The sun itself is not dangerous to fish in nature. In nature, sun is the only light they have. It's also a natural light and therefore the best, obviously. BUT ... your fish are not living in nature. The bigger the container with water, the longer it takes for it to warm up under the sun. Lakes, oceans, rivers, etc ... won't warm up (if at all) as quickly as a small 10 gallon tank will. Sun over a small home tank can overheat the water to too high a temperature for fish. Even the biggest tank doesn't compare to natural environment of fish such as lakes, rives, and oceans. So, I don't think it's a good idea to leave your tank in the sun all day. As for algae, sun will cause algal blooms in your tank. And while algae are not dangerous to fish (unless they're cyano-bacteria), the tank can begin to look unsightly with too much algae in it.
Now, your tank really is overstocked. In my opinion, Angelfish need at least 20-30 gallons of water (I personally wouldn't put even 1 Angelfish in anything smaller than 30 gallons). A Pleco .... will need something around at least 75 gallons as it can reach even around 20" in length! Rainbow Sharks should not be kept in anything smaller than 55 gallons either. I don't think they're compatible with Angelfish:
"The Rainbow Shark can be kept in a large community tank if there is plenty of cover to hide in. This larger fish is too aggressive for beginners. Very closely related to the Red Tailed Black Shark. Hollows and hiding places are recommended. Only one Rainbow Shark should be kept in each tank as they are intolerant of their own species." ( from:
http://www.aquariumlife.net/profiles...ark/100090.asp )
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Good luck with it 