When unexpected events occur such as generator faults or excessive demand, the electricity system operator requires either additional generation to run as back up, or a reduction in electricity demand to ensure the system remains balanced. Such generation is commonly referred to as “reserve”. Electricity generated from wind at a given time is one variable currently managed as part of the demand supply balance among others. The system operator procures reserve services commercially, as part of balancing services. DECC does not hold data on energy produced from reserve services which is part of commercial arrangements the system operator has with providers.