The fundamental problem isn't Solaris, but the lack of good alternatives. That is why people choose solars. It is not like there are many other good choices, but Solars are just so uber they are picked all the time. Like I said, i started with Windpower and only used solars initially to recharge batteries (and that aspect of them has been broken / nerfed or was never ported to IC2). They no longer take stacks of batteries that can be auto-ejected into chests anymore.
Anyway, if you want to "Fix" the whole situation, do this by looking at the power systems people DON'T use and make them competitive. This is what game designers do whenever they patch a game, such as WoW or RTS game and what not. They look at what ISN'T being used and try and buff it. It is a knee-jerk reaction to bring the nerf bat on what is being used instead of looking at why other things are not being used and fixing them.
Ill take this challenge and "Fix" each alternate power system so that they are more attractive and will compete with Solar (old style, not this nerfed crap).
Windpower:
The problem with wind-power is that by its very nature you need LONG DISTANCE power transfers. You need to move your EU's through a very long cable which means a lot of power loss. If this problem were solved, Windpower would be a great choice.
Problem 1: We need a way to convert LV to EV and back again cheaply. The current setup requires a lot of transformers to convert between the two as well a lot of highly lossy refined iron cable. Your best bet is the not even insulate it because that is a metric tun of rubber required to fully insulate it. You are also going to need a heck of a lot of this cable.
Possible solution: Make a transformer between LV and EV. Try bronze cables (and fix the bronze formula to yeild 4 dust. How does 4 dusts turn into 2 dusts? If you wanted to somewhat accurate on how bronze was really made it would be 8 copper to 1 tin (actually its should be 19:1 ratio but you can't do that in minecraft)). The EV transfer cost should be cheaper, if we are trying to be realistic. After all in the real world we do use EV to transfer power precisely because it is far more efficient.
Water Power:
This has never been a good choice. It just produces far to little power.
I purpose two new modes for this to make it a useful power option.
Mode 1: Tidal Generator. In this mode It generates 0.001 EU for each still water block within a 100 block radius. This a shallow pond will not give much power, but if you are actually on an ocean where the water gets deep really fast, it will add up. I have no idea how many still water blocks would be in that volume so these numbers are a guess. This should produce a lot of power. The big draw-back is that you need to be near an ocean.
Mode 2: Moving water. In a 1 block radius around it, it looks for moving water. It traces that water to its source and the delta in height from the source block to it represents the Power P in the water. For each block around it, the power can be P x 0.01. So a 64 height water fall will give you .64EU. With 4 faces covered it would be 2.56 EU. If you count the corners that could be 5.12 EU. If you stack the generators you might subtract 1 power from all of them for each generator in the stack.
Geo Thermal generator:
This is almost fine, but a small change is needed. It should eject empty cells into a box next to it to recover the empty cells.
Filling those cells should be automated although this is a finite resource because it requires lava source blocks. Pumps should operate without a miner and you should run a pipe to a lake. It should drain the entire lake filling lava cells. It should not require much power, but can be partnered with a generator (geo thermal would be a good choice). It should draw from the farthest connected source lava block to the closest. It would be even more ideal if it would draw empty cells from a chest and eject full cells into the same chest.
With the above changes, the lure of solars isn't so strong.