Two of our three tanks are against east facing windows.  Whenever the sun shines directly on them, I keep the blinds closed so they don't heat up.  If your tanks don't heat up from the late evening sun, I don't see a problem letting the sun shine on them.  JMO. 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
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