I found the solution myself:
But i still have some warnings:
rule "PV-Leistung - Strahlung Average"
when
Item stromzaehler1_radiation received update
then
stromzaehler1_radiation_Avrg_10min.postUpdate(stromzaehler1_radiation.averageSince(now.minusMinutes(10), "rrd4j"))
stromzaehler1_radiation_Avrg_30min.postUpdate(stromzaehler1_radiation.averageSince(now.minusMinutes(30), "rrd4j"))
end
Items:
Number stromzaehler1_radiation "Stromzähler PV Total-Strahlung [%.2f]" <solarplant> (gSolarStrahlung)
Number stromzaehler1_radiation_Avrg_10min "Strom Total-Strahlung avg 10min [%.2f]" <solarplant> (gSolarStrahlung)
Number stromzaehler1_radiation_Avrg_30min "Strom Total-Strahlung avg 30min [%.2f]" <solarplant> (gSolarStrahlung)