## 2 Methodology
### Study Area  
Determination of the appropriate time period for issuance of the certificates which ESCO supplies based on a performed project by Organic Rankine Cycle in Iran's petrochemical industry is the case study of this article, as shown in the overview in Figure 6. By utilizing ORC technology and generating the electricity, methane gas consumption is reduced indirectly. Consequently, the ESCO, in addition to benefiting from the generated electricity, will be able to supply the certificates in the market equivalent to the amount of saved methane gas. To this end, ESCO will implement the ORC technology to convert the wasted heat to the electricity and under an EPC, will receive a portion of the benefits of the produced electricity. Then, since the produced electricity leads to less consumption of methane gas for electricity production, it is assumed that ESCO could supply the certificates in the ESC market based on the amount of saved methane gas from this viewpoint. Figure 5: Classification of the risk factors in the ESCO business by consideration of the ESC market (Source: authors classification). The reason that this case study is considered, is that Iran's petrochemical industry is one of the main industries of Iran with considerable capacity [35; 36] and due to the high rate of the low temperature heat flows in this industry [37], the implementation of ORC can result in the conversion of the significant amount of wasted heat to the electricity. However, the price of fuel methane gas in Iran's petrochemical industry is less than 3 cents per cubic meter, which is symptomatic of a significant difference to the price of methane gas in well-known gas hubs such as Henry Hub and National Balancing Point (NBP), which is a virtual trading point in the United Kingdom for the trade of gas [38]. Because of this, heat recovery projects are considered high risk and uneconomical in the petrochemical industry of Iran. In addition to the low price of fuel methane gas, ORC technology is more expensive than other kinds of technologies for heat recovery such as Steam Rankine Cycle (SRC), which is another challenge in achieving the mentioned opportunity [39]. Asalouyeh is one of the main hubs of the petrochemical industry in Iran and also has large power plants, which is the area of study in this article. The National Iranian Gas Company (NIGC) is the gas supplier in Iran. Therefore, according to Figure 4, the National Iranian Gas Company and petrochemical agencies in Asalouyeh are considered as the supervisory authority and market participants, respectively. The petrochemical plants that use fuel methane gas more than the standard set by the legislator should purchase energy efficiency certificates from the market, which is supplied based on a performer methane gas saving project through the related concept in Figure 6 about ORC implementation in another petrochemical plant. In fact, selling the certificate of saved methane gas in the ESC market is a way to increase the benefit and reduce the risk of ESCO for implementing the ORC technology. This is not justified only based on the benefits of produced electricity and that the certificate sale will be effective if the appropriate time period is determined for certificates sale by the market regulator. To this end, the explained steps in the methodology section should be taken. First, NPV is calculated based on the values of the involved variables through the following assumptions for a sensitivity analysis, then, after recognizing the main risk factors through sensitivity analysis, the probability distributions of the important risk factors are extracted for risk assessment and right time period determination for certificate sale. * Implementation of one MW ORC. * Investment cost equals 2000 dollars per kilowatt [40]. * Construction period of one year and consideration of the benefit for 10 years. * The time period at which the ESCO sells the certificates and owns the generated electricity are considered equal (see Figure 2).