A joined blade rotor system (1, 100, 200, 500, 700, 800, 900) to install on or forming part of horizontal axis wind turbine comprising: - a number of joined blade assemblies (2, 101, 201, 201a, 301, 501, 601, 701, 801, 901) extending radially from a central hub (20, 120, 220, 520, 720, 820, 920) having a substantially horizontal axis; wherein - each joined blade assembly (2, 101, 201, 201a, 301, 501, 601, 701, 801, 901) comprises at least two blades, a first blade (10, 110, 210, 310, 410, 510, 610, 710, 810, 910) and a second blade (30, 130, 230, 330, 430, 530, 630, 730, 830, 930) or more blades in different rotor planes, said first and second blades are connected by one or more brace systems (40, 140, 150, 160, 240, 250, 260, 340, 340a, 450, 540, 541, 640, 740, 840, 940) to each other; - the brace system(s) (40, 140, 150, 160, 240, 250, 260, 340, 340a, 450, 540, 541, 640, 740, 840, 940) comprise brace strut(s) (41, 141, 262, 542) hinged or rigidly connected to a second blade (30, 130, 230, 330, 430, 530, 630, 730, 830, 930) and hinged or rigidly connected to a first blade (10, 110, 210, 310, 410, 510, 610, 710, 810, 910), the brace strut(s) (41, 141, 262, 542) being rigidly connected to at least either the second blade (30, 130, 230, 330, 430, 530, 630, 730, 830, 930) or the first blade (10, 110, 210, 310, 410, 510, 610, 710, 810, 910), and - the first blade(s) (10, 110, 210, 310, 410, 510, 610, 710, 810, 910) and the second blade(s) (30, 130, 230, 330, 430, 530, 630, 730, 830, 930) are connected, such as attached, to a central hub (20, 120, 220, 520, 720, 820, 920) directly or using a root mounting (550, 750, 850, 950) and pitch bearings with a gap (28, 128) and a stagger (29, 129) distances. - a number of joined blade assemblies (2, 101, 201, 201a, 301, 501, 601, 701, 801, 901) extending radially from a central hub (20, 120, 220, 520, 720, 820, 920) having a substantially horizontal axis; - each joined blade assembly (2, 101, 201, 201a, 301, 501, 601, 701, 801, 901) comprises at least two blades, a first blade (10, 110, 210, 310, 410, 510, 610, 710, 810, 910) and a second blade (30, 130, 230, 330, 430, 530, 630, 730, 830, 930) or more blades in different rotor planes, said first and second blades are connected by one or more brace systems (40, 140, 150, 160, 240, 250, 260, 340, 340a, 450, 540, 541, 640, 740, 840, 940) to each other; - the brace system(s) (40, 140, 150, 160, 240, 250, 260, 340, 340a, 450, 540, 541, 640, 740, 840, 940) comprise brace strut(s) (41, 141, 262, 542) hinged or rigidly connected to a second blade (30, 130, 230, 330, 430, 530, 630, 730, 830, 930) and hinged or rigidly connected to a first blade (10, 110, 210, 310, 410, 510, 610, 710, 810, 910), the brace strut(s) (41, 141, 262, 542) being rigidly connected to at least either the second blade (30, 130, 230, 330, 430, 530, 630, 730, 830, 930) or the first blade (10, 110, 210, 310, 410, 510, 610, 710, 810, 910), and - the first blade(s) (10, 110, 210, 310, 410, 510, 610, 710, 810, 910) and the second blade(s) (30, 130, 230, 330, 430, 530, 630, 730, 830, 930) are connected, such as attached, to a central hub (20, 120, 220, 520, 720, 820, 920) directly or using a root mounting (550, 750, 850, 950) and pitch bearings with a gap (28, 128) and a stagger (29, 129) distances.