Bringing Utility-Scale Solar Power to the Grid  

REW has an article on some of the issues to resolve as distributed solar PV becomes widespread across the electricity grid - Bringing Utility-Scale Solar Power to the Grid.

Over time the electrical grid will transform into a more distributed configuration, incorporating many new energy resources, including solar. Already, the solar energy industry has matured to the point where utilities are integrating multi-megawatt photovoltaic projects on a regular basis. If the growth in PV installations continues at its current rate, 5 percent to 10 percent penetration nationwide could be achieved in less than a decade with higher levels in some localities. The challenge of controlling and delivering solar energy to a commercial power grid in a coordinated way over a broad spectrum of grid conditions is critical to this endeavor’s success. System reliability, integration with existing systems and control infrastructure and installation economics pose key technical issues to be overcome.

Utilities are being challenged to embrace this rapidly evolving wave of change. Some have concerns that integrating a high volume of inverter-based photovoltaic systems and other distributed generation sources will lead to instabilities and the possibility of unsafe grid operations. Variable energy production and the fact that peak production from these sources does not always coincide with peak demand can reduce the value of PV’s impact on utility operating economics. ...

As an increasing number of utility-scale PV power plants are being connected to the grid, problems are being identified. These relate to the distributed PV resource’s intermittent nature and the inherent conflict between a power generation source and existing grid interconnect standards governing distributed PV system connection to the grid.

Both problems are complex and their final solution may be realized only when interconnection standards have been changed to embrace PV as a key energy generation asset for utilities. Additionally, smart grid communications infrastructure will likely be required to fully solve these problems at a level that addresses high PV penetration in the case of highly distributed solar generation. ...

As PV penetration increases, the problem of how PV systems detect and react to grid variations becomes increasingly critical to overall grid stability. More interactive controls are required to ensure that inverters will disconnect when necessary, but will be able to stay on-line when drops in utility voltage and frequency levels occur. PV can assist in riding through these temporary fluctuations. This function is typically implemented by a sophisticated set of algorithms that perform passive monitoring and active control within an inverter to determine if an unintentional island has been created (where the PV system sends power into a section of the utility grid experiencing an outage). Present-day inverters cannot differentiate between a true utility outage (where anti-islanding is necessary) and a grid disturbance or brownout in which the PV system could actually help support grid stability. Even if these inverters could differentiate between these conditions, current regulations sometimes require the inverter to disconnect from the grid when additional power is most needed.