“…In most cases, electrical energy was sold by generators to consumers (102 of 130 papers). In other cases, the market paid for flexibility, either alongside a market for the sale of energy (11 of 130 papers) [56,62,63,90,[101][102][103][104][105][106][107], or in a flexibility only market (10 of 130 papers) [47,49,69,76,77,79,[108][109][110][111]. Finally, some markets traded ancillary services such as reactive power, either alongside energy (five of 130 papers) [50,51,[112][113][114], or as a standalone ancillary services market (two of 130 papers) [61,115].…”