check for negative electricity production (issue 281)

Author: jeffbourdier

src/geophires_x/SurfacePlant.py

@@ -152,6 +152,9 @@ def electricity_heat_production(self, enduse_option: EndUseOptions, availability
 
         # next do the electricity produced - the same for all, except enduse=5, where it is recalculated
         ElectricityProduced = availability * etau * nprod * prodwellflowrate
+        if ElectricityProduced.max() < 0:
+            raise RuntimeError('Electricity production calculated as negative.  '
+                               'Check maximum temperature for power plant type.')
 
         if enduse_option == EndUseOptions.ELECTRICITY:
             # pure electricity