Accordingly, the P70 (P90) value defines the DNI, which is exceeded in 70% (90%) of the years.Īccordingly, the DNI value related to P90 / P70 for a given site are lower compared to P50, which represents the long-term average. P50 refers to 50% of the years exceeding the value. Thus, P-values of solar radiation (DNI) are provided to judge the reliability of the solar resource of a project. P70 or P90 values are a common practice in the financial world, and widely applied for PV and wind energy projects. P-measures represent a value that is exceeded by XX % of the population of a data set. The P50, P70 and P90 values and their meaning Lenders and banks usually take the most conservative approach to the commercial base case for financing of a project.ĥ. TMYs are the ”fuel” input for calculating the energy produced by the plant, and thus it is highly influences the predicted income of a plant through power sales. However, the accuracy of DNI data can be improved step by step during the project development process, as each improvement involves additional cost. For each project the DNI potential should be assessed as accurate as possible. One of the greatest uncertainties for CSP energy production estimates is the reliability of DNI. Uncertainty of the long-term average of solar irradiance … Hence, a TMY is not suitable as the only base for system or component design.ģ. Extreme weather conditions are filtered out for the TMY. 1 min data) with realistic frequency distribution. Satellite data can provide the long-term base, while ground-measurements deliver the more accurate data with highest time-resolution (e.g. Almost no CSP project site will have historic data from a meteorological station available for such a period. The TMY shall be based on as many years as possible – ideally using up to 30 years of site-specific observations. This is prerequisite for reliable simulation of plant performance. The TMY shall also have realistic frequency distributions especially for DNI. It shall represent the P50 case, which means that it will be exceeded in 50 % of all years. The goal of a TMY is to represent the long-term average meteorological conditions at a site. A 60 min time resolution for TMY and performance model is currently the standard, but higher time resolution can lead to more realistic simulation results. Also ambient air temperature, humidity and wind are relevant for CSP. For Concentrating Solar Power (CSP) first of all this is Direct Normal Irradiance (DNI).
Therefore, TMYs need to cover a full year and shall provide the most relevant meteorological parameters for the technology to be evaluated. It shall well represent the characteristic meteorological conditions of average years at a site.Įnergy performance calculations to predict the potential annual energy production of a CSP plant require a TMY as input. A Typical Meteorological Year (TMY) is a data set giving values in high time resolution.