Where is the power go ???

[monogram]

Hello,

I have small solar system running on 2 x 310W panel with MPPT charge controller and four Sams Club Golf Cart battery 6V GC2.
During this July time, the panels generated 4.3kWh a day
I have a device that running 115Wh and it running continuously at 24hrs a day for 7 days a week.

Here is the math:
- Daily Solar generate: 4300Wh
- Daily power usage (consumed) : 115Wh x 24 hours = 2760Wh
==> base on the above, I should have 1540Wh available right?

But in the reality, every morning when I wake up at 6AM, the battery show 24V

The question I have is:

Where is the 1540Wh extra (4300-2760) go to?
Why the battery get to that 24V level, should it be higher?

Please help to explain this.

Regards,
Key

[SunEagle]

Did you measure that 4.3kWh or just calculate it?

I calculate that you have 620 watts of panels and for them to get 4.3kWh they would have to produce full nameplate power for 6.9 hours (4300wh / 620w = 6.9 hours) which I find hard to believe because those panels can't do that.

So my answer is that you are not losing that 1540wh because you are not generating it.

[monogram]

Hi SunEagle,

That 4.3kWh is actual power (readout from my MPPT) that was produced by 610W panels. I also check it with my KillAWatt meter and it report the same 4.3kWh. The average power output from panels was 450-530W. When the day is cool (85F) with sun, the power output up to 650W from 610W panel, it's very nice, right. For yesterday data, sun rise at around 6:30AM and sun set at around 7:30PM.


The question I have is:

Where is the 1540Wh extra (4300wh - 2760wh) go to?
Why the battery get to that 24V level, should it be higher?

Please help to explain this.

Regards,
Key

2019-07-03_083953.jpg2019-07-03_084709.jpg

[SunEagle]

I would not trust the readout of that CC. If you were getting the full amount of watt hours generated from your panels as it showed you would not be having an issue with your battery voltage.

No panel will ever generate it's nameplate wattage and most will not generate anywhere close to their nameplate except for the few hours the sun is before and after it hits the peak. So I would expect close to zero output in the early morning and late afternoon hours unless the panel is pointed directly at the sun during that time.

What I do not understand is if you believed in the CC readout you would believe the battery voltage is above 24V. Why do you feel the battery is not getting above 24v?

[monogram]

The 4.3kWh readout not only coming from CC but the KillAWatt also read the same wattage as well as my external current claim and my Fluke volt meter. When the CC display 31V at 21A then my Fluke show 31V with external clam meter display 21A also, therefore I feel confident that the readout is correct.

Let assumed the readout 4.3kWh per day is the correct value.
The device consumed 115W per hour which equivalent to 2760Wh per day.
The battery was fully charged from Solar by around 2PM.
By 6AM the next day, the battery voltage show 24.1V should it be higher?

Since the device only use 2760Wh while the panel produced 4300Wh, Where is the extra power go to???


Here is the current panel readout (the number matched with external clam meter and Fluke)
2019-07-03_101528.jpg

[SunEagle]

A possible reason for the 12.1V at 6 am is because your battery is barely providing the amount of amp hours your load consumes at night.

I won't argue with you about your production but based on your end result of having a low voltage on the battery at the end of the night I would say either you are not producing the calculated (or measured) watt hours or you are consuming more than your calculated watt hours.

Physics does not argue facts. You are not losing the extra watt hours. You are either not producing them or consuming them. They will not just disappear into thin air.

[monogram]

Do you know what is the usable capacity AH for Sams Club Golf Cart battery GC2 in brand new condition?

[PNPmacnab]

I'm sure if we were there, the problem would be obvious. With a load of only about 100W, most inverters are not that efficient, a battery has losses, wiring, etc. It doesn't strike me as that odd a number.

[Bala]

The amount your panels can produce on a good day is not the determining factor in your calculations.

The figures you need to consider are the storage capacity of your battery bank and the amount of power used.

Once your batteries are fully charged then it does not matter how much more your panels produce, that energy is mostly wasted.

So once your batteries stop getting charge from the panels in the afternoon you then have to draw power from the batteries alone until the sun starts charging them again the next morning.

