Peak Power on a perfect day

nepalmnepalm Registered Users Posts: 5
I recently installed a 7.56 kw system in Colorado consisting of 36 REC210s and an SMA7000. I've been monitoring my system for the past week and have peaked out around 6500 w on any given day.

Taking time of year, solar radiation, tilt etc into consideration, should this system ever hit 7560 w at one point of the day.

thanks.

Comments

  • audredgeraudredger Solar Expert Posts: 272 ✭✭
    Re: Peak Power on a perfect day

    That depends, some installers compute wire size for up to 3% loss between panels & inverter, the max efficency of the inverter is listed as 97.1%. So, 7560 * .97 = 7333.2 watts * .971 = 7120 watts. March is not the best month to look for max output... sun is still to low, cooler temps help. if you refegerate the panels to say 40degrees in june you may get 7560..

    Note: the California solar website rates the REC210AE-US 210W as having a output of 182.7 watts. If they are correct then you have a 6577 watt aray.

    6500 watts from a 6577 array ain't bad!
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Peak Power on a perfect day

    as to can it ever hit 7.56kw, yes it can under the right circumstances and would most likely be short lived and rare.
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Peak Power on a perfect day

    6500W is pretty good for February.

    What's your orientation?

    I bet you will get over 7560W on some sunny but not too hot day.
  • Ralph DayRalph Day Solar Expert Posts: 975 ✭✭✭✭
    Re: Peak Power on a perfect day

    My Mx60 showed a peak of 2945watts today, total of 2100 watts of panels. Then things warmed up and it only chugged along (quietly) at 2-2.1kw.

    Ralph
  • Solar GuppySolar Guppy Solar Expert Posts: 1,987 ✭✭✭
    Re: Peak Power on a perfect day

    MX60 watts display = Make believe watts , usually 5-10% above actual, I've tested over 6 different units over the years, they all error on the optimistic side. Every single time I see a post about so magic array harvest values, its always an Outback charger that is what reported the values. Does make for some very happy customers though:roll:
  • boBboB Solar Expert Posts: 1,007 ✭✭✭✭
    Re: Peak Power on a perfect day
    MX60 watts display = Make believe watts , usually 5-10% above actual, I've tested over 6 different units over the years, they all error on the optimistic side. Every single time I see a post about so magic array harvest values, its always an Outback charger that is what reported the values. Does make for some very happy customers though:roll:

    He was seeing more like 40% above nameplate rating. That's quite a bit higher than even 5 to 10 %, so, unless his unit was reading extra special high, that he was most likely seeing a real, higher than typical power level. It can happen, although kind of rare to be that high. OR, maybe OB cal habits or methods have changed ?

    BTW, Henry, does your Yokogawa use an external shunt ? Or the internal one ?
    (used for all the reference tests I imagine) Hopefully it is the internal one since a test instrument is only as good as the references used.

    boB
  • RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: Peak Power on a perfect day

    I have a Flex Max 80 here and its also reading over actual panel input and actual output to battery.

    If only MorningStar had a 80A MPPT Controller.
  • Ralph DayRalph Day Solar Expert Posts: 975 ✭✭✭✭
    Re: Peak Power on a perfect day

    I notice those peaks all the time, typically on edge of cloud events. Yesterday was just after genset shutdown, the pv had not been contributing but a few hundred watts. On shutdown with panels cold -5C or so, they ramped right up (to whatever actual watts) then as they warmed up they ramped down to the usual working level.

    Can't get excited about the peaks, but they're fun to see now and then.

    Ralph
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Peak Power on a perfect day
    RWB wrote: »
    I have a Flex Max 80 here and its also reading over actual panel input and actual output to battery.

    If only MorningStar had a 80A MPPT Controller.

    i would think the outback meters could be recalibrated somehow. even if you could do it you need something to calibrate against or you would be guessing. why not ask outback to resolve the accuracy of the meter?
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: Peak Power on a perfect day
    MX60 watts display = Make believe watts , usually 5-10% above actual, I've tested over 6 different units over the years, they all error on the optimistic side. Every single time I see a post about so magic array harvest values, its always an Outback charger that is what reported the values. Does make for some very happy customers though:roll:

    Hey, I have a pair of CTs around an SMA inverter and I'm seeing the same kind of Make Believe Watts. I'm starting to think "+/- x %" is mostly "+" and not so much on "-".
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: Peak Power on a perfect day
    niel wrote: »
    i would think the outback meters could be recalibrated somehow. even if you could do it you need something to calibrate against or you would be guessing. why not ask outback to resolve the accuracy of the meter?

