[SOLVED] PV panel operation for control circuit

Hi,

I'm working through the theory part of a little solar PV circuit, and wanted to ask a couple of questions before continuing with an erroneous design...

For a sweeping statement/generalisation, which of the following defines a PV panel, please:

a) A PV panel is a voltage source that develops a current based on irradiance.

b) A PV panel is a variable and finite current source, whose current is proportional to irradiance, and it develops a voltage as well.

My understanding is b).

Below is the block diagram and flow chart for the circuit, is the correct "ON" flow chart b)? The load + control circuit require at least 100mA to 120mA to operate.



I've attached the schematic too, but I don't think it's needed for such general questions. (The battery charger IC can be configured for "weak" sources such as PV panels, it adjusts charge/load current accordingly, but I think I'd prefer to control the enable pin as it would be unfortunate for the op amp and voltage reference to be starved of operating current and cut out, so the whole circuit on or off - except for the op amp configured as a comparator, which needs to be on all the time - but not somewhere inbetween seems the best option based on what I need it do.)

The following are the calculations I've done for what I may expect from the little hobby panels - until I can actually get outside during the day to measure them, based on a sticker on a proper panel (I'm (un)professional to the last...), I contacted the panel maker and they have no Isc, Voc, Mppt chart for either panel, ..., the only info. I have to go on is 2V/200mA and 1V/200mA. Only as a general rule of thumb answer, do those numbers look realistic approximations for what are probably not high efficiency PV panels - "toy" panels?



Also, I assume a 250mA fuse between panels and electronics would be suitable?

This has me stumped - so the Isc current doesn't reach the electronics what are suitable current limiting blocks, please? I read you can fry your equipment if you do not bear this in mind.

Thanks.

d123 said:

Hi,

I'm working through the theory part of a little solar PV circuit, and wanted to ask a couple of questions before continuing with an erroneous design...

For a sweeping statement/generalisation, which of the following defines a PV panel, please:

a) A PV panel is a voltage source that develops a current based on irradiance.

b) A PV panel is a variable and finite current source, whose current is proportional to irradiance, and it develops a voltage as well.

My understanding is b).

Click to expand...

Let's talk about this part of your post first. It's a bit tricky. If this were a Usenet newsgroup where the crowd tends to be much rougher than in a moderated web forum, some participants will probably twist your proposed definitions - and each other's words - and argue for the sake of arguing.

Broadly speaking, power sources do not "develop" or generate current by themselves. They generate voltage. Current flows only when a load is connected to the voltage source. PV = photovoltaic. The name itself indicates that it develops a voltage when light falls on it. It then has the capability to make current flow through a load, and through itself at the same time. See if you can come up with a better definition based on this explanation.

Hi,

Thanks. I think the purpose of the question(s) may have been misinterpreted, then, and intention was certainly not to start an arguing the toss discussion on semantics. I thought the purpose of forums such as this one was for people with similar interests to ask questions and share knowledge and avoid unpleasantries.

Point of asking for feedback was because after reading that downstream circuitry needs to be protected from overcurrents, mainly Isc, and looking at some mppt graphs, I got the impression that the current generated is not controlled by the load but increases independently of the actual load as the sunlight gets brighter, and I wanted to have that clear before continuing with a simple circuit design that may be based on erroneous thinking and damaging a delicate little ~40mA motor or other ICs in the circuit.

So like any other power supply, with a PV panel the load draws the needed current, not the supply pumps whatever current it has available into the load. Thanks for the explanation.

"See if you can come up with a better definition based on this explanation." - I don't need or have aspirations to do so, I was asking for an appropriate description and if I've understood your definition then that is more than satisfactory to clear up the doubt I had, thank you.