This is where you determine the storage capacity of your battery bank and do some math with the amount of energy used overnight.

So basically, kwh of storage - kwh used, and you will get a ballpark of what the bank should be at in the morning.

[sdold]

That 4.3kWh is actual power (readout from my MPPT) that was produced by 610W panels. I also check it with my KillAWatt meter and it report the same 4.3kWh.

The Kill A Watt meter is an AC-only device, how did you use it to measure the energy produced by your panels? I'm with Suneagle, I don't think it's likely that you are getting the energy (Wh) you think you are. Where are you located?

- Daily power usage (consumed) : 115Wh x 24 hours = 2760Wh

Your device doesn't consume 115Wh, it consumes 115W (watts). Energy is watts (power) multiplied by time, so it's 115W x 24h = 2760Wh.

[SunEagle]

Do you know what is the usable capacity AH for Sams Club Golf Cart battery GC2 in brand new condition?

Most FLA type batteries can be safely discharge about 25% daily. Going more will usually reduce the number of "cycle" over it's life.

So for a quick calculation I would use 25% of total watt hours. That can be calculated using your battery system Ah rating x the battery voltage x 25%.

Again you can discharge the battery more but you will not get anywhere close to the estimated number of cycles.

[NochiLife]

...No panel will ever generate it's nameplate wattage and most will not generate anywhere close to their nameplate except for the few hours the sun is before and after it hits the peak. So I would expect close to zero output in the early morning and late afternoon hours unless the panel is pointed directly at the sun during that time.

Not to get into an argument about solar panel ratings, but I have 12 SolarWorld SW245 panels, totaling (245 * 12) = 2,940W rated capacity. With a Morningstar Tristar TS-MPPT-60, I have several times seen sustained output past 3,200W (hitting the 60A output current limit on the MPPT). Here's a photo of my system stats from May 29, 2017 @ 1:10 PM:
2017-05-29 13.10.03.jpg
(If I recall correctly here, there were a lot of big puffy clouds outside, and I was running an 1,800W water distillation unit...so when the sun peeked around the clouds, the batteries took all the available power.)

I've also seen similar this year (on March 10, 2019 @ 3:13 PM); note the new display on my system, but still the same Morningstar Tristar TS-MPPT-60:
IMG_20190310_151340181.jpg

That being said, I do agree that it is quite unlikely for panels to produce their nameplate power (much less MORE than the nameplate power)...but would like to float the idea that it IS posslble.

[SunEagle]

I agree that producing nameplate wattage is a possibility. What I am trying to indicate is that nameplate wattage is a value that was produced in a strict lab environment. That doesn't mean it can't produce the wattage in a normal environment but it is highly unlikely that it will.

I have also been in the electrical field for over 40 years and I can tell you that unless a measuring instrument is formally and yearly calibrated it can tend to provide false information. I am not saying your equipment is wrong but based on my experience a single measuring tool is not always 100% accurate all the time.

If your and the OP equipment is measuring properly then I will stand down but in the OP's case if the panels were generating what is being measured and the batteries are doing their job they would not be having the problem of having low battery voltage in the morning. Watts in does not always equal Watts out because of the accuracy % of the measuring tools. So I don't think the OP is losing the watt hours they calculate. I just think they are not generating as much as their equipment is measuring.

[Mike90250]

Exceeding nameplate power for short periods, or in bright winter / snow conditions is expected. Panels are rated at about 70F. warmer and you get less voltage, colder you get more.
Unusually bright sun reflecting off snow on a cold day and you can expect a lot more power out of panels. I see it myself several times a year.

620w of panels producing 662w of power is certainly possible and likely, but only under specific and unusual conditions.

[sdold]

If he's getting 4300Wh daily out of these panels, that's nearly seven hours at STC power. Is it really possible to have that much insolation anywhere?

Monogram:
1. How are you using the Kill-a-watt meter to measure your energy (Watt hours) produced? How are you connecting it?
2. Where are you located?
3. What is the panel orientation? Direction, Tilt degrees, etc.