I may have messed up? Sun Electric Panels...

YostFMXYostFMX Solar Expert Posts: 94 ✭✭✭
Came across a post about Sun Electric's evergreen "B" panels and how they are not a standard voltage? and the inverter to make them work is $500-$700. I bought 3 panels, 205 watts, and was going hook them up to a 12v Xantrex C60 charge controller I also bought. Did I mess up? is this not going to work? I'm going to get a picture of the voltage info...


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: I may have messed up? Sun Electric Panels...

    The Evergreen 205 Watt panels have a Vmp of 18.4, I believe. Whereas it is not "ideal" for a 12 Volt system and PWM type controller they will work with no significant power loss.
  • YostFMXYostFMX Solar Expert Posts: 94 ✭✭✭
    Re: I may have messed up? Sun Electric Panels...

    This is what it says on it:

    Vmp 18.40 V
    IMP 11.15 A
    Voc 22.80
    Isc 12.10 A

    I put the panel in the sun and put a volt meter on it and it reads 22.2 Volts. So this will work when I hook up to a 12V charge controller (12V batteries, 12V inverter)? How can that be? Isn't there only supossed to be 13.5 Volts input at the most for 12V controller? What am I missing? Isn't having 22.8 Volts input going to fry it?
  • Volvo FarmerVolvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: I may have messed up? Sun Electric Panels...

    The C60 will accept panels with up to 55 Voc without burning up.


    I'm not exactly sure how the PWM works on the C60, but basically, the battery voltage will hold the panels Voc and/or Vmp down to battery voltage. This might not be the most elegant way to explain it, but you will not burn up the inverter because it is tied to the battery, and the charge controller will not generally let the batteries go over 13V in it's normal configuration.
  • RCinFLARCinFLA Solar Expert Posts: 1,398 ✭✭✭✭
    Re: I may have messed up? Sun Electric Panels...

    They are the correct panels for 12v lead acid battery system running on an PWM controller. When you figure in voltage drop due to real sun exposed temperature rise , some wiring, and PWM controller loss you just make the 15v to 15.5 vdc for bulk/equalizing charging.

    Three 11 amp panels in parallel will provide 33 amps peak which is well within the 60 amps capability of the C60 controller. C60 allows up to 55vdc input so you can even stack two panels in series if you ever want to go to a 24 vdc system Just need a fourth panel so you have two sets of two in series.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: I may have messed up? Sun Electric Panels...

    the pvs if paralleled will work going through the pwm controller to batteries. the controller is the regulation circuits to keep voltages inline with what the battery needs without hurting the battery. it does have to go to the controller and the battery too as you can't just go straight to an inverter and many other 12vdc electronic items as the higher voltages would kill them. we need the higher voltages to overcome losses along the way and still have plenty of headroom to push power into batteries that sometimes go into the 15+ voltage range. also higher temps seen by the pvs will lower the voltage some and all of this necessitates a higher voltage from the pv to start with.
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: I may have messed up? Sun Electric Panels...

    Just to put it simply,, a PV will "take on" the voltage of the battery so to speak. Just as if you were to take a fully charged 12 volt battery, with an at rest voltage of ~12.7 vdc, and put it under load,, the apparent voltage would drop to say,, 12.2. That doesn't mean the battery is dead, it just means that the battery is under load. Putting a PV "under load" will translate it's out put voltage to that of the battery, while "pushing" power into the battery. As the battery voltage rises, so will the PV out put voltage. Just as in the same way you load a battery, the voltage drops,, but if you plug in more battery to the circuit, the voltage will appear to rise.

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: I may have messed up? Sun Electric Panels...

    Oh the fun of panel Voltages! Hold on to your hat!

    Panels have three Voltage ratings: the nominal (in this case 12 Volts), the Voltage open circuit (in this case 22.8 ), and the Voltage at maximum power (in this case 18.4). The panel will only show 22.8 Volts when all it is connected to is a meter; once you put a load on it the Voltage will go down and the current will go up. Its "ideal" power point is Vmp * Imp: 18.4 * 11.15 = 205.16 Watts.

    When using a PWM controller, you are essentially switching the panels on & off the battery to come up with the proper charge Voltage setting. On 12 Volts this will be around 14.4 for a flooded cell battery. Since panels are current sources rather than Voltage sources (a hard concept to come to terms with) their actual Voltage output will vary quite a bit depending on how much light falls on them, what the battery SOC is, the panel temperature, and how much wiring is involved. We usually expect a "12 Volt" panel to have a Vmp of about 17.5, which allows a PWM controller to maintain the proper charging Voltage despite the inevitable system losses. A Vmp of 18.4 means there's a bit "extra" Voltage available. It is not outside the range of usability, unlike some "24 Volt" panels which have a Vmp of 26 or so: too high for 12 Volts, too low for 24 Volts.

