# Evaluation of Investments in Wind Energy Projects, under Uncertainty. State of the Art Review
## 4 Results Analysis
### Studies with a Real Options Approach, Based on the Ends and Purposes of Its Application
Techniques to Model Uncertainties  
To model uncertainties, stochastic processes of the Markov process type [58], Geometric Brownian movement-BGM [57; 108; 122], the binomial model of [PERSON], [PERSON], and [PERSON] [122], and reversal of the mean [86] were used. The options that have been used during the evaluation are the compound type, construction time, either to carry out, postpone, or abandon the investment [86; 122], the option of waiting for a better opportunity in market trends to decide when to invest or abandon [108], and the option of building portfolios with possible areas for the development of wind farm projects [57]. Techniques to Evaluate Used Options  
For evaluate the options, techniques such as dynamic programming [57; 58], the options-games model [58; 108], Monte Carlo simulations [57; 58; 122], decision trees [122], the binomial model of [PERSON], [PERSON], and [PERSON] [122], and optimization algorithm [86] have been used. Evaluation of Renewable Energy Technologies  
Uncertainties  
For the evaluation of renewable energy technologies, electricity prices were considered as uncertainty [58; 76], as were: learning speed [76], electricity demand [58], government policies [32], feed-in rates-subsides [32; 115], alternative technologies [32], and the intermittency of the wind [115]. Techniques to Model Uncertainties  
Stochastic processes of the Markov chains type [58], Geometric Brownian Motion-GBM [32; 76], and complex formulations [115] were used. The options that have been used are: the option to invest now or wait for when conditions are more favorable [76], to take advantage of the learning effect to anticipate the option to invest and exercise it earlier [76], the option to invest in one or more technologies, whether wind or thermal [58; 76], or wind or gas [32]. Techniques to Evaluate Used OptionsTechniques such as dynamic programming [58; 115], option-games model [58], Monte Carlo simulation [32; 58; 115], and technological learning curves [76] were used. Evaluation of the Impact of Regulatory Policies on Wind Energy Projects  
Uncertainties  
For the evaluation of the impact of regulatory policies in wind energy projects, electricity price [55; 73; 92; 111; 126], changes in asset rates [126], energy production [73; 111], investments or capital costs [107; 111], price index [111], production certificates or feed-in rates-subsides [32; 73; 74; 107], credit policy [91], wind speed [92], wind turbines hours of use [55], carbon price [55], government policies [32], and alternative technologies [32] were considered as uncertainties. Techniques to Model Uncertainties  
To model uncertainties, stochastic processes of the reversion of the mean type [111; 126], Geometric Brownian Movement-GBM [32; 55; 73; 74; 92; 107], and the Markov process [74; 91], have been used. The options used during the evaluation they were the options to invest now, postpone or abandon and the option of capacity generated by support schemes [73; 74; 92; 107], the compound option, associated with changes in wind turbines rates [126], options underlying the change in monthly or annual rate, modeled as an Asian call option on the wind differential [126] the option to invest now, postpone, or abandon [111], to adjust capacity [55; 91; 111], as generated by regulatory frameworks; and the option to choose between technologies due to policy changes [32]. Techniques to Evaluate Used Options  
To evaluate the options, techniques such as decision trees [111], Monte Carlo simulations [32; 74; 111; 126], Black-Scholes [92; 107], Monte Carlo (least squares) [55; 73; 107], dynamic programming [74; 91; 92], and technological learning curves [74] have been used. Evaluation of Wind Energy Systems  
Uncertainties  
For the evaluation of wind energy systems, feed rate-subsides [115], intermittency of the wind [115], future deployment of wind energy process [86], and wind speed [116] were used as uncertainties.