Is this normal to only see 150 watts at most from a 270 watt panel? It is a lg solar panel i bought from solar blvd. I am in so cal and i face the panel towards the sun but the most i see is 150+- from on the kid. Amps on the kid show about 8-9+- amps and volts are around 28-30 volts on the kids display. I have 15 days to return this panel with no charge and only have 3 more days left. I have been testing this panel for 5 days now.
Hi mondo,
To get the maximum power from a PV module, it must be at right angles to the sun, and the sun must directly overhead, at perhaps about 12:30 PM, local time, and with no shadows or clouds.
Furthermore you will probably not see more than about 75% of the rated (STC) output -- on very warm/hot days, the power will be somewhat lower than 75% of STC. Plus, the power from the PV must have somewhere to go. There must be a load that meets or exceeds the capability of the PV to deliver power to that load, to see the maximum that the PV can do at that moment.
When you are measuring the PV output on the KID, is the KID trying to charge a battery? And what charge state is the KID indication on its display (ie, Bulk, Absorb, etc)?
FWIW, Vic
Quote from: mondo on October 14, 2014, 05:30:26 PM
Is this normal to only see 150 watts at most from a 270 watt panel? It is a lg solar panel i bought from solar blvd. I am in so cal and i face the panel towards the sun but the most i see is 150+- from on the kid. Amps on the kid show about 8-9+- amps and volts are around 28-30 volts on the kids display.
If you are seeing 28-30 volts at 8-9+ amps then that works out at 225 to 270+ watts from the solar panel.
dgd
I have a 80 amp marinehybrid battery which have a 12 volt dometic fridge and small clock connected to it. When i check the display it is usually in bulk mppt or absorb at about 14.5 volts on the battery. Overnight the battery would run down to about 12.3-4 volts at most and by about 10-11 it would be in absorb.
The settings are 14.6 120 minutes, 13.2 float, 16 equalize 60 minutes. I have not used equalize yet. The input is set on solar on. Would solar o&p be better for my small system?
Yes, the numbers works out to be over 220+ watts but i am confused because the kids display never exceeds 150 or so. I just worry it could be the module at fault.
Another thing. The panel is 24 volts and my battery bank is 12 volts. If that makes any difference, i would like to know.
As DGD says, you are getting pretty close to rated watts. Amps times Volts is Watts so 30X9 is 270 and 30X8 is 240 .
Tom
I guess i am a bit confused as why there is a discrepancy between the display and the math. So since the kid is displaying 150 and the calculations works out to be higher, then the excess wattage are just being dissipated away?
Quote from: mondo on October 14, 2014, 07:59:23 PM
I guess i am a bit confused as why there is a discrepancy between the display and the math. So since the kid is displaying 150 and the calculations works out to be higher, then the excess wattage are just being dissipated away?
ok, so the current you are seeing is probably the output current to the battery.
That 150 watts must be battery voltage times output current which is 10+ amps by 14.6 volts.
The reason you are not seeing more than 150watts is because the controller is limiting the output current in absorb stage.
It would be interesting to see these readings in BULK MPPT mode with bright solar conditions on a well aligned panel.
dgd
Also, mondo, if your KID Firmware is not 1742, you should probably Update the FW to 1742.
The later versions of FW have even better accuracy of voltage and possibly current readout.
Get the Firmware here:
http://www.midnitesolar.com/firmware.php?firmwareProduct_ID=4
FWIW, Vic
Quote from: mondo on October 14, 2014, 07:59:23 PM
I guess i am a bit confused as why there is a discrepancy between the display and the math. So since the kid is displaying 150 and the calculations works out to be higher, then the excess wattage are just being dissipated away?
dgd answered your question... The watts going into the battery is the battery amps times the battery voltage. You mistakenly multiplied the battery amps by the input voltage rather than the battery voltage.
dgd alluded to something else...I will elaborate:
When the battery is full (float) or near full (absorb), the battery will not accept all the current that your panels could produce. By the time the sun is high enough to produce full power in the panel, your battery is already charged up enough that it won't accept full power.
