With the widespread adoption of photovoltaic (PV) systems across the world, many researchers, industry players, and regulators have been exploring the use of reactive power from PV to support the grid. This thesis is the first to comprehensively quantify and analyse the techno-economic cost and benefits of reactive power support using PV. On top of formulating the cost of PV reactive power and identifying the feasible range of its monetary incentives, this thesis has also proposed practical methods to implement the reactive power dispatch effectively and efficiently, with and without communication infrastructure. The findings and approaches in this work can therefore help power system planners and operators towards better integration of PV into the electrical grid, both in terms of regulation and implementation.