What Max PV Output do you get? and temperature.

Gazz
Gazz Solar Expert Posts: 38
As we are supposed to be in summer in the UK my output is climbing. What I have been noticing is the effect of heat on my panels. They are 12 Sanyo HIT240 = 2880 kW. The other sunny hot day I got a nice smooth output all day, with 2.35kW for about 4 hrs around midday. I have tried to calculate what output I should be getting factoring temperature and other loses. Whether or not I have got this exactly right I understand that I could lose about 6% for temp and about 14% for cables and inverter loses this would give me close to what I am getting.

This is all OK and as the sun moves around my calculation seems to work and if it is a bit cooler that also works. My problem is when the day is not so clear and the sunny spells are shorter I am getting outputs of up to 3.1kW which normal settles down to about 2.8kW. I understand the panels will be cooler but how can it account for such a difference.

In summary a full sunny day I get a nice curve which peaks at 3.35kW but on a mixed day it seems to peak around 2.8kW, is this just all temperature?

Thanks
Gary

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: What Max PV Output do you get? and temperature.

    Gary;

    Trying to predict panel output to 100% accuracy is like trying to predict the lottery numbers. Good luck with either.
    Temperature plays a big part, but so does sun angle and atmospheric conditions. There's this wonderful little surprise called an "edge of cloud event" for instance that will send panel output soaring. Basically its when the moisture in the edge of a passing cloud acts like a lens and concentrates more light on the panels rather than blocking it. Greater than 100% STC is entirely possible under such conditions. The ambient temperature is likely to be cooler when such events occur, adding to the glory.

    Sounds like your Sanyo's are outperforming expectations. Be happy! :D
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: What Max PV Output do you get? and temperature.

    Have you measured the temperatures of the solar panels themselves yet? I would have guessed more losses due to temperature and less for inverter/wiring losses (assuming you have around a ~3kW GT

    85% is about maximum on a "great/cool" day for me (near San Francisco CA--not too hot, not too cold). Otherwise, average around 77% peak (average day, have not washed panels, etc.).

    I would not expect 100% or more of rated power unless is it sub freezing and/or you have snow/sand/etc. for reflected energy.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Gazz
    Gazz Solar Expert Posts: 38
    Re: What Max PV Output do you get? and temperature.

    Thanks, I have read about the edge effect but did not know how long the effect would last.

    I would still be interested is knowing what max sustained outputs people get compared to there rated system size, I do not know anybody else with a system to compare mine to.
  • Gazz
    Gazz Solar Expert Posts: 38
    Re: What Max PV Output do you get? and temperature.
    BB. wrote: »
    Have you measured the temperatures of the solar panels themselves yet? I would have guessed more losses due to temperature and less for inverter/wiring losses (assuming you have around a ~3kW GT

    85% is about maximum on a "great/cool" day for me (near San Francisco CA--not too hot, not too cold). Otherwise, average around 77% peak (average day, have not washed panels, etc.).

    I would not expect 100% or more of rated power unless is it sub freezing and/or you have snow/sand/etc. for reflected energy.

    -Bill

    Bill, the more I learn the more I find it hard to understand achieving sustained 2.8-2.9kw on a system that is rated at 2.88kW. It is being measured on a sunny beam from a sunny boy SB3000 inverter. The sunny beam gives a daily total which matches my meter. I am not complaing just curious. I was told Sanyo panels were good and I paid a premium for having them as compared to a cheap panel. In the UK it is still relativly new so I have nothing to compare to.
    Gary
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: What Max PV Output do you get? and temperature.

    The Sanyo panels are very good (they are my installer's favorite--Last I talked to him, he has never had a return--Cannot say that for some other vendors).

    Solar Panels have a "standard test condition"--Which is a panel at room temperature that is hit with a very bright "sun lamp" for a few tens of seconds to test its output before shipping.

    While it is a very valid/accurate test for in a lap--It does not represent "field conditions"... Basically warm weather, frequently installed on a warm roof with not to much ventilation (panels installed with less than ~5-6" from panel rear to roof. Also, of that 1,000 watts per square meter of energy from the sun, much of that goes into heating the dark colored solar array itself. Raising the temperature of the cells upwards of 35C (~63F rise).

    Use and average of -0.38% power loss per oC rise and ~25C room temperature (for STC), a typical derating could easily be (assuming worse case temperature rise, panels mounted near roof, no wind, noon time sun):
    • 1 - Power Derating per oC * ( ambient temperature + rise above ambient - STC rating temperature) = Temperature Derating factor for solar array
    • 1 - 0.0038 * (35C roof temp + 35C rise - 25C STC) = 0.791 of Rated output at 35C roof temp
    • 1 - 0.0038 * (25C roof temp + 35C rise - 25C STC) = 0.867 of Rated output at 25C roof temp

    So, right off the start, you could be looking at ~13% to 20% of fall of in solar panel production just due to temperature rise in the summer.

