk charge when the sun was at its maximum elevation? The charge controller will reduce it's solar harvesting once you are in absorption and then drop it close to zero once your batteries are full and it switches to float.
 
Good point. For accurate testing you do have to make sure your batteries are a bit run down so the charge controller is in bulk charge mode. Before testing today I did run the battery down a bit. The Victron bluetooth monitor indicates whether you are in bulk, absorption or float. It was in bulk when the listed reading was made.
 
You can directly calculate what your flat mounted panels should produce. The amount of solar radiation per unit area on a flat mounted collector is the cosine of the solar zenith angle. You can look up the solar zenith angle for any particular place and time here:
https://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html
For 37 degrees north ( I am guessing for southern Utah) the peak solar elevation (at solar noon) was 31 degrees - ie the highest the sun was in the sky was 31 degrees above the horizon. The SZA is 90 - elevation (it is the angle from the zenith) = 59 degrees. Cos(59) = 0.51. So best case scenario you should get 51% of your rated output, once you take into account some dirt on the panels, charge controller inefficiency etc, 44% is REALY good.
 
Zirdu

Howdy...please comment how long you have had the Solar Cynergy flex panels and how you mounted them ....

I am trying to know best mounting scheme for two of the same I just bought.

How long have you had them in use?

Many thanks

David Graves
 
David: I installed the first two 120 watt panels about 15 months ago. They worked very well. A few months ago I installed two more.

The installation I used was a custom made mount using samall pieces of 1 inch square aluminum tubing, which I attached to roof with VHB tape. I then used screws to screw the panels to the tubing. I posted an explanation of my installation method here: http://www.wanderthewest.com/forum/topic/14865-flexible-solar-panel-installation/?hl=%2Bflexible+%2Bsolar+%2Bpanel
 
I have two 160's on the roof and an 85 portable that I installed legs onto, allowing it to tilt at about a 45 degree angle. Sorry I don't have some actual data to share, but I think that little 85 watt tilted placed directly towards the sun can put out as much as my two 160's that lie flat, especially this time of year.

I have seen here on this forum that there is a mount for your roof panels that will allow them to be tilted, but I have always wondered how practical they are, since you would have to climb up top to raise them and of course maybe the direction you have your camper parked may not be conducive to raising the panel anyway. I may do this mod anyway.

The other mod I would really like to do, and one that I think would make a huge difference, is to get rid of that factory 12 gauge wire coming down from the roof and replace it with 6 gauge, but I will need to tear up the headliner and who knows what else.
 
To save you some work - increasing your wire size really won't make much difference in your solar efficiency. If you have a PWM charge controller it will make essentially no difference at all. If you have an MPPT charge controller, you could get a slight increase, but you probably get more by putting your two panels in series if you have not already done so.

The angle relative to the incident sun light makes by far the biggest difference (a factor of 2 for Zirdu) so having a second portable panel is a great way to get extra solar.
 
Thanks Zirdu,

Of course I read and admired your installment plan for the flex panels.

In hindsight, do you get much flutter at highway sppeds or any comments now they have some miles under them ?

I am tempted to simply glue one on roof and use second as a portable....angled to suit latitude and time of day.

Has anyone heard of cons ( heat , other ? ) to mounting a Solar Cynergy flex panel directly on the aluminum roof skin ?

Many thanks

David Graves

North Oregon coast
 
I was getting 5 amps out of my panels yesterday, sunny day but there hasn't been much of a load on the batteries lately. Might be interesting to run them down a bit and see.
 
I have two of the 120W solar cynergy semi-flexible panels on my roof as well. The main issue (and it could be significant) with gluing them down is the unknown reliability of these panels. There have been lots of failures of various brands of semi flexible panels, and these panels are relatively new, so no one knows how long they will last. This is why I didn't glue mine down and bought a spare that I use as a portable.

What I ended up doing is taking three 4' long 1/8" thick x 1" wide aluminum flat bars, and installing counter sunk M5 screws through the flat bar where the grommets for the panels are with some JB weld to stop the screws spinning. The screw heads are flush with the bottom side of the flat bar. I then VHB taped these bars down to my roof, screw head side down, with the result being 12 M5x12mm studs sticking straight up (but no roof penetrations). I then bolted the panels down to these studs with nylock nuts and large washers. The panels are side by side and the bars run perpendicular to the long axis of the panels. Essentially you end up with panels mounted almost flush to the roof, that can be easily unbolted if they ever need to be replaced.

My mount was a cheaper alternative to something like these:
http://www.weldmountsystem.com/products-fasteners-stainless-studs.php

The panels have been performing as expected so far - about 160W peak output during the autumn and 120W at this time of year. I have checked the mounting a couple of times and no issues so far.


DavidGraves said:
Thanks Zirdu,

Of course I read and admired your installment plan for the flex panels.

In hindsight, do you get much flutter at highway sppeds or any comments now they have some miles under them ?

I am tempted to simply glue one on roof and use second as a portable....angled to suit latitude and time of day.

Has anyone heard of cons ( heat , other ? ) to mounting a Solar Cynergy flex panel directly on the aluminum roof skin ?

Many thanks

David Graves

North Oregon coast
Click to expand...
 
rando said:
To save you some work - increasing your wire size really won't make much difference in your solar efficiency. If you have a PWM charge controller it will make essentially no difference at all. If you have an MPPT charge controller, you could get a slight increase, but you probably get more by putting your two panels in series if you have not already done so.
Click to expand...
According this chart in my PWM controller manual, 12 gauge is not recommended. I figured that my run is about 22 feet.

