Here are various ways to line things up with the sun so that they are pointing straight at it. I do this mainly for solar cooking but it can be used for photovoltaic/solar electric panels and many other things too.
Using shadows to line up with the sun
Here are some techniques for using shadows to line things up with the sun.
Using a perpendicluar shadow (e.g. for a solar cooker)
The following photos show a very simple trick for lining something up if it has a flat edge that is supposed to be perpendicular to the sun. In this case it's a Modified CooKit solar cooker. I simply hold my finger standing vertically up in front of the front edge of the cooker. If the shadow made by my finger and the front edge form a right angle (i.e. 90 degree angle) then the cooker is facing the sun directly.
Using the shadow behind an object
Sometimes your object forms a useful shadow below and/or behind it. Many solar cookers do this. In the photos below I'm using a box to demonstrate. In the first three photos I'm lining it up so that the sun is in front of it.
But maybe I want the opening of the box facing the sun directly. Once I've got the box facing the sun horizontally as shown above, then I tilt the box up or down as illustrated below. In the photo on the left there is too much shadow below the front part of the box. So I tilt the box backward until the shadow just vanishes from the front. At that point the box opening is facing the sun directly.
Homemade/DIY sun finder tools
You can also make simple tools that can be used for lining up many different things. One type of tool has a hole for the sun to go through and something behind it for the resulting light to shine on. The nice thing about these tools are they line the object up both vertically and horizontally.
The first is one I've used a lot and in the photos below I'm using it attached to the side of a fresnel lens solar cooker. You can imagine doing the same thing with a photovoltaic/solar electric panel instead. Details on how I made it and video of it in use can be found on my homemade/DIY sun finder page.
And another way to do it is to simply get a hollow tube and let the sun shine through it onto something. If a shadow with a shiny circle inside it is formed then it's lined up with the sun both horizontally and vertically.
Using the cooking pot's reflection in a solar cooker
The basic idea is that if you can see your cooking pot everywhere in the solar cooker's reflectors then so can the sun... almost. The sun's rays come at the reflectors everywhere parallel to each other. So to optimize it, look at it from the sun's point of view. Face your solar cooker and hold your eyes and head angle stiff while you move around looking straight ahead.
Ideally the sun would see the cooking pot everywhere in the reflector. Since the pot is black, the sun should see black everywhere.
Here are some of the views I saw when looking straight at the reflector at different locations.
Below is another trick for doing this. Face your cooker from as far away as you can and with the shadow from your head located on the cooking pot. It uses your distance from the cooker to make your sightlines to the different parts of the reflector more parallel to each other. Rearrange the reflector and/or cooking pot until you see as much of the cooking pot as possible reflected in the reflector.