Confused on solar specs \ Grape Solar

Chief RA · Jun 16, 2015

During a decent solar day, over 10 hrs you might get about 2.5 amps average per solar hour or 25 watts. Realize that is an estimate but it will not be far off. Chief

gettinthere · Jun 16, 2015

Semiflex 100w panel? According to Mainesail, who of course did some thorough digging, all those 100w semiflex.panels are made in the same chinese factory and private labeled for various retailers. A few months ago I bought 2 from Renogy for $200 each. So far so good.
It seems that the off brand mppt controllers are suspect. Buy quality there. I added another Blue Sky 2512. I had one already on a pair of 140w panels. A total of 480w was too much and indeed I often see 26 amps going into the batteries. You can do some interpolating to figure what you might get with your setup.

Beware...all the flex panels offer a 5 year workmanship warranty vs the glass panels 25 year PERFORMANCE guarantee.

Chief RA · Jun 16, 2015

Its a 24hr day so don't get too excited about your given amperage reading. Reread my above estimate. Chief,EE

mitiempo · Jun 17, 2015

Skipper said:
If I get a Grape Solar Photoflex 100w panel, I'll need to also get an MPPT controller.

The panel is rated at 100w, 17.8v, equaling 5.62 amps of current. So, If I install the controller which brings the volts down to (example) 12, will that bring the current up to 8.3 amps? What is the reality of specs actually getting to the batteries, since I presumably can't let 17.8 volts pass through?

Also, anyone use Grape Solar? Comments?

14.4 volts is the charging voltage - not 12. With a good (Morningstar, Blue Sky, Victron for example) you would get 6.95 amps or less in full sun.

Stu Jackson · Jun 17, 2015

Skipper said:
..............The panel is rated at 100w, 17.8v, equaling 5.62 amps of current. So, If I install the controller which brings the volts down to (example) 12, will that bring the current up to 8.3 amps? What is the reality of specs actually getting to the batteries, since I presumably can't let 17.8 volts pass through?

......... Comments?

Isn't that the whole purpose of the controller? It acts as a "regulator" for the panels and controls the voltage being supplied to the battery bank. The amperage is determined by the controller and the input that's coming, well, uhm, in, from the panels.

Chief RA · Jun 17, 2015

Skipper:
We are all providing you info and it is correct. Stu explains the controller/regulator concept and mitiempo provided you with regulated voltage present after the controller. Voltage does not move, it is the potential that prompts current flow through whatever resistive properties that are present in the circuit.
In order to get max current from your panel it must be facing FULL sun all day & the sun is only present for about 10 hrs a day. That fact alone just dropped your daily output by 58%!
Realize that voltage does not pass through at all, only current. Whenever panels are connected to batteries such a huge load draws down the voltage anyway without even considering what the controller does. That voltage will slowly rise as the current flow decreases as full charge is approaching. This is where the regulator/controller starts to hold down the voltage to around 14.4v depending on state of charge. Once the battery bank is at full charge the solar panels are doing little good unless you are watching TV or something to utilize that extra power. This factor is what most people do not realize and therefore think lots of panels is the answer. Not if you don't have the appropriate sized battery bank! Thanks mitiempo and Stan, as I was to busy to write this all up yesterday for him. Chief (the ol' Professor)

PGIJon · Jun 17, 2015

Chief RA said:
& the sun is only present for about 10 hrs a day.

Well Chief of course you are correct but your statement.... well that depends.. here in Florida right now we have sun 14 hours a day... Your gong to have almost 15 hours and Oslo will have 18 hour and 11 minutes of sun....

Chief RA · Jun 17, 2015

Jon: It is used as a basic reference over long term concepts and can be varied as you point out depending on your location. Most important is did you relocate the panel all day to catch morning AND evening sun? Probably not; thus 10hrs. Many people can't calculate for avg. concepts and end up fooling themselves.
The main point is to help others to understand the calculations and why they must be so low for avg.
Chief

Maine Sail · Jun 17, 2015

Skipper said:
If I get a Grape Solar Photoflex 100w panel, I'll need to also get an MPPT controller.

