What are Eco Power Plants?

I was also intrigued by this and decided to buy it. The Eco Power Plant provides power to the city like other power plants. It doesn't say how large each one is, but in my city, they're relatively small compared to an oil or even coal power plant (for comparison, one of the Ecos is roughly the size of HALF of the regular city storage facility buildings). Each one has a capacity of 28 for power. I like the small size and that it allowed me to get rid of two of my dirty coal power plants for each of the two Eco Power Plants in this starter pack. I have limited space at the moment and these can be placed right up against each other in a small area. Since you're already using OMEGA Power Plants, I'm not sure if this would be better or not, since OMEGAs actually pack 100 capacity, but the Eco Power plants were easier for me to attain (I'm new to the OMEGA items, so 10,000 NeoSimoleons was hard for me to attain in order to buy my first OMEGA Power Plant, and why I currently still only have one). For $5.99, I'm happy with the purchase and would probably by another pack if it was offered since it does come with some SimCash and coins. 

Hope this helps!