IMG_3882.JPG
 
craig333 said:
I was getting 5 amps out of my panels yesterday, sunny day but there hasn't been much of a load on the batteries lately. Might be interesting to run them down a bit and see.
Click to expand...
Another thing you can do to see if the panels can put out more power than the batteries are absorbing is to turn on the vent fans, internal and external lights and fridge until no more increase in amps are indicated. At that point, you will see maximum amps produced under present conditons.

Paul

ps. Almost said under current conditions. :)
 
captainphx said:
According this chart in my PWM controller manual, 12 gauge is not recommended. I figured that my run is about 22 feet.

attachicon.gif
IMG_3882.JPG
Click to expand...
This is a little misleading - the table appears to be a standard 3% voltage drop table and not specific to solar power. Limiting your voltage drop to 3% is good practice for sensitive electronics, but really doesn't matter in this case. The way a PWM charge controller works is that during the bulk of your charging, the battery pulls the solar panel voltage down to the battery voltage. Most '12V' solar panels provide their maximum power at ~17V (called Vmp). For a 160W panel, this means you get the rated out put at 17V and 9.5A. The PWM charge controller is dragging that voltage down to your battery charge voltage, say 13.6V while still providing the same 9.5A.

As long as you are losing less than 17 - 13.6 = 3.4V in your wiring, using larger wire won't improve anything. The caveat here is that your wire still needs to be rated to carry your current without over heating - the limit for 12 AWG wire is 45A:
https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity

As an aside, the voltage gap between the Vmp and your battery voltage is where MPPT chargers get their 'extra' power from. An MPPT charge controller will allow the panel to operate at 17V and 9.5A, and will convert that to 13.6V and 11.8A, giving you an extra 2.3A or about 25% more power. This is why wire size does make some difference with MPPT and not PWM.
 
rando said:
This is a little misleading - the table appears to be a standard 3% voltage drop table and not specific to solar power. Limiting your voltage drop to 3% is good practice for sensitive electronics, but really doesn't matter in this case. The way a PWM charge controller works is that during the bulk of your charging, the battery pulls the solar panel voltage down to the battery voltage. Most '12V' solar panels provide their maximum power at ~17V (called Vmp). For a 160W panel, this means you get the rated out put at 17V and 9.5A. The PWM charge controller is dragging that voltage down to your battery charge voltage, say 13.6V while still providing the same 9.5A.

As long as you are losing less than 17 - 13.6 = 3.4V in your wiring, using larger wire won't improve anything. The caveat here is that your wire still needs to be rated to carry your current without over heating - the limit for 12 AWG wire is 45A:
https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity

As an aside, the voltage gap between the Vmp and your battery voltage is where MPPT chargers get their 'extra' power from. An MPPT charge controller will allow the panel to operate at 17V and 9.5A, and will convert that to 13.6V and 11.8A, giving you an extra 2.3A or about 25% more power. This is why wire size does make some difference with MPPT and not PWM.
Click to expand...
Hello Rando,
I just came across this thread while designing my auxiliary power system. Thank you for your awesome explanation of where the extra power comes from with an MPPT controller. Also, I've been looking at the 3% loss chart for wire sizes and then wondering how everyone is getting away with such small wires! Would you say the 10% loss chart is a better choice or are you aware of a solar wiring chart?
Thanks,
Dave
 
To answer the op's question, I have two 100W panels mounted on the roof. My rule of thumb is that "ideally" each should generate 5 amps for a total of 10 amps. Only occasionally do I see more than 10 and often less when clouds, smoke, sun angle, shadows etc hinder more optimum performance. With 120W panels I would expect that you would use 6 amps per panel as that "ideal".

One of the best things about the solar panels is that even in poor solar conditions they often raise a tired battery-bank's voltage high enough so that the separator will stay shut and allow the truck's system to charge the house batteries while driving.

Alan
 
A 10% loss would be fine, and in most cases still conservative. I am not aware of a table for solar as it depends on several other variables - panel Vmp, charge voltage, wire length etc. How many watts of solar are you installing and which charge controller? We can probably steer you in the right direction.

AdventureDave said:
Hello Rando,
I just came across this thread while designing my auxiliary power system. Thank you for your awesome explanation of where the extra power comes from with an MPPT controller. Also, I've been looking at the 3% loss chart for wire sizes and then wondering how everyone is getting away with such small wires! Would you say the 10% loss chart is a better choice or are you aware of a solar wiring chart?
Thanks,
Dave
Click to expand...
 
rando said:
You can directly calculate what your flat mounted panels should produce. The amount of solar radiation per unit area on a flat mounted collector is the cosine of the solar zenith angle. You can look up the solar zenith angle for any particular place and time here:
https://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html
For 37 degrees north ( I am guessing for southern Utah) the peak solar elevation (at solar noon) was 31 degrees - ie the highest the sun was in the sky was 31 degrees above the horizon. The SZA is 90 - elevation (it is the angle from the zenith) = 59 degrees. Cos(59) = 0.51. So best case scenario you should get 51% of your rated output, once you take into account some dirt on the panels, charge controller inefficiency etc, 44% is REALY good.
Click to expand...
Rando this is a great bit of info for me and the linked site is bookmarked! Real clear explanation, thanks
 
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