Good to know. I was doing it in a cheaper, crapier way (straight into a batbox and using copper cables) and figured if I could just use glass fibre cables the problem would be solved. I just want to know WHY it either NEEDS a trasnformer (in your case) or WHY it just stops because it feels like it... because i don't think it should be losing ALL the power.
This has been answered several times already, but allow me to take a crack at it this time:
There's this thing, it's called Resistance, measured in Ohms. Basically, it's the universe telling you that no, you can't actually make a perpetual motion machine. At least not until Superconductors came out, but that's a whole 'nother discussion. Basically, it means you lose a certain percentage of the energy transmitted through a wire.
In Minecraft, the different wires have different levels of energy loss. Go look up the actual numbers on the Wiki. That's what it is there for.
Now then, we also need to talk about 'packet sizes'. You see, energy can be transmitted in several sized packages, each with a maximum value. Low Voltage, for example, runs at packet size 32. If you try to output more than 32 Eu/tic into a copper wire, it'll melt. Medium Voltage is 128, and High Voltage is 512. Extreme Voltage goes up to some 2k+.
So if you have a solar panel, it's outputting 1 Eu/tic. So if you get more than five blocks away with insulated copper wire, it's never going to produce any energy.
For this reason, despite the fact that higher voltage wires (other than Fibre, we'll talk about that in a moment) have a higher energy loss per packet, they actually end up lower losses over long distances, because you have fewer packets running through the wire.
Allow me to provide an example:
You have 512 energy you want to ship along 50 blocks.
If you are using Copper Wires, you'll need Low Voltage, so that's 16 packets, each of which is losing 1eu every 5 blocks, for a total loss of 160.
However, if you are using triple-insulated HV wire, despite the fact that you are losing .8 eu per square, you only have a single packet, so you'll only lose 40 Eu total. Three times as efficient!
Now then, Fiber Cable is a different beastie all together. Basically, it's the ultimate wire, since it goes 50 blocks without losing any energy, and can handle up to 512. The tradeoff is that it eats up diamonds like candy, if you don't have RP2 to use silver instead of redstone in the formula. Even then, you still eat up a diamond per six fiber cables.
Now then, going back to your original problem:
Tin cable also can go up to 50 blocks without losing any energy. However, all of your solar panels are only outputting 1 Eu/tic packets. So each one gets hit for energy loss once you hit the 50 block mark, thus losing the sum and totality of your energy production.
Solution number 1:
About 49 blocks down, put in a batbox. This will store energy, and compact it to, at most, 32 Eu/tic. Which means we can't use tin cabling anymore. So use Fiber Cable to get the rest of the way down.
Solution number 2:
See above, but use an MFSU. This will not only store a whopping Ten Meelion Dolllars EU but will also convert it to HV. Meaning now the packet size is 512, so if you do experience any energy loss, it will be measured in half-percents. More expensive, and it assumes that you have something on the other end that can handle HV power, but it's more energy efficient.
Solution number 3:
Find and install EnderChests mod (Chickenbones Version). Have an MFSU up by your solar plants. Have it charge up Lapotron Crystals. Have an enderchest on the other end attuned to it. Complete 100% energy efficient transportation, assuming you have Buildcraft or RP2 to automate the shuffling of lapotron crystals. Most expensive solution of all, but it's pretty boss.