    You panels/system may do better--Just some basic numbers and plug in equations (with your numbers) you can use to estimate your output.

    "Edge of Cloud" events are only going to last seconds to a few minutes at time (typically).

    If you have an IR Thermometer and access to the panels, you can take a quick temperature measurement and see what your actual ambient+rise temperature is for your installation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: What Max PV Output do you get? and temperature.

    My panels run consistently higher averaged output than most because of the elevation. Normal for me is 80-84%, depending on the time of year. Just two weeks ago they hit a record 89% efficiency, and that was no cloud event. The typical panel+controller or GT MPPT efficiency is 77%, but many do better.

    Note that your HIT panels have an efficiency rating of 19%, which makes them the best of the bunch. Usually monocrystalines are 1% less than that and polycrystaline 2% below that. Furthermore the data sheet says the output tolerance is up to +10%! That would make your "240 Watt" panels potentially 264 Watts, or a 3.1kW array.

    Hmm. Where did we just see that number before in this thread? :D
  • Gazz
    Gazz Solar Expert Posts: 38
    Re: What Max PV Output do you get? and temperature.
    My panels run consistently higher averaged output than most because of the elevation. Normal for me is 80-84%, depending on the time of year. Just two weeks ago they hit a record 89% efficiency, and that was no cloud event. The typical panel+controller or GT MPPT efficiency is 77%, but many do better.

    Note that your HIT panels have an efficiency rating of 19%, which makes them the best of the bunch. Usually monocrystalines are 1% less than that and polycrystaline 2% below that. Furthermore the data sheet says the output tolerance is up to +10%! That would make your "240 Watt" panels potentially 264 Watts, or a 3.1kW array.

    Hmm. Where did we just see that number before in this thread? :D

    Can you clarify what you mean by "normal for me is 80-84%" is that a days output or are you talking about instantaneous output.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: What Max PV Output do you get? and temperature.
    Gazz wrote: »
    Can you clarify what you mean by "normal for me is 80-84%" is that a days output or are you talking about instantaneous output.

    Averaged full-sun output. In other words over the course of the day the output is 80 to 84 percent of the STC panel rating. At any given moment it will vary by the sun angle, ambient temperature, battery & load demands.
    I'm off grid so the system works a bit differently than GT.
  • Gazz
    Gazz Solar Expert Posts: 38
    Re: What Max PV Output do you get? and temperature.

    Sorry for being stupid but how do you arrive at an STC for any given day. I have found web sites that calculate yearly and monthly outputs averages but how do you arrive at the maximum output for a given day. The best I have achieved in one day is 19kw/h but I have no idear what would be considered a maximum to work out my %.
    Gary
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: What Max PV Output do you get? and temperature.

    My panels are only running at about 71 -73% this time of year due to temperature and angle of incidence. Ambient temps now are over 100F midday and I just measured the panel back side temps with an IR gun at 130F, I suspect the face temps are even higher. In the Spring time my 12.5 array will max peak my pair of 5200 watt inverters at 10.4 KW as will cloud edge events that is 83+%. I have seen in April/May on a particularly cold day( under 70F at noon) when the panel angle is pretty optimal a flat line @ 10.4KW at solar noon, not for long but is surely there. Well designed system I would say.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: What Max PV Output do you get? and temperature.

    STC is Standard Test Conditions; the "nameplate" rating of the panels. In your case 240 Watts.

    What we'd "normally" expect to see from your array would be: 2880 Watts @ 'X' efficiency * hours of equivalent good sun = Watt hours produced per day. This "daily harvest" is what matters most, rather than peaks at any point during the day. It's also why panel angle is not quite as simple as some would have it, because the "ideal" angle at solar noon is not the best angle for total Watt hours through the course of the day.

    So with yours the prediction might be: 2880 Watts @ 77% = 2217 * 4 hours minimum = 8870 DC Watt hours. (Factor inverter efficiency to get the AC Watt hours, usually about 10% less).

    Your 19 kW hours per day looks like you have a lot of sun hours. At 6 "equivalent" that would be the 3.1 kW array number popping up again (19,000 / 6 = 3166).

    That's why we use the conservative factors; so people aren't disappointed. Much. :p
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: What Max PV Output do you get? and temperature.

