diff --git a/fhem/CHANGED b/fhem/CHANGED
index fcaa6390d..2e47aa593 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
+ - bugfix: 76_SolarForecast: negative SoC forecast when using optPower
  - feature: 76_SolarForecast: Version 1.58.6
  - bugfix: 72_FRITZBOX: Fehler bei rename von Devices
  - bugfix: 76_SolarForecast: opt load if battery load control is deactivated
diff --git a/fhem/FHEM/76_SolarForecast.pm b/fhem/FHEM/76_SolarForecast.pm
index ed68cf896..c419e1440 100644
--- a/fhem/FHEM/76_SolarForecast.pm
+++ b/fhem/FHEM/76_SolarForecast.pm
@@ -160,6 +160,7 @@ BEGIN {
 
 # Versions History intern
 my %vNotesIntern = (
+  "1.58.7" => "05.10.2025  fix negative SoC forecast when using optPower Forum: https://forum.fhem.de/index.php?msg=1348954 ",
   "1.58.6" => "03.10.2025  __batChargeMgmt code changed, new sub ___batChargeSaveResults, remove reading Battery_ChargeRecommended_XX ".
                            "_calcReadingsTomorrowPVFc: bugfix generating readings of tomorrow ".
                            "__batChargeOptTargetPower: complete rework, Attr ctrlBatSocManagementXX new keys 'loadStrategy', 'weightOwnUse' ".
@@ -12049,7 +12050,7 @@ sub __batChargeOptTargetPower {
               $hsurp->{$hod}{$sbn}{pneedmin}   = $bpinmax;
               
               $runwh += $hsurp->{$hod}{speff} / $befficiency;                                                    # um Verbrauch reduzieren
-              $hsurp->{$hod}{$sbn}{fcendwh} = sprintf "%.0f", $runwh;          
+              $hsurp->{$hod}{$sbn}{fcendwh} = sprintf "%.0f", max (0, $runwh);          
               
               if ($nhr eq '00') {
                   $otp->{$sbn}{target} = $csocwh <= $lowSocwh ? $bpinreduced : $bpinmax;
diff --git a/fhem/contrib/DS_Starter/76_SolarForecast.pm b/fhem/contrib/DS_Starter/76_SolarForecast.pm
index 269f5f909..c419e1440 100644
--- a/fhem/contrib/DS_Starter/76_SolarForecast.pm
+++ b/fhem/contrib/DS_Starter/76_SolarForecast.pm
@@ -160,6 +160,7 @@ BEGIN {
 
 # Versions History intern
 my %vNotesIntern = (
+  "1.58.7" => "05.10.2025  fix negative SoC forecast when using optPower Forum: https://forum.fhem.de/index.php?msg=1348954 ",
   "1.58.6" => "03.10.2025  __batChargeMgmt code changed, new sub ___batChargeSaveResults, remove reading Battery_ChargeRecommended_XX ".
                            "_calcReadingsTomorrowPVFc: bugfix generating readings of tomorrow ".
                            "__batChargeOptTargetPower: complete rework, Attr ctrlBatSocManagementXX new keys 'loadStrategy', 'weightOwnUse' ".
@@ -12049,7 +12050,7 @@ sub __batChargeOptTargetPower {
               $hsurp->{$hod}{$sbn}{pneedmin}   = $bpinmax;
               
               $runwh += $hsurp->{$hod}{speff} / $befficiency;                                                    # um Verbrauch reduzieren
-              $hsurp->{$hod}{$sbn}{fcendwh} = sprintf "%.0f", $runwh;          
+              $hsurp->{$hod}{$sbn}{fcendwh} = sprintf "%.0f", max (0, $runwh);          
               
               if ($nhr eq '00') {
                   $otp->{$sbn}{target} = $csocwh <= $lowSocwh ? $bpinreduced : $bpinmax;
@@ -27849,7 +27850,7 @@ to ensure that the system configuration is correct.
            <tr><td> <b>pinmax</b>    </td><td>the maximum possible charging power in watts (optional)                                                       </td></tr>
            <tr><td>                  </td><td>                                                                                                              </td></tr>
            <tr><td> <b>pinreduced</b></td><td>The reduced charging power in watts (optional). The value is set in Reading Battery_ChargeOptTargetPower_XX   </td></tr>
-           <tr><td>                  </td><td>if there is no PV surplus or if the calculated charging power falls below this value.                         </td></tr>
+           <tr><td>                  </td><td>if the calculated charging power falls below this value or the SoC <= lowSoC.                                 </td></tr>
            <tr><td>                  </td><td>This means that the value can also be applied in the case of demand charging from the public grid.            </td></tr>
            <tr><td>                  </td><td>                                                                                                              </td></tr>
            <tr><td> <b>poutmax</b>   </td><td>the maximum possible discharge power in watts (optional)                                                      </td></tr>
@@ -30544,7 +30545,7 @@ die ordnungsgemäße Anlagenkonfiguration geprüft werden.
            <tr><td> <b>pinmax</b>    </td><td>die maximal mögliche Ladeleistung in Watt (optional)                                                     </td></tr>
            <tr><td>                  </td><td>                                                                                                         </td></tr>
            <tr><td> <b>pinreduced</b></td><td>Die reduzierte Ladeleistung in Watt (optional). Der Wert wird im Reading Battery_ChargeOptTargetPower_XX </td></tr>
-           <tr><td>                  </td><td>gesetzt wenn kein PV-Überschuß vorhanden ist oder die kalkulierte Ladeleistung unter diesen Wert fällt.  </td></tr>
+           <tr><td>                  </td><td>gesetzt wenn die kalkulierte Ladeleistung unter diesen Wert fällt oder der SoC <= lowSoC beträgt.        </td></tr>
            <tr><td>                  </td><td>Somit kann der Wert auch im Fall der Anforderungsladung aus dem öffentlichen Netz zur Anwendung kommen.  </td></tr>
            <tr><td>                  </td><td>                                                                                                         </td></tr>
            <tr><td> <b>poutmax</b>   </td><td>die maximal mögliche Entladeleistung in Watt (optional)                                                  </td></tr>