Solar Panels at 45.0° North

JoshKJoshK Solar Expert Posts: 232 ✭✭
So if I install at a latitude of 45.0° in eastern South Dakota, what kind of power can I expect on a clear day from a panel rated at 250 watts during my Summer? And Winter? I'm sure the factory watt rating is based on Florida or the equator. Never-mind system efficiencies, I'm just curious about the panel itself today. Thanks for any help.
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Comments

  • VicVic Solar Expert Posts: 3,113 ✭✭✭✭
    Hi JoshK,

    Have you looked at the NREL's PV Watts Calculator?

    You can enter your location data and see the results:

    http://pvwatts.nrel.gov/

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    Thanks, I learned Winter is about 1/2 of summer. But I can't figure out what to expect for DC watts.
  • PhotowhitPhotowhit Solar Expert Posts: 5,658 ✭✭✭✭✭
    JoshK wrote: »
    So if I install at a latitude of 45.0° in eastern South Dakota, what kind of power can I expect on a clear day from a panel rated at 250 watts during my Summer? And Winter? I'm sure the factory watt rating is based on Florida or the equator. Never-mind system efficiencies, I'm just curious about the panel itself today. Thanks for any help.

    There is a lot to that simple question, Going to the site Vic posted will help, They have an input for this, but they only do grid tied connections, will this be grid tied or off grid?

    Some basic starting points. The factory numbers are based on a 'flash test with a set value/strength of light. In the real world panels typically produce less when they get hot. Most manufacturers include a NOCT value (Normal Operating Cell Temperature) This tends to run about 70-75% of the panels label rating. You can find solar isolation charts for your area that will give you the average number of sunny hours per day during each month. between the 2 you can get some idea of how much solar energy your panels will produce. Grid tied system may pass onto the grid @95% of this off grid you must have your system large enough to assure that your batteries get fully charge at least once a week and don't fall below 50% of capacity. typically an array 3 - 4x a grid tied array is required to produce and use the same amount of energy as a grid connected system.

    Typically a fixed array should be angled within 10-15 degrees of your latitude and face south for optimum year round production. Northern installations often choose to vary the angle once or twice a year, to adjust for seasonal variance of the sun angle. some choosing to have a vertical or near vertical angle during low angle winter months to help with shedding snow.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    This would be a DC load, so no inverter at all. I have found the best angle during summer is 70° and in the winter 22°. So you're saying that when they rated it at 250watts it was not tested at NOCT? That seems a bit odd.
  • VicVic Solar Expert Posts: 3,113 ✭✭✭✭
    Vic wrote: »
    Hi JoshK,

    Have you looked at the NREL's PV Watts Calculator?

    You can enter your location data and see the results:

    http://pvwatts.nrel.gov/

    Good Luck, Vic

    If you actually use the link above, and enter your location data, you can find the result for different PV module elevation angles for a place that is very near the exact location that you are interested in. FWIW, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • PhotowhitPhotowhit Solar Expert Posts: 5,658 ✭✭✭✭✭
    JoshK wrote: »
    This would be a DC load, so no inverter at all. I have found the best angle during summer is 70° and in the winter 22°. So you're saying that when they rated it at 250watts it was not tested at NOCT? That seems a bit odd.

    Well they are all tested at a standard, and they vary in the NOCT values, look yours up, or if you don't have any yet look for the PDF spec sheet. What is normal? Higher elevations will have higher values as well, colder sunny days produce the best. hot not as well... For what it's worth there is also a set of values for NOCT values... The panel rating values I think are called STC - Standard Test Conditions. I think, I've seen these values getting farther apart. I think some of that is high transmission coating put on the glass, which in theory should help light passing through, but also help the cells heat up...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    Photowhit wrote: »
    don't have any yet
    I actually don't have any picked out. I need an idea of how my location affects the specs. Does 250w mean I can expect 249w, or just 120w... I don't need a perfect answer, an educated guess is good.
    Vic wrote: »
    If you actually use the link above
    I actually did right away when you posted it. I am very good at clicking. It's one of my specialties. This question is about DC without inverters though.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    As a rule of thumb you will get ~ 73% of STC out of the panels and for a complete off-grid system you can use 50% of name plate STC to what you will use in a light bulb or whatever is plugged in to the inverter output ( 120V AC).. don't get too hooked on these numbers as they will vary across the year and these are yr long averages, some days are great8), others not so:cry:... plan your system and use the averages .....:D

    Oh, unless you want to do what most of us did to start, go right to using an inverter DC is much more expensive, if the building is more than a 1 room cabin, and fixtures etc are harder to locate etc... a few DC light are workable but the distance from the source starts to have larger line losses ...
     
    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
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    Thanks for the replies, I have learned from them. But I would like to re-word the question as a hypothetical.

