The problem isn't with the basic IC2 solar panels. Those make hardly any energy, and require a massive field of them if you want to generate a significant amount of power. The issue is the solar panels from the various addons, where a single block can generate hundreds of eu per tick without any additional setup or maintenance.
You see, it's all about the economy of space. Even if an ultimate hybrid solar panel costs as much or more than what it would take to make enough plain solar panels to generate that much eu per tick, the ultimate hybrid solar panel only takes one block an a couple of wires to use, causing all other forms of eu generation to be obsolete, because they just can't compare. If you were to make enough plain solar panels to make that much energy, it would require a massive area and tons of wiring, including a lot of transformers. You would need more than 512 solar panels, so you can make up for energy loss over distance and the fact that ultimate hybrid solar panels generate some eu at night as well (unless you're already operating in an eternal day age/dimension). All that space and wiring only accounts for the equivalent of one ultimate hybrid solar panel, though. If you are using more than 1, then you will have to multiply the space all the basic solar panels would take up by that amount.
That may be a lot of space, but not only is it a fair drawback for free easy power, but it's a realistic one as well. I once heard that even if you covered all the land on earth with solar panels, it would only generate enough electricity to meet 1/3 of the world's needs (whoops, way wrong). Now, I heard that a long time ago, and obviously solar panels continue to be developed to be more efficient as time goes on. Even then, there is an upper limit on how much power they can produce. The sun only produces a certain amount of energy per square meter. Even if solar panels became 100% efficient, they can't produce more energy than the sun is giving them. Thus, there is a limit on how much energy can be gotten from sunlight. I'm pretty sure the amount of sunlight that hits a square meter of earth every 1/20 of a second, even on the sunniest of days, doesn't come close to making the amount of power it would take to accomplish the work of 512 eu per tick.