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Making Solar Grid-Friendly

Why integrating utility-scale solar will follow the wind model.

The world’s power generation systems continue to transition to cleaner, more renewable and sustainable sources. That effort will be greatly aided by integrated and comprehensive grid interconnection solutions. Utility-scale, grid-connected solar photovoltaic (PV), as well as wind, has become increasingly attractive as a generation resource, both in terms of economics and operational fl exibility. The technology needed to interconnect these renewable power sources is now well proven in the field.


Grid operators want solar to act like traditional power plants — to support stability and integrity during grid disturbances.


Following the rapid growth of the wind power industry in recent years, the solar power market is expanding on a global scale. A recent report by industry research firm IMS Research estimates that new PV installations grew last year by 130% — to 17.5 gigawatts (GW). The report predicts that total installed solar capacity will grow to as much as 58 GW by the end of 2011. IMS forecasts that the global PV inverter market will reach $8.5 billion by 2014, growing at a compound annual rate of nearly 25%. This rapid domestic growth is expected to propel the United States to overtake Germany as the world’s largest market for PV modules in 2014, according to the European Photovoltaic Industry.

But as an intermittent energy source, like wind power, utility-scale solar power plants today must meet stringent requirements for both reliability and grid-friendliness (grid management capability when interconnecting to the integrated, interstate transmission system. Such requirements have bee in place in Europe and Australia for quite some time, but have only recently become a reality for solar power plants in the U. S. and Canada. In light of its rapidly growing market, more stringent interconnection requirements are expected in North America for both wind and solar resources, as more megawatt-scale plants come online.

Realizing the full potential of solar power in the generation mix will require comprehensive wide-area solutions. One such solution would allow conversion systems for individual solar plants to stay on-line during grid disturbances to support and stabilize the grid system voltage by injecting or absorbing reactive power. Thus, true steady-state control of power factor and dynamic control should be seen as the hallmarks of special-purpose grid interconnection systems.

Interconnection Technology

Today, solar generating plants must meet power factor and low- and high-voltage ride-through requirements, as well as provide voltage control at the Point of Interconnection (POI). In addition, solar plants are required to act as a “good utility citizen.” That is, they must first be grid-friendly and cannot disconnect from the utility when they are most needed, such as during power system disturbances. Secondly, they must actively support the grid so that when disturbances do occur, the plant is prepared to help the grid recover. Solar power plants should also provide day-to-day voltage support to help keep the system voltages smooth and stable, even if the power output of the plant varies due to clouds or other factors during the course of the day.

True dynamic voltage control and steady-state control of power factor are hallmarks of advanced grid