When use Zener Diode and when use Voltage Regulator IC in regulating voltage?

Question

This question maybe general question, but I have my own case like below.

I'm planning to make solar cell phone charger.

I found 1 solar cell with this specification as follows:

Brand: Staryu
Type: Polycrystalline Solar Module
Model : Staryu-10w
Rated Maximum Power : 10wp
Voltage At Maximum Power : 17.5V
Current At Maximum Power : 0.571A
Open Circuit Current : 21V
Short Circuit Voltage : 0.64A
Dimensions : 354 x 251 x 18mm
Maximum system voltage : 1000V

Here I summaried properties (specification) that I'm sure I know its purpose.

• Max Power: 10WP (Watt-Peak)
• Max Voltage: 17.5V
• Max Current: 0.517A

We know common properties in average phone chargers are like these:

• Power: 10W
• Voltage: 5V
• Current: 2A

Since that solar cell voltage and current is not syncroun with charger properties, so I'm applying Power Formula so that solar cell will syncroun with phone charger.

Because current is not able to regulate, so I will regulate the voltage one. With this basic formula, all I need to do is just reduce voltage to 5V so that the current will increase to 2A as same as phone charger with Zener or IC Voltage Regulator? (still a question).

P = I * V
10W = I * 5V
I = 2A

So especially for my case, should I use Zener Diode or Voltage Regulator IC in regulating Voltage?

What simple case that we should use zener diode or voltage regulator IC?

Note:

• Correct any statements or calculation that I made if I'm wrong.

Answer 1

The Zener diode will just convert any excess voltage directly into heat, meaning that you will get 5V at 500mA. A linear regulator will do the same. Only switching regulators are able to deliver a higher current at their output than what they consume at their input (while lowering the voltage).

This means that neither a Zener diode, nor a linear voltage regulator IC will work for your purpose. You need to build a buck converter.

In general, you only use linear regulators when you need a low power, low noise voltage rail and you don't really care about efficiency. Zeners are cheaper but even less efficient and very inaccurate.