A design Concept?

I have just commissioned (wired, connected inspected and approved) my Grid Connected Solar Array (1Kw) - another 400w to add eventually.

There are 24 panels (40w a-Si Panels) - into a Sunny Boy 2Kw inverter

they are wired so that 8 panels are in series (1 set ~440v), and the 3 sets are in parallel (~3.6 amp).

What I have noticed is in low light conditions (morning before the sun is directly on them, and evening after the sun drops behind the hill) There is enough light for the panels to generate power, BUT, not enough to generate the minimum required power for the inverter (234 v).

Anyone have any ideas for boosting power output?
Maybe some sort of dynamic, programable wiring "harness"?

Thanks

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: A design Concept?

    There is simply not enough energy in the sunlight falling on your panels at those times to generate enough power to "turn on" the SunnyBoy and have enough power left over to "sell" to the grid.

    From my post a few days ago--you can see that the difference between "full sun" and "dark" is a huge range:
    • sunlight on an average day ranges from 32 000 to 100 000 lux
    • TV studios are lit at about 1 000 lux [i.e. 1000 lumens
    per square metre]
    • a bright office has about 400 lux of illumination
    • At sunset and sunrise, ambient outdoor light is also about
    400 lux (if the sky is clear).
    • moonlight represents about 1 lux
    • starlight measures a mere 0.00005 lux

    Basically, from Full Sun to Sunset is almost a 2,000:1 ratio... So a 2kW array would generate ~1 watt at sunset--your inverter probably needs 10-50 watts just operate. You will only get useful power when the panels have direct sunlight on them.

    Back to the question how to get the most power out of your solar PV system...

    1. No shade (or, at least, no shade between 9am and 3pm). This includes no small shadows from plants/trees, electrical wires, stand pipes, and dirty panels. (dirty panels can cost you 5%-10% output loss).
    2. Keep the panel pointed at the sun... Normally a fixed array is cheapest to install, least amount of maintenace, and withstand wind the best. Tilting to point at the sun 4 times a year (seasonal changes) can get you more power.
    3. Keep your panels cool... Mount them off of the roof by 6" ore more to get air flow underneath.
    4. Match your panel Vmp voltage to your inverter's requirements... Typically, you may get a percent or so more power if your minimum Vmp panel operating voltage is keep toward the lower voltage side of the inverter's acceptable input voltage range (less capacitance switching losses if input voltage is kept low(er)).
    5. Get the most efficient Grid Tied Inverter you can, and put as many panels as it can support on its input (don't run a 3kW inverter with 1.5 kW of panels--the inverter will be less efficient overall).
    6. Make sure your AC Mains power is stable--really bad power (voltage and/or frequency excursions) can kick the inverter off-line for 5 minutes until power is stable again (required for safety reasons).

    Those are some basic suggestions I can think of off the top of my head.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: A design Concept?

    > 1. No shade (or, at least, no shade between 9am and 3pm). This includes no small shadows from plants/trees, electrical wires, stand pipes
    Best I can do : )
    and at this time of year, it is more like 10 - 5 (or 6) the panels are in full Sun.

    > dirty panels. (dirty panels can cost you 5%-10% output loss).
    They might need a cleaning - ill check

    > 2. Keep the panel pointed at the sun... Normally a fixed array is cheapest to install, least amount of maintenace, and withstand wind the best. Tilting to point at the sun 4 times a year (seasonal changes) can get you more power.

    yes - fixed, ground mount installation, I have no way to adjust the angle or move the panels. I will consider what would be needed to make the angle adjustable - positively NO way to change compass facing.

    > 3. Keep your panels cool... Mount them off of the roof by 6" ore more to get air flow underneath.

    not a problem - ground mount, min clearance (from ground) is 10-12 inches, with about 6.5 feet at the top edge

    > 4. Match your panel Vmp voltage to your inverter's requirements... Typically, you may get a percent or so more power if your minimum Vmp panel operating voltage is keep toward the lower voltage side of the inverter's acceptable input voltage range (less capacitance switching losses if input voltage is kept low(er)).

    please help me out here :
    the inverter will accept 234 - 600v, and up to 15 amps.
    I am feeding it ~440 v (calculated) at about 3.6 amps

    440v = 8 panels with a V output (measured range between 50 and 59v) (using 55v as a mean) in series. each panel is 1.17 amps. == 1 "set"

    3 "sets" of panels (as above) each "set" is in parallel.
    so this should be 440v at ~3.6amp

    Inverter is a Sunny Boy 2100u (grid tie)

    > 5. Get the most efficient Grid Tied Inverter you can, and put as many panels as it can support on its input (don't run a 3kW inverter with 1.5 kW of panels--the inverter will be less efficient overall).

    currently I have about 1kw (24 x 40 watt - rated) and will be adding another 8, possibly 12 more 40 watt panels.