    If you short the panel's output leads it will read zero Volts and 12.1 Amps - the Isc (short-circuit current; the 'I' is for "Intensity", and old term for Amperage).

    You have to have more than battery Voltage available in order for any current to flow, as that is dependent on Voltage difference.
  • YostFMXYostFMX Solar Expert Posts: 94 ✭✭✭
    Re: I may have messed up? Sun Electric Panels...

    Thanks everyone! I get it now... was stressing for a little there... haha I thought I screwed myself. Sounds good. Was hopping to be getting 50 amps max out of my panels, but 33 max is ok. I've got to vertial wind generators that I'm making, but thats probably a whole nother can of worms huh? I think the volts go up the faster it spins which looks like it would be bad for the controller...
  • RCinFLARCinFLA Solar Expert Posts: 1,398 ✭✭✭✭
    Re: I may have messed up? Sun Electric Panels...

    PV panels are much easier to understand then the output of permanent magnet alternators.

    Model of a solar cell is an illumination based current source that is capped in it maximum voltage by the inherent shunt diode of the cell. The conduction point of this inherent diode (for silicon) is about 0.50 vdc at 25 deg C. So below this voltage the cell acts pretty much like a current source where the current level is based on the illumination level. For a full sun (about 1000 watts/sq. meter) a good quality cell will produce about 35 mA's per square centimeter of solar cell. A 5" by 5" square solar cell has about 160 sq. centimeters so will produce about 160 sq cm X 0.035 amps/sq cm. = 5.6 amps. Power wise this is about 13% to 15% conversion efficiency of the 1000 watts/sq. meter of full solar illumination power. The lower the sun is in the sky, the more atmosphere the solar illumination must pass through so there is lower solar illumination power at lower sun angles. Then there is clouds, and trees, and such that can block the sun. An earth orbiting satellite above the atmosphere gets about 1370 watts/sq. meter of solar illumination.

    At full sun illumination the cell will produce this current against whatever resistance load is presented up to the point where the cell's inherent diode starts to conduct and shunts some of the illumination generated current back across the cell. The maximum power point (Vmp) is external loading such that the inherent diode of the cell just barely starts to conduct. This is about 0.52 volt per cell at 25 degs C. If the cell is left without any external load, all the 5.6 amps will be shunted back down the cells inherent diode. As the shunt diode get more current its voltage rises. At 5.6 amps of shunting it will have a diode voltage of about 0.65 vdc at 25 degs C. This is the open circuit voltage (Voc).

    Now this inherent diode has a negative temperature coefficient of about -2 mV/deg C. As the cell gets hotter in the sun, its inherent diode conduction point will go down by this temp coefficient. Going from 25 degs C to 50 degs C there will be a 25 degs C delta so the cell voltages will drop by approximately 0.002 volt X 25 deg C or about -0.05 volt. So the Vmp would go from 0.52 vdc at 25 degs C to about 0.47 vdc at 50 degs C. This is about -0.35% per deg C.

    Now your panels have 36 cell connected in series so the total panel will have an Vmp of 36 x 0.52v or about 18.7 vdc at 25 deg C or 36 x 0.47v or 16.9 vdc at 50 deg C. Voc will also change by about the same temp coefficient.

    There is some series resistance and shunt resistance associated with each cell but we will ignore that for this first approximation.

    A permanent magnet alternator's voltage and current are dependant on rpm's, mechanical torque driven, and loading. It is a complex relationship. Mechanical power is torque x rpm's. At a given wind speed you will have the rpm go down as you load the alternator electrically. An increase in electrical load will put more mechanical loading torque on the windmill. There will be an optimum loading to get the right rpm and torque to get the maximum output power from the alternator. This will depend on the blades diameter and efficiency along with the number of turns of wire and their gauge in the alternator. Higher voltage alternators are wound with more turns of smaller diameter wire to give the desired voltage and current based on the blade size and average wind velocity.

    Too much wind and the windmill can run away with itself. Three methods are used to control rpm's., a tail guide to turn windmill out of the wind, mechanical breaking, and electrical loading. All or a single method may be employed. Large commercial windmills use a complex mechanical transmission and variable blade pitch to drive an alternator that must keeps it rpm constant to syncronize AC power with the grid. You will hear about load diversion controllers. When windpower cannot be consumed because batteries are fully charged or there is not enough electrical load, the controller will kick in a diversion load. A common diversion load is a hot water heater. The purpose is to keep a minimum electrical load on the alternator to prevent the windmill from over rpm'g. A windmill can self destruct if it spins too fast. They can be dangerous if allowed to get out of control.

    A general rule of thumb, if you don't have an average wind speed of greater then 10-15 mph. don't bother with wind power. Average wind speed of greater then 20 mph starts to look good for windpower.
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