Since you are now limited to OP Generators and Geothermals.
Use advanced Generator!
Slag Generator is a very good one, used with wood gassificator + centrifuge, you'll get a pretty impressive amount of energy per wood, + scrap (and while farming wood, you'll also collect leaves, sapplings wich you can also use as a way of generating energy, and apple, for food!) ... (it's quite OP with Forestry but ... Forestry is actuall OP in my mind since it replace green generator The better is not to use Forestry, as me ^^) [/quote]
You know that a centrifuge is totally not early-game.
I speak about what I do when I start a new game. And I start with a single generator, since charcoal is incredible cheap. If I happen to find some lava-sees while digging for redstone (which normally happens) I build 1 or 2 Geothermals next... or even 6 if I want fast generation, Geothermals don't cost that much. If I don't happen to find much lava I go for the same amount of generators and build 1-2 Electric furnaces and 1-2 Cokeovens for Charcoal-production.
If I started with the geothermals I try for early Netheraccess and build some Redstone-Engines, a Pump and harvest lots of Cobblestone (well... that one is easy). After this I start collecting some stuff for a world-anchor and make myself a nice netherportal. I also dig very... enthusiastic to find a mining-shaft or a dungeon (the first gives you lots of rails and the second gives you steel). I then start to build BC-Tanks and lots of buckets and try to get a mystcraft-age with crystals. If I get the crystals I build two portals and always fill my geothermals with lava from the nether (still by hand...). I then build a rolling-machine to make Railcraft-Tanks and the stuff for automated-lava-transportation. After this I have endless EU.
When I start with Generators because I can't find enough lava (does not happen that often). I automated them with the coke-ovens and E-Furnaces so that they get automatically feed with charcoal. I also search for Birchwood, since it is the easiest to harvest by hand (Oaks and Pines are sometimes too tall, to harvest without building) I then go for about 25 to 36 (5x5 or 6x6) Birchs, which I repeatedly slaughter to produce charcoal.
Both methods are far more efficient than solars have ever been. Wind was a very good early-game source and water was awesome with redpower-automation. But Geothermals and Generators beat them very easy exspecially since Tree-Farms and Netherpumping supplies you with an endless amount of ressources for these Generators.
Thats where the balance-suggestions come from. Without GregTech you normally start with some renewable sources. Wind was the best option, Solars the worst. Water was somewhere in between, but it was incredible spammy. Also a Generator to recharge batpacks was something that almost everyone had. But after this the renewable sources got very bad in efficiency. Solars are shitty because they are so incredible expensive... and don't work if it is raining or night. Large-Windparks are either inefficient or incredibly spread out... which also makes them look ugly. Water was a good one, since it could be abused with Redpower, but the easy thing would have been keeping the fuel-value of a waterbucket and halfing the EU/t Output to 1. So at the end it always was clever to go back to Generators or Geothermals, but the problem was people had no use for a lot of EU so they kept their early-generators and just increased the number of them.
Gregs does have some of the same issues, since the basic machines are also very cheap in EU-Consumption. The Industrial Centrifuge requires 5 EU/t to run which is hilarious. It really should be MV, since I have never seen an industrial centrifuge working with LV (well I could use one at home if it uses LV).