    "I just bought a new solar panel that said 250 watts. So why do I only get XXX watts when I test it? All conditions are ideal except that I live 45 degrees north of the equator. Maybe the extra attenuation of the light by the atmosphere is the cause."

    Now if the XXX answer is 220 watts then I can say my max watts are about 220 in the summer and 110 in the winter.
    Let's say the load is a 12v home-made weather-station like contraption.
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    A solar panel's main (useful) rating is Vmp and Imp.

    Vmp--Voltage Maximum Power -- The specification is at ~25C. As panels get hot, Vmp falls
    Imp--Current Maximum Power -- The typical full sun (noon time, clear day) amount of current from the solar panel

    In reality, things vary. Obviously, angle of sun, weather, and even air temperature all affect the performance of a solar panel.

    In full sun noon time sun on a clear/sunny day, a solar panel can output near Imp... Add a few clouds, 50% of current or less is common.

    So--What we talk about for off grid solar power systems with a battery bank to store daytime energy for night/poor weather use is talk about "hours of sun" per day... This is basically, if you took the motion of the sun across the sky, added "typical weather conditions" and made it "noon time equivalent sun (~1,000 Watts per square meter)--That is the "hours of sun per day".

    So, if you have a 250 Watt panel and the appropriate charge controller (PWM/MPPT) and Battery Bank (voltage), you would see something like:
    • 250 Watts * 0.61 DC system efficiency * 2 hours per day of sun = 305 Watt*Hours per day (average deep winter sun)
    • 250 Watts * 0.61 DC system efficiency * 4 hours per day of sun = 610 WH per day (typical South West US minimum average sun ~9 months a year)
    • 250 Watts * 0.61 DC system efficiency * 6 hours per day of sun = 915 WH per day (typical very sunny summer location)
    Take the Watt*Hours of energy and divide by battery bank voltage:
    • 610 WH per day / 12 volt battery bank = ~ 50.8 Amp*Hours of "useful" energy
    If you don't want a battery bank, but want to power "something" (water pump, radio, etc.) directly--Then you need to look deeper into the needs of the load and how best to power that with a solar array.

    I am not quite sure where your question is going--So, please ask more questions. It can be a very complex subject and generic answers may be more confusing than helpful.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,658 ✭✭✭✭✭
    JoshK wrote: »
    Thanks for the replies, I have learned from them. But I would like to re-word the question as a hypothetical.

    "I just bought a new solar panel that said 250 watts. So why do I only get XXX watts when I test it? All conditions are ideal except that I live 45 degrees north of the equator. Maybe the extra attenuation of the light by the atmosphere is the cause."

    Now if the XXX answer is 220 watts then I can say my max watts are about 220 in the summer and 110 in the winter.
    Let's say the load is a 12v home-made weather-station like contraption.

    No you have conflicting information in your question, Idea conditions would include atmospheric conditions being very cold, Panels in direct 90 degrees angle to the incoming sun. If cold enough the panels will produce more than the panel name plate. In general they will produce more energy per hour of direct exposure in the winter than in the summer.

    Winter just has shorter hours of sunlight, in the northern hemisphere.

    Yes the 'extra' atmosphere it passes through will reduce the in coming light a bit, but heat has a large impact on the numbers as well.

    If you are looking for black and white, connect to the grid.

    Do you plan on this being a sunny day use only? Storing the energy in batteries for use has a large effect on the amount of energy needed for the system to work.

    Other wise you will have other issues, a 12 volt system? Solar panels are designed for charging voltage for a 12 or 24 volt system, which is @18 and 36 volts. or grid tied panels which range from 26-30 volts in general. So you will have losses in many areas here. not storing the energy, and you'll loose some wattage to the higher voltage, or in conversion. If storing energy there will be other losses...

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • scrubjaysnestscrubjaysnest Solar Expert Posts: 175 ✭✭✭
    JoshK wrote: »
    Thanks, I learned Winter is about 1/2 of summer. But I can't figure out what to expect for DC watts.

    As others have stated there are a lot of variables that affect the panels output. Another big one is state of charge, soc, of the battery. Since a battery at 50% soc will take a higher current then one say at 90% you will get closer to the panel rating at 50% vs 90%. This of course requires enough sun light hitting the panel.
    Bottom line there is no way to guess what the panel's actual output will be for your conditions. These conditions not only change from day to day and month to month but also hour to hour.

    If you want to test a panel for your conditions we know from ohm's law the following E/I= resistance; this will give you a value load to test the panel. An example, an 80 watt panel; Vmp = 18.1 volts and Imp = 4.47 amps. Watts = Vmp X Imp; 18.1 X 4.47 = 80.907 watts. This is at NOCT of 50 deg C. Now to find the test load. E/I=load; 18.1/4.47=4.05 ohms. You can use a 10 ohm 100 watt variable resistor and set it to 4.05 ohms. Set the panel up in full sun between 10 am through 3 pm with the resistor connected. Measure both the voltage across the resistor and the current through it. Watts = E measured X I measured. This is a lot of work to test the panel. It will also not produce the same from day to day. There is no way to say what a panel will produce vs the panels rating.

