Over Paneling Questions
verdigo
Solar Expert Posts: 428 ✭✭
I have found a really good deal on some more PV and I need an additional 1200 watts to reach my inverter's upper limits. I am thinking of over paneling for those cloudy days but am concerned about exceeding the inverter's 3600 watts in the sell mode if the sun comes out. Will it limit its self and continue to sell or just shut down?
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Comments
For a wind/water turbine, having not enough dump load, the "unregulated" charging sources can eventually over charge the battery and cause it to have a short life.
With solar power, the MPPT charge controller is usually set for a higher voltage (like absorb voltage) and running 100%. The hybrid inverter is dumping enough current to keep the battery bank at float.
The question will be--What happens when the hybrid inverter output is less than the available charging current. Will the MPPT controller over charge (i.e., hold the battery at absorb vs float voltage when the sun is up, or can you program the MPPT controller and the hybrid inverter to somehow "share" float voltage"... Honestly, I do not know.
If you have the current shunt (Whizbang Jr.)--One would hope that the Midnite MPPT charge controller can be programmed to not over charge the battery based on current flow--But I would ask Midnite directly if boB or Ryan do not reply here:
http://midnitesolar.com/Forum/
It gets a bit interesting... If you have two controllers trying to hold "float voltage"... How does the MPPT controller know when it is OK to supply more current vs reducing current because it exceeds the hybrid inverter's ability to regulate... You don't want the MPPT controller to produce less current than the Inverter's ability to dump power the grid.
-Bill
If you are straight off grid, the charge controller(s) should manage charging and loads just fine, as long as you don't withdraw more power than can be replaced. Overpaneling will not help much on cloudy days, until you get way up there, better to run the genset and/or reduce loads till the clouds clear.
The Classic's CAN be set to current limit their output, so a overpaneled array in full sun won't boil the batteries.
|| 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 ,
-Bill
I don't think you have a problem, but If you're worried you might ask over at the Midnite Forum (They designed the CC and understand and may have had a hand in designing the inverter)
I would suggest not going above ~4,640 Watts on a 464 AH @ 48 volt battery bank.
And if using the 0.77 panel+controller deratings:
3,600 watts / 0.77 = 4,675 Watt array (more likely to hit the MPPT > than Inverter crossover point (if no other loads).
-Bill
|| 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 ,
Not much water usage. The batteries are in eternal float or a couple of volts under when the inverter is selling. The inverter takes care of battery charging with a short absorb and then goes to float for 4 or five hours. Then the sun comes up and the inverter begins selling once the Classic pushes the voltage up to the inverter's programmed sell set point. The set point is a couple of volts below float voltage.
The Classic never gets out of bulk because the inverter's sell set point is much lower than the sell set point. So it sells everything it produces. Once a month I simulate a power outage by shutting off the grid connection and discharge the batteries. Then I re-connect the grid and let the inverter do a proper absorb charge for two hours. I then check SGs and sometimes do an EQ if the SGs are off much.
Long story short the batteries are not being baked because the inverter takes care of the batteries. The question concerns the inverter, and is (what happens if I over panel and the inverter reaches its 3600 watt capacity in sell mode and maybe exceeds it). Will it fault out and shut down or will it limit its self to the 3600 watts? There are no other loads unless the grid goes down and even then I have it set up to not use the inverter's internal transfer switch.
The only reason I ask this is because I am normally not home during week days, but I would like to sell power at or near capacity. I suppose I can go ahead and over panel and just shut down a string if the weather is forcast cold and clear. Summer months probably won't be an issue.
My system is similar to yours. I solved the issue by using the charging amp limits on my Classics.
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|| 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 ,
No, I have AGMs which can tolerate a very high charge rate if needed. But that is not really relevant unless their is a grid outage and I am in "off grid mode".
Most of the time I am selling to the grid. My "sell RE" voltage is at or near my float voltage so the Classics stay in Bulk mode and everything I make is being sold with very little (or no) net charge into the batteries.
It is a bit complicated for me since I have 2 arrays and 2 classics. I think I have the combined output amps set to something like 75 amps which with a sell voltage of about 54V puts max output at about 4000 watts which in theory could still overwhelm my GVFX3648s ability to sell but in reality it would only happen if both arrays (with combined STC rating of 4500watts) where seeing cloud edge effects simultaneously. Also one of them is on a tracker so they are rarely at exactly the same orientation.
I have been considering buying another inverter and CC. I built my system and wired with expansion in mind. Hopefully I will be able to be patient and pick up some used or on sale equipment. Anyway thanks for the info.
-Bill