Yuval,
If you are referring to Economic ROI regarding renewable energy projects there are many-many different models. I agree that it is hard to find a good economic model of investment and return.
Much of this renewable energy modeling is made even harder to define due to the politicization (is that a word?) of the energy system review and approval costs, power incentive value vs return of capital value.
For example the use of production taxes vs. cap & trade models, vs. other varying incentive models (differing credits for solar, wind, small hydro, bio-gas, wave energy, etc.) Mix in a large amount of renewable energy regulation & associated fees and you have a very difficult to model, non-linear capital return and production value situation.
Please feel free to write a book on the subject and call out the impact of various political and economic models separately from pure equalized energy production costs & values. After all, once power hits the grid its all equalized in Kilowatts! Let the market decide.
My view is that there is a real need for better management of these review process steps, incentives & regulations to make modeling more accurate and simpler to implement. This would have the immediate effect of making renewable energy simpler to design, cheaper and available sooner. Cut the red tape and you will increase renewable energy availability.
Jess
DoradoVista, Inc. see us at -
http://SmallHydro.com