I have been playing around with the different parameters related to storage devices (across timeslices). I have two concerns with the STG_LOSS parameter:
1) As VAR_ACT_s represents the energy stored at the beginning of timeslice s (p.229 of part II), wouldn't it be more rational to use G_YRFR_s1 in the equation on p.230 of part II ?
2) A second, and more critical issue I have is that, when analyzing the numerical value of the storage losses, remarkably low values of losses occur which do not correspond to the ones I calculate by hand by following the equation on p.230.
As a test case, I use a storage device with STG_EFF equal to 1, and STG_LOSS equal to 0.25.
I used 4 seasonal timeslices (SU, FA, WI, SP, each lasting 25% of the year) and three daynite timeslices (D,P,N in that order, day and night representing 40% of the 'day', while peak represents 20%) => G_YRFR = 0.1 for WID and WIN, and G_YRFR = 0.05 for WIP.
The storage process is declared on the DAYNITE level as is the stored commodity. The storage device is only used in the winter (as I made sure that demand couldn't be reached without the storage device in the winterpeak).
I get the following values:

Period 
2010 
2010 
2010 
Attribute 
Vintage\TimeSlice 
WID 
WIP 
WIN 
VAR_Act 
2010 
0.000648133 
3.153816015 

VAR_FIn 
2010 
3.1536 

0.000648222 
VAR_FOut 
2010 

3.1536 


G_YRFR 
0.1 
0.05 
0.1 
My calculations state that the activity variable of WIP (given all values of WID), should amount
, which is clearly lower than the ones according to VEDA/TIMES.
As I increased the STG_loss parameter, the difference between what I calculate and the VEDA/TIMES results diverge stronger.
Does anyone has an idea what is going wrong here?