نرخ بازده داخلی از سیستم های متصل به شبکه فتوولتائیک: تجزیه و تحلیل حساسیت جامع

At present, photovoltaic grid-connected systems (PVGCS) are experiencing a formidable market growth. This is mainly due to a continuous downward trend in PV cost together with some government support programmes launched by many developed countries. However, government bodies and prospective owners/investors are concerned with how changes in existing economic factors – financial incentives and main economic parameters of the PVGCS – that configure a given scenario may affect the profitability of the investment in these systems. Consequently, not only is a mere estimate of the economic profitability in a specific moment required, but also how this profitability may vary according to changes in the existing scenario. In order to enlighten decision-makers and prospective owners/investors of PVGCS, a sensitivity analysis of the internal rate of return (IRR) to some economic factors has been carried out. Three different scenarios have been assumed to represent the three top geographical markets for PV: the Euro area, the USA and Japan. The results obtained in this analysis provide clear evidence that annual loan interest, normalised initial investment subsidy, normalised annual PV electricity yield, PV electricity unitary price and normalised initial investment are ordered from the lowest to the highest impact on the IRR. A short and broad analysis concerning the taxation impact is also provided.

Recently, the number of PV grid-connected systems (PVGCS) has grown sharply worldwide. This development has been brought about mainly by means of a continuous downward trend in PV costs together with a wide variety of supporting policies that different developed countries have launched. These strategies or policies are implemented with financial incentives, such as granting a subsidy per kWp of installed capacity or a payment per kWh produced and sold. In other words, these financial incentives can be broadly categorised as generation-based –feed-in tariff, net metering, green certificates and investment-focused – initial investment subsidies or rebates, low-interest loans. First, this paper briefly reviews some policies together with main financial incentives aimed at supporting PV systems. Then, some parameters related to the profitability of an investment are also briefly discussed. By means of classical analysis of investment projects applied to PVGCS [1], some equations are proposed here for the estimation of those parameters. The internal rate of return (IRR) is emphasized, since this profitability index is probably one of the most meaningful for investors. Additionally, three different economic scenarios have been assumed for the estimation of the IRR to represent the top three geographical markets for PV: the Euro area, USA and Japan. Obviously, possible changes in the factors that are involved in the calculation of the internal rate of return – financial incentives and main economic parameters of the PVGCS – cause variations in this profitability index. In order to show the influence of those factors, a sensitivity analysis – properly adapted for each economic scenario considered – has been carried out. Decision-makers in developed countries may take advantage of this sensitivity analysis when planning grid-connected PV supporting measures that might vary over time, according to the renewable energy policy of each country. Besides, these variations of supporting measures may take place while a prospective owner is planning whether or not to invest in a PVGCS, or some time after the investment has been made. Consequently, the results of this analysis may prove useful to provide an assessment of how the IRR is to change when any of the incentives considered or economic parameters of the system is altered. The results of the proposed analysis are shown in tables and graphics in the last part of the paper.

Government bodies and prospective owners of PV grid-connected systems are concerned with how changes in existing economic factors that configure a given scenario may affect the profitability of the investment in those systems. The aim of this paper has been to provide some guidance on this worrying aspect, which is to be highly appreciated. In order to achieve this, a sensitivity analysis of the internal rate of return to some existing financial incentives and main economic parameters of the PVGCS has been carried out. Three different economic scenarios have been assumed to represent the three top geographical markets for PV: the Euro area, the USA and Japan. This sensitivity analysis of the internal rate of return of a PVGCS, provides clear evidence that annual loan interest, normalised initial investment subsidy, normalised annual PV electricity yield, PV electricity unitary price and normalised initial investment are ordered from lowest to highest effect – [EPV]kWp and pu exert the same influence – in scenarios B and C. With regards to scenario A, this sensitivity ranking – also according to lowest to highest effect on the IRR – differs slightly: normalised initial investment subsidy, annual loan interest, normalised annual PV electricity yield, PV electricity unitary price and normalised initial investment, where [EPV]kWp and pu exert the same influence, as well. It is worth mentioning there is an almost negative linear relation between the IRR and annual loan interest for the three scenarios. Also, the annual loan interest and the normalised initial investment subsidy – which are incentives controlled by governmental bodies – exert a relatively smaller influence on IRR when compared to other factors, in the three scenarios considered. The normalised initial investment – which is mainly determined by the PV market- is at the other end of the sensitivity, since it has a negative and extremely high influence on the IRR. Normalised annual PV electricity yield – determined by both the climate of the PV system site and the state of the art – and PV electricity unitary price – commonly fixed by government bodies – have an outstanding positive influence on the IRR for the three economic scenarios considered. In scenario C – close to the Japanese area – variations in financial incentives and main economic parameters have in general a much bigger influence on the IRR than those experienced by this profitability index in scenarios A and B. The three factors that influence the IRR most – [PVIN]kWp, [EPV]kWp and pu – show in scenario C the lowest values for the three base cases considered. Obviously, this leads to achieve the lowest profitability of all these base cases. Deviations of [PVIN]kWp heavily impact on the base case value of the IRR, due to the obvious variations of the normalised initial investment cost of the system itself together with an additional effect of the variation of the overall life-cycle cost of the system: in fact, the loan duration here doubles those of the other two scenarios. Deviations of [EPV]kWp and pu exert a high influence on the profitability of the PVGCS, probably because the smallest values for these parameters together with the smallest value for [PVIN]kWp, are found in base case for scenario C, as mentioned earlier. However, this finding has not been satisfactorily explained yet and it should be dealt with in further work. From a qualitative point of view, this unusual sensitivity of the IRR in this scenario may well owe a good deal to the long lasting and wide experience concerning planning and designing PVGCS supporting measures that the Japanese administration has achieved during the last two decades. In this sense, a well-balanced situation and an unstable equilibrium in the base case for scenario C –also probably due to the maturity of the Japanese market – might, by guesswork, explain this great sensitivity of IRR to the above factors. A short and broad analysis of the influence of taxation on the IRR shows that the latter decreases smoothly and almost linearly as the tax factor increases. Taxation impacts hardest on the base case IRR for scenario A – in both absolute and relative terms- since the largest value for this parameter is achieved here.