Photovoltaic systems can be in different relation to the public electric grid: Off-grid systems are not connected to the grid, thus avoiding cabling costs (e. g. in remote locations) but usually requiring accumulators for storage. On-grid systems, which comprise the largest part of photovoltaic power installed worldwide, on the other hand, are directly connected to the grid so that excess energy production as well as excess energy storage is buffered to and from the grid - accumulators are rarely used in on-grid systems, making them much cheaper per installed Watt-peak.