    > 6. Make sure your AC Mains power is stable--really bad power (voltage and/or frequency excursions) can kick the inverter off-line for 5 minutes until power is stable again (required for safety reasons).

    as stable as *I* can make them :)
    actually they are not bad

    What I am thinking of is possibly a device that does not exist (can not exist?)

    imagine a device that accepts all panel inputs. Then accepts settings (program limits) min and max voltage and amperage that the inverter can handle.
    This device then 'manages' the wiring configuration - (using my 24 x 40 watt panels as an example).

    In low light conditions, this device allows all 24 panels to connect in series producing (maybe) enough voltage to activate the inverter.
    in Full sun conditions, the device "rewires" the panels into (my current hardwired configuration) of 8 panels in series, and 3 groups in parallel.

    basically some device that can DYNAMICALLY control the wiring configuration of the panels. Dynamically, from moment to moment, changing the wiring configuration between series and parallel, producing power in a more usable manner in sub optimal light conditions.
    conditions.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: A design Concept?

    I would not bother changing the panel wiring to drop the voltage down from 440 to in the high 200's... Yes, you can save some power, but it would cost you more wire to home run another string, more fusing, and such... It is just another data point as you first layout a system design.

    The automatic series/parallel switch to step up the panel voltage a dawn/dusk... Read my previous post.

    Even if you can design such a system, you would only generate ~1 watt of power at dawn/dusk using a 2kW set of panels. There is nothing out there that can do grid tied power at 1 watt... And it is such little power, the best a 2 kW system could do at dawn/dusk is charge a single 2,000 mA AA NiMH battery (say one hour in the morning and 1 hour in the evening--even if it could be done--which it really cannot be done for a reasonable $$$/wattage).


    Solar panels need sunlight on their face to generate any significant power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Roderick
    Roderick Solar Expert Posts: 253 ✭✭
    Re: A design Concept?

    I agree with BB's first reply - it's not worth chasing the extra few watt-hours at dawn and dusk. Even if you could re-wire in an attempt to get a higher voltage at dusk, the current is likely so low that the voltage might not even improve, and besides, in 5 minutes, it would be too dark to do anything more.

    Better to optimize your wiring for best performance when there is a lot of sun, I say. If your inverter is like mine, it's most efficient when the input voltage is near the bottom end of the range. So it might pay to go with 4 strings of 6, assuming you could make minimum voltage on a hot day. You would have to look at the graphs of your inverter's efficiency and decide for yourself. But again, the a-Si panels could degrade over time, so the minimum voltage you get today might be higher than 2 years from now.
  • System2
    System2 Posts: 6,290 admin
    Re: A design Concept?

    Just to be sure I am being clear
    I was talking about a Chip - an electronic device of some sort -
    which would "manage" the wiring.

    again using my 24 panels as an example
    ie: at one point in time it might 'wire' 12 panels into 2 'sets' as the sun passes behind some clouds. then a few minutes later as the sun comes out from behind the clouds, it changes the configuration to be 3 sets of 8 panels, then as the day wains, it reconfigures again and crates 1 set of all 24 panels.

    groups of panels are "wired" serially, sets of panels are "wired" parallel.

    Do you follow what I am getting at?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: A design Concept?

    Yes, but it will not get you any useful increase in power...

    Basically, once there is a minimum value of sunlight per square ft/meter on the panel--enough to bias the panel near Vmp... Then any additional light pretty produces current (above zero amps).

    Once the level of light falls below a minimum value--and the panel cannot output full voltage, it is because the current output is effectively near zero...

    Also, remember that P=V*I... So even if you can get voltage back up somehow, the current will be near zero. So P will be near zero.

    Ain't going to work/be cost effective for many different reasons.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: A design Concept?

    the electronics or relays needed to do such a feat will consume any possible gain, if any, realized by doing that. you'd probably gain more by going to a larger wire to reduce what little voltage drop there is and percentage wise that probably isn't much.
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: A design Concept?

    I'll give this a shot ...

    Your 440V will be maintained as long as there is sufficient current. Solar Panels will operate at or above the vmp as long as the current is available. The mppt tracking of the inverter will adjust to harvest the most available wattage.

    In dusk/dawn, the inverter is finding that the current is to low for even the basic tar loss of the inverter ( think minimum power to keep the inverter online ) and the voltage drops to the minimum input as the mppt attempts to keep the inverter online, which it can't as the wattage is not available

    Rewiring the panels for 220V will not increase the wattage available and will make no difference at all. There is no "chip" that can be an active matrix and switch hundred of volts and rewire panels, a switch box could be made but would require all panels have homeruns and would be less efficient with 12X the wire length