If the extent of all rasters are same.. it can be done easily.
1. List all rasters in a folder
2. Loop through list to select rasters from particular year. ( It can be done by matching the year with the name of raster. As u have mentioned name include year)
3. Then sum of all the raster can be done.
If u r comfortable with R I can share code that I have already written to accomplish this task.