    The half-dozen or so OutBacks I see on a regular basis where the charge controller output passes through its own shunts on an FN-DC are within 20 or 30 watts. During some recent high output days here I was seeing that same 20 or 30 watts that I've seen on lower output days, which tells me that they are reporting power before whatever the charge controller is consuming.

    And before anyone questions the FN-DC, I routinely calibrate FN-DCs with a Fluke 289 (which is not a cheap Chinese DMM) and I've yet to find one that isn't within +/- 0.1 amp under load.
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: Peak Power on a perfect day
    RWB wrote: »
    I have a Flex Max 80 here and its also reading over actual panel input and actual output to battery.

    If only MorningStar had a 80A MPPT Controller.

    We're closer to the Sun right now than in the Summer. The day of closest approach is around January 3rd. The difference is 6% more solar radiation to the ground compared to the low which happens in July or so. After I corrected my software for orbital geometry the 10 to 15 percent over nameplate values I'd been seeing dropped by a couple of percentage points.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Peak Power on a perfect day

    All the more reason for a god battery monitor to see just what is going in to the battery ( and out at night)

    EJ
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • boBboB Solar Expert Posts: 1,007 ✭✭✭✭
    Re: Peak Power on a perfect day
    RWB wrote: »
    I have a Flex Max 80 here and its also reading over actual panel input and actual output to battery.

    If only MorningStar had a 80A MPPT Controller.

    The input current reading of the MX/MF will read especially high because it is a calculated number from the output current and voltage and input voltage.
    The problem is that it does not take converter efficiency into account, which ~could~ be done but is not easy to do well.

    In fact, measuring DC current accurately is quite a feat in itself. The Fluke meter is pretty good as is the Yokogawa power meters and some other well calibrated lab meters and methods.
    You gotta be real careful how it is done to get good numbers.

    boB
  • RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: Peak Power on a perfect day
    tallgirl wrote: »
    We're closer to the Sun right now than in the Summer. The day of closest approach is around January 3rd. The difference is 6% more solar radiation to the ground compared to the low which happens in July or so. After I corrected my software for orbital geometry the 10 to 15 percent over nameplate values I'd been seeing dropped by a couple of percentage points.

    Ok so to make sure I get what your saying right let me confirm this with you:

    January 3rd is the Earth is Closest to the Sun and this generates 6% more Solar Radiation to the ground/solar panels which can be turned into electricity.

    So your saying that its not fair to compare your panels output on January 3rd to its output in July because the panel is actually getting 6% Less Solar Radiation in July than in January. You have to factor in the 6% Radiation Increase when your comparing the 2 different readings. Interesting indeed.

    One question I have is this: Assuming that the panel is fixed at the correct tilt for its location and the sun is at 1000wm, what time of year would give you max solar radiation that PV's are looking for? What time of year should you see max wattage output assuming the temp was always 70F.

    I think I'm asking that right. Maybe its more complicated than that.

    tallgirl - The half-dozen or so OutBacks I see on a regular basis where the charge controller output passes through its own shunts on an FN-DC are within 20 or 30 watts. During some recent high output days here I was seeing that same 20 or 30 watts that I've seen on lower output days, which tells me that they are reporting power before whatever the charge controller is consuming.

    And before anyone questions the FN-DC, I routinely calibrate FN-DCs with a Fluke 289 (which is not a cheap Chinese DMM) and I've yet to find one that isn't within +/- 0.1 amp under load.

    I have seen up to 1Amp difference between the FM out to battery reading vs what the WattsUp meter was actually reading being put out the battery. Sometimes the output and actual output was very close and alot of times it was off by .2-.5 amps, which bothers me for the simple fact that I can not rely on the actual readings of the FM80 for daily solar totals or current Watt Hour Totals.

    So TallGirl you think its just because the reading does not take into account for the losses created during the DC to DC Conversion Process of the MPPT? If that's the case then its good to know what is actually going on with the machine.