The panel is rated at 100w, 17.8v, equaling 5.62 amps of current. So, If I install the controller which brings the volts down to (example) 12, will that bring the current up to 8.3 amps? What is the reality of specs actually getting to the batteries, since I presumably can't let 17.8 volts pass through?

Also, anyone use Grape Solar? Comments?

An MPPT controller will provide a boost while the batteries are in bulk charge. You can expect this boost to be in the 7-22% range all dependent upon panel temp and panel voltage. In hot areas MPPT provides less boost because panel temp is higher.. Your charge voltage at the battery will be somewhere between 12.4 & 14.4 +/- volts, not 12V, unless you are severely discharging your batteries into the danger zone. MPPT operates on the voltage differential between the batteries and the PV so the bigger the voltage differential the more boost it can provide.. The larger the voltage spread between battery & PV the more "MPPT Boost" you will see.

As for Grape solar these panels are Chinese and all made in the same factory as the other Chinese "Solbian copies", this despite the manufacturers (sticker-licker companies) trying to deny it. Renogy, Grape, Shine, eBay semi-flexibles, Go Power etc. are all coming our of the same factory...

The problem with them is they use low grade cells and are often riddled with microcracking causing them to under perform the spec. I have seen far too many of these Chinese semi-flexibles not performing to spec so be sure yours are!! Best bet with Chinese semi-flexibles is to go with the most reputable of the resellers. In my experience this is GoPower.

If you only buy one panel it is hard to compare it to spec so the manufacturers often get away with it if it under performs. If you buy two panels you can A/B them and send back the one that is under performing.

Below is some real world data over 7 days in early May in Maine. Weather wise it was a rather crappy week with not a single bright sunny day, but this is real world for Maine.... Two identical 140W panels were placed side by side laying flat, like they would be on a boat. The MPPT average for the 7 days was 31.42 Ah's per day and the PWM was 26.06 Ah's per day or a 20.8% boost for the MPPT over the PWM controller. if the weather had been better the data would be better. It is not uncommon for me to see daily averages on a 140W panel of 50 + Ah's per day, even in Maine.

Right now the Genasun GV-10 MPPT is the absolute best deal going in a quality MPPT controller (quality being the key word) for a 100W panel at about $98.00 - $109.00. A few weeks ago this controller was $170.00 but they were able to take a massive price cut due to the volume growth of this controller in sectors outside the marine & RV market.....

PGIJon · Jun 17, 2015

Chief RA said:
Jon: It is used as a basic reference over long term concepts and can be varied as you point out depending on your location. Most important is did you relocate the panel all day to catch morning AND evening sun? Probably not; thus 10hrs. Many people can't calculate for avg. concepts and end up fooling themselves.
The main point is to help others to understand the calculations and why they must be so low for avg.
Chief

I totally agree... was just giving you a hard time...

Sorry

Chief RA · Jun 17, 2015

MS: Those readings are so low you even surprised me! You did indicate it was a bad sun week though. Hopefully we will impart the info that amps tend to be much lower than most realize. Chief

Chief RA · Jun 17, 2015

Not a problem Jon. Check out those readings on MS input! Chief

Maine Sail · Jun 17, 2015

Chief RA said:
MS: Those readings are so low you even surprised me! You did indicate it was a bad sun week though. Hopefully we will impart the info that amps tend to be much lower than most realize. Chief

Look at the summary above each day as to the weather and remember this was early May in Maine....... It was a horrible week! It is not uncommon for me to see 50+ Ah's per day, with good weather, from a 140W panel....

One thing folks often don't grasp is that a 140W panel at 25C/77F is only a 101W panel at 45C/113F...... Most disreputable companies do not show the Pmax or Vpmax at 45C just 25C thus misleading consumers on the true performance of the PV as it heats up.......

To keep it simple the "averages" I tell my customers & readers is to use the Ipmax at 25C and multiply by 3.5 - 5.5 hours per day, depending upon location. These will be relative safe "averages"...

This lower performance has a lot to do with aiming restrictions. On boats flat panels work best unless you are there to manually manipulate them all day.

I have found, through lots and lots of data collection, that you can figure on about 3.0 - 4.5 hours of full rated current output per day at the 25C Ipmax spec, on average, for the Northern climates.

