| 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.