Evaluation method

Abstract

The invention is directed to an evaluation method for determining a power reduction due to ageing of at least one photovoltaic module at constant radiation intensity with a measurement of an electric variable that may change after a period of time such as cell current, cell voltage and/or cell power, without additional sensors for measuring the radiation intensity, with the following steps fixing at least one class k that can be compared year by year and within which a daily power curve or portions of the daily power curve of the photovoltaic module can be compared to each other due to the radiation intensity and the outside temperature to be expected as well as the radiation time, the class k corresponding to a defined period of a year, measuring energy output values Ek,n that can be compared year by year from a comparable power curve Pk,n (t) through the variable delivered by the photovoltaic generator so that energy differences are determined on the basis of the classes k, n being the respective year, indicating a power reduction of the photovoltaic module with respect to one or several previous years from the energy output value E k,n directly delivered by the photovoltaic module by calculating the difference with respect to the energy outputs Ek,i of the years i to be compared, data of comparable days having a comparable power curve P(t) of the photovoltaic module being observed over several years.

1 . An evaluation method for determining a power reduction due to ageing of at least one photovoltaic module at constant radiation intensity by measuring an electric variable that may change after a period of time such as cell current, cell voltage and/or cell power without additional sensors for measuring the radiation intensity
 with the following steps
 fixing at least one class k that can be compared year by year and within which a daily power curve or portions of the daily power curve of the photovoltaic module can be compared to each other due to the radiation intensity and the outside temperature to be expected as well as the radiation time, the class k corresponding to a defined period of a year, 
 measuring energy output values Ek,n that can be compared year by year from a comparable power curve Pk,n (t) through the variable delivered by the photovoltaic generator so that energy differences are determined on the basis of the classes k, n being the respective year, 
 indicating a power reduction of the photovoltaic module with respect to one or several previous years from the energy output value E k,n directly delivered by the photovoltaic module by calculating the difference with respect to the energy outputs Ek,i of the years i to be compared, 
 data of comparable days having a comparable power curve P(t) of the photovoltaic module being observed over several years. 
   
     
     
         2 . The evaluation method as set forth in  claim 1 , characterized by acquiring and/or filing a daily curve of the power P(t) of the generator as well as of the energy output E of the day for the generator, in particular in a data bank,
 determining a daily power curve Pk,n(t) the course of which is comparable at least with a daily power curve Pk,i(t) from previous years i and   filing the daily output curve Pk,n(t) found and the energy output Ek,n in a data bank.   
     
     
         3 . The evaluation method as set forth in  claim 1 , characterized by forming daily classes kj, which are allocated to fixed time intervals of a day. 
     
     
         4 . The evaluation method as set forth in  claim 1 , characterized by forming and evaluating a first derivation of the function P(t). 
     
     
         5 . The evaluation method as set forth in  claim 1 , characterized in that only energy output values are compared which come from measurement periods comprising only one daily power peak. 
     
     
         6 . The evaluation method as set forth in  claim 1 , characterized in that data with comparable power curve P(t) of the photovoltaic module are observed over several years. 
     
     
         7 . The evaluation method as set forth in  claim 4 , characterized by determining comparable days in one step by determining and evaluating the number of zero crossings of the first derivation P′(t) is determined and evaluated. 
     
     
         8 . The evaluation method as set forth in  claim 4 , characterized by determining comparable days in two steps by
 a. evaluating the first derivation P′(t) of the function P(t) using a first criterion and   b. evaluating the daily power curve P(t) using a second criterion.   
     
     
         9 . The evaluation method as set forth in  claim 8 , characterized by the first criterion for evaluating the first derivation P′(t) by the fact that the extreme values of the first derivation P′(t) will not exceed an upper limit value P′max and will not fall below a lower limit value P′min or that the area included by the curve of the first derivation P′(t) will not exceed a fixed limit value. 
     
     
         10 . The evaluation method as set forth in  claim 8 , characterized by the second criterion for this evaluation of the daily power curve P(t) by the fact that the daily energy output Etag is formed and that this daily energy output lies above a fixed limit value or that the maximum of the daily power curve P(t) lies within a tolerance band Pabs_min and Pabs max. 
     
     
         11 . The evaluation method as set forth in  claim 1 , characterized by specifying limit values in the first year of measurement and verifying the limit values in the following years. 
     
     
         12 . The evaluation method as set forth in  claim 1 , characterized by acquiring at least one average value ΔEmittel,n from the k energy output difference values ΔEk,n for the year n as a measure for power reduction. 
     
     
         13 . A solar plant with means for carrying out the measurement method as set forth in  claim 1 .