    BB's response in post 11 is the place to start.

  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    So what I gather is my location is not a significant detriment. Solar panels should work in SD as well as they work in FL on a day with similar weather. Correct? And I do understand output varies massively with weather. Thanks again for all the info.
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    It does depend on what you have connected.

    A simple PWM controller (on/off type)--The Vmp just needs to be higher than Vbatt charging... The only time (usually) that PWM is affected is by Hot Weather when the Vmp of a ~17.5 volt output panel fall towards 15 volts on a sunny/hot/day and you are charging a cool battery bank (or equalizing which required ~15+ volts). Otherwise, Imp is relatively unaffected by panel temperature (and Imp actually rises very slightly as panels get hot).

    A PWM controller simply passes Current from the panel to the battery bank. No fancy "transformations".

    However if you have an MPPT type controller (mppt type charge controller, mppt input GT inverter, etc.)--There is a pretty significant swing between very hot weather and near/sub freezing temperatures. Vary hot weather will reduce Vmp by upwards of 20% (relatively to Vmp standard test conditions). And well below freezing temperatures can increase the Vmp by 10-15% or so (some vendors may claim 20%).

    However, if you already have 1/2 the hours of sun because you are in the North, 10-15% "extra output" is not going to make a huge improvement over what they see in Florida.

    MPPT type charge controllers are "transformers" of electricity. They take high voltage/low current and down convert or "transform" to low voltage/high current needed to charge the battery bank (with ~95% efficiency at higher output power).

    Vmp * Imp * 0.95 = Vbatt * Ibatt

    The various rules of thumbs we use around here work pretty accurately for moderate to warm climates. Yes, for MPPT in very cold regions, you will get "more energy" in deep winter than "predicted"--But it is usually not worth the extra math/discussion. There is not enough sun in deep winter and the generator is going to be needed, at times, anyway for folks living through the winter.

    -Bil
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    Yep, this question is founded in the fact that even during the peak of our Summer, the sun is still in our South. We never get sun from directly overhead. One benefit asking the question I did is learning how comparable my experience would be compared to the ones I read online of people further South. I'm learning.
  • Alaska ManAlaska Man Solar Expert Posts: 252 ✭✭
    I live in Fairbanks Alaska off-grid, last summer my array was a total 960 watts. I can produce good power even in the winter, just not for long. The best I have seen from my array was 760W on a clear, bright cool, sunny day. With my panels at 90° tilt from the sun. I would not let the fact you live in the North deter your endeavors.

    I would use about 175W as a wild a$$ assumption for your panel, of typical output on a nice day, in direct sun, in the fall or winter, but like the others have said, so many variables to figure in here.
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    Thanks, hearing you can hit 760 out of 960 is great, that's 79.2% sun. That's very good to hear for so far North. Thank you.
    So if you are at 65N and I am at 45N then 86.15% is a reasonable estimate for me.
    Summer = 215w peak
    Winter = 107w peak

    I think I can begin to get a feel for brightness vs. power available when I look outside now. This helps the brainstorming a lot. Many thanks!
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,034 ✭✭✭✭✭
    I have a client near the Army base in Fairbanks. He has about 8,000 watts and charges most every day. It is really a matter of not taking the battery so deep that you cannot recharge in the short absorb time that the sun is out in winter. He runs about 125% input to max solar on his controllers.Even in low light he is getting quite a bit of power for an offgrid home. It works well.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    Yea that would be a nice size system in the summer, but would make for some frugal winters. Still a nice system though.
  • Alaska ManAlaska Man Solar Expert Posts: 252 ✭✭
    I'll tell ya even in the summer I will often run the genny to bulk charge in the morning. I can get from 75%-80% capacity up to low-mid 90% in under an hour about 45 minutes or so. Then let the sun top off the battery bank. It's the last 5% that takes 4-6 hours. That's a lot of petrol, if done everyday, but sunshine is free. At least for now.

    I do believe will start to see a "Sunshine Tax" in the near future.
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    So it sounds like you operate between 75 and 100. If you operated between 50 and 75 would the panels keep up? I wonder if that would be gentler on your batteries too, giving better life.
  • Alaska ManAlaska Man Solar Expert Posts: 252 ✭✭
    For maximum life cycles you really want to operate with a 20% Depth of Discharge. When the bank was about 2 - 3 months old I did bring it down into the 40% D.O.D. range just to break it all in. If you go to 50% D.O.D. your batteries are dead, if you go lower than that, you are causing serious damage. This will either kill your batteries or seriously shorten their life.

