Maximum power point traking
The first thing you will need to do is observe the power by monitoring the voltage and current coming from the cell with analog electronics or IC's. You then multiply the current and power (best done digitally) and then try and find the maximum point.



To find the maximum point, you need is some kind of control scheme the best one is called Preturb and Observe that monitors the point on the power curve and 'climbs up the hill'. There are variations and other ways to find the maximum power point, but this one is the most widely used and is not to difficult to implement or debug.



Here is the link for the paper which the image was pulled.