    PV Watts has some listing for Great Brittan. Using Finningley (find place nearby that has similar weather--Could not find any better place that was not on coast) for 2.88 kW array, fixed mount, and 0.77 derating:
    "Station Identification"
    "City:","Finningley"
    "State:","GBR"
    "Lat (deg N):", 53.48
    "Long (deg W):", 1.00
    "Elev (m): ", 17
    "Weather Data:","IWEC"

    "PV System Specifications"
    "DC Rating:"," 2.9 kW"
    "DC to AC Derate Factor:"," 0.770"
    "AC Rating:"," 2.2 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 53.5"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 0.1 pound/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (pound)"
    1, 1.19, 74, 0.06
    2, 1.83, 107, 0.08
    3, 2.64, 173, 0.13
    4, 3.66, 234, 0.18
    5, 4.23, 271, 0.20
    6, 4.41, 269, 0.20
    7, 4.48, 279, 0.21
    8, 4.14, 263, 0.20
    9, 3.15, 195, 0.15
    10, 1.78, 109, 0.08
    11, 1.26, 72, 0.05
    12, 0.94, 57, 0.04
    "Year", 2.81, 2103, 1.58

    Not a lot of sun... Anyway, there is also an hourly output page which looks like this (for a "typical day"):
    1995, 6, 11, 05:00, 0
    1995, 6, 11, 06:00, 1
    1995, 6, 11, 07:00, 17
    1995, 6, 11, 08:00, 115
    1995, 6, 11, 09:00, 298
    1995, 6, 11, 10:00, 371
    1995, 6, 11, 11:00, 427
    1995, 6, 11, 12:00, 910
    1995, 6, 11, 13:00, 842
    1995, 6, 11, 14:00, 789
    1995, 6, 11, 15:00, 735
    1995, 6, 11, 16:00, 308
    1995, 6, 11, 17:00, 135
    1995, 6, 11, 18:00, 22
    1995, 6, 11, 19:00, 9
    1995, 6, 11, 20:00, 0

    Here is another PV calculator, European based, that may work better for you (note, its input and output is much different vs PV Watts--So you will need to read the instructions carefully to ensure you get a "valid" output for your system):

    PVGIS--European/African Solar Power Calculator Program

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Gazz
    Gazz Solar Expert Posts: 38
    Re: What Max PV Output do you get? and temperature.
    STC is Standard Test Conditions; the "nameplate" rating of the panels. In your case 240 Watts.

    What we'd "normally" expect to see from your array would be: 2880 Watts @ 'X' efficiency * hours of equivalent good sun = Watt hours produced per day. This "daily harvest" is what matters most, rather than peaks at any point during the day. It's also why panel angle is not quite as simple as some would have it, because the "ideal" angle at solar noon is not the best angle for total Watt hours through the course of the day.

    So with yours the prediction might be: 2880 Watts @ 77% = 2217 * 4 hours minimum = 8870 DC Watt hours. (Factor inverter efficiency to get the AC Watt hours, usually about 10% less).

    Your 19 kW hours per day looks like you have a lot of sun hours. At 6 "equivalent" that would be the 3.1 kW array number popping up again (19,000 / 6 = 3166).

    That's why we use the conservative factors; so people aren't disappointed. Much. :p


    I have attached a picture of a days output, it was a very good day and not hot, but as you can see the output was close to 2.9kw for over an hour. So was I getting 100% STC during that time.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: What Max PV Output do you get? and temperature.

    I don't know about your inverter specifically, but many solar devices will tend to over estimate output by 5% and sometimes even 10% (precision costs money). There are a few out there that are accurate to within 2%, but it is not common.

    Also, even good quality Mono-crystalline panels can lose upwards of 3% of their output power in the first year of operation (sunlight is tough on stuff).

    Anyway, 18.7 kWH per day--That is a pretty good average output for my 3.5 kW GT system here in "sunny" California--Colour me impressed (I can get a bit over 20 kWH on a nice spring day).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: What Max PV Output do you get? and temperature.

    I'm impressed too.

    I guess you could say those Sanyo panels are a "HIT" around here. :p
  • Gazz
    Gazz Solar Expert Posts: 38
    Re: What Max PV Output do you get? and temperature.

    Thanks for all your help, it seems as if what I have is doing a good job, problem is in, not so sunny UK we don't sem to have a good run of great days, so most good days are offset with some bad ones. Suppose the one advantage which is how I got the 19kwh is that we do get some sunny days but at a cool temperature. But what I have learnt is that temperature does make great difference.

    As regards to accuracy its quite accurate as we have a calibrated meter so we can claim the government payment on what is generated and it matches the inverter reading virtually dead on.

    Gary