I don't see anything going wrong in your example.

However, since the documentation was written, the interpretation of STG_LOSS has been changed (by agreement with the ETSAP Project Head) to mean the annual loss. In other words, the STG_LOSS parameter gives the losses that would occur if the amount would be stored for **one year's time**.

Here is a manual loss calculation for your case:

As you can see, the time that the energy is actually being stored is very short in your case, and therefore the losses are also very small. The "Daily Time" above gives the daily fraction of the year for each of the timeslices. The total calculated loss is equal to the difference in the results for the inputs and outputs. Note also that the activity is the sum of the amounts stored during the 91 winter days, and so the daily amounts stored are much smaller.

To state this in another way: From the results, one can easily calculate the average residence time of the energy stored in the storage. In the example, it is only **7.2 hours** before being discharged. And the total amount of energy stored over the whole year is 3.154464. Therefore, the total losses can be calculated as 7.2/8760*0.25*3.154464 = 0.0006482.

The losses are assumed **directly proportional** to both the storage time and the amount of stored, whenever the losses are specified as a positive fraction. The ** storage time** in any timeslice is calculated from G_YRFR(r,s) and the number of storage cycles, as an average of the current and the preceding timeslice (for daily storage, the number of storage cycles is the number of days in the parent timeslice).

Finally, the STG_LOSS parameter can be alternatively specified also as a negative value, and then it is assumed to represent the reciprocal of the average storage residence time (as a year fraction) in an exponentially decaying storage with no discharge. In this case the losses are not directly proportional to the storage time, due to the assumed exponential decay. But when the value of STG_LOSS or the actual residence times are small (discharge taking into account), the resulting actual losses are close to identical in both ways.