Try disconnecting the panel in the morning and then reconnect it at noon. With full noontime power available, and a discharged battery, you should see higher watts going into the battery. Of course, by noon the panels are hot, and that limits their full potential... when hot your panel should still produce 200 watts (if the battery will accept it)
If the battery will not accept all the power that the panel could potentially produce, the panel only produces enough power to charge the battery. The "excess wattage" is NOT being dissipated away. It's not being produced. The panel only produces power if there is somewhere for the power to go.
--vtMaps
I think i am understanding now but am still learning. I will have to do more experimenting with a depleted battery. As you can probably tell, all this is really still new to me. Thanks for helping me understand.
How would i check what firmware i have on the kid. I just bought it this month.
mondo,
When you first power-up the KID, the firmware version is displayed, while the LEDs are going through the scan pattern. FWIW, Vic
I am looking at the kid manual on page 30 which explains the status screens. It shows 9.5 amps with the battery voltage at 12.7 but the wattage is reading 257. If the watt reading on the status screen is supposed to be battery volts times current, then the watt should only read about 120 but instead it is showing 257. So what you are saying is in absorb stage is why the wattage is lower than it would be if it was in bulk stage. Tomorrow i will connect the kid to a worn out battery and see if the wattage raises. I dont have enough loads to draw my current battery below 12.35.
How would i check fw after the kid is already all setup? I cant remember what the firmware number was. Would i need to reset the kid? If so, what is the proper procedure?
Quote from: mondo on October 16, 2014, 03:13:26 AM
I am looking at the kid manual on page 30 which explains the status screens. It shows 9.5 amps with the battery voltage at 12.7 but the wattage is reading 257. If the watt reading on the status screen is supposed to be battery volts times current, then the watt should only read about 120 but instead it is showing 257.
Think of the Kid as a box that takes power in and lets power out. Of course the Kid is not 100% efficient, which means more power goes in than comes out.
The power (watts) going in is the PV voltage times the PV current (amps).
The power (watts) going out is Battery voltage times Battery current (amps).
In your question, the 9.5 amps is the PV current. You multiplied it by Battery voltage.
If you multiply battery voltage (12.7) times battery current (20.24 amps), you get 257 watts which is the power going into the battery.
--vtMaps
Eariler it was stated that the watt reading is what it is when you take the battery voltage x panel amps, both numbers on the display. Now we are taking battery voltage x 'battery current', a number not on the screen display at all. I can divide 257 by 12.7 and get 20.24 but 20.24 is not displayed so i am not sure that corresponds to the previous post about 150watts = 14.6volts x 10amps. If what you are saying is true, then in bulk mppt stage the battery current would rise higher which will display more watts on the display? So in bulk mode the watt calculation would be battery voltage x battery current, but in absorb stage the wattage is calculated by panel amps x battery voltage? I am just trying to get a clear understanding of what is displayed on the kids status screen and how those numbers are calculated.
Quote from: mondo on October 16, 2014, 12:11:35 PM
So in bulk mode the watt calculation would be battery voltage x battery current, but in absorb stage the wattage is calculated by panel amps x battery voltage?
The watts going into the battery is always battery voltage times battery current. period.
If the PV current happens to be the same as the battery current, then yes, the watts into the battery could be described as battery voltage times PV current. and by the way, in a PWM controller the PV current actually is the same as the battery current.
An MPPT controller can take high volts and low amps from the PV and make low volts and high amps for the battery. volts X amps in = volts X amps out (minus an efficiency loss).
--vtMaps
I have been testing out my kid for a few months now. The display calculations on my kid are always, battery voltage reading x amp reading = watts reading, all on the first display screen. Very different from the manuals example calculation of battery voltage reading x "battery current" (reading not shown) = watts reading. I understand how to calculate the numbers but i dont understand why my kid calculates watts = battery voltage x pv current. My kid has never shown watt numbers other than battery voltage x pv current, numbers all shown on the first display.
For instance, if my kid were to show, on the first display screen, 12.7 volts and 9.5 amps, then the watts reading would show 120w and not 257w like on the manual.
Something is not right with my kid.
Am i comparing apples to oranges here? Is the manuals example using 12 volt panels to a 12 volt battery? Would the calculations differ this much because i am using 24 volt panels to a 12 volt battery?
