There's a reason they call solar/wind etc power alternative power. If it was cheaper, simpler and more reliable than mains power it would not be alternative. Have you looked at the cost of solar panels? How many you'll need will of course depend on the size of your tank. iirc my fairly basic, relatively small reef averaged around 300-400 watts over a day. Peaking somewhere around 1200 if we count the heaters. You'd need enough panels to run the tank, plus charge batteries to last you over night. Plus you'd need enough capacity to do that on cloudy days. So you'd probably need somewhere in the region of 3000 watts worth of panels which is...Ahh...About $15,000 from the looks of it. Batteries, controllers, installation etc would be probably be that much on top of it.