AGOs comprise a purpose-built hut with lots of insulation, electrical heaters and heat storage devices (water bottles!). Power is provided by wind and solar power generators and can be used directly or to charge batteries for later use. For example, no power can be generated during windless periods in the 24-hour darkness of winter. The batteries may become exhausted if all the scientific instruments are left running. So, control electronics selectively stop scientific instrumentation to economise on power until an orderly re-start can take place when power becomes available again.