Solar Freaks

Hi everyone.

I'm trying to create a MPPT for a personal project.

My solar panel is rated at 20 W (Voc = 21.6 V, Isc = 1.3 A, Vmpp = 17.2 V, Impp = 1.17 A) and it is charging a 12 V lead acid battery.

From reading various articles I understand that a MPPT is a DC-DC converter that is controlled by some analog or digital controller. I intend to use a microcontroller to sense the voltage and current coming from the panel, and then adjust by using PWM on the DC-DC converter. Does this mean that I need to actually design my own converter? Or can I buy a commercially-available model for this, such as the LTC1149 (http://cds.linear.com/docs/Datasheet/1149fa.pdf), which can output 12 V for me no problem?

It seems like with these commercially-available the switch is internal, so I won't be able to control the load that the panel sees. I guess what I don't understand is the load that appears on the output of the panel.

Any help or clarification on this is much appreciated.

Thanks!