12 Inventories

12 Inventories
  31.12.2011 31.12.2012
  CHF thousands    
  Certificates of origin 12,038 16,350
  Emission certificates 4,138 2,141
  Emission certificates held for trading 3,158 2,614
  Gas 9,451 14,539
  Material inventories 9,009 9,246
  Total 37,794 44,890

Inventories consist of material inventories, gas inventories and certificates, and are valued at the lower of acquisition costs and net realisable value. Certificates that are not necessary for own generation needs and which are held for trading purposes are valued at fair value less selling costs. No impairment was recognised in the current financial year or in the previous year.