Locations of photovoltaic (PV) systems affect the variability and uncertainty of their power generation, and as a result the amount of flexible resources needed to balance supply and demand. However, studies on the integration of renewable electricity into power systems focus on the total amount of renewable generation, and not their locations. This paper uses a hidden state, spatial-statistical model to simulate how locational arrangements and balancing policies affect the need for reserves load following and regulation in California's power system when including 12 GW of photovoltaic generators and 9.5 GW of wind. Our results show that locations of utility-scale PV systems significantly affect on the amount of reserves needed for balancing their variability and uncertainty. When PV is geographically dispersed the additional load following and regulation reserve needs are small; on average <1.2% and <0.05% of installed PV capacity respectively. These rise to 5.6% and 0.2% in centralized scenarios. Most the benefits of this dispersion can be achieved with relatively few, 25, systems. These are sized at roughly 500 MW each, which is about the size of the largest systems in California today. Almost all of the load following reserve need is driven by errors in the hourly forecasts of solar generation. These can be mitigated either by better forecasts, or dispersing plants. Siting policies for PV must weigh system flexibility against other locational concerns, such as the energy and capacity value of the solar resource in an area. We find a small trade off between energy and reserves; where dispersed systems require less reserves but also have lower capacity factors than more centralized systems. However, we find a much greater trade-off between energy and capacity value in California; where the regions that produce the most energy on average in the Mojave desert tend to be cloudy during current peak demand hours, which occur during Summer afternoons. (C) 2016 Elsevier Ltd. All rights reserved.