The majority of the cost stems from paying gas-fired power plants to fire up to replace wind turbines in remote locations that have to be switched off due to cabling bottlenecks. Costs will also be driven higher because network companies are taking some power lines out of service temporarily to enable upgrades. Neso said constraint costs were highly sensitive to wholesale energy costs, weather patterns, network and generator failures and changes to the network. “To reduce this element of constraint costs, new network should be built. Constraint costs are the biggest single element of the costs Neso incurs to balance supply and demand on Britain’s electricity system.