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Yes, i understand voltage vs current curves for a solar panel.
So..if solar output Uoc=7V, Isc=0.33A , maximum power is about ~1,28W when the matched load is ~30Ohm.
If solar intensivity changes lets say 6V 0,25A, now 30Ohm load is not matched. Power P=U*I, U=P/I , I=P/U . If dc-dc buck is lowering voltage using pwm , current is growing. And thats the way how is optimized new current ant voltage levels for the load ?
If load is too high, output is near Voc, if very low, then current is near Isc.
V_out=V_in / Duty, I_out=I_in*Duty
or MPPT is needed for all energy harvesting methods such as thermo, wind, piezo etc
Nice ! Example for understanding : So i connected MCU as a solar panel load. MCU wake up from sleep and measure sensors values, the current consumption will increase, and load to solar panel increase, but load resistance decrease assuming R=U/I?That would be correct if you say "load resistance" instead of just "load". A high, or heavy load is one which draws a lot of current and is thus a low resistance.
MPPT can be used for many energy harvesting methods. As well as solar, it is also fairly common with small wind power systems.
So it can be used for every energy harvester ? Because pjezo ar TEG's are constant output impedance, MPP will be at 50% from Voc and Isc ?
So, if there are DC-DC buck between solar cell and mcu, what it should do ? It should increase current equal to load consumed current at that moment? But then voltage drops?
No, i think that 4.4W will be in perfect conditions, when irradiance is very high, and load is matched ... In my example, increased load is show as work point changes to the left (current increases, load resistance decreases)..I think you still misunderstand. Are you of the belief that you will always be able to get 4.4W from your solar panel?
Can you point me...
wdariusw, It sounds like you are attempting to build a solar site evaluation device, perhaps a "logger'....these are readily available already built ( http://www.solarpathfinder.com/PF?id=JX9yF4Qr as a quick example) many with very sophisticated capabilities......If you are seriously considering a large PV/RE installation then it would be fiscally irresponsible not to asses the site for at least a year....given the length of time involved in a real site assessment, it is best to use tools that you have 100% confidence in, typically not first generation DIY devices....If your intended purpose is NOT about site assessment then perhaps disclosing your actual intended purpose would help get better suggestions.
Fish