That is the only thing i can think of... Anyone out there have readings, from the first display screen, using 24 volt panels to a 12 volt battery bank, to share. Or maybe, 12 volt panels to a 12 volt battery bank first display screen readings. It would really help me wrap my head around this.
The watts display will be way off if you do not run PV minus to its terminal and battery minus to its terminal. The Kid is different from the Classic. You must have these conductors separated. I hope that is your only problem, otherwise contact tech support and they will be able to help you.
Quote from: Robin on January 18, 2015, 07:26:37 PM
The watts display will be way off if you do not run PV minus to its terminal and battery minus to its terminal. The Kid is different from the Classic. You must have these conductors separated. I hope that is your only problem, otherwise contact tech support and they will be able to help you.
Pv and battery negative wires run to their terminals on the kid. The pv negative wire is not joined with the battery negative wire.
The kid does not display PV current anywhere, the only current it display are Battery and Load,
the Current on the main Status Screen where it displays the Watts is Battery current and Output watts to the battery not the amount of watts coming in from the PV panel.
It Works like this: battery voltage displayed X Output Current to battery = Output watts to battery. I think you are confusing the currents.
gotta keep in mind that to keep the same amount of watts (minus efficiency) when you are bringing higher voltage down to a lower voltage the PV current will be lower and the battery voltage will be higher.
For example:
- 120v PV and 1 amp = 120W (into the kid.)
- 12v Battery 10 amps = 120W this is assuming no losses and 100% conversion efficiency.
You cannot take 120v and 10A = 1,200W. Not correct.
Right now in winter if you have a 250W panel you will see less power out because the panels are rated in perfect conditions and perfect sunlight to panel angle.
Please let me know if you have any more questions,
Mario Rodriguez
PV modules are rated at whats called STC (standard test conditions) of 1000 watts per meter squared. Now in the real world we are around 750-800 Watts per meter squared.
What this means is we can assume 75-80% of what the panel is rated for IF we have it perfectly angled and it is solar noon and the sky is crystal blue.
So a 250 watt module I would expect to see around 200 watts if all is perfect.
Ryan
PV panels at higher elevations can produce more power than STC. Can be more than perfect? ;D Less air = a boost in solar radiation hitting the PV cells. Our system at 8800 feet regularly produces more than the panels 624 watt STC rating. Bright sun, clear pollution free sky, low humidity, cool weather. There's gotta be benefits to counter all the losses; engine power down, cooling system less effective, reduced output from furnace, etc.
altitude effects link (http://www.egia.org/Academy/rockymountainexchange2011/docs/CharlesBicknell.pdf) PV specific on page 18-20
Quote from: Mario on January 22, 2015, 04:27:54 PM
The kid does not display PV current anywhere, the only current it display are Battery and Load,
It would be useful if the input current could be displayed.
I always assumed the KID probably used an internal shunt in the negative input hence the requirement not to common connect the input and output negatives.
This would provide a reasonably accurate input current measurement.
Or am I incorrect and there is only a shunt in the negative output line?
Or am I completely wrong and the shunt(s) are in the positive line(s)?
Dgd
Mario,
Can you add a PV input voltage and amperage screen to the scroll? I know the PV voltage is there, but I would also like to see the input amperage if possible.
Also, I think the wattage number includes the wattage to the batteries and to a load if used, your thoughts. ( I am using PM divert and believe the wattage includes the wattage going to the batteries and the heater)
If i am confusing the currents it is because i am following the manual. If i am wrong the manual is wrong. Forum member vt said the current displayed is pv current, so i checked andnit does say its pv current. The example in the manual makes no sense at all and is very misleading. One would think 257 watts from 12.7 x 9.5 from a controller is too good to be true, which it is. My numbers never matched the manuals numbers and it confused me from the start. It took many attempts asking on this forum, phone calls, and emails to tech support to finally be told, the manual is wrong. I am very disappointed it took this long.
I am also disappointed my last email was totally ignored by tech support.
Hi Mondo,
The Kid manual is currently being updated. If any part is confusing to anyone I would like to know about it.
I will be checking into this and seeing what can be done to make it totally clear.
Doug