PhD Thesis - Energy Systems Research Unit - University of Strathclyde

5.5 Micro-trigeneration system economic performance metricsThe third and final part of the assessment process involved assessing the economicperformance of the micro-trigeneration system. As explained in Chapter 4 threecriteria were used to financially assess the system’s performance for each scenario:the present worth (PW), the internal rate of return (IRR) and the payback period(PP). Also, as discussed in Chapter 4 all three criteria were further analysed on thebasis of two variable financial scenarios, that is:a scenario with a constant LPG price and variable electricity tariffs to assessthe sensitivity of the system’s financial viability to variable electricity tariffs(±50% of the current electricity tariffs 7 ); anda scenario with a constant electricity tariff and variable LPG prices to assessthe sensitivity of the system’s financial viability to variable LPG prices(maximum and minimum current LPG prices 7 ).In both scenarios the assumed Feed in Tariff (FIT) was set at 0.50 € per kWhexported 7 .5.5.1 Present worth5.5.1.1 Present worth assuming a variable electricity tariff scenarioFigure 5.11 shows the calculated PW of all scenarios for the 3 household building(Scenario 1) and the 6 household building (Scenario 2) for different electricity tariffs,and a constant LPG price of 1.187 € per kg. Given the value of the different energyproducts involved, throughout the economic analysis the scenarios were fully definedto include all differentiating aspects (e.g. type of building fabric, appliances’electrical efficiency etc.). Considering the magnitude of the PW as a measure of aproject’s financial feasibility, Figure 5.11 shows how the present worth of a projectvaries with varying electricity tariffs, for different building sizes and occupancies,building fabric efficiencies and appliances’ electrical efficiencies.7 For details refer to Section 4.3.2.1 in Chapter 4.208