Hi inetdog. That is a very concrete example and clear explanation. Thank you so much. Got the MPPT relevance to resistence elements good but ask that you check me on this conclusion below cause it seems to violate common sense.
I.e--in this example the only way to increase power output is to increase resistance. 120 volt panel, 1000 watt, vmp of 30 volts. If I hook to 120 volt, 2000 watt element I've got a resistance of 7.2 ohms. Now if we wanted the perfect element to dump excess juice from a 120 volt battery this would be perfect match because would get full 2k output. (16.67 amps x 120v). But, Imp of panel only 8.3 amp so according to your instruction you multipy 8.3 by 7.2 ohm=60 volts. Then times 8.3 again and only get 500 watts from 1k panel at full solar.
But if use 120 volt 1000 watt element the resistance doubles to 14.4 ohms and you get almost full 1000 watt flow thru.
* So assuming you say this is correct would it be right to say that the only way you can ever get a perfect match and no loss at noon is to have the element and panel the same in voltage and watts?
Been ages since I actually tried to measure this, but my feeling is I'd get about 90% of maximum power for 4 hours or 9 out of the 10 amps in your example before I started rapidly dropping to 5 amps. If anyone can contradict this please do. So 90 amp/hrs plus whatever dribbles you get after 4 hours ain't too bad but the mppt problem is a bummer for sure. Probably a deal killer.
The general consensus is there is no mppt fix to this strictly dc direct connection? Like can't put a mppt controller in between? Believe I got that impression when read this whole thread a week ago but will review. Don't need to know why. Would be beyond me I'm sure.
Got the Thermostat issue covered in this increasingly metaphysical system. High dc volt Relays
Fear I'm asking too many questions at once but at the moment maybe you are willing to linger in beginners corner but maybe not next week so thinking ahead and maybe being a little too grabby.
Thanks again for the illumination and good day.
I.e--in this example the only way to increase power output is to increase resistance. 120 volt panel, 1000 watt, vmp of 30 volts. If I hook to 120 volt, 2000 watt element I've got a resistance of 7.2 ohms. Now if we wanted the perfect element to dump excess juice from a 120 volt battery this would be perfect match because would get full 2k output. (16.67 amps x 120v). But, Imp of panel only 8.3 amp so according to your instruction you multipy 8.3 by 7.2 ohm=60 volts. Then times 8.3 again and only get 500 watts from 1k panel at full solar.
But if use 120 volt 1000 watt element the resistance doubles to 14.4 ohms and you get almost full 1000 watt flow thru.
* So assuming you say this is correct would it be right to say that the only way you can ever get a perfect match and no loss at noon is to have the element and panel the same in voltage and watts?
Been ages since I actually tried to measure this, but my feeling is I'd get about 90% of maximum power for 4 hours or 9 out of the 10 amps in your example before I started rapidly dropping to 5 amps. If anyone can contradict this please do. So 90 amp/hrs plus whatever dribbles you get after 4 hours ain't too bad but the mppt problem is a bummer for sure. Probably a deal killer.
The general consensus is there is no mppt fix to this strictly dc direct connection? Like can't put a mppt controller in between? Believe I got that impression when read this whole thread a week ago but will review. Don't need to know why. Would be beyond me I'm sure.
Got the Thermostat issue covered in this increasingly metaphysical system. High dc volt Relays
Fear I'm asking too many questions at once but at the moment maybe you are willing to linger in beginners corner but maybe not next week so thinking ahead and maybe being a little too grabby.
Thanks again for the illumination and good day.
Originally posted by inetdog
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