    Some people think that if you have the capacity you should use it. My array now could, on a good day, bring up to full charge even from a 40% D.O.D. but batteries are expensive and getting a few more years out of them only makes financial sense to me.

    You'll get down there from time to time anyway, cloudy weather, winter storms etc. It's okay from time to time, but in my opinion you should operate within the 20% D.O.D range and make sure to bring the bank to float charge once a week.

    This "Rule" pissed me off to no end when I first started this Solar Education, but it is what it is. So with my 1,760 AH bank at 6 Volt, I get to use 220AH at 12 Volts. That's a lot of battery AH that I can't tap. That's why I'm so stoked about what Solar City is doing. They are coming out with a "House Battery" that will put an end to all that unused storage.

    http://www.solarcity.com/residential/energy-storage
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    Alaska Man wrote: »
    If you go to 50% D.O.D. your batteries are dead

    I must use a different terminology. When I say 50% i mean 50% of the operating range, and I consider that to be +/- 10% rated. So a 12v battery to me has an operating range of 10.8v - 13.2v. When I say 50% I mean 12.000v. What operating range do you guys figure on?

    PS - One of the things I do is manufacture small electronics. So 12v source, 5v and 3.3v circuits.
  • Alaska ManAlaska Man Solar Expert Posts: 252 ✭✭
    Range is 12.0V to 14.5 V. charging for a 12.V battery bank. At 12v you are totally discharged and your battery is dead. If you operate at 10.8 your killing your batteries or killed them already. Under DRAW or having a LOAD on the bank, some people set Low-Voltage to disconnect at 11.5V. I've never heard of or seen anyone operating down at 10.8V

    I operate from 12.2v to 12.6v. while under a load/draw at 12.2v I typically recharge. Resting Voltage I would guess to be around 12.4v.
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    Your numbers might be more in line with a car's starter battery. But a deep-cycle type would follow my range. This might explain why you have a hard time getting that last 5% into it, I think you might be overcharging them.
    I have researched since reading your last post, with some even being on this website:




    100%
    12.7
    2.12


    90%
    12.5
    2.08


    80%
    12.42
    2.07


    70%
    12.32
    2.05


    60%
    12.20
    2.03


    50%
    12.06
    2.01


    40%
    11.9
    1.98


    30%
    11.75
    1.96


    20%
    11.58
    1.93


    10%
    11.31
    1.89


    0
    10.5
    1.75


    Back to top
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    I see you posted the same thing while I was composing. I do agree that 12v should be a minimum for best life on a rechargeable. But if this was a one-time use battery you would discharge to 10.5 before throwing it away.
  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    That's probably our misunderstanding, is that I am giving the range of a one-time-use battery and recommending you stay above 50% for rechargeables. You are just talking rechargeables.
  • Alaska ManAlaska Man Solar Expert Posts: 252 ✭✭
    I'll let others chime in here.

    From what I see from your chart 80% capacity or 20% D.O.D. is still 12.4v and best life for your bank is to operate above that.

    14.5v is under charge as soon as you disconnect the charger you will read 12.6 - 12.7.

    14.5v charging to "float" is typical.

    Since I live off grid and been doing this for a few years now, I think I would know the difference between a car battery and a house battery.

    If you want to charge down to 10.8v go for it.


  • JoshKJoshK Solar Expert Posts: 232 ✭✭
    Alaska Man wrote: »
    If you want to [dis-]charge down to 10.8v go for it.
    For a smoke-alarm hell yea. For a solar system, never.

    If you use an Engergizer battery life tester it supports my +/- 10% range perfectly. Like I said, -10% is when you throw away a one-time-use battery. It's not what you do to a reachargeable.
  • LokiC2LokiC2 Registered Users Posts: 2
    So as not to get too technical, let me give you my experience. I'm at 46o north and at an elevation of 2884 feet. I have an array of monocrystalline panels, 1040W. In Winter, the panels are tilted at 20o, in Spring and Fall they are tilted at 44o and during the Summer they are tilted at 68o. On a cloudy, pretty dark day in the middle of Winter, the panels output 40-90W, enough to run my well pump directly (no batteries or inverter). On a sunny Winter day, they meet the full requirement of the pump, 350W and I'm sure have capacity left over. In Winter, on a sunny day, the pump will run from 8:30am to 3:45pm. I tell you, I get a real kick watching the sun directly pull water out of a deep well.

    Now, a friend of mine puts up solar powered radio links in the countryside and has tried both polycrystalline and monocrystalline panels and says there is no comparison in this area, the monocrystalline panels substantially out perform the polycrystalline panels in low light conditions. He uses 225W panels to run 3-4 radios off a single tower. He powers the radios directly from the batteries and uses a small charge controller to keep the batteries charged. I would guess the radios use no more that 15-20W DC 24 hours per day, 7 days per week. He has never had a tower run out of power, which is saying something because we get extremely cloudy, foggy weeks during the Winter.
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