"45 Watt Solar Panel Kit" ? Why is this kit called a "45 Watt" kit? Why not...say a... "30 Watt" kit?

I have never measured more than 30 watts. The greatest voltage was 14.5 and the highest current was 1.9 amps. If Watts = Volts * Amps or in this case 14.5 * 1.9 = 27.6 Watts. This reading was obtained 12:30 PM on June 20, 2011.  Though many other readings were close, this was the highest seen during 2011.

NOTE: Current was kept flowing to the battery bank as long as additional load was added to keep the Charge Controller Cuttoff Voltage at 14.5 or below. The current flow being measured included that consumed by the battery plus the additional load. I switch often between 5 different HF VOM's with no noticeable difference in voltages or amperages.

I would like to hear how others have read wattages at higher levels

Thanks for any comments

Views: 644

Comment by Dale Marshall on January 2, 2012 at 11:18pm

Actually thats probably close, But Angle of the panels..Sometimes a more direct Angle toward the sun. Will boost. Most of our higher wattages are because of  larger wire size we use and charge controllers. Fine tuning should bring it up around 37.5 watts. You never get 100 % of rated power because of losses.

Comment by Bill K on January 3, 2012 at 1:48am

One has to determine when you started to monitor the wattage...were you getting 30 watts on June 21, 2011? Or have you just recently put up the kit, say, within the last 2 months? If it's the latter, you have a low sun angle and this will cause less photons to enter the panels, resulting in a lower wattage....now that we've passed winter equinox, you will see more and more wattage increase as the sun begins to get higher in the sky...

Comment by Anon E mouse on January 3, 2012 at 9:43am

Dale M. -

I am intrigued by the 37.5 Watts. Would you please explain the method used to get this measurement? The volts, amps, where and how they were measured? Thanks for your input.

To ALL -

I change the angle of the panel frame with shims keeping its orientation within 5 degrees of perpendicular to the sun at "high-noon" actually about 1:00 PM CST at my location near Kansas City.

Thanks all

Comment by Hillbilly Gene on January 3, 2012 at 11:45am

Hi Anon E mouse,

The specification of each HF 15-watt panel is Pmax at 17.5 volts with 0.86 amps flowing, which is stated on the back of each panel That comes out to 15.05 watts per panel.  Times 3 = 45 watts per HF 3-panel kit.

After approximately 6 months of “seasoning”, each panel output can degrade 20 percent.  (See page 9 of the HF kit manual.)  Whipping the math around, 80 percent of 15.05 watts comes out to 12.04 watts output per panel after 6 months.  Times 3 = 36.12 watts per kit.

Additionally, once the panel gets above room temperature of approximately 70ºF the output will decrease (page 5 of the kit manual), although they don’t give any indication of the decrease of output per degree rise.

On that same page they state their “working” rated output of 15 Watts at approximately 14.5 volts, which is their charge controller upper cut-off voltage.  That 15-watts/14.5-volts would indicate 1.03 amps flowing right before cut-off to the battery.  Time 3 = 3.09 amps flowing to the battery before the “seasoning period”.  This is how you are testing your kit, except you are testing after that seasoning period.


All of these specifications are taken with 1,000 Watts per-square-meter laboratory “perfect sunshine” test equipment at 25ºC temperature. (77ºF)  That specification is found on the back of each HF panel.


Is HF, to put it kindly, “pulling your leg” about their specifications of their 15-watt panels?  No, not any more than any other solar panel maker.  They all use that same equivalent “perfect sunshine” test equipment.  And no panel maker is going to brag about its panel output on a “real world” basis if the numbers are smaller.  Which they will be.  General Motors is not going to brag about the dependability of their automobiles after 150,000 miles are on them.  Both manufactures will say, “it depends”.


I am referring only to a “pure” HF 45-Watt 3-panel Kit: only three HF panels and using the included, unmodified, HF charge controller.  No combiner box.  Once you start comparing the “pure” kit with anyone else’s modified kit you are starting to compare apples to oranges, as they say.


After wading through this stuff you may see why you aren’t getting the advertised 45 watts out of each kit.


By the way, a cheap trick I use to adjust my panels “just right” to the sun is to C-clamp a short 1 x 4 board, at a 90-degree angel from the front surface of the panel, to the side of the panel array.  Then I adjust the array for minimum shadow from the stick.  Can’t get the panel angel to the sun any better than that.  It, of course, changes after a few minutes.


Hillbilly Gene

Comment by Dale Marshall on January 3, 2012 at 12:13pm

Hillbilly gene did all the correct explaining.

Comment by Anon E mouse on January 3, 2012 at 4:26pm

First of all, I have to really thank you guys for the time you took to explain how to read the specifications....

I know you took quite a bit of time and trouble to create your response and I really appreciate this and I don't want to offend anyone, but ...

I'm just a poor Missouri boy with a few cheap HF meters, and with one abiding philosophy "If I can't measure it ... it doesn't exist."  I guess the old saying is actually ... "you have to show me".

Its been a while since I have actually read the shorted amps on each individual panel. It was a year-ago last October when I purchased the first set. Those peak amp readings have misplaced for the moment but I do remember showing them to the local HF Manager and at the cuttoff of 14.5 volts the current running through each panel resulted in less than 10 watts per panel netting about 28 watts total.

But it does seem to me that if they advertised the "Kit" as "45 Watt Kit" the kit should be able to do 45 watts worth of work as measured at the load. My measurements of the kit's actual performance was calculated using the voltage across the load and the current through the load.

