Photovoltaic system in northern climes to 5.61 kWh/m²/day in the sunniest regions. For large systems, the energy gained by using tracking systems can outweigh the added complexity (trackers can increase efficiency by 30% or more). For very large systems, the added maintenance of tracking is a substantial detriment. Tracking is not required for flat panel and low-concentration photovoltaic systems. For high-concentration photovoltaic systems, dual axis tracking is a necessity. Pricing trends affect the balance between adding more stationary solar panels versus having fewer panels that track. When solar panel prices drop, trackers become a less attractive option. Systems designed to deliver alternating
Mir Docking Module November, leaving STS-71 as the only Shuttle-"Mir" docking mission requiring "Kristall" to be relocated. In addition to simplifying space shuttle docking missions, "Mir"'s docking module was also used as a carrier for two new photovoltaic arrays, mounted to the module in boxes, which were later deployed on "Kvant"-1 during spacewalks. The first, the "Mir" Cooperative Solar Array, was jointly designed by NASA and Russia in order to test designs for the future International Space Station. The array was 42 m² in area, and provided 6.7 kW of power when installed on the station during expedition EO-21 in 1996. The array