add flushing of val epoch resluts (#256)

* add flushing of val epoch resluts

* add docstring back base_model.py

* log to csv only when end of accumbatch

pvnet/models/base_model.py

@@ -666,7 +666,8 @@ def validation_step(self, batch: dict, batch_idx):
         # Sensor seems to be in batch, station, time order
         y = batch[self._target_key][:, -self.forecast_len :, 0]
 
-        self._log_validation_results(batch, y_hat, accum_batch_num)
+        if (batch_idx + 1) % self.trainer.accumulate_grad_batches == 0:
+            self._log_validation_results(batch, y_hat, accum_batch_num)
 
         # Expand persistence to be the same shape as y
         losses = self._calculate_common_losses(y, y_hat)
@@ -743,6 +744,7 @@ def on_validation_epoch_end(self):
             print("Failed to log validation results to wandb")
             print(e)
 
+        self.validation_epoch_results = []
         horizon_maes_dict = self._horizon_maes.flush()
 
         # Create the horizon accuracy curve