    Does Morning Star have the same issue with their new MPPT 45 and 60? If not why can't Outback do this on this Flex Max series? Its one of the only complaints with the device so far. The voltage reading during Night time is the 2nd complaint I have with it.
    Bob - The input current reading of the MX/MF will read especially high because it is a calculated number from the output current and voltage and input voltage.
    The problem is that it does not take converter efficiency into account, which ~could~ be done but is not easy to do well.

    So you know for a fact that this is what is going on Bob? if so then Thanks for explaining exactly why this happens. Basicaly its doing a math problem and displaying the answer vs reading actual DC output via a Shunt?
  • boBboB Solar Expert Posts: 1,007 ✭✭✭✭
    Re: Peak Power on a perfect day
    RWB wrote: »

    So you know for a fact that this is what is going on Bob? if so then Thanks for explaining exactly why this happens. Basicaly its doing a math problem and displaying the answer vs reading actual DC output via a Shunt?

    Yes, and the only reason I know is that it was originally my fault. :blush:
    Live and learn.

    boB
  • a0128958a0128958 Solar Expert Posts: 316 ✭✭✭
    Re: Peak Power on a perfect day
    tallgirl wrote: »
    We're closer to the Sun right now than in the Summer. The day of closest approach is around January 3rd. The difference is 6% more solar radiation to the ground compared to the low which happens in July or so. ...

    As RWB said later, this is interesting and helpful to know. I didn't know this either. Thank you.

    What I've learned is that insolation for a cloudless day is not just a function of the number of sunlight hours for a given day; it's also a function of a 2nd variable, that is how far away the sun is to the earth.

    Looks to me that the only way (in the field) to affirm solar panel harvest for a given day is to first know an accurate insolation number for the day. And that this will require an accurate solar radiation meter with ability to integrate the readings into an insolation number.

    Many thanks.

    Best regards,

    Bill
  • RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: Peak Power on a perfect day

    Yea my partner just picked up a insolation meter today and it was reading 960 W per square meter today in Atlanta.

    The meter is here http://daystarpv.com/solarmeter.html

    So I guess with the meter you can figure out the correct angle for the panel if your doing a non fixed portable setup and you know how much insolation is available for your panels at any given time.

    Were looking to test all our fold able panels this way all summer.

    Is there any advice anybody has on this subject?
  • mike95490mike95490 Solar Expert Posts: 9,571 ✭✭✭✭✭
    Re: Peak Power on a perfect day

    PV watts is the best overall "setter upper" - you can play with angles all day, and only waste a few sheets of paper !

    For portable panels, I set mine to minimize the shadow it casts. that ALWAYS places it perpendicular to the sun (for 10 minutes) so I'll pre-aim it, and get a couple hours of non-attended, near peak power.
    http://www.mike-burgess.org/images/Mono_2005_CS_056.JPG

    No meter needed.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: Peak Power on a perfect day

    Yea the meter is just to test the efficiency of the panels vs the actual available power from the sun.

    The meter is the only way we know what the panels have to work with as far as actual insolation goes.
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Peak Power on a perfect day

    Actually, setting a DVM to 10 Amp full scale and connecting to a spare panel is also a good way of measuring the sun too. Output current is very porporational to sunlight intensity.

    In fact, that is what the simple solar power meters do anyway.

    Here is a simple build it yourself solar power measurement meter:

    Micro Circuits Labs do-it-yourself solar irradiance meter

    He also sells data loggers and kits to build your own data logger:

    Micro Circuits Labs

    And he has a nice section on how solar panels/power works:

    Solar Power Basics

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • a0128958a0128958 Solar Expert Posts: 316 ✭✭✭
    Re: Peak Power on a perfect day

    And here's an online calculator that computes peak solar irradiation on a cloudless day, given lattitude, longitude, elevation, day of year, air temperature and RH:

    http://clearskycalculator.com/pyranometer.htm

    Best regards,

    Bill
  • RWBRWB Solar Expert Posts: 168 ✭✭✭✭✭
    Re: Peak Power on a perfect day

    Thanks for the awesome links guys!

    I'm digging the affordable meters............

    I'm learning something new everyday LOL
Sign In or Register to comment.