Hi,
I am an electronics noob. I have some questions regarding a particular application.
I have to move a small cylindrical rod using a solenoid (whose capacity is 1.5kg lifting force and rated at 12V). My application requires me to energize the solenoid only when I get a signal from somewhere. So I searched and found MOSFETs as switches and capacitors as charge storage units.

Suppose, I have a source (assuming a constant supply of sorts), and store energy in the capacitor. I want to discharge the capacitor only when needed. A MOSFET can be used as a switch in this case to control the flow when needed, provided it gets a signal from somewhere, say a photodiode (just saying, open to suggestions). This seems like a solution. But...

1) Is it possible to store that much energy in a capacitor to energize a solenoid which I mentioned? If so, any specific ratings or numbers?
2) Will the photodiode, getting a light signal, be enough to open the gate of the MOSFET? Or is there another method to give a signal to open the gate of Mosfet?
3) If the capacitor can store and discharge; if the MOSFET + sensing circuit works; how do I make it robust for long-term usage? how do I make the connection, on a PCB or something?
4) Are there components I am missing (like a resistor?) that need to be considered?
5) Any basic schematic would be helpful for me to understand the connection.

My space is pretty limited, it is for a small-scale application, like an area of 15cm X 6cm with a height of 5cm.

Very much appreciate the help. Thanks!

 

Welcome to AAC!

Forget the capacitor part. You will need an extremely large capacitor to store enough charge to energize the solenoid. You need a power supply instead of the capacitor.

Here is the design scheme:

photodiode -> amplifier -> MOSFET -> power supply -> solenoid

 

Mr C is quite right, and the challenge being that while operating a solenoid from a capacitor has been done, it is usually for just a very short time, a few milliseconds. Next, depending on how much force is required, the energy stored in the capacitor will be quite a lot, and so the capacitor may be quite large.
So the current required for the solenoid, and the length of time it needs to be operated need to be known.