My Original Request was ..."I would like to hear how others have read wattages at higher levels"

Now I may have made an error, in trying to test the "45 Watt Kit" in this manner ... and if so I would like to be corrected. That the only way I will learn. (Please no Spec-Talk...Just actual readings.)

Thanks again for your trouble

Comment by Hillbilly Gene on January 3, 2012 at 5:40pm

Hi Anon E mouse,

I am an old Hillbilly who also has a very strong Missouri “Show Me” State attitude, and it has served me well.

Let me put it this way:  If you took your brand new car advertised as 450 horsepower to a shop with an accurate Dynamometer and the shop couldn’t get the machine to register the advertised 450 horses, then you could say you were cheated.  You can’t test it on the street and get valid results.


If you took your brand new HF solar panels to a laboratory with a 1,000 watts per-square-meter “sunshine source” and tested your panels under the AM 1.5 standards, and the laboratory couldn’t get 15 watts out of each panel, then you could say you were cheated.  You can’t test the Isc of the panels in the October sun and get valid results.


All I can say is you didn’t measure your panels like the factory did.  You can only compare your panels with others who have tested theirs exactly as you did.

 I hope I didn’t fall under your constraints of too much Spec-Talk.

At one time or another we all have to come to terms with the HF (or any solar panel manufacturer) advertised laboratory output and the real world.


Quote: "I would like to hear how others have read wattages at higher levels"

Others will have to chime in here; I have not bothered to check the wattage on mine. 


And, no, I’m not offended.


Hillbilly Gene

Comment by Anon E mouse on January 3, 2012 at 6:26pm

I sorry but I have no patience with Specs in "Watts" or "Horsepower".

In my world the focus is on actual performance and it is always measured by realworld parameters, such as the time it takes to reach the quarter-mile marker from a rest position at the startline.

When I put GM's ZZ-4 crate engine in my 79 vette,  I looked past the "355 hp" in the bold lettering and I focused on the (torque vs rpm) power curves. When I decided on GM's 700r4 3 speed overdrive auto-transmission, my focus was on the gear-ratios and how they would deliver the torque to the rear tires.

In truth I also relied on persons with racetrack experience for their recommendations regarding how well this engine and transmission held up under stress.

I always try to seek out those with actual experience. This explains why I joined this forum and why I truely respect and appreciate your comments.

Thanks again

Comment by Jim on January 3, 2012 at 8:44pm

But AEM... when advertising a product's ability to produce a given output you must reference all measurements to specific and fixed values. In any formula, for one value to be meaningful, all other values must not vary.

That is why "lab testing" is used as a reference. No variables to skew the measured results. Real world results will always vary because the real world is variable. Lab results will usually be based on "perfect" or "best case" situations. If all product suppliers use the same testing scenarios then the results can be reliably used for product comparision.

You stated "such as the time it takes to reach the quarter-mile marker from a rest position at the startline." In your world, you know that altitude (atmospheric pressure), ambient temperture, barometric pressure, water grains and driver ability are all real world parameters that will affect that quarter mile time. For some of those variables you can apply a mathamatical correction, but it would not be fair to compare that ZZ-4 motor to another motor with all those variables affecting it's apparent ability to traverse that quarter mile.

Those torque vs. RPM (and I'm sure compared against the HP vs RPM) curves you quote are just like the 355 HP number, they are derived from testing against fixed references in a controlled "lab type" environvment. For example, that 355 number means absoultly nothing unless you specify what RPM was required to obtain that number. If it took say 10,000 RPM to achieve that 355 and usable RPM is 4,500 you know that the HP number will probably be considerably less so it is for practical purposes a false claim.

Horsepower numbers are ambigous unless specified to where it is measured (specific brake horsepower), on a shop dyno (at the flywheel) or chassis dyno (at the rear wheels). Then unless you specify the parisitc losses in the drive train, the results are variable.

Audio watts are ambigous unless referenced to a specific load (ohms) at a specific frequency.

RF transmitter power numbers are ambigous unless the antenna impedance and frequency is specified and then lab measurements are used referencing an isotropic (labortory) antenna.

The point is that all of those specs will be different (and usually lower) in the real world but are acceptable for comparisions to other makers of like equipment. The companys that make these products do not live in your world of putting it down the track against a competitor but must market these products in their world in which they have to prove their product in the lab with other makers of like products.

But of course remember, your mileage may vary...

Comment by Anon E mouse on January 3, 2012 at 10:44pm

Do specs sell cars, I still believe in performance. The word gets around about real mpg. Those manufacturers that can't produce what they claim eventually lose. Back to the case at point, solar panels.

I recently obtained a panel made in the USA, it was spec'd at 240 watts, with a peak of 8 amps given an operating voltage of 30 volts. Guess what, the last sunny day I measured the short-circuit amps and it read 8.2 amps while its operating voltage ranged between 29 and 32 volts. It just about burnt the point off my meter's lead. (Maybe the Chinese have a different sun.)  By my rough math 8a x 30v = 240 watts. I would conclude that this American made PV panel does in fact live up to its specs, however they were established.

Since when did calculating watts produced by a solar panel become "rocket science"?

I am sorry to repeat my self...hasn't anybody here actually read the short-circuit amps of these panels?

I propose a simple request for anyone interested. Just measure the amps produced by these 3 panels in series with the charge controller and measure the volts across the controllers input terminals. Then if the product of these two values exceed 30 watts, please let me know by updating this forum's thread.

By the way I have made a very efficient High Definition UHF antenna out of clothes hangers. No I don't think there are any specs. It just works like a champ.

PS: I think we kicked this "Spec this" and "Spec that" thing to death. How about some actual data? It might not be perfect, but hey ...its a starting point.

Thanks again ... Its been fun!


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