Down South 4.0 - 5.5+ hours per day the closer to the equator you get. These are full current ratings at 25C panel temp. Of course weather can play a huge role and you could see slightly more or slightly less. Generally speaking it is best to size for worst case scenarios, like the week above, as I do, and I've yet to hear anyone complain they had too much solar..

Some folks use 5 hours per day in the Northeast, at Ipmax 25C, but after lots of monitoring of my own panels, and customers, I found that to be a little to generous as an average for sizing. Some days it will be more some less but here in Maine 3.50 - 4.5 hours at 25C Ipmax full output, as an average sizing number, seems to work best.

centerline · Jun 17, 2015

PGIJon said:
Well Chief of course you are correct but your statement.... well that depends.. here in Florida right now we have sun 14 hours a day... Your gong to have almost 15 hours and Oslo will have 18 hour and 11 minutes of sun....

If you figure your output based on a 12 or 14 hour day, you are going to be disappointed in the actual numbers the battery sees...
Most of us set up/size our systems so they can be depended to give adaquate power year round, not for just a few months out of the year.

Its not daylight that matters, but DIRECT sunlight on the panel... so a glancing ray from the sun that is near the horizon is useless on a flat mounted panel to get the panel to put out anythng but a slight trickle of what it is capable of.

Its not what YOU see the sun doing, but what matters is what the panel sees the sun doing... a 10hr sun day is a good average unless you have the panels mounted in such away that they will follow/track the sun.

Then the variable becomes how much sun there is vs cloud cover or shading of the panel, and the outside temperature.
A panel on a cold sunny winter day will produce more power than it will on a hot sunny summer day.

And unless you are actually in oslo with your panels, the long summer day there wont help you.

There are alway variables and extremes, but when figuring solar potential, the 10hr day is a good, average number to work with for most of the world, due to the arc of the sun over the panel during that time, which is much more effective on the panel than is the glancing rays in the early morning and very late afternoon/evening...

Stu Jackson · Jun 17, 2015

What Maine Sail & Chief and centerline are discussing is what, in (GASP!) high school math are called VARIABLES.

In any economic or mathematical analysis, those variables are used to ESTIMATE projected results, which can end up being in a RANGE of possible outcomes.

Sorry to be an 11th grade professor, but

10 hours times 20A (panel rating) times 50% (shading, sun angle effect on output) = 100 ah per day

15 hours times 20A times 33.33% = the SAME 100 ah

Those VARIABLES, as measured and reported by Maine Sail, end up making up what REALITY may show you.

This is NOT an exact science, 'cuz the sun moves around, panels sometimes don't, clouds happen, and the amount of hours of sunlight in FL is, as reported

)) different than in Maine.

The reality also is that an MPPT controller will provide more output from the same panels as PWM as Maine Sail has so properly MEASURED, recorded and reported.

Add to that the SOC of your battery bank. BATTERY ACCEPTANCE is rarely understood by most electrical "beginners" but the simplest answer is that as batteries get fuller they can accept less charge. So, a "more full" bank will take less current than an "emptier" bank - same panel, same sun, same controller.

Understand the analogy between water and electricity: voltage is pressure and current is flow.

Put these all together and you'll "get it."

Good luck.

Johnb · Jun 17, 2015

MPPT stands for maximum power point tracking.

There is a mismatch between the voltage and current from solar panels and batteries. The maximum power (not max current or max voltage but the product of the two) that the panel can deliver is not at the same voltage as the batteries, usually 2 to 4 volts higher in a typical 12 volt system. The MPPT controller alleviates this mismatch and delivers more of the power available from the panels.

Stu Jackson · Jun 17, 2015

Skipper said:
.........and would the controller typically leave other specs alone like wattage. If the answer were "yes", then I could do the amperage math for rated charging voltage for a given controller.

Glad to help.

Back to 11th grade again:

wattage is volts times amps (or something like that, right?)

Volts is pressure, amps is current or flow.

So "changing" from volts and amps to watts is just saying the same thing.

I see this all the time. Why bother?

If your goal is to figure out how to size the wires from the panel to the controller, then that's a different story.

If it is all you are trying to do, please say so and we can point you to resources to do just that.

If not, then you're simply saying either:

"2 plus 2"

or

"four"

Same thing, right?