Current Limiter-is it even needed

[rahdirs]

@betwixt: bear with me,but i'm not trying to extract more than what it can offer.Not trying to break laws of thermodynamics.I am not trying to force the panel to provide more power than it can provide.I just want to use power it provides,however low it is.Even if Panel of 250 W(rated.) can only provide 20-30 W at dark,i want to harvest it.(Difficult,but i want to try it)
I agree that panel can't maintain voltage & it's voltage drops more at partial light.If at same load,it was generating 18 V at full light & i understand that voltage may drop to 4/6 V at partial light.I can use DC-DC conversion.I understand that the panel is also not capable of supplying that amount of power that it was providing at full light.I want to provide power drop from PSU(mains)
I am trying to help the panel with PSU.

Even using MPPT,that it ensures that you get the most power possible from your solar panels at any point in time.You still agree that power is much lower than 250 W.Say for example 60 W,using MPPT under low light.I want to provide remaining (250 - 60) = 190 W from mains.

Definitely there must be a way to do power addition,of course difficult to implement.Is it really impossible to do this kind of adding power.

MPPT is to operate panel at that voltage where it can deliver max.power at that light intensity.
I'm talking of a hybrid circuit that lets panel produce whatever it produces,just add some power to it from mains & deliver it to battery.

 

[betwixt]

I still think two diodes is your simplest solution. One from the PV, one from the PSU. As the PV produces a higher voltage than the PSU it will reverse bias the PSU diode and stop it's current. It will be a gradual change-over with whichever produces most power winning over the other.

Brian.

 

[rahdirs]

@betwixt: Yes,i already did that of using two Schottky diodes to switch between PSU & PV before posting that other thread "Varying Vcc Power Amplifier".

I just wanted to add one circuit component to it.When PV voltage is low,not to pass through diode,then use a DC-DC boost converter.
Still,do you think using a DC-DC boost converter is flawed.

 

[betwixt]

Yes, if you want to optimize the PV output the very best you can achieve will be to use an MPPT controller then combine the output with your other sources through diodes. The dominant source will provide most of the current, whichever that is at the time. The MPPT will give you most available power from the PV and as it's output drops, the other sources will start to take over so it should do what you want.

Brian.

 

[rahdirs]

@betwixt: I agree with you,that if you want to make PV most efficient,then you need to MPPT. It'll ensure that the PV operates at the maximum power point.
But MPPTs are quite costly.
So,what i thought is when voltage is less just step it up(DC-Dc convert)it.I agree that it isn't efficient as MPPT but it should still be better than simple solar panel & cheap.

I can boost solar voltage right,to bring it to 15 V right or in previous post did you mean that you can't use boost converter.
I can use boost converter right,but it isn't efficient as MPPT. Are you saying this ???

Because,i read that MPPTs also involve boosting circuitry.

 

[betwixt]

No, I'm saying MPPT is the only way you can optimize the power output. Even MPPT will not allow you to get power out of nothing.

The point you are misunderstanding is WHY the PV voltage has dropped, it's because the PV is pushing out all it can but is unable to sustain it's output voltage. It isn't recoverable energy, what you are seeing is the panel already overloaded because you are trying to take out more than the sunlight is putting in. W=V*I, if you try to get more Watts at lower voltage you have to draw more current and it's that very current that you are lacking in the first place. A boost converter doesn't produce voltage from nowhere, it converts a low voltage at high current into a high voltage at low current.

An MPPT is like a boost converter but has a major difference, instead of just converting current into voltage it analyses the PV output to maximize the power extracted from it. As the PV output is highly variable as light conditions and temperature change, it does it by dynamically changing the load current while monitoring the voltage so it can find the point where V * I is maxmum. They are complicated but the math behind them requires quite a lot of computing power and the components in them have to cater for both high voltage and high current at the same time.

Brian.

 

[rahdirs]

It isn't recoverable energy,W=V*I, if you try to get more Watts at lower voltage you have to draw more current and it's that very current that you are lacking in the first place.

Oh,so you are saying that you can't harvest energy of solar panel under low light conditions,even by using MPPT or any other circuit.

Hypothetically speaking, for a panel of voltage 18 V under full light & 10 A.
At low light, suppose it's giving 6 V.Earlier i was trying to boost it to 15 V.
6*I = 15*Is, considering 100% efficiency(theoretical),Is = I/2.5,but I is small,so Is would also be very small.

Wouldn't I in low-light be even 2-3 A,when it's giving 10 A in full light ???
Will the current be much lower than this at partial light???