diff --git a/fhem/CHANGED b/fhem/CHANGED
index 7a4acfe72..c7bfc906c 100644
--- a/fhem/CHANGED
+++ b/fhem/CHANGED
@@ -1,5 +1,6 @@
 # Add changes at the top of the list. Keep it in ASCII, and 80-char wide.
 # Do not insert empty lines here, update check depends on it
+ - change:  76_SolarForecast: minor change calculation Today PV deviation
  - change:  49_SSCam: change internal logic for sending data and their Saving
  - change: 10_SOMFY.pm: Signalduino modif and doc cleanup - msg1298875
  - feature: 74_AutomowerConnect.pm: reduce spikes in border region after a hull
diff --git a/fhem/FHEM/76_SolarForecast.pm b/fhem/FHEM/76_SolarForecast.pm
index dd1243de2..fc0968a6c 100644
--- a/fhem/FHEM/76_SolarForecast.pm
+++ b/fhem/FHEM/76_SolarForecast.pm
@@ -158,6 +158,7 @@ BEGIN {
 
 # Versions History intern
 my %vNotesIntern = (
+  "1.17.8" => "16.04.2024  calcTodayPVdeviation: change of calculation ",
   "1.17.7" => "09.04.2024  export pvHistory to CSV, making attr affectMaxDayVariance obsolete ", 
   "1.17.6" => "07.04.2024  new sub writeToHistory with many internal changes in pvHistory write process ". 
                            "_transferInverterValues: react on inverter etotal behavior ",
@@ -10205,13 +10206,12 @@ sub calcTodayPVdeviation {
       my $sstime = timestringToTimestamp ($date.' '.ReadingsVal ($name, "Today_SunSet", '22:00').':00');
       return if($t < $sstime);
 
-      my $diff = $pvfc - $pvre;
-      $dp      = sprintf "%.2f" , (100 * $diff / $pvre);
+      $dp = sprintf "%.2f", (100 - (100 * $pvfc / $pvre));
   }
   else {
       my $rodfc = ReadingsNum ($name, 'RestOfDayPVforecast', 0);
-      my $dayfc = $pvre + $rodfc;                                            # laufende Tagesprognose aus PVreal + Prognose Resttag
-      $dp       = sprintf "%.2f", (100 * ($pvfc - $dayfc) / $dayfc);
+      my $fcun  = $pvfc - $rodfc;                                            # laufende PV Prognose aus Tagesprognose - Prognose Resttag
+      $dp       = sprintf "%.2f", (100 - (100 * $pvre / $fcun));
   }
 
   $data{$type}{$name}{circular}{99}{tdayDvtn} = $dp;