# P50-P90

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hi

if i have real meterologic data ( 10 min interval ) for minimum 10 year

and i want to estimate P50 and P90

in miscellaneous tools we have some parameter to change Following the data

HOw can i know what is the parameter ?

Especially annual variability?

and if i have real data - output energy + radiation + temperature from 2 year

how can i change the parameter ??

i want to know estimate P90 more exact

thanks

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The annual variability is the RMS of the normal distribution of your annual data.

If you have 10 years of meteo data for your site, you can import them (create 10 *.MET files in PVsyst - each MET file is for one year).

Then since version 6.37, you have a new tool in "Meteo tables and graphs" > button "Compare", for comparing different meteo files and establish the RMS of their distribution.

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• 9 months later...

Dear Mermoud,

I have a question about the calculation of P90, P75 and P99:

according the PVsyst Help, in oder to calculate P90, P95 and P99 the following coefficients will be applied to sigma:

"NB: In the Gaussian distribution, P90 represents a shift of -1.28 sigma, P95 => -1.64 sigmas, and P99 => -2.35 sigmas."

but in literature (for example Wikipedia https://fr.wikipedia.org/wiki/Loi_normale) I have found other coefficients:

68 % d'entre elles sont dans l'intervalle [{x} -sigma; {x}+sigma];

95 % d'entre elles sont dans l'intervalle [{x} -2sigma; {x} + 2sigma];

99,7 % d'entre elles sont dans l'intervalle [{x} - 3sigma;{x} + 3sigma].

According to the literature, I should use the following coefficient:

P68 = -1 sigma,

P90 = -1.645 sigma,

P95 = -1.96 sigma,

P99 = -2,58 sigma.

Could you please clarify this inconsistency?

BR

Marco

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In a normal distribution, 68% of the "events" are between -sigma and + sigma.

But 16% are above + sigma.

Therefore above the value (Average - Sigma), you have 68% + 16% = 84% of the event. This corresponds to P84.